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diff --git a/6935.txt b/6935.txt new file mode 100644 index 0000000..56244d4 --- /dev/null +++ b/6935.txt @@ -0,0 +1,9084 @@ +The Project Gutenberg EBook of The Radio Amateur's Hand Book +by A. Frederick Collins + +Copyright laws are changing all over the world. Be sure to check the +copyright laws for your country before downloading or redistributing +this or any other Project Gutenberg eBook. + +This header should be the first thing seen when viewing this Project +Gutenberg file. Please do not remove it. Do not change or edit the +header without written permission. + +Please read the "legal small print," and other information about the +eBook and Project Gutenberg at the bottom of this file. Included is +important information about your specific rights and restrictions in +how the file may be used. You can also find out about how to make a +donation to Project Gutenberg, and how to get involved. + + +**Welcome To The World of Free Plain Vanilla Electronic Texts** + +**eBooks Readable By Both Humans and By Computers, Since 1971** + +*****These eBooks Were Prepared By Thousands of Volunteers!***** + + +Title: The Radio Amateur's Hand Book + +Author: A. Frederick Collins + +Release Date: November, 2004 [EBook #6935] +[This file was first posted on February 13, 2003] + +Edition: 10a + +Language: English + +Character set encoding: iso-8859-1 + +*** START OF THE PROJECT GUTENBERG EBOOK, THE RADIO AMATEUR'S HAND BOOK *** + + + + +Produced by Alan Millar and the Online Distributed Proofreading Team. + + + +[Transcriber's Note: The illustrations have been included with +the eBook version of this work. The image files have been named +in a straightforward manner that corresponds to the numbering in +the text; thus, Illustration 7 is included as file "fig007.png", +while Illustration (A) 22 is included as file "fig022a.png".] + + + + + + +THE RADIO AMATEUR'S HAND BOOK + +[Illustration: A. Frederick Collins, Inventor of the Wireless +Telephone, 1899. Awarded Gold Medal for same, Alaska Yukon Pacific +Exposition, 1909.] + + + + +THE RADIO AMATEUR'S HAND BOOK + +A Complete, Authentic and Informative Work on Wireless Telegraphy and +Telephony + +BY + +A. FREDERICK COLLINS + +Inventor of the Wireless Telephone 1899; Historian of Wireless +1901-1910; Author of "Wireless Telegraphy" 1905 + +1922 + + + + +TO + +WILLIAM MARCONI + +INVENTOR OF THE WIRELESS TELEGRAPH + + + + +INTRODUCTION + + +Before delving into the mysteries of receiving and sending messages +without wires, a word as to the history of the art and its present day +applications may be of service. While popular interest in the subject +has gone forward by leaps and bounds within the last two or three +years, it has been a matter of scientific experiment for more than a +quarter of a century. + +The wireless telegraph was invented by William Marconi, at Bologna, +Italy, in 1896, and in his first experiments he sent dot and dash +signals to a distance of 200 or 300 feet. The wireless telephone was +invented by the author of this book at Narberth, Penn., in 1899, and +in his first experiments the human voice was transmitted to a distance +of three blocks. + +The first vital experiments that led up to the invention of the +wireless telegraph were made by Heinrich Hertz, of Germany, in 1888 +when he showed that the spark of an induction coil set up electric +oscillations in an open circuit, and that the energy of these waves +was, in turn, sent out in the form of electric waves. He also showed +how they could be received at a distance by means of a ring detector, +which he called a _resonator_ + +In 1890, Edward Branly, of France, showed that metal filings in a tube +cohered when electric waves acted on them, and this device he termed a +_radio conductor_; this was improved upon by Sir Oliver Lodge, who +called it a coherer. In 1895, Alexander Popoff, of Russia, constructed +a receiving set for the study of atmospheric electricity, and this +arrangement was the earliest on record of the use of a detector +connected with an aerial and the earth. + +Marconi was the first to connect an aerial to one side of a spark gap +and a ground to the other side of it. He used an induction coil to +energize the spark gap, and a telegraph key in the primary circuit to +break up the current into signals. Adding a Morse register, which +printed the dot and dash messages on a tape, to the Popoff receptor he +produced the first system for sending and receiving wireless telegraph +messages. + +[Illustration: Collins' Wireless Telephone Exhibited at the Madison +Square Garden, October 1908.] + +After Marconi had shown the world how to telegraph without connecting +wires it would seem, on first thought, to be an easy matter to +telephone without wires, but not so, for the electric spark sets up +damped and periodic oscillations and these cannot be used for +transmitting speech. Instead, the oscillations must be of constant +amplitude and continuous. That a direct current arc light transforms a +part of its energy into electric oscillations was shown by Firth and +Rogers, of England, in 1893. + +The author was the first to connect an arc lamp with an aerial and a +ground, and to use a microphone transmitter to modulate the sustained +oscillations so set up. The receiving apparatus consisted of a +variable contact, known as a _pill-box_ detector, which Sir Oliver +Lodge had devised, and to this was connected an Ericsson telephone +receiver, then the most sensitive made. A later improvement for +setting up sustained oscillations was the author's _rotating +oscillation arc_. + +Since those memorable days of more than two decades ago, wonderful +advances have been made in both of these methods of transmitting +intelligence, and the end is as yet nowhere in sight. Twelve or +fifteen years ago the boys began to get fun out of listening-in to +what the ship and shore stations were sending and, further, they began +to do a little sending on their own account. These youngsters, who +caused the professional operators many a pang, were the first wireless +amateurs, and among them experts were developed who are foremost in +the practice of the art today. + +Away back there, the spark coil and the arc lamp were the only known +means for setting up oscillations at the sending end, while the +electrolytic and crystal detectors were the only available means for +the amateur to receive them. As it was next to impossible for a boy to +get a current having a high enough voltage for operating an +oscillation arc lamp, wireless telephony was out of the question for +him, so he had to stick to the spark coil transmitter which needed +only a battery current to energize it, and this, of course, limited +him to sending Morse signals. As the electrolytic detector was +cumbersome and required a liquid, the crystal detector which came into +being shortly after was just as sensitive and soon displaced the +former, even as this had displaced the coherer. + +A few years ahead of these amateurs, that is to say in 1905, J. A. +Fleming, of England, invented the vacuum tube detector, but ten more +years elapsed before it was perfected to a point where it could +compete with the crystal detector. Then its use became general and +workers everywhere sought to, and did improve it. Further, they found +that the vacuum tube would not only act as a detector, but that if +energized by a direct current of high voltage it would set up +sustained oscillations like the arc lamp, and the value of sustained +oscillations for wireless telegraphy as well as wireless telephony had +already been discovered. + +The fact that the vacuum tube oscillator requires no adjustment of its +elements, that its initial cost is much less than the oscillation arc, +besides other considerations, is the reason that it popularized +wireless telephony; and because continuous waves have many advantages +over periodic oscillations is the reason the vacuum tube oscillator is +replacing the spark coil as a wireless telegraph transmitter. +Moreover, by using a number of large tubes in parallel, powerful +oscillations can be set up and, hence, the waves sent out are radiated +to enormous distances. + +While oscillator tubes were being experimented with in the research +laboratories of the General Electric, the Westinghouse, the Radio +Corporation of America, and other big companies, all the youthful +amateurs in the country had learned that by using a vacuum tube as a +detector they could easily get messages 500 miles away. The use of +these tubes as amplifiers also made it possible to employ a loud +speaker, so that a room, a hall, or an out-of-door audience could hear +clearly and distinctly everything that was being sent out. + +The boy amateur had only to let father or mother listen-in, and they +were duly impressed when he told them they were getting it from KDKA +(the Pittsburgh station of the Westinghouse Co.), for was not +Pittsburgh 500 miles away! And so they, too, became enthusiastic +wireless amateurs. This new interest of the grown-ups was at once met +not only by the manufacturers of apparatus with complete receiving and +sending sets, but also by the big companies which began broadcasting +regular programs consisting of music and talks on all sorts of +interesting subjects. + +This is the wireless, or radio, as the average amateur knows it today. +But it is by no means the limit of its possibilities. On the contrary, +we are just beginning to realize what it may mean to the human race. +The Government is now utilizing it to send out weather, crop and +market reports. Foreign trade conditions are being reported. The Naval +Observatory at Arlington is wirelessing time signals. + +Department stores are beginning to issue programs and advertise by +radio! Cities are also taking up such programs, and they will +doubtless be included soon among the regular privileges of the +tax-payers. Politicians address their constituents. Preachers reach +the stay-at-homes. Great singers thrill thousands instead of hundreds. +Soon it will be possible to hear the finest musical programs, +entertainers, and orators, without budging from one's easy chair. + +In the World War wireless proved of inestimable value. Airplanes, +instead of flying aimlessly, kept in constant touch with headquarters. +Bodies of troops moved alertly and intelligently. Ships at sea talked +freely, over hundreds of miles. Scouts reported. Everywhere its +invisible aid was invoked. + +In time of peace, however, it has proved and will prove the greatest +servant of mankind. Wireless messages now go daily from continent to +continent, and soon will go around the world with the same facility. +Ships in distress at sea can summon aid. Vessels everywhere get the +day's news, even to baseball scores. Daily new tasks are being +assigned this tireless, wireless messenger. + +Messages have been sent and received by moving trains, the Lackawanna +and the Rock Island railroads being pioneers in this field. Messages +have also been received by automobiles, and one inventor has +successfully demonstrated a motor car controlled entirely by wireless. +This method of communication is being employed more and more by +newspapers. It is also of great service in reporting forest fires. + +Colleges are beginning to take up the subject, some of the first being +Tufts College, Hunter College, Princeton, Yale, Harvard, and Columbia, +which have regularly organized departments for students in wireless. + +Instead of the unwieldy and formidable looking apparatus of a short +time ago, experimenters are now vying with each other in making small +or novel equipment. Portable sets of all sorts are being fashioned, +from one which will go into an ordinary suitcase, to one so small it +will easily slip into a Brownie camera. One receiver depicted in a +newspaper was one inch square! Another was a ring for the finger, with +a setting one inch by five-eighths of an inch, and an umbrella as a +"ground." Walking sets with receivers fastened to one's belt are also +common. Daily new novelties and marvels are announced. + +Meanwhile, the radio amateur to whom this book is addressed may have +his share in the joys of wireless. To get all of these good things out +of the ether one does not need a rod or a gun--only a copper wire made +fast at either end and a receiving set of some kind. If you are a +sheer beginner, then you must be very careful in buying your +apparatus, for since the great wave of popularity has washed wireless +into the hearts of the people, numerous companies have sprung up and +some of these are selling the veriest kinds of junk. + +And how, you may ask, are you going to be able to know the good from +the indifferent and bad sets? By buying a make of a firm with an +established reputation. I have given a few offhand at the end of this +book. Obviously there are many others of merit--so many, indeed, that +it would be quite impossible to get them all in such a list, but these +will serve as a guide until you can choose intelligently for yourself. + +A. F. C. + + + + +CONTENTS + + +CHAPTER + +I. HOW TO BEGIN WIRELESS + +Kinds of Wireless Systems--Parts of a Wireless System--The Easiest Way +to Start--About Aerial Wire Systems--About the Receiving +Apparatus--About Transmitting Stations--Kinds of Transmitters--The +Spark Gap Wireless Telegraph Transmitter--The Vacuum Table Telegraph +Transmitter--The Wireless Telephone Transmitter. + +II. PUTTING UP YOUR AERIAL + +Kinds of Aerial Wire Systems--How to Put Up a Cheap Receiving +Aerial--A Two-wire Aerial--Connecting in the Ground--How to Put up a +Good Aerial--An Inexpensive Good Aerial--The Best Aerial That Can be +Made--Assembling the Aerial--Making a Good Ground. + +III. SIMPLE TELEGRAPH AND TELEPHONE RECEIVING SETS + +Assembled Wireless Receiving Sets--Assembling Your Own Receiving +Set--The Crystal Detector--The Tuning Coil--The Loose Coupled Tuning +Coil--Fixed and Variable Condensers--About Telephone Receivers-- +Connecting Up the Parts--Receiving Set No. 2--Adjusting the No. 1 +Set--The Tuning Coil--Adjusting the No. 2 Set. + +IV. SIMPLE TELEGRAPH SENDING SETS + +A Cheap Transmitting Set (No. 1)--The Spark Coil--The Battery--The +Telegraph Key--The Spark Gap--The Tuning Coil--The High-tension +Condenser--A Better Transmitting Set (No. 2)--The Alternating Current +Transformer--The Wireless Key--The Spark Gap--The High-tension +Condenser--The Oscillation Transformer--Connecting Up the +Apparatus--For Direct Current--How to Adjust Your Transmitter. Turning +With a Hot Wire Ammeter--To Send Out a 200-meter Wave Length--The Use +of the Aerial Switch--Aerial Switch for a Complete Sending and +Receiving Set--Connecting in the Lightning Switch. + +V. ELECTRICITY SIMPLY EXPLAINED + +Electricity at Rest and in Motion--The Electric Current and its +Circuit--Current and the Ampere--Resistance and the Ohm--What Ohm's +Law Is--What the Watt and Kilowatt Are--Electromagnetic +Induction--Mutual Induction--High-frequency Currents--Constants of an +Oscillation Circuit--What Capacitance Is--What Inductance Is--What +Resistance Is--The Effect of Capacitance. + +VI. HOW THE TRANSMITTING AND RECEIVING SETS WORK + +How Transmitting Set No. 1 Works--The Battery and Spark Coil +Circuit--Changing the Primary Spark Coil Current Into Secondary +Currents--What Ratio of Transformation Means--The Secondary Spark Coil +Circuit--The Closed Oscillation Circuit--How Transmitting Set No. 2 +Works-With Alternating Current--With Direct Current--The Rotary Spark +Gap--The Quenched Spark Gap--The Oscillation Transformer--How +Receiving Set No. 1 Works--How Receiving Set No. 2 Works. + +VII. MECHANICAL AND ELECTRICAL TUNING + +Damped and Sustained Mechanical Vibrations--Damped and Sustained +Oscillations--About Mechanical Tuning--About Electric Tuning. + +VIII. A SIMPLE VACUUM TUBE DETECTOR RECEIVING SET + +Assembled Vacuum Tube Receiving Set--A Simple Vacuum Tube Receiving +Set--The Vacuum Tube Detector--Three Electrode Vacuum Tube +Detector--The Dry Cell and Storage Batteries--The Filament +Rheostat--Assembling the Parts--Connecting Up the Parts--Adjusting the +Vacuum Tube Detector Receiving Set. + +IX. VACUUM TUBE AMPLIFIER RECEIVING SETS + +A Grid Leak Amplifier Receiving Set. With Crystal Detector--The Fixed +Resistance Unit, or Grid Leak--Assembling the Parts for a Crystal +Detector Set--Connecting up the Parts for a Crystal Detector--A Grid +Leak Amplifying Receiving Set With Vacuum Tube Detector--A Radio +Frequency Transformer Amplifying Receiving Set--An Audio Frequency +Transformer Amplifying Receiving Set--A Six Step Amplifier Receiving +Set with a Loop Aerial--How to Prevent Howling. + +X. REGENERATIVE AMPLIFICATION RECEIVING SETS + +The Simplest Type of Regenerative Receiving Set--With Loose Coupled +Tuning Coil--Connecting Up the Parts--An Efficient Regenerative +Receiving Set. With Three Coil Loose Coupler--The A Battery +Potentiometer--The Parts and How to Connect Them Up--A Regenerative +Audio Frequency Amplifier--The Parts and How to Connect Them Up. + +XI. SHORT WAVE REGENERATIVE RECEIVING SETS + +A Short Wave Regenerative Receiver, with One Variometer and Three +Variable Condensers--The Variocoupler--The Variometer--Connecting Up +the Parts--Short Wave Regenerative Receiver with Two Variometers and +Two Variable Condensers--The Parts and How to Connect Them Up. + +XII. INTERMEDIATE AND LONG WAVE REGENERATIVE RECEIVING SETS + +Intermediate Wave Receiving Sets--Intermediate Wave Set With Loading +Coils--The Parts and How to Connect Them Up--An Intermediate Wave Set +with Variocoupler Inductance Coils--The Parts and How to Connect Them +Up--A Long Wave Receiving Set--The Parts and How to Connect Them Up. + +XIII. HETERODYNE OR BEAT LONG WAVE TELEGRAPH RECEIVING SET + +What the Heterodyne or Beat Method Is--The Autodyne or Self-heterodyne +Long Wave Receiving Set--The Parts and Connections of an Autodyne or +Self-heterodyne, Receiving Set--The Separate Heterodyne Long Wave +Receiving Set--The Parts and Connections of a Separate Heterodyne Long +Wave Receiving Set. + +XIV. HEADPHONES AND LOUD SPEAKERS + +Wireless Headphones--How a Bell Telephone Receiver is Made--How a +Wireless Headphone is Made--About Resistance, Turns of Wire and +Sensitivity of Headphones--The Impedance of Headphones--How the +Headphones Work--About Loud Speakers--The Simplest Type of Loud +Speaker--Another Simple Kind of Loud Speaker--A Third Kind of Simple +Loud Speaker--A Super Loud Speaker. + +XV. OPERATION OF VACUUM TUBE RECEPTORS + +What is Meant by Ionization--How Electrons are Separated from +Atoms--Action of the Two Electrode Vacuum Tube--How the Two Electrode +Tube Acts as a Detector--How the Three Electrode Tube Acts as a +Detector--How the Vacuum Tube Acts as an Amplifier--The Operation of a +Simple Vacuum Tube Receiving Set--Operation of a Regenerative Vacuum +Tube Receiving Set--Operation of Autodyne and Heterodyne Receiving +Sets--The Autodyne, or Self-Heterodyne Receiving Set--The Separate +Heterodyne Receiving Set. + +XVI. CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH DIRECT CURRENT + +Sources of Current for Telegraph Transmitting Sets--An Experimental +Continuous Wave Telegraph Transmitter--The Apparatus You Need--The +Tuning Coil--The Condensers--The Aerial Ammeter--The Buzzer and Dry +Cell--The Telegraph Key--The Vacuum Tube Oscillator--The Storage +Battery--The Battery Rheostat--The Oscillation Choke Coil--Transmitter +Connectors--The Panel Cutout--Connecting Up the Transmitting +Apparatus--A 100-mile C. W. Telegraph Transmitter--The Apparatus You +Need--The Tuning Coil--The Aerial Condenser--The Aerial Ammeter--The +Grid and Blocking Condensers--The Key Circuit Apparatus--The 5 Watt +Oscillator Vacuum Tube--The Storage Battery and Rheostat--The Filament +Voltmeter--The Oscillation Choke Coil--The Motor-generator Set--The +Panel Cut-out--The Protective Condenser--Connecting Up the +Transmitting Apparatus--A 200-mile C. W. Telegraph Transmitter--A +500-mile C. W. Telegraph Transmitter--The Apparatus and Connections-- +The 50-watt Vacuum Tube Oscillator--The Aerial Ammeter--The Grid Leak +Resistance--The Oscillation Choke Coil--The Filament Rheostat--The +Filament Storage Battery--The Protective Condenser--The +Motor-generator--A 1000-mile C. W. Telegraph Transmitter. + +XVII. CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH ALTERNATING +CURRENT + +A 100-mile C. W. Telegraph Transmitting Set--The Apparatus +Required--The Choke Coils--The Milli-ammeter--The A. C. Power +Transformer--Connecting Up the Apparatus--A 200- to 500-mile C. W. +Telegraph Transmitting Set-A 500- to 1000-mile C. W. Telegraph +Transmitting Set--The Apparatus Required--The Alternating Current +Power Transformer-Connecting Up the Apparatus. + +XVIII. WIRELESS TELEPHONE TRANSMITTING SETS WITH DIRECT AND +ALTERNATING CURRENTS + +A Short Distance Wireless Telephone Transmitting Set--With 110-volt +Direct Lighting Current--The Apparatus You Need--The Microphone +Transmitter--Connecting Up the Apparatus--A 25- to 50-mile Wireless +Telephone Transmitter--With Direct Current Motor Generator--The +Apparatus You Need--The Telephone Induction Coil--The Microphone +Transformer--The Magnetic Modulator--How the Apparatus is Connected +Up--A 50- to 100-mile Wireless Telephone Transmitter--With Direct +Current Motor Generator--The Oscillation Choke Coil--The Plate and +Grid Circuit Reactance Coils--Connecting up the Apparatus--A 100- to +200-mile Wireless Telephone Transmitter--With Direct Current Motor +Generator--A 50- to 100-mile Wireless Telephone Transmitting Set--With +100-volt Alternating Current--The Apparatus You Need--The Vacuum Tube +Rectifier--The Filter Condensers--The Filter Reactance Coil-- +Connecting Up the Apparatus--A 100- to 200-mile Wireless Telephone +Transmitting Set--With 110-volt Alternating Current--Apparatus +Required. + +XIX. THE OPERATION OF VACUUM TUBE TRANSMITTERS + +The Operation of the Vacuum Tube Oscillator--The Operation of C. W. +Telegraph Transmitters with Direct Current--Short Distance C. W. +Transmitter--The Operation of the Key Circuit--The Operation of C. W. +Telegraph Transmitting with Direct Current--The Operation of C. W. +Telegraph Transmitters with Alternating Current--With a Single +Oscillator Tube--Heating the Filament with Alternating Current--The +Operation of C. W. Telegraph Transmitters with Alternating Current-- +With Two Oscillator Tubes--The Operation of Wireless Telephone +Transmitters with Direct Current--Short Distance Transmitter--The +Microphone Transmitter--The Operation of Wireless Telephone +Transmitters with Direct Current--Long Distance Transmitters--The +Operation of Microphone Modulators--The Induction Coil--The Microphone +Transformer--The Magnetic Modulator--Operation of the Vacuum Tube as a +Modulator--The Operation of Wireless Telephone Transmitters with +Alternating Current--The Operation of Rectifier Vacuum Tubes--The +Operation of Reactors and Condensers. + +XX. HOW TO MAKE A RECEIVING SET FOR $5.00 OR LESS. + +The Crystal Detector--The Tuning Coil--The Headphone--How to Mount the +Parts--The Condenser--How to Connect Up the Receptor. + +APPENDIX + +Useful Information--Glossary--Wireless Don'ts. + + + + +LIST OF FIGURES + + +Fig. 1.--Simple Receiving Set + +Fig. 2.--Simple Transmitting Set + +(A) Fig. 3.--Flat Top, or Horizontal Aerial + +(B) Fig. 3.--Inclined Aerial + +(A) Fig. 4.--Inverted L Aerial + +(B) Fig. 4--T Aerial + +Fig. 5.--Material for a Simple Aerial Wire System + +(A) Fig. 6.--Single Wire Aerial for Receiving + +(B) Fig. 6.--Receiving Aerial with Spark Gap Lightning Arrester + +(C) Fig. 6.--Aerial with Lightning Switch + +Fig. 7.--Two-wire Aerial + +(A) Fig. 8.--Part of a Good Aerial + +(B) Fig. 8.--The Spreaders + +(A) Fig. 9.--The Middle Spreader + +(B) Fig. 9.--One End of Aerial Complete + +(C) Fig. 9.--The Leading in Spreader + +(A) Fig. 10.--Cross Section of Crystal Detector + +(B) Fig. 10.--The Crystal Detector Complete + +(A) Fig. 11.--Schematic Diagram of a Double Slide Tuning Coil + +(B) Fig. 11.--Double Slide Tuning Coil Complete + +(A) Fig. 12.--Schematic Diagram of a Loose Coupler + +(B) Fig. 12.--Loose Coupler Complete + +(A) Fig. 13.--How a Fixed Receiving Condenser is Built up + +(B) Fig. 13.--The Fixed Condenser Complete + +(C) and (D) Fig. 13.--Variable Rotary Condenser + +Fig. 14.--Pair of Wireless Headphones + +(A) Fig. 15.--Top View of Apparatus Layout for Receiving Set No. 1 + +(B) Fig. 15.--Wiring Diagram for Receiving Set No. 1 + +(A) Fig. 16.--Top View of Apparatus Layout for Receiving Set No. 2 + +(B) Fig. 16.--Wiring Diagram for Receiving Set No. 2 + +Fig. 17.--Adjusting the Receiving Set + +(A) and (B) Fig. 18.--Types of Spark Coils for Set No. 1 + +(C) Fig. 18.--Wiring Diagram of Spark Coil + +Fig. 19.--Other Parts for Transmitting Set No. 1 + +(A) Fig. 20.--Top View of Apparatus Layout for Sending Set No. 1 + +(B) Fig. 20.--Wiring of Diagram for Sending Set No. 1 + +Fig. 21.--Parts for Transmitting Set No. 2 + +(A) Fig. 22.--Top View of Apparatus Layout for Sending Set No. 2 + +(B) Fig. 22.--Wiring Diagram for Sending Set No. 2 + +Fig. 23.--Using a 110-volt Direct Current with an Alternating current +Transformer + +Fig. 24.--Principle of the Hot Wire Ammeter + +Fig. 25.--Kinds of Aerial Switches + +Fig. 26.--Wiring Diagram for a Complete Sending and Receiving Set No. 1 + +Fig. 27.--Wiring Diagram for Complete Sending and Receiving Set No. 2 + +Fig. 28.--Water Analogue for Electric Pressure + +Fig. 29.--Water Analogues for Direct and Alternating Currents + +Fig. 30.--How the Ammeter and Voltmeter are Used + +Fig. 31.--Water Valve Analogue of Electric Resistance + +(A) and (B) Fig. 32.--How an Electric Current is Changed into Magnetic +Lines of Force and These into an Electric Current + +(C) and (D) Fig. 32.--How an Electric Current Sets up a Magnetic Field + +Fig. 33.--The Effect of Resistance on the Discharge of an Electric +Current + +Fig. 34.--Damped and Sustained Mechanical Vibrations + +Fig. 35.--Damped and Sustained Electric Oscillations + +Fig. 36.--Sound Wave and Electric Wave Tuned Senders and Receptors + +Fig. 37.--Two Electrode Vacuum Tube Detectors + +Fig. 38.--Three Electrode Vacuum Tube Detector and Battery Connections + +Fig. 39.--A and B Batteries for Vacuum Tube Detectors + +Fig. 40.--Rheostat for the A or Storage-battery Current + +(A) Fig. 41.--Top View of Apparatus Layout for Vacuum Tube Detector +Receiving Set + +(B) Fig. 41.--Wiring Diagram of a Simple Vacuum Tube Receiving Set + +Fig. 42.--Grid Leaks and How to Connect them Up + +Fig. 43.--Crystal Detector Receiving Set with Vacuum Tube Amplifier +(Resistance Coupled) + +(A) Fig. 44.--Vacuum Tube Detector Receiving Set with One Step +Amplifier (Resistance Coupled) + +(B) Fig. 44.--Wiring Diagram for Using One A or Storage Battery with +an Amplifier and a Detector Tube + +(A) Fig. 45.--Wiring Diagram for Radio Frequency Transformer +Amplifying Receiving Set + +(B) Fig. 45.--Radio Frequency Transformer + +(A) Fig. 46.--Audio Frequency Transformer + +(B) Fig. 46.--Wiring Diagram for Audio Frequency Transformer +Amplifying Receiving Set. (With Vacuum Tube Detector and Two Step +Amplifier Tubes) + +(A) Fig. 47.--Six Step Amplifier with Loop Aerial + +(B) Fig. 47.--Efficient Regenerative Receiving Set (With Three Coil +Loose Coupler Tuner) + +Fig. 48.--Simple Regenerative Receiving Set (With Loose Coupler Tuner) + +(A) Fig. 49.--Diagram of Three Coil Loose Coupler + +(B) Fig. 49.--Three Coil Loose Coupler Tuner + +Fig. 50.--Honeycomb Inductance Coil + +Fig. 51.--The Use of the Potentiometer + +Fig. 52.--Regenerative Audio Frequency Amplifier Receiving Set + +Fig. 53.--How the Vario Coupler is Made and Works + +Fig. 54.--How the Variometer is Made and Works + +Fig. 55.--Short Wave Regenerative Receiving Set (One Variometer +and Three Variable Condensers) + +Fig. 56.--Short Wave Regenerative Receiving Set (Two Variometer +and Two Variable Condensers) + +Fig. 57.--Wiring Diagram Showing Fixed Loading Coils for Intermediate +Wave Set + +Fig. 58.--Wiring Digram of Intermediate Wave Receptor with One Vario +Coupler and 12 Section Bank-wound Inductance Coil + +Fig. 59.--Wiring Diagram Showing Long Wave Receptor with Vario +Couplers and 8 Bank-wound Inductance Coils + +Fig. 60.--Wiring Diagram of Long Wave Autodyne, or Self-heterodyne +Receptor (Compare with Fig. 77) + +Fig. 61.--Wiring Diagram of Long Wave Separate Heterodyne Receiving +Set + +Fig. 62.--Cross Section of Bell Telephone Receiver + +Fig. 63.--Cross Section of Wireless Headphone + +Fig. 64.--The Wireless Headphone + +Fig. 65.--Arkay Loud Speaker + +Fig. 66.--Amplitone Loud Speaker + +Fig. 67.--Amplitron Loud Speaker + +Fig. 68.--Magnavox Loud Speaker + +Fig. 69.--Schematic Diagram of an Atom + +Fig. 70.--Action of Two-electrode Vacuum Tube + +(A) and (B) Fig. 71.--How a Two-electrode Tube Acts as Relay or a +Detector + +(C) Fig. 71--Only the Positive Part of Oscillations Goes through the +Tube + +(A) and (B) Fig. 72.--How the Positive and Negative Voltages of the +Oscillations Act on the Electrons + +(C) Fig. 72.--How the Three-electrode Tube Acts as Detector and +Amplifier + +(D) Fig. 72.--How the Oscillations Control the Flow of the Battery +Current through the Tube + +Fig. 73.--How the Heterodyne Receptor Works + +Fig. 74.--Separate Heterodyne Oscillator + +(A) Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter. + +(B) Fig. 75.--Apparatus for Experimental C. W. Telegraph Transmitter. + +Fig. 76.--Experimental C. W. Telegraph Transmitter + +Fig. 77--Apparatus of 100-mile C. W. Telegraph Transmitter + +Fig. 78.--5- to 50-watt C. W. Telegraph Transmitter (with a Single +Oscillation Tube) + +Fig. 79.--200-mile C. W. Telegraph Transmitter (with Two Tubes in +Parallel) + +Fig. 80.--50-watt Oscillator Vacuum Tube + +Fig. 81.--Alternating Current Power Transformer (for C. W. Telegraphy +and Wireless Telephony) + +Fig. 82.--Wiring Diagram for 200- to 500-mile C. W. Telegraph +Transmitting Set. (With Alternating Current.) + +Fig. 83--Wiring Diagram for 500- to 1000-mile C. W. Telegraph +Transmitter + +Fig. 84.--Standard Microphone Transmitter + +Fig. 85.--Wiring Diagram of Short Distance Wireless Telephone Set. +(Microphone in Aerial Wire.) + +Fig. 86.--Telephone Induction Coil (used with Microphone Transmitter). + +Fig. 87.--Microphone Transformer Used with Microphone Transmitter + +Fig. 88.--Magnetic Modulator Used with Microphone Transmitter + +(A) Fig. 89.--Wiring Diagram of 25--to 50-mile Wireless Telephone. +(Microphone Modulator Shunted Around Grid-leak Condenser) + +(B) Fig. 89.--Microphone Modulator Connected in Aerial Wire + +Fig. 90.--Wiring Diagram of 50- to 100-mile Wireless Telephone +Transmitting Set + +Fig. 91.--Plate and Grid Circuit Reactor + +Fig. 92.--Filter Reactor for Smoothing Out Rectified Currents + +Fig. 93.--100- to 200-mile Wireless Telephone Transmitter + +(A) and (B) Fig. 94.--Operation of Vacuum Tube Oscillators + +(C) Fig. 94.--How a Direct Current Sets up Oscillations + +Fig. 95.--Positive Voltage Only Sets up Oscillations + +Fig. 96.--Rasco Baby Crystal Detector + +Fig. 97.--How the Tuning Coil is Made + +Fig. 98.--Mesco loop-ohm Head Set + +Fig. 99.--Schematic Layout of the $5.00 Receiving Set + +Fig. 100.--Wiring Diagram for the $5.00 Receiving Set + + + + +LIST OF ILLUSTRATIONS + + +A. Frederick Collins, Inventor of the Wireless Telephone, 1899. + Awarded Gold Medal for same, Alaska Yukon Pacific Exposition, 1909 + +Collins' Wireless Telephone Exhibited at the Madison Square Garden, + October, 1908 + +General Pershing "Listening-in" + +The World's Largest Radio Receiving Station. Owned by the Radio + Corporation of America at Rocky Point near Port Jefferson, L. I. + +First Wireless College in the World, at Tufts College, Mass + +Alexander Graham Bell, Inventor of the Telephone, now an ardent + Radio Enthusiast + +World's Largest Loud Speaker ever made. Installed in Lytle + Park, Cincinnati, Ohio, to permit President Harding's + Address at Point Pleasant, Ohio, during the Grant Centenary + Celebration to be heard within a radius of one square + +United States Naval High Power Station, Arlington, Va. General + view of Power Room. At the left can be seen the Control + Switchboards, and overhead, the great 30 K.W. Arc Transmitter + with Accessories + +The Transformer and Tuner of the World's Largest Radio Station. + Owned by the Radio Corporation of America at Rocky Point + near Port Jefferson, L. I. + +Broadcasting Government Reports by Wireless from Washington. + This shows Mr. Gale at work with his set in the Post Office + Department + +Wireless Receptor, the size of a Safety Match Box. A Youthful + Genius in the person of Kenneth R. Hinman, who is only + twelve years old, has made a Wireless Receiving Set that fits + neatly into a Safety Match Box. With this Instrument and + a Pair of Ordinary Receivers, he is able to catch not only + Code Messages but the regular Broadcasting Programs from + Stations Twenty and Thirty Miles Distant + +Wireless Set made into a Ring, designed by Alfred G. Rinehart, of + Elizabeth, New Jersey. This little Receptor is a Practical Set; + it will receive Messages, Concerts, etc., measures 1" by 5/8" by + 7/8". An ordinary Umbrella is used as an Aerial + + + + +CHAPTER I + +HOW TO BEGIN WIRELESS + + +In writing this book it is taken for granted that you are: _first_, +one of the several hundred thousand persons in the United States who +are interested in wireless telegraphy and telephony; _second_, that +you would like to install an apparatus in your home, and _third_, that +it is all new to you. + +Now if you live in a city or town large enough to support an +electrical supply store, there you will find the necessary apparatus +on sale, and someone who can tell you what you want to know about it +and how it works. If you live away from the marts and hives of +industry you can send to various makers of wireless apparatus +[Footnote: A list of makers of wireless apparatus will be found in the +_Appendix_.] for their catalogues and price-lists and these will give +you much useful information. But in either case it is the better plan +for you to know before you start in to buy an outfit exactly what +apparatus you need to produce the result you have in mind, and this +you can gain in easy steps by reading this book. + +Kinds of Wireless Systems.--There are two distinct kinds of wireless +systems and these are: the _wireless telegraph_ system, and the +_wireless telephone_ system. The difference between the wireless +telegraph and the wireless telephone is that the former transmits +messages by means of a _telegraph key_, and the latter transmits +conversation and music by means of a _microphone transmitter_. In +other words, the same difference exists between them in this respect +as between the Morse telegraph and the Bell telephone. + +Parts of a Wireless System.--Every complete wireless station, whether +telegraph or telephone, consists of three chief separate and distinct +parts and these are: (a) the _aerial wire system_, or _antenna_ as it +is often called, (b) the _transmitter_, or _sender_, and (c) the +_receiver_, or, more properly, the _receptor_. The aerial wire is +precisely the same for either wireless telegraphy or wireless +telephony. The transmitter of a wireless telegraph set generally uses +a _spark gap_ for setting up the electric oscillations, while usually +for wireless telephony a _vacuum tube_ is employed for this purpose. +The receptor for wireless telegraphy and telephony is the same and may +include either a _crystal detector_ or a _vacuum tube detector_, as +will be explained presently. + +The Easiest Way to Start.--First of all you must obtain a government +license to operate a sending set, but you do not need a license to put +up and use a receiving set, though you are required by law to keep +secret any messages which you may overhear. Since no license is needed +for a receiving set the easiest way to break into the wireless game is +to put up an aerial and hook up a receiving set to it; you can then +listen-in and hear what is going on in the all-pervading ether around +you, and you will soon find enough to make things highly entertaining. + +Nearly all the big wireless companies have great stations fitted with +powerful telephone transmitters and at given hours of the day and +night they send out songs by popular singers, dance music by jazz +orchestras, fashion talks by and for the ladies, agricultural reports, +government weather forecasts and other interesting features. Then by +simply shifting the slide on your tuning coil you can often tune-in +someone who is sending _Morse_, that is, messages in the dot and dash +code, or, perhaps a friend who has a wireless telephone transmitter +and is talking. Of course, if you want to _talk back_ you must have a +wireless transmitter, either telegraphic or telephonic, and this is a +much more expensive part of the apparatus than the receptor, both in +its initial cost and in its operation. A wireless telegraph +transmitter is less costly than a wireless telephone transmitter and +it is a very good scheme for you to learn to send and receive +telegraphic messages. + +At the present time, however, there are fifteen amateur receiving +stations in the United States to every sending station, so you can see +that the majority of wireless folks care more for listening in to the +broadcasting of news and music than to sending out messages on their +own account. The easiest way to begin wireless, then, is to put up an +aerial and hook up a receiving set to it. + +About Aerial Wire Systems.--To the beginner who wants to install a +wireless station the aerial wire system usually looms up as the +biggest obstacle of all, and especially is this true if his house is +without a flag pole, or other elevation from which the aerial wire can +be conveniently suspended. + +If you live in the congested part of a big city where there are no +yards and, particularly, if you live in a flat building or an +apartment house, you will have to string your aerial wire on the roof, +and to do this you should get the owner's, or agent's, permission. +This is usually an easy thing to do where you only intend to receive +messages, for one or two thin wires supported at either end of the +building are all that are needed. If for any reason you cannot put +your aerial on the roof then run a wire along the building outside of +your apartment, and, finally, if this is not feasible, connect your +receiver to a wire strung up in your room, or even to an iron or a +brass bed, and you can still get the near-by stations. + +An important part of the aerial wire system is the _ground_, that is, +your receiving set must not only be connected with the aerial wire, +but with a wire that leads to and makes good contact with the moist +earth of the ground. Where a house or a building is piped for gas, +water or steam, it is easy to make a ground connection, for all you +have to do is to fasten the wire to one of the pipes with a clamp. +[Footnote: Pipes are often insulated from the ground, which makes them +useless for this purpose.] Where the house is isolated then a lot of +wires or a sheet of copper or of zinc must be buried in the ground at +a sufficient depth to insure their being kept moist. + +About the Receiving Apparatus.--You can either buy the parts of the +receiving apparatus separate and hook them up yourself, or you can buy +the apparatus already assembled in a set which is, in the beginning, +perhaps, the better way. + +The simplest receiving set consists of (1) a _detector_, (2) a _tuning +coil_, and (3) a _telephone receiver_ and these three pieces of +apparatus are, of course, connected together and are also connected to +the aerial and ground as the diagram in Fig. 1 clearly shows. There +are two chief kinds of detectors used at the present time and these +are: (a) the _crystal detector_, and (b) the _vacuum tube detector_. +The crystal detector is the cheapest and simplest, but it is not as +sensitive as the vacuum tube detector and it requires frequent +adjustment. A crystal detector can be used with or without a battery +while the vacuum tube detector requires two small batteries. + +[Illustration: Fig. 1.--Simple Receiving Set.] + +A tuning coil of the simplest kind consists of a single layer of +copper wire wound on a cylinder with an adjustable, or sliding, +contact, but for sharp tuning you need a _loose coupled tuning coil_. +Where a single coil tuner is used a _fixed_ condenser should be +connected around the telephone receivers. Where a loose coupled tuner +is employed you should have a variable condenser connected across the +_closed oscillation circuit_ and a _fixed condenser_ across the +telephone receivers. + +When listening-in to distant stations the energy of the received +wireless waves is often so very feeble that in order to hear +distinctly an _amplifier_ must be used. To amplify the incoming sounds +a vacuum tube made like a detector is used and sometimes as many as +half-a-dozen of these tubes are connected in the receiving circuit, or +in _cascade_, as it is called, when the sounds are _amplified_, that +is magnified, many hundreds of times. + +The telephone receiver of a receiving set is equally as important as +the detector. A single receiver can be used but a pair of receivers +connected with a head-band gives far better results. Then again the +higher the resistance of the receivers the more sensitive they often +are and those wound to as high a resistance as 3,200 ohms are made for +use with the best sets. To make the incoming signals, conversation or +music, audible to a room full of people instead of to just yourself +you must use what is called a _loud speaker_. In its simplest form +this consists of a metal cone like a megaphone to which is fitted a +telephone receiver. + +About Transmitting Stations--Getting Your License.--If you are going +to install a wireless sending apparatus, either telegraphic or +telephonic, you will have to secure a government license for which no +fee or charge of any kind is made. There are three classes of licenses +issued to amateurs who want to operate transmitting stations and these +are: (1) the _restricted amateur license_, (2) the _general amateur +license_, and (3) the _special amateur license_. + +If you are going to set up a transmitter within five nautical miles of +any naval wireless station then you will have to get a _restricted +amateur license_ which limits the current you use to half a _kilowatt_ +[Footnote: A _Kilowatt_ is 1,000 _watts_. There are 746 watts in a +horsepower.] and the wave length you send out to 200 _meters_. Should +you live outside of the five-mile range of a navy station then you can +get a general amateur license and this permits you to use a current of +1 kilowatt, but you are likewise limited to a wave length of 200 +meters. But if you can show that you are doing some special kind of +wireless work and not using your sending station for the mere pleasure +you are getting out of it you may be able to get a _special amateur +license_ which gives you the right to send out wave lengths up to 375 +meters. + +When you are ready to apply for your license write to the _Radio +Inspector_ of whichever one of the following districts you live in: + + First District..............Boston, Mass. + Second " ..............New York City + Third " ..............Baltimore, Md. + Fourth " ..............Norfolk, Va. + Fifth " ..............New Orleans, La. + Sixth " ............. San Francisco, Cal. + Seventh " ............. Seattle, Wash. + Eighth " ............. Detroit, Mich. + Ninth " ..............Chicago, Ill. + +Kinds of Transmitters.--There are two general types of transmitters +used for sending out wireless messages and these are: (1) _wireless +telegraph_ transmitters, and (2) _wireless telephone_ transmitters. +Telegraph transmitters may use either: (a) a _jump-spark_, (b) an +_electric arc_, or (c) a _vacuum tube_ apparatus for sending out dot +and dash messages, while telephone transmitters may use either, (a) an +_electric arc_, or (b) a _vacuum tube_ for sending out vocal and +musical sounds. Amateurs generally use a _jump-spark_ for sending +wireless telegraph messages and the _vacuum tube_ for sending wireless +telephone messages. + +The Spark Gap Wireless Telegraph Transmitter.--The simplest kind of a +wireless telegraph transmitter consists of: (1) a _source of direct or +alternating current_, (2) a _telegraph key_, (3) a _spark-coil_ or a +_transformer_, (4) a _spark gap_, (5) an _adjustable condenser_ and +(6) an _oscillation transformer_. Where _dry cells_ or a _storage +battery_ must be used to supply the current for energizing the +transmitter a spark-coil can be employed and these may be had in +various sizes from a little fellow which gives 1/4-inch spark up to a +larger one which gives a 6-inch spark. Where more energy is needed it +is better practice to use a transformer and this can be worked on an +alternating current of 110 volts, or if only a 110 volt direct current +is available then an _electrolytic interrupter_ must be used to make +and break the current. A simple transmitting set with an induction +coil is shown in Fig. 2. + +[Illustration: Fig 2.--Simple Transmitting Set.] + +A wireless key is made like an ordinary telegraph key except that +where large currents are to be used it is somewhat heavier and is +provided with large silver contact points. Spark gaps for amateur work +are usually of: (1) the _plain_ or _stationary type_, (2) the +_rotating type_, and (3) the _quenched gap_ type. The plain spark-gap +is more suitable for small spark-coil sets, and it is not so apt to +break down the transformer and condenser of the larger sets as the +rotary gap. The rotary gap on the other hand tends to prevent _arcing_ +and so the break is quicker and there is less dragging of the spark. +The quenched gap is more efficient than either the plain or rotary gap +and moreover it is noiseless. + +Condensers for spark telegraph transmitters can be ordinary Leyden +jars or glass plates coated with tin or copper foil and set into a +frame, or they can be built up of mica and sheet metal embedded in an +insulating composition. The glass plate condensers are the cheapest +and will serve your purpose well, especially if they are immersed in +oil. Tuning coils, sometimes called _transmitting inductances_ and +_oscillation transformers_, are of various types. The simplest kind is +a transmitting inductance which consists of 25 or 30 turns of copper +wire wound on an insulating tube or frame. An oscillation transformer +is a loose coupled tuning coil and it consists of a primary coil +formed of a number of turns of copper wire wound on a fixed insulating +support, and a secondary coil of about twice the number of turns of +copper wire which is likewise fixed in an insulating support, but the +coils are relatively movable. An _oscillation transformer_ (instead of +a _tuning coil_), is required by government regulations unless +_inductively coupled_. + +The Vacuum Tube Telegraph Transmitter.--This consists of: (1) a +_source of direct or alternating current_, (2) a _telegraph key_, (3) a +_vacuum tube oscillator_, (4) a _tuning coil_, and (5) a _condenser_. +This kind of a transmitter sets up _sustained_ oscillations instead of +_periodic_ oscillations which are produced by a spark gap set. The +advantages of this kind of a system will be found explained in Chapter +XVI. + +The Wireless Telephone Transmitter.--Because a jump-spark sets up +_periodic oscillations_, that is, the oscillations are discontinuous, +it cannot be used for wireless telephony. An electric arc or a vacuum +tube sets up _sustained_ oscillations, that is, oscillations which are +continuous. As it is far easier to keep the oscillations going with a +vacuum tube than it is with an arc the former means has all but +supplanted the latter for wireless telephone transmitters. The +apparatus required and the connections used for wireless telephone +sets will be described in later chapters. + +Useful Information.--It would be wise for the reader to turn to the +Appendix, beginning with page 301 of this book, and familiarize +himself with the information there set down in tabular and graphic +form. For example, the first table gives abbreviations of electrical +terms which are in general use in all works dealing with the subject. +You will also find there brief definitions of electric and magnetic +units, which it would be well to commit to memory; or, at least, to +make so thoroughly your own that when any of these terms is mentioned, +you will know instantly what is being talked about. + + + + +CHAPTER II + +PUTTING UP YOUR AERIAL + + +As inferred in the first chapter, an aerial for receiving does not +have to be nearly as well made or put up as one for sending. But this +does not mean that you can slipshod the construction and installation +of it, for however simple it is, the job must be done right and in +this case it is as easy to do it right as wrong. + +To send wireless telegraph and telephone messages to the greatest +distances and to receive them as distinctly as possible from the +greatest distances you must use for your aerial (1) copper or aluminum +wire, (2) two or more wires, (3) have them the proper length, (4) have +them as high in the air as you can, (5) have them well apart from each +other, and (6) have them well insulated from their supports. If you +live in a flat building or an apartment house you can string your +aerial wires from one edge of the roof to the other and support them +by wooden stays as high above it as may be convenient. + +Should you live in a detached house in the city you can usually get +your next-door neighbor to let you fasten one end of the aerial to his +house and this will give you a good stretch and a fairly high aerial. +In the country you can stretch your wires between the house and barn +or the windmill. From this you will see that no matter where you live +you can nearly always find ways and means of putting up an aerial that +will serve your needs without going to the expense of erecting a mast. + +Kinds of Aerial Wire Systems.--An amateur wireless aerial can be +anywhere from 25 feet to 100 feet long and if you can get a stretch of +the latter length and a height of from 30 to 75 feet you will have one +with which you can receive a thousand miles or more and send out as +much energy as the government will allow you to send. + +The kind of an aerial that gives the best results is one whose wire, +or wires, are _horizontal_, that is, parallel with the earth under it +as shown at A in Fig. 3. If only one end can be fixed to some elevated +support then you can secure the other end to a post in the ground, but +the slope of the aerial should not be more than 30 or 35 degrees from +the horizontal at most as shown at B. + +[Illustration: (A) Fig. 3.--Flat top, or Horizontal Aerial.] + +[Illustration: (B) Fig. 3.--Inclined Aerial.] + +The _leading-in wire_, that is, the wire that leads from and joins the +aerial wire with your sending and receiving set, can be connected to +the aerial anywhere it is most convenient to do so, but the best +results are had when it is connected to one end as shown at A in Fig. +4, in which case it is called an _inverted L aerial_, or when it is +connected to it at the middle as shown at B, when it is called a _T +aerial_. The leading-in wire must be carefully insulated from the +outside of the building and also where it passes through it to the +inside. This is done by means of an insulating tube known as a +_leading-in insulator_, or _bulkhead insulator_ as it is sometimes +called. + +[Illustration: (A) Fig. 4.--Inverted L Aerial.] + +[Illustration: (B) Fig. 4.--T Aerial.] + +As a protection against lightning burning out your instruments you can +use either: (1) an _air-gap lightning arrester,_ (2) a _vacuum tube +protector_, or (3) a _lightning switch_, which is better. Whichever +of these devices is used it is connected in between the aerial and an +outside ground wire so that a direct circuit to the earth will be +provided at all times except when you are sending or receiving. So +your aerial instead of being a menace really acts during an electrical +storm like a lightning rod and it is therefore a real protection. The +air-gap and vacuum tube lightning arresters are little devices that +can be used only where you are going to receive, while the lightning +switch must be used where you are going to send; indeed, in some +localities the _Fire Underwriters_ require a large lightning switch to +be used for receiving sets as well as sending sets. + +How to Put Up a Cheap Receiving Aerial.--The kind of an aerial wire +system you put up will depend, chiefly, on two things, and these are: +(1) your pocketbook, and (2) the place where you live. + +A Single Wire Aerial.--This is the simplest and cheapest kind of a +receiving aerial that can be put up. The first thing to do is to find +out the length of wire you need by measuring the span between the two +points of support; then add a sufficient length for the leading-in +wire and enough more to connect your receiving set with the radiator +or water pipe. + +You can use any size of copper or aluminum wire that is not smaller +than _No. 16 Brown and Sharpe gauge._ When you buy the wire get also +the following material: (1) two _porcelain insulators_ as shown at A +in Fig. 5; (2) three or four _porcelain knob insulators_, see B; (3) +either (a) an _air gap lightning arrester,_ see C, or (b) a _lightning +switch_ see D; (4) a _leading-in porcelain tube insulator,_ see E, and +(5) a _ground clamp_, see F. + +[Illustration: Fig. 5.--Material for a Simple Aerial Wire System.] + +To make the aerial slip each end of the wire through a hole in each +insulator and twist it fast; next cut off and slip two more pieces of +wire through the other holes in the insulators and twist them fast and +then secure these to the supports at the ends of the building. Take +the piece you are going to use for the leading-in wire, twist it +around the aerial wire and solder it there when it will look like A in +Fig. 6. Now if you intend to use the _air gap lightning arrester_ +fasten it to the wall of the building outside of your window, and +bring the leading-in wire from the aerial to the top binding post of +your arrester and keep it clear of everything as shown at B. If your +aerial is on the roof and you have to bring the leading-in wire over +the cornice or around a corner fix a porcelain knob insulator to the +one or the other and fasten the wire to it. + +[Illustration: (A) Fig. 6.--Single Wire Aerial for Receiving.] + +[Illustration: (B) Fig. 6.--Receiving Aerial with Air Gap Lightning +Arrester.] + +[Illustration: (C) Fig. 6.--Aerial with Lightning Switch.] + +Next bore a hole through the frame of the window at a point nearest +your receiving set and push a porcelain tube 5/8 inch in diameter and +5 or 6 inches long, through it. Connect a length of wire to the top +post of the arrester or just above it to the wire, run this through +the leading-in insulator and connect it to the slider of your tuning +coil. Screw the end of a piece of heavy copper wire to the lower post +of the arrester and run it to the ground, on porcelain knobs if +necessary, and solder it to an iron rod or pipe which you have driven +into the earth. Finally connect the fixed terminal of your tuning coil +with the water pipe or radiator inside of the house by means of the +ground clamp as shown in the diagrammatic sketch at B in Fig. 6 and +you are ready to tune in. + +If you want to use a lightning switch instead of the air-gap arrester +then fasten it to the outside wall instead of the latter and screw the +free end of the leading-in wire from the aerial to the middle post of +it as shown at C in Fig. 6. Run a wire from the top post through the +leading-in insulator and connect it with the slider of your tuning +coil. Next screw one end of a length of heavy copper wire to the lower +post of the aerial switch and run it to an iron pipe in the ground as +described above in connection with the spark-gap lightning arrester; +then connect the fixed terminal of your tuning coil with the radiator +or water pipe and your aerial wire system will be complete as shown at +C in Fig. 6. + +A Two-wire Aerial.--An aerial with two wires will give better results +than a single wire and three wires are better than two, but you must +keep them well apart. To put up a two-wire aerial get (1) enough _No. +16_, or preferably _No. 14_, solid or stranded copper or aluminum +wire, (2) four porcelain insulators, see B in Fig. 5, and (3) two +sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for the +_spreaders_, and bore 1/8-inch hole through each end of each one. Now +twist the ends of the wires to the insulators and then cut off four +pieces of wire about 6 feet long and run them through the holes in the +wood spreaders. Finally twist the ends of each pair of short wires to +the free ends of the insulators and then twist the free ends of the +wires together. + +For the leading-in wire that goes to the lightning switch take two +lengths of wire and twist one end of each one around the aerial wires +and solder them there. Twist the short wire around the long wire and +solder this joint also when the aerial will look like Fig. 7. Bring +the free end of the leading-in wire down to the middle post of the +lightning switch and fasten it there and connect up the receiver to it +and the ground as described under the caption of _A Single Wire +Aerial_. + +[Illustration: Fig. 7.--Two Wire Aerial.] + +Connecting in the Ground.--If there is a gas or water system or a +steam-heating plant in your house you can make your ground connection +by clamping a ground clamp to the nearest pipe as has been previously +described. Connect a length of bare or insulated copper wire with it +and bring this up to the table on which you have your receiving set. +If there are no grounded pipes available then you will have to make a +good ground which we shall describe presently and lead the ground wire +from your receiving set out of the window and down to it. + +How to Put Up a Good Aerial.--While you can use the cheap aerial +already described for a small spark-coil sending set you should have a +better insulated one for a 1/2 or a 1 kilowatt transformer set. The +cost for the materials for a good aerial is small and when properly +made and well insulated it will give results that are all out of +proportion to the cost of it. + +An Inexpensive Good Aerial.--A far better aerial, because it is more +highly insulated, can be made by using _midget insulators_ instead of +the porcelain insulators described under the caption of _A Single Wire +Aerial_ and using a small _electrose leading-in insulator_ instead of +the porcelain bushing. This makes a good sending aerial for small sets +as well as a good receiving aerial. + +The Best Aerial that Can Be Made.--To make this aerial get the +following material together: (1) enough _stranded or braided wire_ for +three or four lengths of parallel wires, according to the number you +want to use (2) six or eight _electrose ball insulators_, see B, Fig. +8; (3) two 5-inch or 10-inch _electrose strain insulators_, see C; (4) +six or eight _S-hooks_, see D; one large _withe_ with one eye for +middle of end spreader, see E; (6) two smaller _withes_ with one eye +each for end spreader, see E; (7) two still smaller _withes_, with two +eyes each for the ends of the end spreaders, see E (8) two _thimbles_, +see F, for 1/4-inch wire cable; (9) six or eight _hard rubber tubes_ +or _bushings_ as shown at G; and (10) two _end spreaders_, see H; one +_middle spreader_, see I; and one _leading-in spreader_, see J. + +[Illustration: (A) Fig. 8--Part of a Good Aerial.] + +[Illustration: (B) Fig. 8.--The Spreaders.] + +For this aerial any one of a number of kinds of wire can be used and +among these are (a) _stranded copper wire;_ (b) _braided copper wire;_ +(c) _stranded silicon bronze wire,_ and (d) _stranded phosphor bronze +wire_. Stranded and braided copper wire is very flexible as it is +formed of seven strands of fine wire twisted or braided together and +it is very good for short and light aerials. Silicon bronze wire is +stronger than copper wire and should be used where aerials are more +than 100 feet long, while phosphor bronze wire is the strongest aerial +wire made and is used for high grade aerials by the commercial +companies and the Government for their high-power stations. + +The spreaders should be made of spruce, and should be 4 feet 10 inches +long for a three-wire aerial and 7 feet 1 inch long for a four-wire +aerial as the distance between the wires should be about 27 inches. +The end spreaders can be turned cylindrically but it makes a better +looking job if they taper from the middle to the ends. They should be +2-1/4 inches in diameter at the middle and 1-3/4 inches at the ends. +The middle spreader can be cylindrical and 2 inches in diameter. It +must have holes bored through it at equidistant points for the hard +rubber tubes; each of these should be 5/8 inch in diameter and have a +hole 5/32 inch in diameter through it for the aerial wire. The +leading-in spreader is also made of spruce and is 1-1/2 inches square +and 26 inches long. Bore three or four 5/8-inch holes at equidistant +points through this spreader and insert hard rubber tubes in them as +with the middle spreader. + +Assembling the Aerial.--Begin by measuring off the length of each wire +to be used and see to it that all of them are of exactly the same +length. Now push the hard rubber insulators through the holes in the +middle spreader and thread the wires through the holes in the +insulators as shown at A in Fig 9. + +Next twist the ends of each wire to the rings of the ball insulators +and then put the large withes on the middle of each of the end +spreaders; fix the other withes on the spreaders so that they will be +27 inches apart and fasten the ball insulators to the eyes in the +withes with the S-hooks. Now slip a thimble through the eye of one of +the long strain insulators, thread a length of stranded steel wire 1/4 +inch in diameter through it and fasten the ends of it to the eyes in +the withes on the ends of the spreaders. + +[Illustration: (A) Fig. 9.--Middle Spreader.] + +[Illustration: (B) Fig. 9.--One End of Aerial Complete.] + +[Illustration: (C) Fig. 9.--Leading in Spreader.] + +Finally fasten a 40-inch length of steel stranded wire to each of the +eyes of the withes on the middle of each of the spreaders, loop the +other end over the thimble and then wrap the end around the wires that +are fixed to the ends of the spreaders. One end of the aerial is shown +complete at B in Fig. 9, and from this you can see exactly how it is +assembled. Now cut off three or four pieces of wire 15 or 20 feet long +and twist and solder each one to one of the aerial wires; then slip +them through the hard rubber tubes in the leading-in spreader, bring +their free ends together as at C and twist and solder them to a length +of wire long enough to reach to your lightning switch or instruments. + +Making a Good Ground.--Where you have to make a _ground_ you can do so +either by (1) burying sheets of zinc or copper in the moist earth; (2) +burying a number of wires in the moist earth, or (3) using a +_counterpoise_. To make a ground of the first kind take half a dozen +large sheets of copper or zinc, cut them into strips a foot wide, +solder them all together with other strips and bury them deeply in the +ground. + +It is easier to make a wire ground, say of as many or more wires as +you have in your aerial and connect them together with cross wires. To +put such a ground in the earth you will have to use a plow to make the +furrows deep enough to insure them always being moist. In the +counterpoise ground you make up a system of wires exactly like your +aerial, that is, you insulate them just as carefully; then you support +them so that they will be as close to the ground as possible and yet +not touch it or anything else. This and the other two grounds just +described should be placed directly under the aerial wire if the best +results are to be had. In using a counterpoise you must bring the wire +from it up to and through another leading-in insulator to your +instruments. + + + + +CHAPTER III + +SIMPLE TELEGRAPH AND TELEPHONE RECEIVING SETS + + +With a crystal detector receiving set you can receive either +telegraphic dots and dashes or telephonic speech and music. You can +buy a receiving set already assembled or you can buy the different +parts and assemble them yourself. An assembled set is less bother in +the beginning but if you like to experiment you can _hook up_, that +is, connect the separate parts together yourself and it is perhaps a +little cheaper to do it this way. Then again, by so doing you get a +lot of valuable experience in wireless work and an understanding of +the workings of wireless that you cannot get in any other way. + +Assembled Wireless Receiving Sets.--The cheapest assembled receiving +set [Footnote: The Marvel, made by the Radio Mfg. Co., New York City.] +advertised is one in which the detector and tuning coil is mounted in +a box. It costs $15.00, and can be bought of dealers in electric +supplies generally. + +This price also includes a crystal detector, an adjustable tuning +coil, a single telephone receiver with head-band and the wire, +porcelain insulators, lightning switch and ground clamp for the aerial +wire system. It will receive wireless telegraph and telephone messages +over a range of from 10 to 25 miles. + +Another cheap unit receptor, that is, a complete wireless receiving +set already mounted which can be used with a single aerial is sold for +$25.00. [Footnote: The Aeriola Jr., made by the Westinghouse Company, +Pittsburgh, Pa.] This set includes a crystal detector, a variable +tuning coil, a fixed condenser and a pair of head telephone receivers. +It can also be used to receive either telegraph or telephone messages +from distances up to 25 miles. The aerial equipment is not included in +this price, but it can be bought for about $2.50 extra. + +Assembling Your Own Receiving Set.--In this chapter we shall go only +into the apparatus used for two simple receiving sets, both of which +have a _crystal detector_. The first set includes a _double-slide +tuning coil_ and the second set employs a _loose-coupled tuning coil_, +or _loose coupler_, as it is called for short. For either set you can +use a pair of 2,000- or 3,000-ohm head phones. + +[Illustration: original © Underwood and Underwood. General Pershing +Listening In.] + +The Crystal Detector.--A crystal detector consists of: (1) _the +frame_, (2) _the crystal_, and (3) _the wire point_. There are any +number of different designs for frames, the idea being to provide a +device that will (a) hold the sensitive crystal firmly in place, and +yet permit of its removal, (b) to permit the _wire point_, or +_electrode_, to be moved in any direction so that the free point of it +can make contact with the most sensitive spot on the crystal and (c) +to vary the pressure of the wire on the crystal. + +A simple detector frame is shown in the cross-section at A in Fig. 10; +the crystal, which may be _galena_, _silicon_ or _iron pyrites_, is +held securely in a holder while the _phosphor-bronze wire point_ which +makes contact with it, is fixed to one end of a threaded rod on the +other end of which is a knob. This rod screws into and through a +sleeve fixed to a ball that sets between two brass standards and this +permits an up and down or a side to side adjustment of the metal point +while the pressure of it on the crystal is regulated by the screw. + +[Illustration: (A) Fig. 10.--Cross Section of Crystal Detector.] + +[Illustration: (B) Fig. 10.--The Crystal Detector Complete.] + +A crystal of this kind is often enclosed in a glass cylinder and this +makes it retain its sensitiveness for a much longer time than if it +were exposed to dust and moisture. An upright type of this detector +can be bought for $2.25, while a horizontal type, as shown at B, can +be bought for $2.75. Galena is the crystal that is generally used, +for, while it is not quite as sensitive as silicon and iron pyrites, +it is easier to obtain a sensitive piece. + +The Tuning Coil.--It is with the tuning coil that you _tune in_ and +_tune out_ different stations and this you do by sliding the contacts +to and fro over the turns of wire; in this way you vary the +_inductance_ and _capacitance_, that is, the _constants_ of the +receiving circuits and so make them receive _electric waves_, that is, +wireless waves, of different lengths. + +The Double Slide Tuning Coil.--With this tuning coil you can receive +waves from any station up to 1,000 meters in length. One of the ends +of the coil of wire connects with the binding post marked _a_ in Fig. +11, and the other end connects with the other binding post marked _b_, +while one of the sliding contacts is connected to the binding post +_c_, and the _other sliding contact_ is connected with the binding +post _d_. + +[Illustration: (A) Fig. 11.--Schematic Diagram of Double Slide Tuning +Coil.] + +[Illustration: (B) Fig. 11.--Double Slide Tuning Coil Complete.] + +When connecting in the tuning coil, only the post _a_ or the post _b_ +is used as may be most convenient, but the other end of the wire which +is connected to a post is left free; just bear this point in mind when +you come to connect the tuning coil up with the other parts of your +receiving set. The tuning coil is shown complete at B and it costs +$3.00 or $4.00. A _triple slide_ tuning coil constructed like the +double slide tuner just described, only with more turns of wire on it, +makes it possible to receive wave lengths up to 1,500 meters. It costs +about $6.00. + +The Loose Coupled Tuning Coil.--With a _loose coupler_, as this kind +of a tuning coil is called for short, very _selective tuning_ is +possible, which means that you can tune in a station very sharply, and +it will receive any wave lengths according to size of coils. The +primary coil is wound on a fixed cylinder and its inductance is varied +by means of a sliding contact like the double slide tuning coil +described above. The secondary coil is wound on a cylinder that slides +in and out of the primary coil. The inductance of this coil is varied +by means of a switch that makes contact with the fixed points, each of +which is connected with every twentieth turn of wire as shown in the +diagram A in Fig. 12. The loose coupler, which is shown complete at B, +costs in the neighborhood of $8.00 or $10.00. + +[Illustration: (A) Fig. 12.--Schematic Diagram of Loose Coupler.] + +[Illustration: (B) Fig. 12.--Loose Coupler Complete.] + +Fixed and Variable Condensers.--You do not require a condenser for a +simple receiving set, but if you will connect a _fixed condenser_ +across your headphones you will get better results, while a _variable +condenser_ connected in the _closed circuit of a direct coupled +receiving set_, that is, one where a double slide tuning coil is used, +makes it easy to tune very much more sharply; a variable condenser is +absolutely necessary where the circuits are _inductively coupled_, +that is, where a loose coupled tuner is used. + +A fixed condenser consists of a number of sheets of paper with leaves +of tin-foil in between them and so built up that one end of every +other leaf of tin-foil projects from the opposite end of the paper as +shown at A in Fig. 13. The paper and tin-foil are then pressed +together and impregnated with an insulating compound. A fixed +condenser of the exact capacitance required for connecting across the +head phones is mounted in a base fitted with binding posts, as shown +at B, and costs 75 cents. (Paper ones 25 cents.) + +[Illustration: (A) Fig. 13.--How a Fixed Receiving Condenser is Built +up.] + +[Illustration: (B) Fig. 13.--The Fixed Condenser Complete.] + +[Illustration: (C) and (D) Fig. 13.--The Variable Rotary Condenser.] + +A variable condenser, see C, of the rotating type is formed of a set +of fixed semi-circular metal plates which are slightly separated from +each other and between these a similar set of movable semi-circular +metal plates is made to interleave; the latter are secured to a shaft +on the top end of which is a knob and by turning it the capacitance of +the condenser, and, hence, of the circuit in which it is connected, is +varied. This condenser, which is shown at D, is made in two sizes, the +smaller one being large enough for all ordinary wave lengths while the +larger one is for proportionately longer wave lengths. These +condensers cost $4.00 and $5.00 respectively. + +About Telephone Receivers.--There are a number of makes of head +telephone receivers on the market that are designed especially for +wireless work. These phones are wound to _resistances_ of from 75 +_ohms_ to 8,000 _ohms_, and cost from $1.25 for a receiver +without a cord or headband to $15.00 for a pair of phones with a cord +and head band. You can get a receiver wound to any resistance in +between the above values but for either of the simple receiving sets +such as described in this chapter you ought to have a pair wound to at +least 2,000 ohms and these will cost you about $5.00. A pair of head +phones of this type is shown in Fig. 14. + +[Illustration: Fig. 14.--Pair of Wireless Head Phones.] + +Connecting Up the Parts--Receiving Set No. 1.--For this set get (1) a +_crystal detector_, (2) a _two-slide tuning coil_, (3) a _fixed +condenser_, and (4) a pair of 2,000 ohm head phones. Mount the +detector on the right-hand side of a board and the tuning coil on the +left-hand side. Screw in two binding posts for the cord ends of the +telephone receivers at _a_ and _b_ as shown at A in Fig. 15. This done +connect one of the end binding posts of the tuning coil with the +ground wire and a post of one of the contact slides with the lightning +arrester or switch which leads to the aerial wire. + +[Illustration: Fig. 15.--Top View of Apparatus Layout for Receiving +Set No. 1.] + +[Illustration: (B) Fig. 15.--Wiring Diagram for Receiving Set No. 1.] + +Now connect the post of the other contact slide to one of the posts of +the detector and the other post of the latter with the binding post +_a_, then connect the binding post _b_ to the ground wire and solder +the joint. Next connect the ends of the telephone receiver cord to the +posts _a_ and _b_ and connect a fixed condenser also with these posts, +all of which are shown in the wiring diagram at B, and you are ready +to adjust the set for receiving. + +Receiving Set No. 2.--Use the same kind of a detector and pair of head +phones as for _Set No. 1_, but get (1) a _loose coupled tuning coil_, +and (2) a _variable condenser_. Mount the loose coupler at the back of +a board on the left-hand side and the variable condenser on the +right-hand side. Then mount the detector in front of the variable +condenser and screw two binding posts, _a_ and _b_, in front of the +tuning coil as shown at A in Fig. 16. + +[Illustration: Fig. 16.--Top view of Apparatus Layout for Receiving +Set No. 2.] + +[Illustration: (B) Fig. 16.--Wiring Diagram for Receiving Set No. 2.] + +Now connect the post of the sliding contact of the loose coupler with +the wire that runs to the lightning switch and thence to the aerial; +connect the post of the primary coil, which is the outside coil, with +the ground wire; then connect the binding post leading to the switch +of the secondary coil, which is the inside coil, with one of the posts +of the variable condenser, and finally, connect the post that is +joined to one end of the secondary coil with the other post of the +variable condenser. + +This done, connect one of the posts of the condenser with one of the +posts of the detector, the other post of the detector with the binding +post _a_, and the post _b_ to the other post of the variable +condenser. Next connect a fixed condenser to the binding posts _a_ and +_b_ and then connect the telephone receivers to these same posts, all +of which is shown in the wiring diagram at B. You are now ready to +adjust the instruments. In making the connections use No. 16 or 18 +insulated copper wire and scrape the ends clean where they go into the +binding posts. See, also, that all of the connections are tight and +where you have to cross the wires keep them apart by an inch or so and +always cross them at right angles. + +Adjusting the No. 1 Set--The Detector.--The first thing to do is to +test the detector in order to find out if the point of the contact +wire is on a sensitive spot of the crystal. To do this you need a +_buzzer_, a _switch_ and a _dry cell_. An electric bell from which the +gong has been removed will do for the buzzer, but you can get one that +is made specially for the purpose, for 75 cents, which gives out a +clear, high-pitched note that sounds like a high-power station. + +Connect one of the binding posts of the buzzer with one post of the +switch, the other post of the latter with the zinc post of the dry +cell and the carbon post of this to the other post of the buzzer. Then +connect the post of the buzzer that is joined to the vibrator, to the +ground wire as shown in the wiring diagram, Fig. 17. Now close the +switch of the buzzer circuit, put on your head phones, and move the +wire point of the detector to various spots on the crystal until you +hear the sparks made by the buzzer in your phones. + +[Illustration: Fig. 17.--Adjusting the Receiving Set.] + +Then vary the pressure of the point on the crystal until you hear the +sparks as loud as possible. After you have made the adjustment open +the switch and disconnect the buzzer wire from the ground wire of your +set. This done, be very careful not to jar the detector or you will +throw it out of adjustment and then you will have to do it all over +again. You are now ready to tune the set with the tuning coil and +listen in. + +The Tuning Coil.--To tune this set move the slide A of the +double-slide tuner, see B in Fig. 15, over to the end of the coil that +is connected with the ground wire and the slide B near the opposite +end of the coil, that is, the one that has the free end. Now move the +slide A toward the B slide and when you hear the dots and dashes, or +speech or music, that is coming in as loud as you can move the B slide +toward the A slide until you hear still more loudly. A very few trials +on your part and you will be able to tune in or tune out any station +you can hear, if not too close or powerful. + +[Illustration: original © Underwood and Underwood. The World's +Largest Radio Receiving Station. Owned by the Radio Corporation of +America at Rocky Point near Point Jefferson, L.I.] + +Adjusting the No. 2 Set.--First adjust the crystal detector with the +buzzer set as described above with _Set No. 1,_ then turn the knob of +your variable condenser so that the movable plates are just half-way +in, pull the secondary coil of your loose-coupled tuner half way out; +turn the switch lever on it until it makes a contact with the middle +contact point and set the slider of the primary coil half way between +the ends. + +Now listen in for telegraphic signals or telephonic speech or music; +when you hear one or the other slide the secondary coil in and out of +the primary coil until the sounds are loudest; now move the contact +switch over the points forth and back until the sounds are still +louder, then move the slider to and fro until the sounds are yet +louder and, finally, turn the knob of the condenser until the sounds +are clear and crisp. When you have done all of these things you have, +in the parlance of the wireless operator, _tuned in_ and you are ready +to receive whatever is being sent. + + + + +CHAPTER IV + +SIMPLE TELEGRAPH SENDING SETS + + +A wireless telegraph transmitting set can be installed for a very +small amount of money provided you are content with one that has a +limited range. Larger and better instruments can, of course, be had +for more money, but however much you are willing to spend still you +are limited in your sending radius by the Government's rules and +regulations. The best way, and the cheapest in the end, to install a +telegraph set is to buy the separate parts and hook them up yourself. + +The usual type of wireless telegraph transmitter employs a _disruptive +discharge,_ or _spark,_ as it is called, for setting up the +oscillating currents in the aerial wire system and this is the type of +apparatus described in this chapter. There are two ways to set up the +sparks and these are: (1) with an _induction coil,_ or _spark-coil,_ +as it is commonly called, and (2) with an _alternating current +transformer_, or _power transformer_, as it is sometimes called. Where +you have to generate the current with a battery you must use a spark +coil, but if you have a 110-volt direct or alternating lighting +current in your home you can use a transformer which will give you +more power. + +A Cheap Transmitting Set (No. 1).--For this set you will need: (1) a +_spark-coil_, (2) a _battery_ of dry cells, (3) a _telegraph key_, (4) +a _spark gap_, (5) a _high-tension condenser_, and (6) an _oscillation +transformer_. There are many different makes and styles of these parts +but in the last analysis all of them are built on the same underlying +bases and work on the same fundamental principles. + +The Spark-Coil.--Spark coils for wireless work are made to give sparks +from 1/4 inch in length up to 6 inches in length, but as a spark coil +that gives less than a 1-inch spark has a very limited output it is +best to get a coil that gives at least a 1-inch spark, as this only +costs about $8.00, and if you can get a 2- or a 4-inch spark coil so +much the better. There are two general styles of spark coils used for +wireless and these are shown at A and B in Fig. 18. + +[Illustration: (A) and (B) Fig. 18.--Types of Spark Coils for Set. No. +1.] + +[Illustration: (C) Fig. 18.--Wiring Diagram of Spark Coil] + +A spark coil of either style consists of (_a_) a soft _iron core_ on +which is wound (_b_) a couple of layers of heavy insulated wire and +this is called the _primary coil_, (_c_) while over this, but +insulated from it, is wound a large number of turns of very fine +insulated copper wire called the _secondary coil_; (d) an +_interrupter_, or _vibrator_, as it is commonly called, and, finally, +(e) a _condenser_. The core, primary and secondary coils form a unit +and these are set in a box or mounted on top of a hollow wooden base. +The condenser is placed in the bottom of the box, or on the base, +while the vibrator is mounted on one end of the box or on top of the +base, and it is the only part of the coil that needs adjusting. + +The vibrator consists of a stiff, flat spring fixed at one end to the +box or base while it carries a piece of soft iron called an _armature_ +on its free end and this sets close to one end of the soft iron core. +Insulated from this spring is a standard that carries an adjusting +screw on the small end of which is a platinum point and this makes +contact with a small platinum disk fixed to the spring. The condenser +is formed of alternate sheets of paper and tinfoil built up in the +same fashion as the receiving condenser described under the caption of +_Fixed and Variable Condensers_, in Chapter III. + +The wiring diagram C shows how the spark coil is wired up. One of the +battery binding posts is connected with one end of the primary coil +while the other end of the latter which is wound on the soft iron core +connects with the spring of the vibrator. The other battery binding +post connects with the standard that supports the adjusting screw. The +condenser is shunted across the vibrator, that is, one end of the +condenser is connected with the spring and the other end of the +condenser is connected with the adjusting screw standard. The ends of +the secondary coil lead to two binding posts, which are usually placed +on top of the spark coil and it is to these that the spark gap is +connected. + +The Battery.--This can be formed of dry cells or you can use a storage +battery to energize your coil. For all coils that give less than a +1-inch spark you should use 5 dry cells; for 1-and 2-inch spark coils +use 6 or 8 dry cells, and for 3 to 4-inch spark coils use 8 to 10 dry +cells. The way the dry cells are connected together to form a battery +will be shown presently. A dry cell is shown at A in Fig, 19. + +[Illustration: Fig. 19.--Other parts for Transmitting Set No. 1] + +The Telegraph Key.--You can use an ordinary Morse telegraph key for +the sending set and you can get one with a japanned iron base for +$1.50 (or better, one made of brass and which has 1/8-inch silver +contact points for $3.00. A key of the latter kind is shown at B). + +The Spark gap.--It is in the _spark gap_ that the high tension spark +takes place. The apparatus in which the spark takes place is also +called the _spark gap_. It consists of a pair of zinc plugs, called +_electrodes_, fixed to the ends of a pair of threaded rods, with knobs +on the other ends, and these screw into and through a pair of +standards as shown at _c_. This is called a _fixed_, or _stationary +spark gap_ and costs about $1.00. + +The Tuning Coil.--The _transmitting inductance_, or _sending tuning +coil_, consists of 20 to 30 turns of _No. 8 or 9_ hard drawn copper +wire wound on a slotted insulated form and mounted on a wooden base. +It is provided with _clips_ so that you can cut in and cut out as many +turns of wire as you wish and so tune the sending circuits to send out +whatever wave length you desire. It is shown at _d_, and costs about +$5.00. See also _Oscillation Transformer_, page 63 [Chapter IV]. + +The High Tension Condenser.--High tension condensers, that is, +condensers which will stand up under _high potentials_, or electric +pressures, can be bought in units or sections. These condensers are +made up of thin brass plates insulated with a special compound and +pressed into a compact form. The _capacitance_ [Footnote: This is the +capacity of the condenser.] of one section is enough for a +transmitting set using a spark coil that gives a 2 inch spark or less +and two sections connected together should be used for coils giving +from 2 to 4 inch sparks. It is shown at _e_. + +Connecting Up the Apparatus.--Your sending set should be mounted on a +table, or a bench, where it need not be moved. Place the key in about +the middle of the table and down in front, and the spark coil to the +left and well to the back but so that the vibrator end will be to the +right, as this will enable you to adjust it easily. Place the battery +back of the spark coil and the tuning coil (oscillation transformer) +to the right of the spark coil and back of the key, all of which is +shown in the layout at A in Fig. 20. + +[Illustration: (A) Fig. 20.--Top View of Apparatus Layout for Sending +Set No. 1.] + +[Illustration: (B) Fig. 20.--Wiring of Diagram for Sending Set No. 1.] + +For the _low voltage circuit_, that is the battery circuit, use _No. +12_ or _14_ insulated copper wire. Connect all of the dry cells +together in _series_, that is, connect the zinc of one cell with the +carbon of the next and so on until all of them are connected up. Then +connect the carbon of the end cell with one of the posts of the key, +the zinc of the other end cell with one of the primary posts of the +spark coil and the other primary post of the spark coil with the other +post of the key, when the primary circuit will be complete. + +For the _high tension circuits_, that is, the _oscillation circuits_, +you may use either bare or insulated copper wire but you must be +careful that they do not touch the table, each other, or any part of +the apparatus, except, of course, the posts they are connected with. +Connect one of the posts of the secondary coil of the spark coil with +one of the posts of the spark gap, and the other post with one of the +posts of the condenser; then connect the other post of the condenser +with the lower spring clip of the tuning coil and also connect this +clip with the ground. This done, connect the middle spring clip with +one of the posts of the spark gap, and, finally, connect the top clip +with the aerial wire and your transmitting set is ready to be tuned. A +wiring diagram of the connections is shown at B. As this set is tuned +in the same way as _Set No. 2_ which follows, you are referred to the +end of this chapter. + +A Better Transmitting Set (No. 2).--The apparatus for this set +includes: (1) an _alternating current transformer_, (2) a _wireless +telegraph key_, (3) a _fixed_, a _rotary_, or a _quenched spark gap_, +(4) a _condenser_, and (5) an _oscillation transformer_. If you have a +110 volt direct lighting current in your home instead of 110 volt +alternating current, then you will also need (6) an _electrolytic +interrupter_, for in this case the primary circuit of the transformer +must be made and broken rapidly in order to set up alternating +currents in the secondary coil. + +The Alternating Current Transformer.--An alternating current, or +power, transformer is made on the same principle as a spark coil, that +is, it has a soft iron core, a primary coil formed of a couple of +layers of heavy wire, and a secondary coil wound up of a large number +of turns of very fine wire. Unlike the spark coil, however, which has +an _open magnetic core_ and whose secondary coil is wound on the +primary coil, the transformer has a _closed magnetic core_, with the +primary coil wound on one of the legs of the core and the secondary +wound on the other leg. It has neither a vibrator nor a condenser. A +plain transformer is shown at A in Fig. 21. + +[Illustration: Fig. 21.--Parts for Transmitting Set No. 2.] + +A transformer of this kind can be bought either (a) _unmounted_, that +is, just the bare transformer, or (b) _fully mounted_, that is, fitted +with an iron stand, mounted on an insulating base on which are a pair +of primary binding posts, while the secondary is provided with a +_safety spark gap_. There are three sizes of transformers of this kind +made and they are rated at 1/4, 1/2 and 1 kilowatt, respectively, they +deliver a secondary current of 9,000, 11,000 and 25,000 volts, +according to size, and cost $16.00, $22.00 and $33.00 when fully +mounted; a reduction of $3.00, $4.00 and $5.00 is made when they are +unmounted. All of these transformers operate on 110 volt, 60 cycle +current and can be connected directly to the source of alternating +current. + +The Wireless Key.--For this transmitting set a standard wireless key +should be used as shown at B. It is made about the same as a regular +telegraph key but it is much heavier, the contact points are larger +and instead of the current being led through the bearings as in an +ordinary key, it is carried by heavy conductors directly to the +contact points. This key is made in three sizes and the first will +carry a current of 5 _amperes_[Footnote: See _Appendix_ for +definition.] and costs $4.00, the second will carry a current of 10 +amperes and costs $6.50, while the third will carry a current of 20 +amperes and costs $7.50. + +The Spark Gap.--Either a fixed, a rotary, or a quenched spark gap can +be used with this set, but the former is seldom used except with +spark-coil sets, as it is very hard to keep the sparks from arcing +when large currents are used. A rotary spark gap comprises a wheel, +driven by a small electric motor, with projecting plugs, or +electrodes, on it and a pair of stationary plugs on each side of the +wheel as shown at C. The number of sparks per second can be varied by +changing the speed of the wheel and when it is rotated rapidly it +sends out signals of a high pitch which are easy to read at the +receiving end. A rotary gap with a 110-volt motor costs about $25.00. + +A quenched spark gap not only eliminates the noise of the ordinary gap +but, when properly designed, it increases the range of an induction +coil set some 200 per cent. A 1/4 kilowatt quenched gap costs $10.00. +[Footnote: See Appendix for definition.] + +The High Tension Condenser.--Since, if you are an amateur, you can +only send out waves that are 200 meters in length, you can only use a +condenser that has a capacitance of .007 _microfarad_. [Footnote: See +Appendix for definition.] A sectional high tension condenser like the +one described in connection with _Set No. 1_ can be used with this +set but it must have a capacitance of not more than .007 microfarad. A +condenser of this value for a 1/4-kilowatt transformer costs $7.00; +for a 1/2-kilowatt transformer $14.00, and for a 1-kilowatt +transformer $21.00. See E, Fig. 19. + +The Oscillation Transformer.--With an oscillation transformer you can +tune much more sharply than with a single inductance coil tuner. The +primary coil is formed of 6 turns of copper strip, or No. 9 copper +wire, and the secondary is formed of 9 turns of strip, or wire. The +primary coil, which is the outside coil, is hinged to the base and can +be raised or lowered like the lid of a box. When it is lowered the +primary and secondary coils are in the same plane and when it is +raised the coils set at an angle to each other. It is shown at D and +costs $5.00. + +Connecting Up the Apparatus. For Alternating Current.--Screw the key +to the table about the middle of it and near the front edge; place the +high tension condenser back of it and the oscillation transformer back +of the latter; set the alternating current transformer to the left of +the oscillation transformer and place the rotary or quenched spark gap +in front of it. + +Now bring a pair of _No. 12_ or _14_ insulated wires from the 110 volt +lighting leads and connect them with a single-throw, double-pole +switch; connect one pole of the switch with one of the posts of the +primary coil of the alternating power transformer and connect the +other post of the latter with one of the posts of your key, and the +other post of this with the other pole of the switch. Now connect the +motor of the rotary spark gap to the power circuit and put a +single-pole, single-throw switch in the motor circuit, all of which is +shown at A in Fig. 22. + +[Illustration: (A) Fig. 22.--Top View of Apparatus Layout for Sending +Set No. 2.] + +[Illustration: (B) Fig. 22.--Wiring Diagram for Sending Set No. 2.] + +Next connect the posts of the secondary coil to the posts of the +rotary or quenched spark gap and connect one post of the latter to one +post of the condenser, the other post of this to the post of the +primary coil of the oscillation transformer, which is the inside coil, +and the clip of the primary coil to the other spark gap post. This +completes the closed oscillation circuit. Finally connect the post of +the secondary coil of the oscillation transformer to the ground and +the clip of it to the wire leading to the aerial when you are ready to +tune the set. A wiring diagram of the connections is shown at B. + +For Direct Current.--Where you have 110 volt direct current you must +connect in an electrolytic interrupter. This interrupter, which is +shown at A and B in Fig. 23, consists of (1) a jar filled with a +solution of 1 part of sulphuric acid and 9 parts of water, (2) a lead +electrode having a large surface fastened to the cover of surface that +sets in a porcelain sleeve and whose end rests on the bottom of the +jar. + +[Illustration: Fig. 23.--Using 110 Volt Direct Current with an +Alternating Current Transformer.] + +When these electrodes are connected in series with the primary of a +large spark coil or an alternating current transformer, see C, and a +direct current of from 40 to 110 volts is made to pass through it, the +current is made and broken from 1,000 to 10,000 times a minute. By +raising or lowering the sleeve, thus exposing more or less of the +platinum, or alloy point, the number of interruptions per minute can +be varied at will. As the electrolytic interrupter will only operate +in one direction, you must connect it with its platinum, or alloy +anode, to the + or _positive_ power lead and the lead cathode to the - +or _negative_ power lead. You can find out which is which by +connecting in the interrupter and trying it, or you can use a polarity +indicator. An electrolytic interrupter can be bought for as little as +$3.00. + +How to Adjust Your Transmitter. Tuning With a Hot Wire Ammeter.--A +transmitter can be tuned in two different ways and these are: (1) by +adjusting the length of the spark gap and the tuning coil so that the +greatest amount of energy is set up in the oscillating circuits, and +(2) by adjusting the apparatus so that it will send out waves of a +given length. + +To adjust the transmitter so that the circuits will be in tune you +should have a _hot wire ammeter_, or radiation ammeter, as it is +called, which is shown in Fig. 24. It consists of a thin platinum wire +through which the high-frequency currents surge and these heat it; the +expansion and contraction of the wire moves a needle over a scale +marked off into fractions of an ampere. When the spark gap and tuning +coil of your set are properly adjusted, the needle will swing farthest +to the right over the scale and you will then know that the aerial +wire system, or open oscillation circuit, and the closed oscillation +circuit are in tune and radiating the greatest amount of energy. + +[Illustration: Fig. 24.--Principle of the Hot Wire Ammeter.] + +To Send Out a 200 Meter Wave Length.--If you are using a condenser +having a capacitance of .007 microfarad, which is the largest capacity +value that the Government will allow an amateur to use, then if you +have a hot wire ammeter in your aerial and tune the inductance coil or +coils until the ammeter shows the largest amount of energy flowing +through it you will know that your transmitter is tuned and that the +aerial is sending out waves whose length is 200 meters. To tune to +different wave lengths you must have a _wave-meter_. + +The Use of the Aerial Switch.--Where you intend to install both a +transmitter and a receptor you will need a throwover switch, or +_aerial switch_, as it is called. An ordinary double-pole, +double-throw switch, as shown at A in Fig. 25, can be used, or a +switch made especially for the purpose as at B is handier because the +arc of the throw is much less. + +[Illustration: Fig. 25.--Kinds of Aerial Switches.] + +Aerial Switch for a Complete Sending and Receiving Set.--You can buy a +double-pole, double-throw switch mounted on a porcelain base for about +75 cents and this will serve for _Set No. 1_. Screw this switch on +your table between the sending and receiving sets and then connect one +of the middle posts of it with the ground wire and the other middle +post with the lightning switch which connects with the aerial. Connect +the post of the tuning coil with one of the end posts of the switch +and the clip of the tuning coil with the other and complementary post +of the switch. This done, connect one of the opposite end posts of the +switch to the post of the receiving tuning coil and connect the +sliding contact of the latter with the other and complementary post of +the switch as shown in Fig. 26. + +[Illustration: Fig. 26.--Wiring Diagram for Complete Sending and +Receiving Set No. 1.] + +Connecting in the Lightning Switch.--The aerial wire connects with the +middle post of the lightning switch, while one of the end posts lead +to one of the middle posts of the aerial switch. The other end post of +the lightning switch leads to a separate ground outside the building, +as the wiring diagrams Figs. 26 and 27 show. + +[Illustration: Fig. 27.--Wiring Diagram for Complete Sending and +Receiving Set No. 2.] + + + + +CHAPTER V + +ELECTRICITY SIMPLY EXPLAINED + + +It is easy to understand how electricity behaves and what it does if +you get the right idea of it at the start. In the first place, if you +will think of electricity as being a fluid like water its fundamental +actions will be greatly simplified. Both water and electricity may be +at rest or in motion. When at rest, under certain conditions, either +one will develop pressure, and this pressure when released will cause +them to flow through their respective conductors and thus produce a +current. + +Electricity at Rest and in Motion.--Any wire or a conductor of any +kind can be charged with electricity, but a Leyden jar, or other +condenser, is generally used to hold an electric charge because it has +a much larger _capacitance_, as its capacity is called, than a wire. +As a simple analogue of a condenser, suppose you have a tank of water +raised above a second tank and that these are connected together by +means of a pipe with a valve in it, as shown at A in Fig. 28. + +[Illustration: Fig. 28.--Water Analogue for Electric Pressure.] + +[Illustration: original © Underwood and Underwood. First Wireless +College in the World, at Tufts College, Mass.] + +Now if you fill the upper tank with water and the valve is turned off, +no water can flow into the lower tank but there is a difference of +pressure between them, and the moment you turn the valve on a current +of water will flow through the pipe. In very much the same way when +you have a condenser charged with electricity the latter will be under +_pressure,_ that is, a _difference of potential_ will be set up, for +one of the sheets of metal will be charged positively and the other +one, which is insulated from it, will be charged negatively, as shown +at B. On closing the switch the opposite charges rush together and +form a current which flows to and fro between the metal plates. +[Footnote: Strictly speaking it is the difference of potential that +sets up the electromotive force.] + +The Electric Current and Its Circuit.--Just as water flowing through a +pipe has _quantity_ and _pressure_ back of it and the pipe offers +friction to it which tends to hold back the water, so, likewise, does +electricity flowing in a circuit have: (1) _quantity_, or _current +strength_, or just _current_, as it is called for short, or +_amperage_, and (2) _pressure_, or _potential difference_, or +_electromotive force_, or _voltage_, as it is variously called, and +the wire, or circuit, in which the current is flowing has (3) +_resistance_ which tends to hold back the current. + +A definite relation exists between the current and its electromotive +force and also between the current, electromotive force and the +resistance of the circuit; and if you will get this relationship +clearly in your mind you will have a very good insight into how direct +and alternating currents act. To keep a quantity of water flowing in a +loop of pipe, which we will call the circuit, pressure must be applied +to it and this may be done by a rotary pump as shown at A in Fig. 29; +in the same way, to keep a quantity of electricity flowing in a loop +of wire, or circuit, a battery, or other means for generating electric +pressure must be used, as shown at B. + +[Illustration: Fig. 29.--Water Analogues for Direct and Alternating +Currents.] + +If you have a closed pipe connected with a piston pump, as at C, as +the piston moves to and fro the water in the pipe will move first one +way and then the other. So also when an alternating current generator +is connected to a wire circuit, as at D, the current will flow first +in one direction and then in the other, and this is what is called an +_alternating current_. + +Current and the Ampere.--The amount of water flowing in a closed pipe +is the same at all parts of it and this is also true of an electric +current, in that there is exactly the same quantity of electricity at +one point of the circuit as there is at any other. + +The amount of electricity, or current, flowing in a circuit in a +second is measured by a unit called the _ampere_, [Footnote: For +definition of _ampere_ see _Appendix._] and it is expressed by the +symbol I. [Footnote: This is because the letter C is used for the +symbol of _capacitance_] Just to give you an idea of the quantity of +current an _ampere_ is we will say that a dry cell when fresh gives a +current of about 20 amperes. To measure the current in amperes an +instrument called an _ammeter_ is used, as shown at A in Fig. 30, and +this is always connected in _series_ with the line, as shown at B. + +[Illustration: Fig. 30.--How the Ammeter and Voltmeter are Used.] + +Electromotive Force and the Volt.--When you have a pipe filled with +water or a circuit charged with electricity and you want to make them +flow you must use a pump in the first case and a battery or a dynamo +in the second case. It is the battery or dynamo that sets up the +electric pressure as the circuit itself is always charged with +electricity. + +The more cells you connect together in _series_ the greater will be +the electric pressure developed and the more current it will move +along just as the amount of water flowing in a pipe can be increased +by increasing the pressure of the pump. The unit of electromotive +force is the _volt_, and this is the electric pressure which will +force a current of _1 ampere_ through a resistance of _1 ohm_; it is +expressed by the symbol _E_. A fresh dry cell will deliver a current +of about 1.5 volts. To measure the pressure of a current in volts an +instrument called a _voltmeter_ is used, as shown at C in Fig. 30, and +this is always connected across the circuit, as shown at D. + +Resistance and the Ohm.--Just as a water pipe offers a certain amount +of resistance to the flow of water through it, so a circuit opposes +the flow of electricity in it and this is called _resistance_. +Further, in the same way that a small pipe will not allow a large +amount of water to flow through it, so, too, a thin wire limits the +flow of the current in it. + +If you connect a _resistance coil_ in a circuit it acts in the same +way as partly closing the valve in a pipe, as shown at A and B in Fig. +31. The resistance of a circuit is measured by a unit called the +_ohm_, and it is expressed by the symbol _R_. A No. 10, Brown and +Sharpe gauge soft copper wire, 1,000 feet long, has a resistance of +about 1 ohm. To measure the resistance of a circuit an apparatus +called a _resistance bridge is used_. The resistance of a circuit can, +however, be easily calculated, as the following shows. + +[Illustration: Fig. 31.--Water Valve Analogue of Electric Resistance. +A- a valve limits the flow of water. B- a resistance limits the flow +of current.] + +What Ohm's Law Is.--If, now, (1) you know what the current flowing in +a circuit is in _amperes_, and the electromotive force, or pressure, +is in _volts_, you can then easily find what the resistance is in +_ohms_ of the circuit in which the current is flowing by this formula: + + Volts E + --------- = Ohms, or --- = R + Amperes I + +That is, if you divide the current in amperes by the electromotive +force in volts the quotient will give you the resistance in ohms. + +Or (2) if you know what the electromotive force of the current is in +_volts_ and the resistance of the circuit is in _ohms_ then you can +find what the current flowing in the circuit is in _amperes_, thus: + + Volts E + ----- = Amperes, or --- = I + Ohms R + +That is, by dividing the resistance of the circuit in ohms, by the +electromotive force of the current you will get the amperes flowing in +the circuit. + +Finally (3) if you know what the resistance of the circuit is in +_ohms_ and the current is in _amperes_ then you can find what the +electromotive force is in _volts_ since: + + Ohms x Amperes = Volts, or R x I = E + +That is, if you multiply the resistance of the circuit in ohms by the +current in amperes the result will give you the electromotive force in +volts. + +From this you will see that if you know the value of any two of the +constants you can find the value of the unknown constant by a simple +arithmetical process. This relation between these three constants is +known as _Ohm's Law_ and as they are very important you should +memorize them. + +What the Watt and Kilowatt Are.--Just as _horsepower_ or _H.P._, is +the unit of work that steam has done or can do, so the _watt_ is the +unit of work that an electric current has done or can do. To find the +_watts_ a current develops you need only to multiply the _amperes_ by +the _volts_. There are _746 watts_ to _1 horsepower, and 1,000 watts +are equal to 1 kilowatt_. + +Electromagnetic Induction.--To show that a current of electricity sets +up a magnetic field around it you have only to hold a compass over a +wire whose ends are connected with a battery when the needle will +swing at right angles to the length of the wire. By winding an +insulated wire into a coil and connecting the ends of the latter with +a battery you will find, if you test it with a compass, that the coil +is magnetic. + +This is due to the fact that the energy of an electric current flowing +in the wire is partly changed into magnetic lines of force which +rotate at right angles about it as shown at A in Fig. 32. The +magnetic field produced by the current flowing in the coil is +precisely the same as that set up by a permanent steel magnet. +Conversely, when a magnetic line of force is set up a part of its +energy goes to make up electric currents which whirl about in a like +manner, as shown at B. + +[Illustration: (A) and (B) Fig. 32.--How an Electric Current is +Changed into Magnetic Lines of Force and These into an Electric +Current.] + +[Illustration: (C) and (D) Fig. 32.--How an Electric Current Sets up a +Magnetic Field.] + +Self-induction or Inductance.--When a current is made to flow in a +coil of wire the magnetic lines of force produced are concentrated, as +at C, just as a lens concentrates rays of light, and this forms an +intense _magnetic field_, as it is called. Now if a bar of soft iron +is brought close to one end of the coil of wire, or, better still, if +it is pushed into the coil, it will be magnetized by _electromagnetic +induction,_ see D, and it will remain a magnet until the current is +cut off. + +Mutual Induction.--When two loops of wire, or better, two coils of +wire, are placed close together the electromagnetic induction between +them is reactive, that is, when a current is made to flow through one +of the coils closed magnetic lines of force are set up and when these +cut the other loop or turns of wire of the other coil, they in turn +produce electric currents in it. + +It is the mutual induction that takes place between two coils of wire +which makes it possible to transform _low voltage currents_ from a +battery or a 110 volt source of current into high pressure currents, +or _high potential currents_, as they are called, by means of a spark +coil or a transformer, as well as to _step up_ and _step down_ the +potential of the high frequency currents that are set up in sending +and receiving oscillation transformers. Soft iron cores are not used +in oscillation inductance coils and oscillation transformers for the +reason that the frequency of the current is so high the iron would not +have time to magnetize and demagnetize and so would not help along the +mutual induction to any appreciable extent. + +High-Frequency Currents.--High frequency currents, or electric +oscillations as they are called, are currents of electricity that +surge to and fro in a circuit a million times, more or less, per +second. Currents of such high frequencies will _oscillate_, that is, +surge to and fro, in an _open circuit_, such as an aerial wire system, +as well as in a _closed circuit_. + +Now there is only one method by which currents of high frequency, or +_radio-frequency_, as they are termed, can be set up by spark +transmitters, and this is by discharging a charged condenser through a +circuit having a small resistance. To charge a condenser a spark coil +or a transformer is used and the ends of the secondary coil, which +delivers the high potential alternating current, are connected with +the condenser. To discharge the condenser automatically a _spark,_ or +an _arc,_ or the _flow of electrons_ in a vacuum tube, is employed. + +Constants of an Oscillation Circuit.--An oscillation circuit, as +pointed out before, is one in which high frequency currents surge or +oscillate. Now the number of times a high frequency current will surge +forth and back in a circuit depends upon three factors of the latter +and these are called the constants of the circuit, namely: (1) its +_capacitance,_ (2) its _inductance_ and (3) its _resistance._ + +What Capacitance Is.--The word _capacitance_ means the _electrostatic +capacity_ of a condenser or a circuit. The capacitance of a condenser +or a circuit is the quantity of electricity which will raise its +pressure, or potential, to a given amount. The capacitance of a +condenser or a circuit depends on its size and form and the voltage of +the current that is charging it. + +The capacitance of a condenser or a circuit is directly proportional +to the quantity of electricity that will keep the charge at a given +potential. The _farad,_ whose symbol is _M,_ is the unit of +capacitance and a condenser or a circuit to have a capacitance of one +farad must be of such size that one _coulomb,_ which is the unit of +electrical quantity, will raise its charge to a potential of one volt. +Since the farad is far too large for practical purposes a millionth of +a farad, or _microfarad_, whose symbol is _mfd._, is used. + +What Inductance Is.--Under the sub-caption of _Self-induction_ and +_Inductance_ in the beginning of this chapter it was shown that it was +the inductance of a coil that makes a current flowing through it +produce a strong magnetic field, and here, as one of the constants of +an oscillation circuit, it makes a high-frequency current act as +though it possessed _inertia_. + +Inertia is that property of a material body that requires time and +energy to set in motion, or stop. Inductance is that property of an +oscillation circuit that makes an electric current take time to start +and time to stop. Because of the inductance, when a current flows +through a circuit it causes the electric energy to be absorbed and +changes a large part of it into magnetic lines of force. Where high +frequency currents surge in a circuit the inductance of it becomes a +powerful factor. The practical unit of inductance is the _henry_ and +it is represented by the symbol _L_. + +What Resistance Is.--The resistance of a circuit to high-frequency +currents is different from that for low voltage direct or alternating +currents, as the former do not sink into the conductor to nearly so +great an extent; in fact, they stick practically to the surface of it, +and hence their flow is opposed to a very much greater extent. The +resistance of a circuit to high frequency currents is generally found +in the spark gap, arc gap, or the space between the electrodes of a +vacuum tube. The unit of resistance is, as stated, the _ohm_, and its +symbol is _R_. + +The Effect of Capacitance, Inductance and Resistance on Electric +Oscillations.--If an oscillation circuit in which high frequency +currents surge has a large resistance, it will so oppose the flow of +the currents that they will be damped out and reach zero gradually, as +shown at A in Fig. 33. But if the resistance of the circuit is small, +and in wireless circuits it is usually so small as to be negligible, +the currents will oscillate, until their energy is damped out by +radiation and other losses, as shown at B. + +[Illustration: Fig. 33.--The Effect of Resistance on the Discharge of +an Electric Current.] + +As the capacitance and the inductance of the circuit, which may be +made of any value, that is amount, you wish, determines the _time +period_, that is, the length of time for a current to make one +complete oscillation, it must be clear that by varying the values of +the condenser and the inductance coil you can make the high frequency +current oscillate as fast or as slow as you wish within certain +limits. Where the electric oscillations that are set up are very fast, +the waves sent out by the aerial will be short, and, conversely, where +the oscillations are slow the waves emitted will be long. + + + + +CHAPTER VI + +HOW THE TRANSMITTING AND RECEIVING SETS WORK + + +The easiest way to get a clear conception of how a wireless +transmitter sends out electric waves and how a wireless receptor +receives them is to take each one separately and follow: (1) in the +case of the transmitter, the transformation of the low voltage direct, +or alternating current into high potential alternating currents; then +find out how these charge the condenser, how this is discharged by the +spark gap and sets up high-frequency currents in the oscillation +circuits; then (2) in the case of the receptor, to follow the high +frequency currents that are set up in the aerial wire and learn how +they are transformed into oscillations of lower potential when they +have a larger current strength, how these are converted into +intermittent direct currents by the detector and which then flow into +and operate the telephone receiver. + +How Transmitting Set No. 1 Works. The Battery and Spark Coil +Circuit.--When you press down on the knob of the key the silver points +of it make contact and this closes the circuit; the low voltage direct +current from the battery now flows through the primary coil of the +spark coil and this magnetizes the soft iron core. The instant it +becomes magnetic it pulls the spring of the vibrator over to it and +this breaks the circuit; when this takes place the current stops +flowing through the primary coil; this causes the core to lose its +magnetism when the vibrator spring flies back and again makes contact +with the adjusting screw; then the cycle of operations is repeated. + +A condenser is connected across the contact points of the vibrator +since this gives a much higher voltage at the ends of the secondary +coil than where the coil is used without it; this is because: (1) the +self-induction of the primary coil makes the pressure of the current +rise and when the contact points close the circuit again it discharges +through the primary coil, and (2) when the break takes place the +current flows into the condenser instead of arcing across the contact +points. + +Changing the Primary Spark Coil Current Into Secondary Currents.--Now +every time the vibrator contact points close the primary circuit the +electric current in the primary coil is changed into closed magnetic +lines of force and as these cut through the secondary coil they set up +in it a _momentary current_ in one direction. Then the instant the +vibrator points break apart the primary circuit is opened and the +closed magnetic lines of force contract and as they do so they cut the +turns of wire in the secondary coil in the opposite direction and this +sets up another momentary current in the secondary coil in the other +direction. The result is that the low voltage direct current of the +battery is changed into alternating currents whose frequency is +precisely that of the spring vibrator, but while the frequency of the +currents is low their potential, or voltage, is enormously increased. + +What Ratio of Transformation Means.--To make a spark coil step up the +low voltage direct current into high potential alternating current the +primary coil is wound with a couple of layers of thick insulated +copper wire and the secondary is wound with a thousand, more or less, +number of turns with very fine insulated copper wire. If the primary +and secondary coils were wound with the same number of turns of wire +then the pressure, or voltage, of the secondary coil at its terminals +would be the same as that of the current which flowed through the +primary coil. Under these conditions the _ratio of transformation_, as +it is called, would be unity. + +The ratio of transformation is directly proportional to the number of +turns of wire on the primary and secondary coils and, since this is +the case, if you wind 10 turns of wire on the primary coil and 1,000 +turns of wire on the secondary coil then you will get 100 times as +high a pressure, or voltage, at the terminals of the secondary as that +which you caused to flow through the primary coil, but, naturally, the +current strength, or amperage, will be proportionately decreased. + +The Secondary Spark Coil Circuit.--This includes the secondary coil +and the spark gap which are connected together. When the alternating, +but high potential, currents which are developed by the secondary +coil, reach the balls, or _electrodes_, of the spark gap the latter +are alternately charged positively and negatively. + +Now take a given instant when one electrode is charged positively and +the other one is charged negatively, then when they are charged to a +high enough potential the electric strain breaks down the air gap +between them and the two charges rush together as described in the +chapter before this one in connection with the discharge of a +condenser. When the charges rush together they form a current which +burns out the air in the gap and this gives rise to the spark, and as +the heated gap between the two electrodes is a very good conductor the +electric current surges forth and back with high frequency, perhaps a +dozen times, before the air replaces that which has burned out. It is +the inrushing air to fill the vacuum of the gap that makes the +crackling noise which accompanies the discharge of the electric spark. + +In this way then electric oscillations of the order of a million, more +or less, are produced and if an aerial and a ground wire are connected +to the spark balls, or electrodes, the oscillations will surge up and +down it and the energy of these in turn, are changed into electric +waves which travel out into space. An open circuit transmitter of this +kind will send out waves that are four times as long as the aerial +itself, but as the waves it sends out are strongly damped the +Government will not permit it to be used. + +The Closed Oscillation Circuit.--By using a closed oscillation circuit +the transmitter can be tuned to send out waves of a given length and +while the waves are not so strongly damped more current can be sent +into the aerial wire system. The closed oscillation circuit consists +of: (1) a _spark gap_, (2) a _condenser_ and (3) an _oscillation +transformer_. The high potential alternating current delivered by the +secondary coil not only charges the spark gap electrodes which +necessarily have a very small capacitance, but it charges the +condenser which has a large capacitance and the value of which can be +changed at will. + +Now when the condenser is fully charged it discharges through the +spark gap and then the electric oscillations set up surge to and fro +through the closed circuit. As a closed circuit is a very poor +radiator of energy, that is, the electric oscillations are not freely +converted into electric waves by it, they surge up to, and through the +aerial wire; now as the aerial wire is a good radiator nearly all of +the energy of the electric oscillations which surge through it are +converted into electric waves. + +How Transmitting Set No. 2 Works. With Alternating Current. The +operation of a transmitting set that uses an alternating current +transformer, or _power transformer,_ as it is sometimes called, is +even more simple than one using a spark coil. The transformer needs no +vibrator when used with alternating current. The current from a +generator flows through the primary coil of the transformer and the +alternations of the usual lighting current is 60 cycles per second. +This current sets up an alternating magnetic field in the core of the +transformer and as these magnetic lines of force expand and contract +they set up alternating currents of the same frequency but of much +higher voltage at the terminals of the secondary coil according to the +ratio of the primary and secondary turns of wire as explained under +the sub-caption of _Ratio of Transformation_. + +With Direct Current.--When a 110 volt direct current is used to +energize the power transformer an _electrolytic_ interruptor is needed +to make and break the primary circuit, just as a vibrator is needed +for the same purpose with a spark coil. When the electrodes are +connected in series with the primary coil of a transformer and a +source of direct current having a potential of 40 to 110 volts, +bubbles of gas are formed on the end of the platinum, or alloy anode, +which prevent the current from flowing until the bubbles break and +then the current flows again, in this way the current is rapidly made +and broken and the break is very sharp. + +Where this type of interrupter is employed the condenser that is +usually shunted around the break is not necessary as the interrupter +itself has a certain inherent capacitance, due to electrolytic action, +and which is called its _electrolytic capacitance_, and this is large +enough to balance the self-induction of the circuit since the greater +the number of breaks per minute the smaller the capacitance required. + +The Rotary Spark Gap.--In this type of spark gap the two fixed +electrodes are connected with the terminals of the secondary coil of +the power transformer and also with the condenser and primary of the +oscillation transformer. Now whenever any pair of electrodes on the +rotating disk are in a line with the pair of fixed electrodes a spark +will take place, hence the pitch of the note depends on the speed of +the motor driving the disk. This kind of a rotary spark-gap is called +_non-synchronous_ and it is generally used where a 60 cycle +alternating current is available but it will work with other higher +frequencies. + +The Quenched Spark Gap.--If you strike a piano string a single quick +blow it will continue to vibrate according to its natural period. This +is very much the way in which a quenched spark gap sets up +oscillations in a coupled closed and open circuit. The oscillations +set up in the primary circuit by a quenched spark make only three or +four sharp swings and in so doing transfer all of their energy over to +the secondary circuit, where it will oscillate some fifty times or +more before it is damped out, because the high frequency currents are +not forced, but simply oscillate to the natural frequency of the +circuit. For this reason the radiated waves approach somewhat the +condition of continuous waves, and so sharper tuning is possible. + +The Oscillation Transformer.--In this set the condenser in the closed +circuit is charged and discharged and sets up oscillations that surge +through the closed circuit as in _Set No. 1_. In this set, however, an +oscillation transformer is used and as the primary coil of it is +included in the closed circuit the oscillations set up in it produce +strong oscillating magnetic lines of force. The magnetic field thus +produced sets up in turn electric oscillations in the secondary coil +of the oscillation transformer and these surge through the aerial wire +system where their energy is radiated in the form of electric waves. + +The great advantage of using an oscillation transformer instead of a +simple inductance coil is that the capacitance of the closed circuit +can be very much larger than that of the aerial wire system. This +permits more energy to be stored up by the condenser and this is +impressed on the aerial when it is radiated as electric waves. + +How Receiving Set No. I Works.--When the electric waves from a distant +sending station impinge on the wire of a receiving aerial their energy +is changed into electric oscillations that are of exactly the same +frequency (assuming the receptor is tuned to the transmitter) but +whose current strength (amperage) and potential (voltage) are very +small. These electric waves surge through the closed circuit but when +they reach the crystal detector the contact of the metal point on the +crystal permits more current to flow through it in one direction than +it will allow to pass in the other direction. For this reason a +crystal detector is sometimes called a _rectifier_, which it really +is. + +Thus the high frequency currents which the steel magnet cores of the +telephone receiver would choke off are changed by the detector into +intermittent direct currents which can flow through the magnet coils +of the telephone receiver. Since the telephone receiver chokes off the +oscillations, a small condenser can be shunted around it so that a +complete closed oscillation circuit is formed and this gives better +results. + +When the intermittent rectified current flows through the coils of the +telephone receiver it energizes the magnet as long as it lasts, when +it is de-energized; this causes the soft iron disk, or _diaphragm_ as +it is called, which sets close to the ends of the poles of the magnet, +to vibrate; and this in turn gives forth sounds such as dots and +dashes, speech or music, according to the nature of the electric waves +that sent them out at the distant station. + +How Receiving Set No. 2 Works.--When the electric oscillations that +are set up by the incoming electric waves on the aerial wire surge +through the primary coil of the oscillation transformer they produce a +magnetic field and as the lines of force of the latter cut the +secondary coil, oscillations of the same frequency are set up in it. +The potential (voltage) of these oscillations are, however, _stepped +down_ in the secondary coil and, hence, their current strength +(amperes) is increased. + +The oscillations then flow through the closed circuit where they are +rectified by the crystal detector and transformed into sound waves by +the telephone receiver as described in connection with _Set No. 1_. +The variable condenser shunted across the closed circuit permits finer +secondary tuning to be done than is possible without it. Where you +are receiving continuous waves from a wireless telephone transmitter +(speech or music) you have to tune sharper than is possible with the +tuning coil alone and to do this a variable condenser connected in +parallel with the secondary coil is necessary. + + + + +CHAPTER VII + +MECHANICAL AND ELECTRICAL TUNING + + +There is a strikingly close resemblance between _sound waves_ and the +way they are set up in _the air_ by a mechanically vibrating body, +such as a steel spring or a tuning fork, and _electric waves_ and the +way they are set up in _the ether_ by a current oscillating in a +circuit. As it is easy to grasp the way that sound waves are produced +and behave something will be told about them in this chapter and also +an explanation of how electric waves are produced and behave and thus +you will be able to get a clear understanding of them and of tuning in +general. + +Damped and Sustained Mechanical Vibrations.--If you will place one end +of a flat steel spring in a vice and screw it up tight as shown at A +in Fig. 34, and then pull the free end over and let it go it will +vibrate to and fro with decreasing amplitude until it comes to rest as +shown at B. When you pull the spring over you store up energy in it +and when you let it go the stored up energy is changed into energy of +motion and the spring moves forth and back, or _vibrates_ as we call +it, until all of its stored up energy is spent. + +[Illustration: Fig. 34.--Damped and Sustained Mechanical Vibrations.] + +If it were not for the air surrounding it and other frictional losses, +the spring would vibrate for a very long time as the stored up energy +and the energy of motion would practically offset each other and so +the energy would not be used up. But as the spring beats the air the +latter is sent out in impulses and the conversion of the vibrations of +the spring into waves in the air soon uses up the energy you have +imparted to it and it comes to rest. + +In order to send out _continuous waves_ in the air instead of _damped +waves_ as with a flat steel spring you can use an _electric driven +tuning fork_, see C, in which an electromagnet is fixed on the inside +of the prongs and when this is energized by a battery current the +vibrations of the prongs of the fork are kept going, or are +_sustained_, as shown in the diagram at D. + +Damped and Sustained Electric Oscillations.--The vibrating steel +spring described above is a very good analogue of the way that damped +electric oscillations which surge in a circuit set up and send out +periodic electric waves in the ether while the electric driven tuning +fork just described is likewise a good analogue of how sustained +oscillations surge in a circuit and set up and send out continuous +electric waves in the ether as the following shows. + +Now the inductance and resistance of a circuit such as is shown at A +in Fig. 35, slows down, and finally damps out entirely, the electric +oscillations of the high frequency currents, see B, where these are +set up by the periodic discharge of a condenser, precisely as the +vibrations of the spring are damped out by the friction of the air and +other resistances that act upon it. As the electric oscillations surge +to and fro in the circuit it is opposed by the action of the ether +which surrounds it and electric waves are set up in and sent out +through it and this transformation soon uses up the energy of the +current that flows in the circuit. + +[Illustration: Fig. 35.--Damped and Sustained Electric Oscillations.] + +To send out _continuous waves_ in the ether such as are needed for +wireless telephony instead of _damped waves_ which are, at the present +writing, generally used for wireless telegraphy, an _electric +oscillation arc_ or a _vacuum tube oscillator_ must be used, see C, +instead of a spark gap. Where a spark gap is used the condenser in the +circuit is charged periodically and with considerable lapses of time +between each of the charging processes, when, of course, the condenser +discharges periodically and with the same time element between them. +Where an oscillation arc or a vacuum tube is used the condenser is +charged as rapidly as it is discharged and the result is the +oscillations are sustained as shown at D. + +About Mechanical Tuning.--A tuning fork is better than a spring or a +straight steel bar for setting up mechanical vibrations. As a matter +of fact a tuning fork is simply a steel bar bent in the middle so that +the two ends are parallel. A handle is attached to middle point of the +fork so that it can be held easily and which also allows it to vibrate +freely, when the ends of the prongs alternately approach and recede +from one another. When the prongs vibrate the handle vibrates up and +down in unison with it, and imparts its motion to the _sounding box_, +or _resonance case_ as it is sometimes called, where one is used. + +If, now, you will mount the fork on a sounding box which is tuned so +that it will be in resonance with the vibrations of the fork there +will be a direct reinforcement of the vibrations when the note emitted +by it will be augmented in strength and quality. This is called +_simple resonance_. Further, if you mount a pair of forks, each on a +separate sounding box, and have the forks of the same size, tone and +pitch, and the boxes synchronized, that is, tuned to the same +frequency of vibration, then set the two boxes a foot or so apart, as +shown at A in Fig. 36, when you strike one of the forks with a rubber +hammer it will vibrate with a definite frequency and, hence, send out +sound waves of a given length. When the latter strike the second fork +the impact of the molecules of air of which the sound waves are formed +will set its prongs to vibrating and it will, in turn, emit sound +waves of the same length and this is called _sympathetic resonance_, +or as we would say in wireless the forks are _in tune_. + +[Illustration: Fig. 36.--Sound Wave and Electric Wave Tuned Senders +and Receptors. A - variable tuning forks for showing sound wave +tuning. B - variable oscillation circuits for showing electric wave +tuning.] + +Tuning forks are made with adjustable weights on their prongs and by +fixing these to different parts of them the frequency with which the +forks vibrate can be changed since the frequency varies inversely with +the square of the length and directly with the thickness [Footnote: +This law is for forks having a rectangular cross-section. Those having +a round cross-section vary as the radius.] of the prongs. Now by +adjusting one of the forks so that it vibrates at a frequency of, say, +16 per second and adjusting the other fork so that it vibrates at a +frequency of, say, 18 or 20 per second, then the forks will not be in +tune with each other and, hence, if you strike one of them the other +will not respond. But if you make the forks vibrate at the same +frequency, say 16, 20 or 24 per second, when you strike one of them +the other will vibrate in unison with it. + +About Electric Tuning.--Electric resonance and electric tuning are +very like those of acoustic resonance and acoustic tuning which I have +just described. Just as acoustic resonance may be simple or +sympathetic so electric resonance may be simple or sympathetic. Simple +acoustic resonance is the direct reinforcement of a simple vibration +and this condition is had when a tuning fork is mounted on a sounding +box. In simple electric resonance an oscillating current of a given +frequency flowing in a circuit having the proper inductance and +capacitance may increase the voltage until it is several times greater +than its normal value. Tuning the receptor circuits to the transmitter +circuits are examples of sympathetic electric resonance. As a +demonstration if you have two Leyden jars (capacitance) connected in +circuit with two loops of wire (inductance) whose inductance can be +varied as shown at B in Fig. 36, when you make a spark pass between +the knobs of one of them by means of a spark coil then a spark will +pass in the gap of the other one provided the inductance of the two +loops of wire is the same. But if you vary the inductance of the one +loop so that it is larger or smaller than that of the other loop no +spark will take place in the second circuit. + +When a tuning fork is made to vibrate it sends out waves in the air, +or sound waves, in all directions and just so when high frequency +currents surge in an oscillation circuit they send out waves in the +ether, or electric waves, that travel in all directions. For this +reason electric waves from a transmitting station cannot be sent to +one particular station, though they do go further in one direction +than in another, according to the way your aerial wire points. + +Since the electric waves travel out in all directions any receiving +set properly tuned to the wave length of the sending station will +receive the waves and the only limit on your ability to receive from +high-power stations throughout the world depends entirely on the wave +length and sensitivity of your receiving set. As for tuning, just as +changing the length and the thickness of the prongs of a tuning fork +varies the frequency with which it vibrates and, hence, the length of +the waves it sends out, so, too, by varying the capacitance of the +condenser and the inductance of the tuning coil of the transmitter the +frequency of the electric oscillations set up in the circuit may be +changed and, consequently, the length of the electric waves they send +out. Likewise, by varying the capacitance and the inductance of the +receptor the circuits can be tuned to receive incoming electric waves +of whatever length within the limitation of the apparatus. + + + + +CHAPTER VIII + +A SIMPLE VACUUM TUBE DETECTOR RECEIVING SET + + +While you can receive dots and dashes from spark wireless telegraph +stations and hear spoken words and music from wireless telephone +stations with a crystal detector receiving set such as described in +Chapter III, you can get stations that are much farther away and hear +them better with a _vacuum tube detector_ receiving set. + +Though the vacuum tube detector requires two batteries to operate it +and the receiving circuits are somewhat more complicated than where a +crystal detector is used still the former does not have to be +constantly adjusted as does the latter and this is another very great +advantage. Taken all in all the vacuum tube detector is the most +sensitive and the most satisfactory of the detectors that are in use +at the present time. + +Not only is the vacuum tube a detector of electric wave signals and +speech and music but it can also be used to _amplify_ them, that is, +to make them stronger and, hence, louder in the telephone receiver and +further its powers of amplification are so great that it will +reproduce them by means of a _loud speaker_, just as a horn amplifies +the sounds of a phonograph reproducer, until they can be heard by a +room or an auditorium full of people. There are two general types of +loud speakers, though both use the principle of the telephone +receiver. The construction of these loud speakers will be fully +described in a later chapter. + +Assembled Vacuum Tube Receiving Sets.--You can buy a receiving set +with a vacuum tube detector from the very simplest type, which is +described in this chapter, to those that are provided with +_regenerative circuits_ and _amplifying_ tubes or both, which we shall +describe in later chapters, from dealers in electrical apparatus +generally. While one of these sets costs more than you can assemble a +set for yourself, still, especially in the beginning, it is a good +plan to buy an assembled one for it is fitted with a _panel_ on which +the adjusting knobs of the rheostat, tuning coil and condenser are +mounted and this makes it possible to operate it as soon as you get it +home and without the slightest trouble on your part. + +You can, however, buy all the various parts separately and mount them +yourself. If you want the receptor simply for receiving then it is a +good scheme to have all of the parts mounted in a box or enclosed +case, but if you want it for experimental purposes then the parts +should be mounted on a base or a panel so that all of the connections +are in sight and accessible. + +A Simple Vacuum Tube Receiving Set.--For this set you should use: (1) +a _loose coupled tuning coil,_ (2) a _variable condenser,_ (3) a +_vacuum tube detector,_ (4) an A or _storage battery_ giving 6 volts, +(5) a B or _dry cell battery_ giving 22-1/2 volts, (6) a _rheostat_ +for varying the storage battery current, and (7) a pair of 2,000-ohm +_head telephone receivers_. The loose coupled tuning coil, the +variable condenser and the telephone receivers are the same as those +described in Chapter III. + +The Vacuum Tube Detector. With Two Electrodes.--A vacuum tube in its +simplest form consists of a glass bulb like an incandescent lamp in +which a _wire filament_ and a _metal plate_ are sealed as shown in +Fig. 37, The air is then pumped out of the tube and a vacuum left or +after it is exhausted it is filled with nitrogen, which cannot burn. + +[Illustration: Fig. 37.--Two Electrode Vacuum Tube Detectors.] + +When the vacuum tube is used as a detector, the wire filament is +heated red-hot and the metal plate is charged with positive +electricity though it remains cold. The wire filament is formed into a +loop like that of an incandescent lamp and its outside ends are +connected with a 6-volt storage battery, which is called the A +battery; then the + or _positive_ terminal of a 22-1/2 volt dry cell +battery, called the B battery, is connected to the metal plate while +the - or _negative_ terminal of the battery is connected to one of the +terminals of the wire filament. The diagram, Fig. 37, simply shows how +the two electrode vacuum tube, the A or dry battery, and the B or +storage battery are connected up. + +Three Electrode Vacuum Tube Detector.--The three electrode vacuum tube +detector shown at A in Fig. 38, is much more sensitive than the two +electrode tube and has, in consequence, all but supplanted it. In this +more recent type of vacuum tube the third electrode, or _grid_, as it +is called, is placed between the wire filament and the metal plate and +this allows the current to be increased or decreased at will to a very +considerable extent. + +[Illustration: Fig. 38.--Three Electrode Vacuum Tube Detector and +Battery Connections.] + +The way the three electrode vacuum tube detector is connected with the +batteries is shown at B. The plate, the A or dry cell battery and one +terminal of the filament are connected in _series_--that is, one after +the other, and the ends of the filament are connected to the B or +storage battery. In assembling a receiving set you must, of course, +have a socket for the vacuum tube. A vacuum tube detector costs from +$5.00 to $6.00. + +The Dry Cell and Storage Batteries.--The reason that a storage battery +is used for heating the filament of the vacuum tube detector is +because the current delivered is constant, whereas when a dry cell +battery is used the current soon falls off and, hence, the heat of the +filament gradually grows less. The smallest A or 6 volt storage +battery on the market has a capacity of 20 to 40 ampere hours, weighs +13 pounds and costs about $10.00. It is shown at A in Fig. 39. The B +or dry cell battery for the vacuum tube plate circuit that gives +22-1/2 volts can be bought already assembled in sealed boxes. The +small size is fitted with a pair of terminals while the larger size is +provided with _taps_ so that the voltage required by the plate can be +adjusted as the proper operation of the tube requires careful +regulation of the plate voltage. A dry cell battery for a plate +circuit is shown at B. + +[Illustration: Fig. 39.--A and B Batteries for Vacuum +Tube Detectors.] + +The Filament Rheostat.--An adjustable resistance, called a _rheostat_, +must be used in the filament and storage battery circuit so that the +current flowing through the filament can be controlled to a nicety. +The rheostat consists of an insulating and a heat resisting form on +which is wound a number of turns of resistance wire. A movable contact +arm that slides over and presses on the turns of wire is fixed to the +knob on top of the rheostat. A rheostat that has a resistance of 6 +ohms and a current carrying capacity of 1.5 amperes which can be +mounted on a panel board is the right kind to use. It is shown at A +and B in Fig. 40 and costs $1.25. + +[Illustration: Fig. 40.--Rheostat for the A or Storage Battery +Current.] + +Assembling the Parts.--Begin by placing all of the separate parts of +the receiving set on a board or a base of other material and set the +tuning coil on the left hand side with the adjustable switch end +toward the right hand side so that you can reach it easily. Then set +the variable condenser in front of it, set the vacuum tube detector at +the right hand end of the tuning coil and the rheostat in front of the +detector. Place the two sets of batteries back of the instruments and +screw a couple of binding posts _a_ and _b_ to the right hand lower +edge of the base for connecting in the head phones all of which is +shown at A in Fig. 41. + +[Illustration: (A) Fig. 41.--Top View of Apparatus Layout for a Vacuum +Tube Detector Receiving Set.] + +[Illustration: (B) Fig. 41.--Wiring Diagram of a Simple Vacuum Tube +Receiving Set.] + +Connecting Up the Parts.--To wire up the different parts begin by +connecting the sliding contact of the primary coil of the loose +coupled tuning coil (this you will remember is the outside one that is +wound with fine wire) to the upper post of the lightning switch and +connect one terminal of this coil with the water pipe. Now connect the +free end of the secondary coil of the tuning coil (this is the inside +coil that is wound with heavy wire) to one of the binding posts of the +variable condenser and connect the movable contact arm of the +adjustable switch of the primary of the tuning coil with the other +post of the variable condenser. + +Next connect the grid of the vacuum tube to one of the posts of the +condenser and then connect the plate of the tube to the _carbon +terminal_ of the B or dry cell battery which is the + or _positive +pole_ and connect the _zinc terminal_ of the - or _negative_ pole to +the binding post _a_, connect the post _b_ to the other side of the +variable condenser and then connect the terminals of the head phones +to the binding posts _a_ and _b_. Whatever you do be careful not to +get the plate connections of the battery reversed. + +Now connect one of the posts of the rheostat to one terminal of the +filament and the other terminal of the filament to the - or _negative_ +terminal of the A or storage battery and the + or _positive_ terminal +of the A or storage battery to the other post of the rheostat. Finally +connect the + or positive terminal of the A or storage battery with +the wire that runs from the head phones to the variable condenser, all +of which is shown in the wiring diagram at B in Fig. 41. + +Adjusting the Vacuum Tube Detector Receiving Set.--A vacuum tube +detector is tuned exactly in the same way as the _Crystal Detector Set +No. 2_ described in Chapter III, in-so-far as the tuning coil and +variable condenser are concerned. The sensitivity of the vacuum tube +detector receiving set and, hence, the distance over which signals and +other sounds can be heard depends very largely on the sensitivity of +the vacuum tube itself and this in turn depends on: (1) the right +amount of heat developed by the filament, or _filament brilliancy_ as +it is called, (2) the right amount of voltage applied to the plate, +and (3) the extent to which the tube is exhausted where this kind of a +tube is used. + +To vary the current flowing from the A or storage battery +through the filament so that it will be heated to the right degree you +adjust the rheostat while you are listening in to the signals or other +sounds. By carefully adjusting the rheostat you can easily find the +point at which it makes the tube the most sensitive. A rheostat is +also useful in that it keeps the filament from burning out when the +current from the battery first flows through it. You can very often +increase the sensitiveness of a vacuum tube after you have used it for +a while by recharging the A or storage battery. + +The degree to which a vacuum tube has been exhausted has a very +pronounced effect on its sensitivity. The longer the tube is used the +lower its vacuum gets and generally the less sensitive it becomes. +When this takes place (and you can only guess at it) you can very +often make it more sensitive by warming it over the flame of a candle. +Vacuum tubes having a gas content (in which case they are, of course, +no longer vacuum tubes in the strict sense) make better detectors than +tubes from which the air has been exhausted and which are sealed off +in this evacuated condition because their sensitiveness is not +dependent on the degree of vacuum as in the latter tubes. Moreover, a +tube that is completely exhausted costs more than one that is filled +with gas. + + + + +CHAPTER IX + +VACUUM TUBE AMPLIFIER RECEIVING SETS + + +The reason a vacuum tube detector is more sensitive than a crystal +detector is because while the latter merely _rectifies_ the +oscillating current that surges in the receiving circuits, the former +acts as an _amplifier_ at the same time. The vacuum tube can be used +as a separate amplifier in connection with either: (1) a _crystal +detector_ or (2) a _vacuum tube detector_, and (_a_) it will amplify +either the _radio frequency currents_, that is the high frequency +oscillating currents which are set up in the oscillation circuits or +(_b_) it will amplify the _audio frequency currents_, that is, the +_low frequency alternating_ currents that flow through the head phone +circuit. + +To use the amplified radio frequency oscillating currents or amplified +audio frequency alternating currents that are set up by an amplifier +tube either a high resistance, called a _grid leak_, or an _amplifying +transformer_, with or without an iron core, must be connected with the +plate circuit of the first amplifier tube and the grid circuit of the +next amplifier tube or detector tube, or with the wire point of a +crystal detector. Where two or more amplifier tubes are coupled +together in this way the scheme is known as _cascade amplification._ + +Where either a _radio frequency transformer_, that is one without the +iron core, or an _audio frequency transformer_, that is one with the +iron core, is used to couple the amplifier tube circuits together +better results are obtained than where a high resistance grid leak is +used, but the amplifying tubes have to be more carefully shielded from +each other or they will react and set up a _howling_ noise in the head +phones. On the other hand grid leaks cost less but they are more +troublesome to use as you have to find out for yourself the exact +resistance value they must have and this you can do only by testing +them out. + +A Grid Leak Amplifier Receiving Set. With Crystal Detector.--The +apparatus you need for this set includes: (1) a _loose coupled tuning +coil_, (2) a _variable condenser_, (3) _two fixed condensers_, (4) a +_crystal detector_, or better a _vacuum tube detector_, (5) an A or _6 +volt storage battery_, (6) a _rheostat_, (7) a B or 22-1/2 _volt dry +cell battery_, (8) a fixed resistance unit, or _leak grid_ as it is +called, and (9) a pair of _head-phones_. The tuning coil, variable +condenser, fixed condensers, crystal detectors and head-phones are +exactly the same as those described in _Set No. 2_ in Chapter III. +The A and B batteries are exactly the same as those described in +Chapter VIII. The _vacuum tube amplifier_ and the _grid leak_ are the +only new pieces of apparatus you need and not described before. + +The Vacuum Tube Amplifier.--This consists of a three electrode vacuum +tube exactly like the vacuum tube detector described in Chapter VIII +and pictured in Fig. 38, except that instead of being filled with a +non-combustible gas it is evacuated, that is, the air has been +completely pumped out of it. The gas filled tube, however, can be used +as an amplifier and either kind of tube can be used for either radio +frequency or audio frequency amplification, though with the exhausted +tube it is easier to obtain the right plate and filament voltages for +good working. + +The Fixed Resistance Unit, or Grid Leak.--Grid leaks are made in +different ways but all of them have an enormously high resistance. +One way of making them consists of depositing a thin film of gold on a +sheet of mica and placing another sheet of mica on top to protect it +the whole being enclosed in a glass tube as shown at A in Fig. 42. +These grid leaks are made in units of from 50,000 ohms (.05 megohm) to +5,000,000 ohms (5 megohms) and cost from $1 to $2. + +[Illustration: Fig. 42.--Grid Leaks and How to Connect Them up.] + +As the _value_ of the grid leak you will need depends very largely +upon the construction of the different parts of your receiving set and +on the kind of aerial wire system you use with it you will have to try +out various resistances until you hit the right one. The resistance +that will give the best results, however, lies somewhere between +500,000 ohms (1/2 a megohm) and 3,000,000 ohms (3 megohms) and the +only way for you to find this out is to buy 1/2, 1 and 2 megohm grid +leak resistances and connect them up in different ways, as shown at B, +until you find the right value. + +Assembling the Parts for a Crystal Detector Set.--Begin by laying the +various parts out on a base or a panel with the loose coupled tuning +coil on the left hand side, but with the adjustable switch of the +secondary coil on the right hand end or in front according to the way +it is made. Then place the variable condenser, the rheostat, the +crystal detector and the binding posts for the head phones in front of +and in a line with each other. Set the vacuum tube amplifier back of +the rheostat and the A and B batteries back of the parts or in any +other place that may be convenient. The fixed condensers and the grid +leak can be placed anywhere so that it will be easy to connect them in +and you are ready to wire up the set. + +Connecting Up the Parts for a Crystal Detector.--First connect the +sliding contact of the primary of the tuning coil to the leading-in +wire and one of the end wires of the primary to the water pipe, as +shown in Fig. 43. Now connect the adjustable arm that makes contact +with one end of the secondary of the tuning coil to one of the posts +of the variable condenser; then connect the other post of the latter +with a post of the fixed condenser and the other post of this with the +grid of the amplifying tube. + +[Illustration: Fig. 43.--Crystal Detector Receiving Set with Vacuum +Tube Amplifier (Resistance Coupled).] + +Connect the first post of the variable condenser to the + or _positive +electrode_ of the A battery and its - or _negative electrode_ with the +rotating contact arm of the rheostat. Next connect one end of the +resistance coil of the rheostat to one of the posts of the amplifier +tube that leads to the filament and the other filament post to the + +or _positive electrode_ of the A battery. This done connect the +_negative_, that is, the _zinc pole_ of the B battery to the positive +electrode of the A battery and connect the _positive_, or _carbon +pole_ of the former with one end of the grid leak and connect the +other end of this to the plate of the amplifier tube. + +To the end of the grid leak connected with the plate of the amplifier +tube connect the metal point of your crystal detector, the crystal of +the latter with one post of the head phones and the other post of them +with the other end of the grid leak and, finally, connect a fixed +condenser in _parallel_ with--that is across the ends of the grid +leak, all of which is shown in the wiring diagram in Fig. 43. + +A Grid Leak Amplifying Receiving Set With Vacuum Tube Detector.--A +better amplifying receiving set can be made than the one just +described by using a vacuum tube detector instead of the crystal +detector. This set is built up exactly like the crystal detector +described above and shown in Fig. 43 up to and including the grid leak +resistance, but shunted across the latter is a vacuum tube detector, +which is made and wired up precisely like the one shown at A in Fig. +41 in the chapter ahead of this one. The way a grid leak and vacuum +tube detector with a one-step amplifier are connected up is shown at A +in Fig. 44. Where you have a vacuum tube detector and one or more +amplifying tubes connected up, or in _cascade_ as it is called, you +can use an A, or storage battery of 6 volts for all of them as shown +at B in Fig. 44, but for every vacuum tube you use you must have a B +or 22-1/2 volt dry battery to charge the plate with. + +[Illustration: (A) Fig. 44--Vacuum Tube Detector Set with One Step +Amplifier (Resistance Coupled).] + +[Illustration: (B) Fig. 44.--Wiring Diagram for Using One A or Storage +Battery with an Amplifier and a Detector Tube.] + +A Radio Frequency Transformer Amplifying Receiving Set.--Instead of +using a grid leak resistance to couple up the amplifier and detector +tube circuits you can use a _radio frequency transformer_, that is, a +transformer made like a loose coupled tuning coil, and without an iron +core, as shown in the wiring diagram at A in Fig. 45. In this set, +which gives better results than where a grid leak is used, the +amplifier tube is placed in the first oscillation circuit and the +detector tube in the second circuit. + +[Illustration: (A) Fig. 45.--Wiring Diagram for a Radio Frequency +Transformer Amplifying Receiving Set.] + +[Illustration: (B) Fig. 45.--Radio Frequency Transformer.] + +Since the radio frequency transformer has no iron core the high +frequency, or _radio frequency_ oscillating currents, as they are +called, surge through it and are not changed into low frequency, or +_audio frequency_ pulsating currents, until they flow through the +detector. Since the diagram shows only one amplifier and one radio +frequency transformer, it is consequently a _one step amplifier_; +however, two, three or more, amplifying tubes can be connected up by +means of an equal number of radio frequency transformers when you will +get wonderful results. Where a six step amplifier, that is, where six +amplifying tubes are connected together, or in _cascade_, the first +three are usually coupled up with radio frequency transformers and the +last three with audio frequency transformers. A radio frequency +transformer is shown at B and costs $6 to $7. + +An Audio Frequency Transformer Amplifying Receiving Set.--Where audio +frequency transformers are used for stepping up the voltage of the +current of the detector and amplifier tubes, the radio frequency +current does not get into the plate circuit of the detector at all for +the reason that the iron core of the transformer chokes them off, +hence, the succeeding amplifiers operate at audio frequencies. An +audio frequency transformer is shown at A in Fig. 46 and a wiring +diagram showing how the tubes are connected in _cascade_ with the +transformers is shown at B; it is therefore a two-step audio frequency +receiving set. + +[Illustration: (A) Fig. 46.--Audio Frequency Transformer.] + +[Illustration: (B) Fig. 46--Wiring Diagram for an Audio Frequency +Transformer Amplifying Receiving Set. (With Vacuum Tube Detector and +Two Step Amplifier Tubes.)] + +A Six Step Amplifier Receiving Set With a Loop Aerial.--By using a +receiving set having a three step radio frequency and a three step +audio frequency, that is, a set in which there are coupled three +amplifying tubes with radio frequency transformers and three +amplifying tubes with audio frequency transformers as described under +the caption _A Radio Frequency Transformer Receiving Set_, you can use +a _loop aerial_ in your room thus getting around the difficulties--if +such there be--in erecting an out-door aerial. You can easily make a +loop aerial by winding 10 turns of _No. 14_ or _16_ copper wire about +1/16 inch apart on a wooden frame two feet on the side as shown in +Fig. 47. With this six step amplifier set and loop aerial you can +receive wave lengths of 150 to 600 meters from various high power +stations which are at considerable distances away. + +[Illustration: (A) Fig. 47.--Six Step Amplifier with Loop Aerial.] + +[Illustration: (B) Fig. 47.--Efficient Regenerative Receiving Set. +(With Three Coil Loose Coupler Tuner.)] + +How to Prevent Howling.--Where radio frequency or audio frequency +amplifiers are used to couple your amplifier tubes in cascade you must +take particular pains to shield them from one another in order to +prevent the _feed back_ of the currents through them, which makes the +head phones or loud speaker _howl_. To shield them from each other the +tubes should be enclosed in metal boxes and placed at least 6 inches +apart while the transformers should be set so that their cores are at +right angles to each other and these also should be not less than six +inches apart. + + + + +CHAPTER X + +REGENERATIVE AMPLIFICATION RECEIVING SETS + + +While a vacuum tube detector has an amplifying action of its own, and +this accounts for its great sensitiveness, its amplifying action can +be further increased to an enormous extent by making the radio +frequency currents that are set up in the oscillation circuits react +on the detector. + +Such currents are called _feed-back_ or _regenerative_ currents and +when circuits are so arranged as to cause the currents to flow back +through the detector tube the amplification keeps on increasing until +the capacity of the tube itself is reached. It is like using steam +over and over again in a steam turbine until there is no more energy +left in it. A system of circuits which will cause this regenerative +action to take place is known as the _Armstrong circuits_ and is so +called after the young man who discovered it. + +Since the regenerative action of the radio frequency currents is +produced by the detector tube itself and which sets up an amplifying +effect without the addition of an amplifying tube, this type of +receiving set has found great favor with amateurs, while in +combination with amplifying tubes it multiplies their power +proportionately and it is in consequence used in one form or another +in all the better sets. + +There are many different kinds of circuits which can be used to +produce the regenerative amplification effect while the various kinds +of tuning coils will serve for coupling them; for instance a two or +three slide single tuning coil will answer the purpose but as it does +not give good results it is not advisable to spend either time or +money on it. A better scheme is to use a loose coupler formed of two +or three honeycomb or other compact coils, while a _variocoupler_ or a +_variometer_ or two will produce the maximum regenerative action. + +The Simplest Type of Regenerative Receiving Set. With Loose Coupled +Tuning Coil.--While this regenerative set is the simplest that will +give anything like fair results it is here described not on account of +its desirability, but because it will serve to give you the +fundamental idea of how the _feed-back_ circuit is formed. + +For this set you need: (1) a _loose-coupled tuning coil_ such as +described in Chapter III, (2) a _variable condenser_ of _.001 mfd._ +(microfarad) capacitance; (3) one _fixed condenser_ of _.001 mfd._; +(4) one _fixed condenser_ for the grid leak circuit of _.00025 mfd._; +(5) a _grid leak_ of 1/2 to 2 megohms resistance; (6) a _vacuum tube +detector_; (7) an _A 6 volt battery_; (8) a _rheostat_; (9) a _B 22 +1/2 volt battery_; and (10) a pair of _2000 ohm head phones_. + +Connecting Up the Parts.--Begin by connecting the leading-in wire of +the aerial with the binding post end of the primary coil of the loose +coupler as shown in the wiring diagram Fig. 48 and then connect the +sliding contact with the water pipe or other ground. Connect the +binding post end of the primary coil with one post of the variable +condenser, connect the other post of this with one of the posts of the +_.00025 mfd._ condenser and the other end of this with the grid of the +detector tube; then around this condenser shunt the grid leak +resistance. + +[Illustration: Fig. 48.--Simple Regenerative Receiving Set. (With +Loose Coupler Tuner.)] + +Next connect the sliding contact of the primary coil with the other +post of the variable condenser and from this lead a wire on over to +one of the terminals of the filament of the vacuum tube; to the other +terminal of the filament connect one of the posts of the rheostat and +connect the other post to the - or negative electrode of the A +battery and then connect the + or positive electrode of it to the +other terminal of the filament. + +Connect the + or positive electrode of the A battery with one post of +the .001 mfd. fixed condenser and connect the other post of this to +one of the ends of the secondary coil of the tuning coil and which is +now known as the _tickler coil_; then connect the other end of the +secondary, or tickler coil to the plate of the vacuum tube. In the +wiring diagram the secondary, or tickler coil is shown above and in a +line with the primary coil but this is only for the sake of making the +connections clear; in reality the secondary, or tickler coil slides to +and fro in the primary coil as shown and described in Chapter III. +Finally connect the _negative_, or zinc pole of the _B battery_ to one +side of the fixed condenser, the _positive_, or carbon, pole to one of +the terminals of the head phones and the other terminal of this to the +other post of the fixed condenser when your regenerative set is +complete. + +An Efficient Regenerative Receiving Set. With Three Coil Loose +Coupler.--To construct a really good regenerative set you must use a +loose coupled tuner that has three coils, namely a _primary_, a +_secondary_ and a _tickler coil_. A tuner of this kind is made like an +ordinary loose coupled tuning coil but it has a _third_ coil as shown +at A and B in Fig. 49. The middle coil, which is the _secondary_, is +fixed to the base, and the large outside coil, which is the _primary_, +is movable, that is it slides to and fro over the middle coil, while +the small inside coil, which is the _tickler_, is also movable and can +slide in or out of the middle _coil_. None of these coils is variable; +all are wound to receive waves up to 360 meters in length when used +with a variable condenser of _.001 mfd_. capacitance. In other words +you slide the coils in and out to get the right amount of coupling and +you tune by adjusting the variable condenser to get the exact wave +length you want. + +[Illustration: (A) Fig. 49.--Diagram of a Three Coil Coupler.] + +[Illustration: (B) Fig. 49.--Three Coil Loose Coupler Tuner.] + +With Compact Coils.--Compact coil tuners are formed of three fixed +inductances wound in flat coils, and these are pivoted in a mounting +so that the distance between them and, therefore, the coupling, can be +varied, as shown at A in Fig. 50. These coils are wound up by the +makers for various wave lengths ranging from a small one that will +receive waves of any length up to 360 meters to a large one that has a +maximum of 24,000 meters. For an amateur set get three of the smallest +coils when you can not only hear amateur stations that send on a 200 +meter wave but broadcasting stations that send on a 360 meter wave. + +[Illustration: Fig. 50.--Honeycomb Inductance Coil.] + +These three coils are mounted with panel plugs which latter fit into a +stand, or mounting, so that the middle coil is fixed, that is, +stationary, while the two outside coils can be swung to and fro like a +door; this scheme permits small variations of coupling to be had +between the coils and this can be done either by handles or by means +of knobs on a panel board. While I have suggested the use of the +smallest size coils, you can get and use those wound for any wave +length you want to receive and when those are connected with +variometers and variable condensers, and with a proper aerial, you +will have a highly efficient receptor that will work over all ranges +of wave lengths. The smallest size coils cost about $1.50 apiece and +the mounting costs about $6 or $7 each. + +The A Battery Potentiometer.--This device is simply a resistance like +the rheostat described in connection with the preceding vacuum tube +receiving sets but it is wound to 200 or 300 ohms resistance as +against 1-1/2 to 6 ohms of the rheostat. It is, however, used as well +as the rheostat. With a vacuum tube detector, and especially with one +having a gas-content, a potentiometer is very necessary as it is only +by means of it that the potential of the plate of the detector can be +accurately regulated. The result of proper regulation is that when the +critical potential value is reached there is a marked increase in the +loudness of the sounds that are emitted by the head phones. + +As you will see from A in Fig. 51 it has three taps. The two taps +which are connected with the ends of the resistance coil are shunted +around the A battery and the third tap, which is attached to the +movable contact arm, is connected with the B battery tap, see B, at +which this battery gives 18 volts. Since the A battery gives 6 volts +you can vary the potential of the plate from 18 to 24 volts. The +potentiometer must never be shunted around the B battery or the latter +will soon run down. A potentiometer costs a couple of dollars. + +[Illustration: (A) Fig. 51.--The Use of the Potentiometer.] + +The Parts and How to Connect Them Up.--For this regenerative set you +will need: (1) a _honeycomb_ or other compact _three-coil tuner_, (2) +two _variable_ (_.001_ and _.0005 mfd_.) _condensers_; (3) a _.00025 +mfd. fixed condenser_; (4) a _1/2 to 2 megohm grid leak_; (5) a _tube +detector_; (6) a _6 volt A battery_; (7) _a rheostat_; (8) a +_potentiometer_; (9) an _18_ or _20 volt B battery_; (10) a _fixed +condenser_ of _.001 mfd. fixed condenser_; and (11) a _pair of 2000 +ohm head phones_. + +To wire up the parts connect the leading-in wire of the aerial with +the primary coil, which is the middle one of the tuner, and connect +the other terminal with the ground. Connect the ends of the secondary +coil, which is the middle one, with the posts of the variable +condenser and connect one of the posts of the latter with one post of +the fixed .00025 mfd. condenser and the other post of this with the +grid; then shunt the grid leak around it. Next connect the other post +of the variable condenser to the - or _negative_ electrode of the _A +battery_; the + or _positive_ electrode of this to one terminal of the +detector filament and the other end of the latter to the electrode of +the A battery. + +Now connect one end of the tickler coil with the detector plate and +the other post to the fixed .001 mfd. condenser, then the other end of +this to the positive or carbon pole of the B battery. + +This done shunt the potentiometer around the A battery and run a wire +from the movable contact of it (the potentiometer) over to the 18 volt +tap, (see B, Fig. 51), of the B battery. + +Finally, shunt the head phones and the .001 mfd. fixed condenser and +you are ready to try out conclusions. + +A Regenerative Audio Frequency Amplifier Receiving Set.--The use of +amateur regenerative cascade audio frequency receiving sets is getting +to be quite common. To get the greatest amplification possible with +amplifying tubes you have to keep a negative potential on the grids. +You can, however, get very good results without any special charging +arrangement by simply connecting one post of the rheostat with the +negative terminal of the filament and connecting the _low potential_ +end of the secondary of the tuning coil with the - or negative +electrode of the A battery. This scheme will give the grids a negative +bias of about 1 volt. You do not need to bother about these added +factors that make for high efficiency until after you have got your +receiving set in working order and understand all about it. + +The Parts and How to Connect Them Up.--Exactly the same parts are +needed for this set as the one described above, but in addition you +will want: (1) two more _rheostats_; (2) _two_ more sets of B 22-1/2 +_volt batteries_; (3) _two amplifier tubes_, and (4) _two audio +frequency transformers_ as described in Chapter IX and pictured at A +in Fig. 46. + +To wire up the parts begin by connecting the leading-in wire to one +end of the primary of the tuning coil and then connect the other end +of the coil with the ground. A variable condenser of .001 mfd. +capacitance can be connected in the ground wire, as shown in Fig. 52, +to good advantage although it is not absolutely needed. Now connect +one end of the secondary coil to one post of a _.001 mfd._ variable +condenser and the other end of the secondary to the other post of the +condenser. + +[Illustration: Fig. 52.--Regenerative Audio Frequency Amplifier +Receiving Set.] + +Next bring a lead (wire) from the first post of the variable condenser +over to the post of the first fixed condenser and connect the other +post of the latter with the grid of the detector tube. Shunt 1/2 to 2 +megohm grid leak resistance around the fixed condenser and then +connect the second post of the variable condenser to one terminal of +the detector tube filament. Run this wire on over and connect it with +the first post of the second rheostat, the second post of which is +connected with one terminal of the filament of the first amplifying +tube; then connect the first post of the rheostat with one end of the +secondary coil of the first audio frequency transformer, and the other +end of this coil with the grid of the first amplifier tube. + +Connect the lead that runs from the second post of variable condenser +to the first post of the third rheostat, the second post of which is +connected with one terminal of the second amplifying tube; then +connect the first post of the rheostat with one end of the secondary +coil of the second audio frequency transformer and the other end of +this coil with the grid of the second amplifier tube. + +This done connect the - or negative electrode of the A battery +with the second post of the variable condenser and connect the + or +positive electrode with the free post of the first rheostat, the other +post of which connects with the free terminal of the filament of the +detector. From this lead tap off a wire and connect it to the free +terminal of the filament of the first amplifier tube, and finally +connect the end of the lead with the free terminal of the filament of +the second amplifier tube. + +Next shunt a potentiometer around the A battery and connect the +third post, which connects with the sliding contact, to the negative +or zinc pole of a B battery, then connect the positive or +carbon pole of it to the negative or zinc pole of a second B +battery and the positive or carbon pole of the latter with one end of +the primary coil of the second audio frequency transformer and the +other end of it to the plate of the first amplifying tube. Run the +lead on over and connect it to one of the terminals of the second +fixed condenser and the other terminal of this with the plate of the +second amplifying tube. Then shunt the headphones around the +condenser. + +Finally connect one end of the tickler coil of the tuner with the +plate of the detector tube and connect the other end of the tickler to +one end of the primary coil of the first audio frequency transformer +and the other end of it to the wire that connects the two B +batteries together. + + + + +CHAPTER XI + +SHORT WAVE REGENERATIVE RECEIVING SETS + + +A _short wave receiving set_ is one that will receive a range of +wave lengths of from 150 to 600 meters while the distance over which +the waves can be received as well as the intensity of the sounds +reproduced by the headphones depends on: (1) whether it is a +regenerative set and (2) whether it is provided with amplifying tubes. + +High-grade regenerative sets designed especially for receiving amateur +sending stations that must use a short wave length are built on the +regenerative principle just like those described in the last chapter +and further amplification can be had by the use of amplifier tubes as +explained in Chapter IX, but the new feature of these sets is the use +of the _variocoupler_ and one or more _variometers_. These tuning +devices can be connected up in different ways and are very popular +with amateurs at the present time. + +Differing from the ordinary loose coupler the variometer has no +movable contacts while the variometer is provided with taps so that +you can connect it up for the wave length you want to receive. All you +have to do is to tune the oscillation circuits to each other is to +turn the _rotor_, which is the secondary coil, around in the _stator_, +as the primary coil is called in order to get a very fine variation of +the wave length. It is this construction that makes _sharp tuning_ +with these sets possible, by which is meant that all wave lengths are +tuned out except the one which the receiving set is tuned for. + +A Short Wave Regenerative Receiver--With One Variometer and Three +Variable Condensers.--This set also includes a variocoupler and a +_grid coil_. The way that the parts are connected together makes it a +simple and at the same time a very efficient regenerative receiver for +short waves. While this set can be used without shielding the parts +from each other the best results are had when shields are used. + +The parts you need for this set include: (1) one _variocoupler_; (2) +one _.001 microfarad variable condenser_; (3) one _.0005 microfarad +variable condenser_; (4) one _.0007 microfarad variable condenser_; +(5) _one 2 megohm grid leak_; (6) one _vacuum tube detector_; (7) one +_6 volt A battery_; (8) one _6 ohm_, 1-1/2 _ampere rheostat_; (9) one +_200 ohm potentiometer_; (10) one 22-1/2 _volt B battery_; (11) one +_.001 microfarad fixed condenser_, (12) one pair of _2,000 ohm +headphones_, and (13) a _variometer_. + +The Variocoupler.--A variocoupler consists of a primary coil wound on +the outside of a tube of insulating material and to certain turns of +this taps are connected so that you can fix the wave length which your +aerial system is to receive from the shortest wave; i.e., 150 meters +on up by steps to the longest wave, i.e., 600 meters, which is the +range of most amateur variocouplers that are sold in the open market. +This is the part of the variocoupler that is called the _stator_. + +The secondary coil is wound on the section of a ball mounted on a +shaft and this is swung in bearings on the stator so that it can turn +in it. This part of the variocoupler is called the _rotor_ and is +arranged so that it can be mounted on a panel and adjusted by means of +a knob or a dial. A diagram of a variocoupler is shown at A in Fig. +53, and the coupler itself at B. There are various makes and +modifications of variocouplers on the market but all of them are about +the same price which is $6.00 or $8.00. + +[Illustration: Fig. 53.--How the Variocoupler is Made and Works.] + +The Variometer.--This device is quite like the variocoupler, but with +these differences: (1) the rotor turns in the stator, which is also +the section of a ball, and (2) one end of the primary is connected +with one end of the secondary coil. To be really efficient a +variometer must have a small resistance and a large inductance as well +as a small dielectric loss. To secure the first two of these factors +the wire should be formed of a number of fine, pure copper wires each +of which is insulated and the whole strand then covered with silk. +This kind of wire is the best that has yet been devised for the +purpose and is sold under the trade name of _litzendraht_. + +A new type of variometer has what is known as a _basket weave_, or +_wavy wound_ stator and rotor. There is no wood, insulating compound +or other dielectric materials in large enough quantities to absorb the +weak currents that flow between them, hence weaker sounds can be heard +when this kind of a variometer is used. With it you can tune sharply +to waves under 200 meters in length and up to and including wave +lengths of 360 meters. When amateur stations of small power are +sending on these short waves this style of variometer keeps the +electric oscillations at their greatest strength and, hence, the +reproduced sounds will be of maximum intensity. A wiring diagram of a +variometer is shown at A in Fig. 54 and a _basketball_ variometer is +shown complete at B. + +[Illustration: Fig. 54.--How the Variometer is Made and Works.] + +Connecting Up the Parts.--To hook-up the set connect the leading-in +wire to one end of the primary coil, or stator, of the variocoupler +and solder a wire to one of the taps that gives the longest wave +length you want to receive. Connect the other end of this wire with +one post of a .001 microfarad variable condenser and connect the other +post with the ground as shown in Fig. 55. Now connect one end of the +secondary coil, or rotor, to one post of a .0007 mfd. variable +condenser, the other post of this to one end of the grid coil and the +other end of this with the remaining end of the rotor of the +variocoupler. + +[Illustration: Fig. 55.--Short Wave Regenerative Receiving Set (one +Variometer and three Variable Condensers.)] + +Next connect one post of the .0007 mfd. condenser with one of the +terminals of the detector filament; then connect the other post of +this condenser with one post of the .0005 mfd. variable condenser and +the other post of this with the grid of the detector, then shunt the +megohm grid leak around the latter condenser. This done connect the +other terminal of the filament to one post of the rheostat, the other +post of this to the - or negative electrode of the 6 volt A +battery and the + or positive electrode of the latter to the other +terminal of the filament. + +Shunt the potentiometer around the A battery and connect the sliding +contact with the - or zinc pole of the B battery and the + or carbon +pole with one terminal of the headphone; connect the other terminal to +one of the posts of the variometer and the other post of the +variometer to the plate of the detector. Finally shunt a .001 mfd. +fixed condenser around the headphones. If you want to amplify the +current with a vacuum tube amplifier connect in the terminals of the +amplifier circuit shown at A in Figs. 44 or 45 at the point where +they are connected with the secondary coil of the loose coupled tuning +coil, in those diagrams with the binding posts of Fig. 55 where the +phones are usually connected in. + +Short Wave Regenerative Receiver. With Two Variometers and Two +Variable Condensers.--This type of regenerative receptor is very +popular with amateurs who are using high-grade short-wave sets. When +you connect up this receptor you must keep the various parts well +separated. Screw the variocoupler to the middle of the base board or +panel, and secure the variometers on either side of it so that the +distance between them will be 9 or 10 inches. By so placing them the +coupling will be the same on both sides and besides you can shield +them from each other easier. + +For the shield use a sheet of copper on the back of the panel and +place a sheet of copper between the parts, or better, enclose the +variometers and detector and amplifying tubes if you use the latter in +sheet copper boxes. When you set up the variometers place them so that +their stators are at right angles to each other for otherwise the +magnetic lines of force set up by the coils of each one will be +mutually inductive and this will make the headphones or loud speaker +_howl_. Whatever tendency the receptor has to howl with this +arrangement can be overcome by putting in a grid leak of the right +resistance and adjusting the condenser. + +The Parts and How to Connect Them Up.--For this set you require: (1) +one _variocoupler_; (2) two _variometers_; (3) one _.001 microfarad +variable condenser_; (4) one _.0005 microfarad variable condenser_; +(5) one _2 megohm grid leak resistance_; (6) one _vacuum tube +detector_; (7) one _6 volt A battery_; (8) one _200 ohm +potentiometer_; (9) one _22-1/2 volt B battery_; (10) one _.001 +microfarad fixed condenser_, and (11) one pair of _2,000 ohm +headphones_. + +To wire up the set begin by connecting the leading-in wire to the +fixed end of the primary coil, or _stator_, of the variocoupler, as +shown in Fig. 56, and connect one post of the .001 mfd. variable +condenser to the stator by soldering a short length of wire to the tap +of the latter that gives the longest wave you want to receive. Now +connect one end of the secondary coil, or _rotor_, of the variocoupler +with one post of the .0005 mfd. variable condenser and the other part +to the grid of the detector tube. Connect the other end of the rotor +of the variocoupler to one of the posts of the first variometer and +the other post of this to one of the terminals of the detector +filament. + +[Illustration: Fig. 56.--Short Wave Regenerative Receiving Set (two +Variometers and two Variable Condensers.)] + +Connect this filament terminal with the - or negative electrode of the +A battery and the + or positive electrode of this with one post +of the rheostat and lead a wire from the other post to the free +terminal of the filament. This done shunt the potential around the +A battery and connect the sliding contact to the - or zinc pole +of the B battery and the + or carbon pole of this to one +terminal of the headphones, while the other terminal of this leads to +one of the posts of the second variometer, the other post of which is +connected to the plate of the detector tube. If you want to add an +amplifier tube then connect it to the posts instead of the headphones +as described in the foregoing set. + + + + +CHAPTER XII + +INTERMEDIATE AND LONG WAVE REGENERATIVE RECEIVING SETS + + +All receiving sets that receive over a range of wave lengths of from +150 meters to 3,000 meters are called _intermediate wave sets_ and all +sets that receive wave lengths over a range of anything more than +3,000 meters are called _long wave sets_. The range of intermediate +wave receptors is such that they will receive amateur, broadcasting, +ship and shore Navy, commercial, Arlington's time and all other +stations using _spark telegraph damped waves_ or _arc_ or _vacuum tube +telephone continuous waves_ but not _continuous wave telegraph +signals_, unless these have been broken up into groups at the +transmitting station. To receive continuous wave telegraph signals +requires receiving sets of special kind and these will be described in +the next chapter. + +Intermediate Wave Receiving Sets.--There are two chief schemes +employed to increase the range of wave lengths that a set can receive +and these are by using: (1) _loading coils_ and _shunt condensers_, +and (2) _bank-wound coils_ and _variable condensers_. If you have a +short-wave set and plan to receive intermediate waves with it then +loading coils and fixed condensers shunted around them affords you the +way to do it, but if you prefer to buy a new receptor then the better +way is to get one with bank-wound coils and variable condensers; this +latter way preserves the electrical balance of the oscillation +circuits better, the electrical losses are less and the tuning easier +and sharper. + +Intermediate Wave Set With Loading Coils.--For this intermediate wave +set you can use either of the short-wave sets described in the +foregoing chapter. For the loading coils use _honeycomb coils_, or +other good compact inductance coils, as shown in Chapter X and having +a range of whatever wave length you wish to receive. The following +table shows the range of wave length of the various sized coils when +used with a variable condenser having a .001 microfarad _capacitance_, +the approximate _inductance_ of each coil in _millihenries_ and prices +at the present writing: + +TABLE OF CHARACTERISTICS OF HONEYCOMB COILS + + Approximate Wave + Length in Meters in + + Millihenries + Inductance .001 mfd. Variable Mounted + Appx. Air Condenser. on Plug + + .040 130-- 375 $1.40 + + .075 180-- 515 1.40 + + .15 240-- 730 1.50 + + .3 330-- 1030 1.50 + + .6 450-- 1460 1.55 + + 1.3 660-- 2200 1.60 + + 2.3 930-- 2850 1.65 + + 4.5 1300-- 4000 1.70 + + 6.5 1550-- 4800 1.75 + + 11. 2050-- 6300 1.80 + + 20. 3000-- 8500 2.00 + + 40. 4000--12000 2.15 + + 65. 5000--15000 2.35 + + 100. 6200--19000 2.60 + + 125. 7000--21000 3.00 + + 175. 8200--24000 3.50 + +These and other kinds of compact coils can be bought at electrical +supply houses that sell wireless goods. If your aerial is not very +high or long you can use loading coils, but to get anything like +efficient results with them you must have an aerial of large +capacitance and the only way to get this is to put up a high and long +one with two or more parallel wires spaced a goodly distance apart. + +The Parts and How to Connect Them Up.--Get (1) _two honeycomb or other +coils_ of the greatest wave length you want to receive, for in order +to properly balance the aerial, or primary oscillation circuit, and +the closed, or secondary oscillation circuit, you have to tune them to +the same wave length; (2) two _.001 mfd. variable condensers_, though +fixed condensers will do, and (3) two small _single-throw double-pole +knife switches_ mounted on porcelain bases. + +To use the loading coils all you have to do is to connect one of them +in the aerial above the primary coil of the loose coupler, or +variocoupler as shown in the wiring diagram in Fig. 57, then shunt one +of the condensers around it and connect one of the switches around +this; this switch enables you to cut in or out the loading coil at +will. Likewise connect the other loading coil in one side of the +closed, or secondary circuit between the variable .0007 mfd. condenser +and the secondary coil of the loose coupler or variocoupler as shown +in Fig. 53. The other connections are exactly the same as shown in +Figs. 44 and 45. + +[Illustration: Fig. 57.--Wiring Diagram Showing Fixed Loading Coils +for Intermediate Wave Set.] + +An Intermediate Wave Set With Variocoupler Inductance Coils.--By using +the coil wound on the rotor of the variocoupler as the tickler the +coupling between the detector tube circuits and the aerial wire system +increases as the set is tuned for greater wave lengths. This scheme +makes the control of the regenerative circuit far more stable than it +is where an ordinary loose coupled tuning coil is used. + +When the variocoupler is adjusted for receiving very long waves the +rotor sets at right angles to the stator and, since when it is in this +position there is no mutual induction between them, the tickler coil +serves as a loading coil for the detector plate oscillation circuit. +Inductance coils for short wave lengths are usually wound in single +layers but _bank-wound coils_, as they are called are necessary to get +compactness where long wave lengths are to be received. By winding +inductance coils with two or more layers the highest inductance values +can be obtained with the least resistance. A wiring diagram of a +multipoint inductance coil is shown in Fig. 58. You can buy this +intermediate wave set assembled and ready to use or get the parts and +connect them up yourself. + +[Illustration: Fig. 58.--Wiring Diagram for Intermediate Wave Receptor +with one Variocoupler and 12 section Bank-wound Inductance Coil.] + +The Parts and How to Connect Them Up.--For this regenerative +intermediate wave set get: (1) one _12 section triple bank-wound +inductance coil_, (2) one _variometer_, and (3) all the other parts +shown in the diagram Fig. 58 except the variocoupler. First connect +the free end of the condenser in the aerial to one of the terminals of +the stator of the variocoupler; then connect the other terminal of the +stator with one of the ends of the bank-wound inductance coil and +connect the movable contact of this with the ground. + +Next connect a wire to the aerial between the variable condenser and +the stator and connect this to one post of a .0005 microfarad fixed +condenser, then connect the other post of this with the grid of the +detector and shunt a 2 megohm grid leak around it. Connect a wire to +the ground wire between the bank-wound inductance coil and the ground +proper, i.e., the radiator or water pipe, connect the other end of +this to the + electrode of the A battery and connect this end also to +one of the terminals of the filament. This done connect the other +terminal of the filament to one post of the rheostat and the other +post of this to the - or negative side of the A battery. + +To the + electrode of the A battery connect the - or zinc pole of the +B battery and connect the + or carbon pole of the latter with one post +of the fixed .001 microfarad condenser. This done connect one terminal +of the tickler coil which is on the rotor of the variometer to the +plate of the detector and the other terminal of the tickler to the +other post of the .001 condenser and around this shunt your +headphones. Or if you want to use one or more amplifying tubes connect +the circuit of the first one, see Fig. 45, to the posts on either side +of the fixed condenser instead of the headphones. + +A Long Wave Receiving Set.--The vivid imagination of Jules Verne never +conceived anything so fascinating as the reception of messages without +wires sent out by stations half way round the world; and in these days +of high power cableless stations on the five continents you can +listen-in to the messages and hear what is being sent out by the +Lyons, Paris and other French stations, by Great Britain, Italy, +Germany and even far off Russia and Japan. + +A long wave set for receiving these stations must be able to tune to +wave lengths up to 20,000 meters. Differing from the way in which the +regenerative action of the short wave sets described in the preceding +chapter is secured and which depends on a tickler coil and the +coupling action of the detector in this long wave set, [Footnote: All +of the short wave and intermediate wave receivers described, are +connected up according to the wiring diagram used by the A. H. Grebe +Company, Richmond Hill, Long Island, N. Y.] this action is obtained by +the use of a tickler coil in the plate circuit which is inductively +coupled to the grid circuit and this feeds back the necessary amount +of current. This is a very good way to connect up the circuits for the +reason that: (1) the wiring is simplified, and (2) it gives a single +variable adjustment for the entire range of wave lengths the receptor +is intended to cover. + +The Parts and How to Connect Them Up.--The two chief features as far +as the parts are concerned of this long wave length receiving set are +(1) the _variable condensers_, and (2) the _tuning inductance coils_. +The variable condenser used in series with the aerial wire system has +26 plates and is equal to a capacitance of _.0008 mfd._ which is the +normal aerial capacitance. The condenser used in the secondary coil +circuit has 14 plates and this is equal to a capacitance of _.0004 +mfd_. + +There are a number of inductance coils and these are arranged so that +they can be connected in or cut out and combinations are thus formed +which give a high efficiency and yet allow them to be compactly +mounted. The inductance coils of the aerial wire system and those of +the secondary coil circuit are practically alike. For wave lengths up +to 2,200 meters _bank litz-wound coils_ are used and these are +wound up in 2, 4 and 6 banks in order to give the proper degree of +coupling and inductance values. + +Where wave lengths of more than 2,200 meters are to be received +_coto-coils_ are used as these are the "last word" in inductance coil +design, and are especially adapted for medium as well as long wave +lengths. [Footnote: Can be had of the Coto Coil Co., Providence, R. I.] +These various coils are cut in and out by means of two five-point +switches which are provided with auxiliary levers and contactors for +_dead-ending_ the right amount of the coils. In cutting in coils for +increased wave lengths, that is from 10,000 to 20,000 meters, all of +the coils of the aerial are connected in series as well as all of the +coils of the secondary circuit. The connections for a long wave +receptor are shown in the wiring diagram in Fig. 59. + +[Illustration: Fig. 59.--Wiring Diagram Showing Long Wave Receptor +with Variocouplers and Bank-wound Inductance Coils] + + + + +CHAPTER XIII + +HETERODYNE OR BEAT LONG WAVE TELEGRAPH RECEIVING SET + + +Any of the receiving sets described in the foregoing chapters will +respond to either: (1) a wireless telegraph transmitter that uses a +spark gap and which sends out periodic electric waves, or to (2) a +wireless telephone transmitter that uses an arc or a vacuum tube +oscillator and which sends out continuous electric waves. To receive +wireless _telegraph_ signals, however, from a transmitter that uses an +arc or a vacuum tube oscillator and which sends out continuous waves, +either the transmitter or the receptor must be so constructed that the +continuous waves will be broken up into groups of audio frequency and +this is done in several different ways. + +There are four different ways employed at the present time to break up +the continuous waves of a wireless telegraph transmitter into groups +and these are: (_a_) the _heterodyne_, or _beat_, method, in which +waves of different lengths are impressed on the received waves and so +produces beats; (_b_) the _tikker_, or _chopper_ method, in which the +high frequency currents are rapidly broken up; (_c_) the variable +condenser method, in which the movable plates are made to rapidly +rotate; (_d_) the _tone wheel_, or _frequency transformer_, as it is +often called, and which is really a modified form of and an +improvement on the tikker. The heterodyne method will be described in +this chapter. + +What the Heterodyne or Beat Method Is.--The word _heterodyne_ was +coined from the Greek words _heteros_ which means _other_, or +_different_, and _dyne_ which means _power_; in other words it means +when used in connection with a wireless receptor that another and +different high frequency current is used besides the one that is +received from the sending station. In music a _beat_ means a regularly +recurrent swelling caused by the reinforcement of a sound and this is +set up by the interference of sound waves which have slightly +different periods of vibration as, for instance, when two tones take +place that are not quite in tune with each other. This, then, is the +principle of the heterodyne, or beat, receptor. + +In the heterodyne, or beat method, separate sustained oscillations, +that are just about as strong as those of the incoming waves, are set +up in the receiving circuits and their frequency is just a little +higher or a little lower than those that are set up by the waves +received from the distant transmitter. The result is that these +oscillations of different frequencies interfere and reinforce each +other when _beats_ are produced, the period of which is slow enough to +be heard in the headphones, hence the incoming signals can be heard +only when waves from the sending station are being received. A fuller +explanation of how this is done will be found in Chapter XV. + +The Autodyne or Self-Heterodyne Long-Wave Receiving Set.--This is the +simplest type of heterodyne receptor and it will receive periodic +waves from spark telegraph transmitters or continuous waves from an +arc or vacuum tube telegraph transmitter. In this type of receptor the +detector tube itself is made to set up the _heterodyne oscillations_ +which interfere with those that are produced by the incoming waves +that are a little out of tune with it. + +With a long wave _autodyne_, or _self-heterodyne_ receptor, as this +type is called, and a two-step audio-frequency amplifier you can +clearly hear many of the cableless stations of Europe and others that +send out long waves. For receiving long wave stations, however, you +must have a long aerial--a single wire 200 or more feet in length will +do--and the higher it is the louder will be the signals. Where it is +not possible to put the aerial up a hundred feet or more above the +ground, you can use a lower one and still get messages in +_International Morse_ fairly strong. + +The Parts and Connections of an Autodyne, or Self-Heterodyne, +Receiving Set.--For this long wave receiving set you will need: (1) +one _variocoupler_ with the primary coil wound on the stator and the +secondary coil and tickler coil wound on the rotor, or you can use +three honeycomb or other good compact coils of the longest wave you +want to receive, a table of which is given in Chapter XII; (2) two +_.001 mfd. variable condensers_; (3) one _.0005 mfd. variable +condenser_; (4) one _.5 to 2 megohm grid leak resistance_; (5) one +_vacuum tube detector_; (6) one _A battery_; (7) one _rheostat_; (8) +one _B battery_; (9) one _potentiometer_; (10) one _.001 mfd. fixed +condenser_ and (11) one pair of _headphones_. For the two-step +amplifier you must, of course, have besides the above parts the +amplifier tubes, variable condensers, batteries rheostats, +potentiometers and fixed condensers as explained in Chapter IX. The +connections for the autodyne, or self-heterodyne, receiving set are +shown in Fig. 60. + +[Illustration: Fig. 60.--Wiring Diagram of Long Wave Antodyne, or +Self-Heterodyne Receptor.] + +The Separate Heterodyne Long Wave Receiving Set.--This is a better +long wave receptor than the self heterodyne set described above for +receiving wireless telegraph signals sent out by a continuous long +wave transmitter. The great advantage of using a separate vacuum tube +to generate the heterodyne oscillations is that you can make the +frequency of the oscillations just what you want it to be and hence +you can make it a little higher or a little lower than the +oscillations set up by the received waves. + +The Parts and Connections of a Separate Heterodyne Long Wave Receiving +Set.--The parts required for this long wave receiving set are: (1) +four honeycomb or other good _compact inductance_ coils of the longest +wave length that you want to receive; (2) three _.001 mfd. variable +condensers_; (3) one _.0005 mfd. variable condenser_; (4) one _1 +megohm grid leak resistance_; (5) one _vacuum tube detector_; (6) one +_A battery_; (7) two rheostats; (8) two _B batteries_, one of which is +supplied with taps; (9) one _potentiometer_; (10) one _vacuum tube +amplifier_, for setting up the heterodyne oscillations; (11) a pair of +_headphones_ and (12) all of the parts for a _two-step amplifier_ as +detailed in Chapter IX, that is if you are going to use amplifiers. +The connections are shown in Fig. 61. + +[Illustration: Fig. 61.--Wiring Diagram of Long Wave Separate +Heterodyne Receiving Set.] + +In using either of these heterodyne receivers be sure to carefully +adjust the B battery by means of the potentiometer. + +[Footnote: The amplifier tube in this case is used as a generator of +oscillations.] + + + + +CHAPTER XIV + +HEADPHONES AND LOUD SPEAKERS + + +Wireless Headphones.--A telephone receiver for a wireless receiving +set is made exactly on the same principle as an ordinary Bell +telephone receiver. The only difference between them is that the +former is made flat and compact so that a pair of them can be fastened +together with a band and worn on the head (when it is called a +_headset_), while the latter is long and cylindrical so that it can be +held to the ear. A further difference between them is that the +wireless headphone is made as sensitive as possible so that it will +respond to very feeble currents, while the ordinary telephone receiver +is far from being sensitive and will respond only to comparatively +large currents. + +How a Bell Telephone Receiver Is Made.--An ordinary telephone receiver +consists of three chief parts and these are: (1) a hard-rubber, or +composition, shell and cap, (2) a permanent steel bar magnet on one +end of which is wound a coil of fine insulated copper wire, and (3) a +soft iron disk, or _diaphragm_, all of which are shown in the +cross-section in Fig. 62. The bar magnet is securely fixed inside of +the handle so that the outside end comes to within about 1/32 of an +inch of the diaphragm when this is laid on top of the shell and the +cap is screwed on. + +[Illustration: Fig. 62.--Cross-section of Bell telephone Receiver.] + +[Illustration: original © Underwood and Underwood. Alexander Graham +Bell, Inventor of the Telephone, now an ardent Radio Enthusiast.] + +The ends of the coil of wire are connected with two binding posts +which are in the end of the shell, but are shown in the picture at the +sides for the sake of clearness. This coil usually has a resistance of +about 75 ohms and the meaning of the _ohmic resistance_ of a receiver +and its bearing on the sensitiveness of it will be explained a little +farther along. After the disk, or diaphragm, which is generally made +of thin, soft sheet iron that has been tinned or japanned, [Footnote: +A disk of photographic tin-type plate is generally used.] is placed +over the end of the magnet, the cap, which has a small opening in it, +is screwed on and the receiver is ready to use. + +How a Wireless Headphone Is Made.--For wireless work a receiver of the +watch-case type is used and nearly always two such receivers are +connected with a headband. It consists of a permanent bar magnet bent +so that it will fit into the shell of the receiver as shown at A in +Fig. 63. + +[Illustration: Fig. 63.--Wireless Headphone.] + +The ends of this magnet, which are called _poles_, are bent up, and +hence this type is called a _bipolar_ receiver. The magnets are wound +with fine insulated wire as before and the diaphragm is held securely +in place over them by screwing on the cap. + +About Resistance, Turns of Wire and Sensitivity of Headphones.--If you +are a beginner in wireless you will hear those who are experienced +speak of a telephone receiver as having a resistance of 75 ohms, 1,000 +ohms, 2,000 or 3,000 ohms, as the case may be; from this you will +gather that the higher the resistance of the wire on the magnets the +more sensitive the receiver is. In a sense this is true, but it is not +the resistance of the magnet coils that makes it sensitive, in fact, +it cuts down the current, but it is the _number of turns_ of wire on +them that determines its sensitiveness; it is easy to see that this is +so, for the larger the number of turns the more often will the same +current flow round the cores of the magnet and so magnetize them to a +greater extent. + +But to wind a large number of turns of wire close enough to the cores +to be effective the wire must be very small and so, of course, the +higher the resistance will be. Now the wire used for winding good +receivers is usually No. 40, and this has a diameter of .0031 inch; +consequently, when you know the ohmic resistance you get an idea of +the number of turns of wire and from this you gather in a general way +what the sensitivity of the receiver is. + +A receiver that is sensitive enough for wireless work should be wound +to not less than 1,000 ohms (this means each ear phone), while those +of a better grade are wound to as high as 3,000 ohms for each one. A +high-grade headset is shown in Fig. 64. Each phone of a headset should +be wound to the same resistance, and these are connected in series as +shown. Where two or more headsets are used with one wireless receiving +set they must all be of the same resistance and connected in series, +that is, the coils of one head set are connected with the coils of the +next head set and so on to form a continuous circuit. + +[Illustration: Fig. 64.--Wireless Headphone.] + +The Impedance of Headphones.--When a current is flowing through a +circuit the material of which the wire is made not only opposes its +passage--this is called its _ohmic resistance_--but a +_counter-electromotive force_ to the current is set up due to the +inductive effects of the current on itself and this is called +_impedance_. Where a wire is wound in a coil the impedance of the +circuit is increased and where an alternating current is used the +impedance grows greater as the frequency gets higher. The impedance of +the magnet coils of a receiver is so great for high frequency +oscillations that the latter cannot pass through them; in other words, +they are choked off. + +How the Headphones Work.--As you will see from the cross-sections in +Figs. 62 and 63 there is no connection, electrical or mechanical, +between the diaphragm and the other parts of the receiver. Now when +either feeble oscillations, which have been rectified by a detector, +or small currents from a B battery, flow through the magnet coils the +permanent steel magnet is energized to a greater extent than when no +current is flowing through it. This added magnetic energy makes the +magnet attract the diaphragm more than it would do by its own force. +If, on the other hand, the current is cut off the pull of the magnet +is lessened and as its attraction for the diaphragm is decreased the +latter springs back to its original position. When varying currents +flow through the coils the diaphragm vibrates accordingly and sends +out sound waves. + +About Loud Speakers.--The simplest acoustic instrument ever invented +is the _megaphone_, which latter is a Greek word meaning _great +sound_. It is a very primitive device and our Indians made it out of +birch-bark before Columbus discovered America. In its simplest form it +consists of a cone-shaped horn and as the speaker talks into the small +end the concentrated sound waves pass out of the large end in whatever +direction it is held. + +Now a loud speaker of whatever kind consists of two chief parts and +these are: (1) a _telephone receiver_, and (2) a _megaphone_, or +_horn_ as it is called. A loud speaker when connected with a wireless +receiving set makes it possible for a room, or an auditorium, full of +people, or an outdoor crowd, to hear what is being sent out by a +distant station instead of being limited to a few persons listening-in +with headphones. To use a loud speaker you should have a vacuum tube +detector receiving set and this must be provided with a one-step +amplifier at least. + +To get really good results you need a two-step amplifier and then +energize the plate of the second vacuum tube amplifier with a 100 volt +B battery; or if you have a three-step amplifier then use the +high voltage on the plate of the third amplifier tube. Amplifying +tubes are made to stand a plate potential of 100 volts and this is the +kind you must use. Now it may seem curious, but when the current flows +through the coils of the telephone receiver in one direction it gives +better results than when it flows through in the other direction; to +find out the way the current gives the best results try it out both +ways and this you can do by simply reversing the connections. + +The Simplest Type of Loud Speaker.--This loud speaker, which is +called, the Arkay, [Footnote: Made by the Riley-Klotz Mfg. Co., +Newark, N. J.] will work on a one- or two-step amplifier. It consists +of a brass horn with a curve in it and in the bottom there is an +adapter, or frame, with a set screw in it so that you can fit in one +of your headphones and this is all there is to it. The construction is +rigid enough to prevent overtones, or distortion of speech or music. +It is shown in Fig. 65. + +[Illustration: Fig. 65.--Arkay Loud Speaker.] + +Another Simple Kind of Loud Speaker.--Another loud speaker, see Fig. +66, is known as the _Amplitone_ [Footnote: Made by the American +Pattern, Foundry and Machine Co., 82 Church Street, N. Y. C.] and it +likewise makes use of the headphones as the sound producer. This +device has a cast metal horn which improves the quality of the sound, +and all you have to do is to slip the headphones on the inlet tubes of +the horn and it is ready for use. The two headphones not only give a +longer volume of sound than where a single one is used but there is a +certain blended quality which results from one phone smoothing out the +imperfections of the other. + +[Illustration: Fig. 66.--Amplitone Loud Speaker.] + +A Third Kind of Simple Loud Speaker.--The operation of the +_Amplitron_, [Footnote: Made by the Radio Service Co., 110 W. 40th +Street, N. Y.] as this loud speaker is called, is slightly different +from others used for the same purpose. The sounds set up by the +headphone are conveyed to the apex of an inverted copper cone which is +7 inches long and 10 inches in diameter. Here it is reflected by a +parabolic mirror which greatly amplifies the sounds. The amplification +takes place without distortion, the sounds remaining as clear and +crisp as when projected by the transmitting station. By removing the +cap from the receiver the shell is screwed into a receptacle on the +end of the loud speaker and the instrument is ready for use. It is +pictured in Fig. 67. + +[Illustration: Fig. 67.--Amplitron Loud Speaker.] + +A Super Loud Speaker.--This loud speaker, which is known as the +_Magnavox Telemegafone_, was the instrument used by Lt. Herbert E. +Metcalf, 3,000 feet in the air, and which startled the City of +Washington on April 2, 1919, by repeating President Wilson's _Victory +Loan Message_ from an airplane in flight so that it was distinctly +heard by 20,000 people below. + +This wonderful achievement was accomplished through the installation +of the _Magnavox_ and amplifiers in front of the Treasury Building. +Every word Lt. Metcalf spoke into his wireless telephone transmitter +was caught and swelled in volume by the _Telemegafones_ below and +persons blocks away could hear the message plainly. Two kinds of these +loud speakers are made and these are: (1) a small loud speaker for the +use of operators so that headphones need not be worn, and (2) a large +loud speaker for auditorium and out-door audiences. + +[Illustration: original © Underwood and Underwood. World's Largest +Loud Speaker ever made. Installed in Lytle Park, Cincinnati, Ohio, to +permit President Harding's Address at Point Pleasant, Ohio, during the +Grant Centenary Celebration to be heard within a radius of one +square.] + +Either kind may be used with a one- or two-step amplifier or with a +cascade of half a dozen amplifiers, according to the degree of +loudness desired. The _Telemegafone_ itself is not an amplifier in the +true sense inasmuch as it contains no elements which will locally +increase the incoming current. It does, however, transform the +variable electric currents of the wireless receiving set into sound +vibrations in a most wonderful manner. + +A _telemegafone_ of either kind is formed of: (1) a telephone receiver +of large proportions, (2) a step-down induction coil, and (3) a 6 volt +storage battery that energizes a powerful electromagnet which works +the diaphragm. An electromagnet is used instead of a permanent magnet +and this is energized by a 6-volt storage battery as shown in the +wiring diagram at A in Fig. 68. One end of the core of this magnet is +fixed to the iron case of the speaker and together these form the +equivalent of a horseshoe magnet. A movable coil of wire is supported +from the center of the diaphragm the edge of which is rigidly held +between the case and the small end of the horn. This coil is placed +over the upper end of the magnet and its terminals are connected to +the secondary of the induction coil. Now when the coil is energized by +the current from the amplifiers it and the core act like a solenoid in +that the coil tends to suck the core into it; but since the core is +fixed and the coil is movable the core draws the coil down instead. +The result is that with every variation of the current that flows +through the coil it moves up and down and pulls and pushes the +diaphragm down and up with it. The large amplitude of the vibrations +of the latter set up powerful sound waves which can be heard several +blocks away from the horn. In this way then are the faint incoming +signals, speech and music which are received by the amplifying +receiving set reproduced and magnified enormously. The _Telemegafone_ +is shown complete at B. + +[Illustration: Fig. 68.--Magnavox Loud Speaker.] + + + + +CHAPTER XV + +OPERATION OF VACUUM TUBE RECEPTORS + + +From the foregoing chapters you have seen that the vacuum tube can be +used either as a _detector_ or an _amplifier_ or as a _generator_ of +electric oscillations, as in the case of the heterodyne receiving set. +To understand how a vacuum tube acts as a detector and as an amplifier +you must first know what _electrons_ are. The way in which the vacuum +tube sets up sustained oscillations will be explained in Chapter XVIII +in connection with the _Operation of Vacuum Tube Transmitters_. + +What Electrons Are.--Science teaches us that masses of matter are made +up of _molecules_, that each of these is made up of _atoms_, and each +of these, in turn, is made up of a central core of positive particles +of electricity surrounded by negative particles of electricity as +shown in the schematic diagram, Fig. 69. The little black circles +inside the large circle represent _positive particles of electricity_ +and the little white circles outside of the large circle represent +_negative particles of electricity_, or _electrons_ as they are +called. + +[Illustration: Fig. 69.--Schematic Diagram of an Atom.] + +It is the number of positive particles of electricity an atom has that +determines the kind of an element that is formed when enough atoms of +the same kind are joined together to build it up. Thus hydrogen, which +is the lightest known element, has one positive particle for its +nucleus, while uranium, the heaviest element now known, has 92 +positive particles. Now before leaving the atom please note that it is +as much smaller than the diagram as the latter is smaller than our +solar system. + +What Is Meant by Ionization.--A hydrogen atom is not only lighter but +it is smaller than the atom of any other element while an electron is +more than a thousand times smaller than the atom of which it is a +part. Now as long as all of the electrons remain attached to the +surface of an atom its positive and negative charges are equalized and +it will, therefore, be neither positive nor negative, that is, it will +be perfectly neutral. When, however, one or more of its electrons are +separated from it, and there are several ways by which this can be +done, the atom will show a positive charge and it is then called a +_positive ion_. + +In other words a _positive ion_ is an atom that has lost some of its +negative electrons while a _negative ion_ is one that has acquired +some additional negative _electrons_. When a number of electrons are +being constantly given by the atoms of an element, which let us +suppose is a metal, and are being attracted to atoms of another +element, which we will say is also a metal, a flow of electrons takes +place between the two oppositely charged elements and form a current +of negative electricity as represented by the arrows at A in Fig. 70. + +[Illustration: Fig. 70.--Action of Two-electrode Vacuum Tube.] + +When a stream of electrons is flowing between two metal elements, as a +filament and a plate in a vacuum tube detector, or an amplifier, they +act as _carriers_ for more negative electrons and these are supplied +by a battery as we shall presently explain. It has always been +customary for us to think of a current of electricity as flowing from +the positive pole of a battery to the negative pole of it and hence we +have called this the _direction of the current_. Since the electronic +theory has been evolved it has been shown that the electrons, or +negative charges of electricity, flow from the negative to the +positive pole and that the ionized atoms, which are more positive than +negative, flow in the opposite direction as shown at B. + +How Electrons are Separated from Atoms.--The next question that arises +is how to make a metal throw off some of the electrons of the atoms of +which it is formed. There are several ways that this can be done but +in any event each atom must be given a good, hard blow. A simple way +to do this is to heat a metal to incandescence when the atoms will +bombard each other with terrific force and many of the electrons will +be knocked off and thrown out into the surrounding space. + +But all, or nearly all, of them will return to the atoms from whence +they came unless a means of some kind is employed to attract them to +the atoms of some other element. This can be done by giving the latter +piece of metal a positive charge. If now these two pieces of metal are +placed in a bulb from which the air has been exhausted and the first +piece of metal is heated to brilliancy while the second piece of metal +is kept positively electrified then a stream of electrons will flow +between them. + +Action of the Two Electrode Vacuum Tube.--Now in a vacuum tube +detector a wire filament, like that of an incandescent lamp, is +connected with a battery and this forms the hot element from which the +electrons are thrown off, and a metal plate with a terminal wire +secured to it is connected to the positive or carbon tap of a dry +battery; now connect the negative or zinc tap of this with one end of +a telephone receiver and the other end of this with the terminals of +the filament as shown at A in Fig. 71. If now you heat the filament +and hold the phone to your ear you can hear the current from the B +battery flowing through the circuit. + +[Illustration: (A) and (B) Fig. 71.--How a Two Electrode Tube Acts as +a Relay or a Detector.] + +[Illustration: (C) Fig. 71.--Only the Positive Part of Oscillations +Goes through the Tube.] + +Since the electrons are negative charges of electricity they are not +only thrown off by the hot wire but they are attracted by the positive +charged metal plate and when enough electrons pass, or flow, from the +hot wire to the plate they form a conducting path and so complete the +circuit which includes the filament, the plate and the B or +plate battery, when the current can then flow through it. As the +number of electrons that are thrown off by the filament is not great +and the voltage of the plate is not high the current that flows +between the filament and the plate is always quite small. + +How the Two Electrode Tube Acts as a Detector.--As the action of a two +electrode tube as a detector [Footnote: The three electrode vacuum +tube has entirely taken the place of the two electrode type.] is +simpler than that of the three electrode vacuum tube we shall describe +it first. The two electrode vacuum tube was first made by Mr. Edison +when he was working on the incandescent lamp but that it would serve +as a detector of electric waves was discovered by Prof. Fleming, of +Oxford University, London. As a matter of fact, it is not really a +detector of electric waves, but it acts as: (1) a _rectifier_ of the +oscillations that are set up in the receiving circuits, that is, it +changes them into pulsating direct currents so that they will flow +through and affect a telephone receiver, and (2) it acts as a _relay_ +and the feeble received oscillating current controls the larger direct +current from the B battery in very much the same way that a telegraph +relay does. This latter relay action will be explained when we come to +its operation as an amplifier. + +We have just learned that when the stream of electrons flow from the +hot wire to the cold positive plate in the tube they form a conducting +path through which the battery current can flow. Now when the electric +oscillations surge through the closed oscillation circuit, which +includes the secondary of the tuning coil, the variable condenser, the +filament and the plate as shown at B in Fig. 71 the positive part of +them passes through the tube easily while the negative part cannot get +through, that is, the top, or positive, part of the wave-form remains +intact while the lower, or negative, part is cut off as shown in the +diagram at C. As the received oscillations are either broken up into +wave trains of audio frequency by the telegraph transmitter or are +modulated by a telephone transmitter they carry the larger impulses of +the direct current from the B battery along with them and these flow +through the headphones. This is the reason the vacuum tube amplifies +as well as detects. + +How the Three Electrode Tube Acts as a Detector.--The vacuum tube as a +detector has been made very much more sensitive by the use of a third +electrode shown in Fig. 72. In this type of vacuum tube the third +electrode, or _grid_, is placed between the filament and the plate and +this controls the number of electrons flowing from the filament to the +plate; in passing between these two electrodes they have to go through +the holes formed by the grid wires. + +[Illustration: (A) and (B) Fig. 72.--How the Positive and Negative +Voltages of Oscillations Act on the Electrons.] + +[Illustration: (C) Fig. 72.--How the Three Electrode Tube Acts as a +Detector and Amplifier.] + +[Illustration: (D) Fig. 72.--How the Oscillations Control the Flow of +the Battery Current through the Tube.] + +If now the grid is charged to a higher _negative_ voltage than the +filament the electrons will be stopped by the latter, see A, though +some of them will go through to the plate because they travel at a +high rate of speed. The higher the negative charge on the grid the +smaller will be the number of electrons that will reach the plate and, +of course, the smaller will be the amount of current that will flow +through the tube and the headphones from the B battery. + +On the other hand if the grid is charged _positively_, see B, then +more electrons will strike the plate than when the grid is not used or +when it is negatively charged. But when the three electrode tube is +used as a detector the oscillations set up in the circuits change the +grid alternately from negative to positive as shown at C and hence the +voltage of the B battery current that is allowed to flow through the +detector from the plate to the filament rises and falls in unison with +the voltage of the oscillating currents. The way the positive and +negative voltages of the oscillations which are set up by the incoming +waves, energize the grid; how the oscillator tube clips off the +negative parts of them, and, finally, how these carry the battery +current through the tube are shown graphically by the curves at D. + +How the Vacuum Tube Acts as an Amplifier.--If you connect up the +filament and the plate of a three electrode tube with the batteries +and do not connect in the grid, you will find that the electrons which +are thrown off by the filament will not get farther than the grid +regardless of how high the voltage is that you apply to the plate. +This is due to the fact that a large number of electrons which are +thrown off by the filament strike the grid and give it a negative +charge, and consequently, they cannot get any farther. Since the +electrons do not reach the plate the current from the B battery cannot +flow between it and the filament. + +Now with a properly designed amplifier tube a very small negative +voltage on the grid will keep a very large positive voltage on the +plate from sending a current through the tube, and oppositely, a very +small positive voltage on the grid will let a very large plate current +flow through the tube; this being true it follows that any small +variation of the voltage from positive to negative on the grid and the +other way about will vary a large current flowing from the plate to +the filament. + +In the Morse telegraph the relay permits the small current that is +received from the distant sending station to energize a pair of +magnets, and these draw an armature toward them and close a second +circuit when a large current from a local battery is available for +working the sounder. The amplifier tube is a variable relay in that +the feeble currents set up by the incoming waves constantly and +proportionately vary a large current that flows through the +headphones. This then is the principle on which the amplifying tube +works. + +The Operation of a Simple Vacuum Tube Receiving Set.--The way a simple +vacuum tube detector receiving set works is like this: when the +filament is heated to brilliancy it gives off electrons as previously +described. Now when the electric waves impinge on the aerial wire they +set up oscillations in it and these surge through the primary coil of +the loose coupled tuning coil, a diagram of which is shown at B in +Fig. 41. + +The energy of these oscillations sets up oscillations of the same +frequency in the secondary coil and these high frequency currents +whose voltage is first positive and then negative, surge in the closed +circuit which includes the secondary coil and the variable condenser. +At the same time the alternating positive and negative voltage of the +oscillating currents is impressed on the grid; at each change from + +to - and back again it allows the electrons to strike the plate and +then shuts them off; as the electrons form the conducting path between +the filament and the plate the larger direct current from the B +battery is permitted to flow through the detector tube and the +headphones. + +Operation of a Regenerative Vacuum Tube Receiving Set.--By feeding +back the pulsating direct current from the B battery through the +tickler coil it sets up other and stronger oscillations in the +secondary of the tuning coil when these act on the detector tube and +increase its sensitiveness to a remarkable extent. The regenerative, +or _feed back_, action of the receiving circuits used will be easily +understood by referring back to B in Fig. 47. + +When the waves set up oscillations in the primary of the tuning coil +the energy of them produces like oscillations in the closed circuit +which includes the secondary coil and the condenser; the alternating +positive and negative voltages of these are impressed on the grid and +these, as we have seen before, cause similar variations of the direct +current from the B battery which acts on the plate and which +flows between the latter and the filament. + +This varying direct current, however, is made to flow back through the +third, or tickler coil of the tuning coil and sets up in the secondary +coil and circuits other and larger oscillating currents and these +augment the action of the oscillations produced by the incoming waves. +These extra and larger currents which are the result of the feedback +then act on the grid and cause still larger variations of the current +in the plate voltage and hence of the current of the B battery +that flows through the detector and the headphones. At the same time +the tube keeps on responding to the feeble electric oscillations set +up in the circuits by the incoming waves. This regenerative action of +the battery current augments the original oscillations many times and +hence produce sounds in the headphones that are many times greater +than where the vacuum tube detector alone is used. + +Operation of Autodyne and Heterodyne Receiving Sets.--On page 109 +[Chapter VII] we discussed and at A in Fig. 36 is shown a picture of +two tuning forks mounted on sounding boxes to illustrate the principle +of electrical tuning. When a pair of these forks are made to vibrate +exactly the same number of times per second there will be a +condensation of the air between them and the sound waves that are sent +out will be augmented. But if you adjust one of the forks so that it +will vibrate 256 times a second and the other fork so that it will +vibrate 260 times a second then there will be a phase difference +between the two sets of waves and the latter will augment each other 4 +times every second and you will hear these rising and falling sounds +as _beats_. + +Now electric oscillations set up in two circuits that are coupled +together act in exactly the same way as sound waves produced by two +tuning forks that are close to each other. Since this is true if you +tune one of the closed circuits so that the oscillations in it will +have a frequency of a 1,000,000 and tune the other circuit so that the +oscillations in it have a frequency of 1,001,000 a second then the +oscillations will augment each other 1,000 times every second. + +As these rising and falling currents act on the pulsating currents +from the B battery which flow through the detector tube and the +headphones you will hear them as beats. A graphic representation of +the oscillating currents set up by the incoming waves, those produced +by the heterodyne oscillator and the beats they form is shown in Fig. +73. To produce these beats a receptor can use: (1) a single vacuum +tube for setting up oscillations of both frequencies when it is called +an _autodyne_, or _self-heterodyne_ receptor, or (2) a separate vacuum +tube for setting up the oscillations for the second circuit when it is +called a _heterodyne_ receptor. + +[Illustration: Fig. 73.--How the Heterodyne Receptor Works.] + +The Autodyne, or Self-Heterodyne Receiving Set.--Where only one vacuum +tube is used for producing both frequencies you need only a +regenerative, or feed-back receptor; then you can tune the aerial wire +system to the incoming waves and tune the closed circuit of the +secondary coil so that it will be out of step with the former by 1,000 +oscillations per second, more or less, the exact number does not +matter in the least. From this you will see that any regenerative set +can be used for autodyne, or self-heterodyne, reception. + +The Separate Heterodyne Receiving Set.--The better way, however, is to +use a separate vacuum tube for setting up the heterodyne oscillations. +The latter then act on the oscillations that are produced by the +incoming waves and which energize the grid of the detector tube. Note +that the vacuum tube used for producing the heterodyne oscillations is +a _generator_ of electric oscillations; the latter are impressed on +the detector circuits through the variable coupling, the secondary of +which is in series with the aerial wire as shown in Fig. 74. The way +in which the tube acts as a generator of oscillations will be told in +Chapter XVIII. + +[Illustration: Fig. 74.--Separate Heterodyne Oscillator.] + + + + +CHAPTER XVI + +CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH DIRECT CURRENT + + +In the first part of this book we learned about spark-gap telegraph +sets and how the oscillations they set up are _damped_ and the waves +they send out are _periodic_. In this and the next chapter we shall +find out how vacuum tube telegraph transmitters are made and how they +set up oscillations that are _sustained_ and radiate waves that are +_continuous_. + +Sending wireless telegraph messages by continuous waves has many +features to recommend it as against sending them by periodic waves and +among the most important of these are that the transmitter can be: (1) +more sharply tuned, (2) it will send signals farther with the same +amount of power, and (3) it is noiseless in operation. The +disadvantageous features are that: (1) a battery current is not +satisfactory, (2) its circuits are somewhat more complicated, and (3) +the oscillator tubes burn out occasionally. There is, however, a +growing tendency among amateurs to use continuous wave transmitters +and they are certainly more up-to-date and interesting than spark gap +sets. + +Now there are two practical ways by which continuous waves can be set +up for sending either telegraphic signals or telephonic speech and +music and these are with: (a) an _oscillation arc lamp_, and (b) a +_vacuum tube oscillator_. The oscillation arc was the earliest known +way of setting up sustained oscillations, and it is now largely used +for commercial high power, long distance work. But since the vacuum +tube has been developed to a high degree of efficiency and is the +scheme that is now in vogue for amateur stations we shall confine our +efforts here to explaining the apparatus necessary and how to wire the +various parts together to produce several sizes of vacuum tube +telegraph transmitters. + +Sources of Current for Telegraph Transmitting Sets.--Differing from a +spark-gap transmitter you cannot get any appreciable results with a +low voltage battery current to start with. For a purely experimental +vacuum tube telegraph transmitter you can use enough B batteries to +operate it but the current strength of these drops so fact when they +are in use, that they are not at all satisfactory for the work. + +You can, however, use 110 volt direct current from a lighting circuit +as your initial source of power to energize the plate of the vacuum +tube oscillator of your experimental transmitter. Where you have a 110 +volt _direct current_ lighting service in your home and you want a +higher voltage for your plate, you will then have to use a +motor-generator set and this costs money. If you have 110 volt +_alternating current_ lighting service at hand your troubles are over +so far as cost is concerned for you can step it up to any voltage you +want with a power transformer. In this chapter will be shown how to +use a direct current for your source of initial power and in the next +chapter how to use an alternating current for the initial power. + +An Experimental Continuous Wave Telegraph Transmitter.--You will +remember that in Chapter XV we learned how the heterodyne receiver +works and that in the separate heterodyne receiving set the second +vacuum tube is used solely to set up oscillations. Now while this +extra tube is used as a generator of oscillations these are, of +course, very weak and hence a detector tube cannot be used to generate +oscillations that are useful for other purposes than heterodyne +receptors and measurements. + +There is a vacuum tube amplifier [Footnote: This is the _radiation_ +UV-201, made by the Radio Corporation of America, Woolworth Bldg., New +York City.] made that will stand a plate potential of 100 volts, and +this can be used as a generator of oscillations by energizing it with +a 110 volt direct current from your lighting service. Or in a pinch +you can use five standard B batteries to develop the plate voltage, +but these will soon run down. But whatever you do, never use a +current from a lighting circuit on a tube of any kind that has a rated +plate potential of less than 100 volts. + +The Apparatus You Need.--For this experimental continuous wave +telegraph transmitter get the following pieces of apparatus: (1) one +_single coil tuner with three clips_; (2) one _.002 mfd. fixed +condenser_; (3) three _.001 mfd. condensers_; (4) one _adjustable grid +leak_; (5) one _hot-wire ammeter_; (6) one _buzzer_; (7) one _dry +cell_; (8) one _telegraph key_; (9) one _100 volt plate vacuum tube +amplifier_; (10) one _6 volt storage battery_; (11) one _rheostat_; +(12) one _oscillation choke coil_; (13) one _panel cut-out_ with a +_single-throw, double-pole switch_, and a pair of _fuse sockets_ on +it. + +The Tuning Coil.--You can either make this tuning coil or buy one. To +make it get two disks of wood 3/4-inch thick and 5 inches in diameter +and four strips of hard wood, or better, hard rubber or composition +strips, such as _bakelite_, 1/2-inch thick, 1 inch wide and 5-3/4 +inches long, and screw them to the disks as shown at A in Fig. 75. Now +wrap on this form about 25 turns of No. 8 or 10, Brown and Sharpe +gauge, bare copper wire with a space of 1/8-inch between each turn. +Get three of the smallest size terminal clips, see B, and clip them on +to the different turns, when your tuning coil is ready for use. You +can buy a coil of this kind for $4.00 or $5.00. + +The Condensers.--For the aerial series condenser get one that has a +capacitance of .002 mfd. and that will stand a potential of 3,000 +volts. [Footnote: The U C-1014 _Faradon_ condenser made by the Radio +Corporation of America will serve the purpose.] It is shown at C. The +other three condensers, see D, are also of the fixed type and may have +a capacitance of .001 mfd.; [Footnote: List No. 266; fixed receiving +condenser, sold by the Manhattan Electrical Supply Co.] the blocking +condenser should preferably have a capacitance of 1/2 a mfd. In these +condensers the leaves of the sheet metal are embedded in composition. +The aerial condenser will cost you $2.00 and the others 75 cents each. + +[Illustration: (A) Fig. 75.--Apparatus for Experimental C. W. +Telegraph Transmitter.] + +[Illustration: Fig. 75.--Apparatus for Experimental C. W. Telegraph +Transmitter.] + +The Aerial Ammeter.--This instrument is also called a _hot-wire_ +ammeter because the oscillating currents flowing through a piece of +wire heat it according to their current strength and as the wire +contracts and expands it moves a needle over a scale. The ammeter is +connected in the aerial wire system, either in the aerial side or the +ground side--the latter place is usually the most convenient. When you +tune the transmitter so that the ammeter shows the largest amount of +current surging in the aerial wire system you can consider that the +oscillation circuits are in tune. A hot-wire ammeter reading to 2.5 +amperes will serve your needs, it costs $6.00 and is shown at E in +Fig. 75. + +[Illustration: United States Naval High Power Station, Arlington Va. +General view of Power Room. At the left can be seen the Control +Switchboards, and overhead, the great 30 K.W. Arc Transmitter with +Accessories.] + +The Buzzer and Dry Cell.--While a heterodyne, or beat, receptor can +receive continuous wave telegraph signals an ordinary crystal or +vacuum tube detector receiving set cannot receive them unless they are +broken up into trains either at the sending station or at the +receiving station, and it is considered the better practice to do this +at the former rather than at the latter station. For this small +transmitter you can use an ordinary buzzer as shown at F. A dry cell +or two must be used to energize the buzzer. You can get one for about +75 cents. + +The Telegraph Key.--Any kind of a telegraph key will serve to break up +the trains of sustained oscillations into dots and dashes. The key +shown at G is mounted on a composition base and is the cheapest key +made, costing $1.50. + +The Vacuum Tube Oscillator.--As explained before you can use any +amplifying tube that is made for a plate potential of 100 volts. The +current required for heating the filament is about 1 ampere at 6 +volts. A porcelain socket should be used for this tube as it is the +best insulating material for the purpose. An amplifier tube of this +type is shown at H and costs $6.50. + +The Storage Battery.--A storage battery is used to heat the filament +of the tube, just as it is with a detector tube, and it can be of any +make or capacity as long as it will develop 6 volts. The cheapest 6 +volt storage battery on the market has a 20 to 40 ampere-hour capacity +and sells for $13.00. + +The Battery Rheostat.--As with the receptors a rheostat is needed to +regulate the current that heats the filament. A rheostat of this kind +is shown at I and is listed at $1.25. + +The Oscillation Choke Coil.--This coil is connected in between the +oscillation circuits and the source of current which feeds the +oscillator tube to keep the oscillations set up by the latter from +surging back into the service wires where they would break down the +insulation. You can make an oscillation choke coil by winding say 100 +turns of No. 28 Brown and Sharpe gauge double cotton covered magnet +wire on a cardboard cylinder 2 inches in diameter and 2-1/2 inches +long. + +Transmitter Connectors.--For connecting up the different pieces of +apparatus of the transmitter it is a good scheme to use _copper +braid_; this is made of braided copper wire in three sizes and sells +for 7,15 and 20 cents a foot respectively. A piece of it is pictured +at J. + +The Panel Cut-Out.--This is used to connect the cord of the 110-volt +lamp socket with the transmitter. It consists of a pair of _plug +cutouts and a single-throw, double-pole_ switch mounted on a porcelain +base as shown at K. In some localities it is necessary to place these +in an iron box to conform to the requirements of the fire +underwriters. + +Connecting Up the Transmitting Apparatus.--The way the various pieces +of apparatus are connected together is shown in the wiring diagram. +Fig. 76. Begin by connecting one post of the ammeter with the wire +that leads to the aerial and the other post of it to one end of the +tuning coil; connect clip _1_ to one terminal of the .002 mfd. 3,000 +volt aerial condenser and the other post of this with the ground. + +[Illustration: Fig. 76--Experimental C.W. Telegraph Transmitter] + +Now connect the end of the tuning coil that leads to the ammeter with +one end of the .001 mfd. grid condenser and the other end of this with +the grid of the vacuum tube. Connect the telegraph key, the buzzer and +the dry cell in series and then shunt them around the grid condenser. +Next connect the plate of the tube with one end of the .001 mfd. +blocking condenser and the other end of this with the clip _2_ on the +tuning coil. + +Connect one end of the filament with the + or positive electrode of +the storage battery, the - or negative electrode of this with one post +of the rheostat and the other post of the latter with the other end of +the filament; then connect clip _3_ with the + or positive side of the +storage battery. This done connect one end of the choke coil to the +conductor that leads to the plate and connect the other end of the +choke coil to one of the taps of the switch on the panel cut-out. +Connect the + or positive electrode of the storage battery to the +other switch tap and between the switch and the choke coil connect the +protective condenser across the 110 volt feed wires. Finally connect +the lamp cord from the socket to the plug fuse taps when your +experimental continuous wave telegraph transmitter is ready to use. + +A 100 Mile C. W. Telegraph Transmitter.--Here is a continuous +wave telegraph transmitter that will cover distances up to 100 miles +that you can rely on. It is built on exactly the same lines as the +experimental transmitter just described, but instead of using a 100 +volt plate amplifier as a makeshift generator of oscillations it +employs a vacuum tube made especially for setting up oscillations and +instead of having a low plate voltage it is energized with 350 volts. + +The Apparatus You Need.--For this transmitter you require: (1) one +_oscillation transformer_; (2) one _hot-wire ammeter_; (3) one _aerial +series condenser_; (4) one _grid leak resistance_; (5) one _chopper_; +(6) one _key circuit choke coil_; (7) one _5 watt vacuum tube +oscillator_; (8) one _6 volt storage battery_; (9) one _battery +rheostat_; (10) one _battery voltmeter_; (11) one _blocking +condenser_; (12) one _power circuit choke coil_, and (13) one +_motor-generator_. + +The Oscillation Transformer.--The tuning coil, or _oscillation +transformer_ as this one is called, is a conductively coupled +tuner--that is, the primary and secondary coils form one continuous +coil instead of two separate coils. This tuner is made up of 25 turns +of thin copper strip, 3/8 inch wide and with its edges rounded, and +this is secured to a wood base as shown at A in Fig. 77. It is fitted +with one fixed tap and three clips to each of which a length of copper +braid is attached. It has a diameter of 6-1/4 inches, a height of +7-7/8 inches and a length of 9-3/8 inches, and it costs $11.00. + +[Illustration: Fig. 77.--Apparatus of 100 Mile C. W. Telegraph +Transmitter.] + +The Aerial Condenser.--This condenser is made up of three fixed +condensers of different capacitances, namely .0003, .0004 and .0005 +mfd., and these are made to stand a potential of 7500 volts. The +condenser is therefore adjustable and, as you will see from the +picture B, it has one terminal wire at one end and three terminal +wires at the other end so that one, two or three condensers can be +used in series with the aerial. A condenser of this kind costs $5.40. + +The Aerial Ammeter.--This is the same kind of a hot-wire ammeter +already described in connection with the experimental set, but it +reads to 5 amperes. + +The Grid and Blocking Condensers.--Each of these is a fixed condenser +of .002 mfd. capacitance and is rated to stand 3,000 volts. It is +made like the aerial condenser but has only two terminals. It costs +$2.00. + +The Key Circuit Apparatus.--This consists of: (1) the _grid leak_; (2) +the _chopper_; (3) the _choke coil_, and (4) the _key_. The grid leak +is connected in the lead from the grid to the aerial to keep the +voltage on the grid at the right potential. It has a resistance of +5000 ohms with a mid-tap at 2500 ohms as shown at C. It costs $2.00. + +The chopper is simply a rotary interrupter driven by a small motor. It +comprises a wheel of insulating material in which 30 or more metal +segments are set in an insulating disk as shown at D. A metal contact +called a brush is fixed on either side of the wheel. It costs about +$7.00 and the motor to drive it is extra. The choke coil is wound up +of about 250 turns of No. 30 Brown and Sharpe gauge cotton covered +magnet wire on a spool which has a diameter of 2 inches and a length +of 3-1/4 inches. + +The 5 Watt Oscillator Vacuum Tube.--This tube is made like the +amplifier tube described for use with the preceding experimental +transmitter, but it is larger, has a more perfect vacuum, and will +stand a plate potential of 350 volts while the plate current is .045 +ampere. The filament takes a current of a little more than 2 amperes +at 7.5 volts. A standard 4-tap base is used with it. The tube costs +$8.00 and the porcelain base is $1.00 extra. It is shown at E. + +The Storage Battery and Rheostat.--This must be a 5-cell battery so +that it will develop 10 volts. A storage battery of any capacity can +be used but the lowest priced one costs about $22.00. The rheostat for +regulating the battery current is the same as that used in the +preceding experimental transmitter. + +The Filament Voltmeter.--To get the best results it is necessary that +the voltage of the current which heats the filament be kept at the +same value all of the time. For this transmitter a direct current +voltmeter reading from 0 to 15 volts is used. It is shown at F and +costs $7.50. The Oscillation Choke Coil.--This is made exactly like +the one described in connection with the experimental transmitter. + +The Motor-Generator Set.--Where you have only a 110 or a 220 volt +direct current available as a source of power you need a +_motor-generator_ to change it to 350 volts, and this is an expensive +piece of apparatus. It consists of a single armature core with a motor +winding and a generator winding on it and each of these has its own +commutator. Where the low voltage current flows into one of the +windings it drives its as a motor and this in turn generates the +higher voltage current in the other winding. Get a 100 watt 350 volt +motor-generator; it is shown at F and costs about $75.00. + +The Panel Cut-Out.--This switch and fuse block is the same as that +used in the experimental set. + +The Protective Condenser.--This is a fixed condenser having a +capacitance of 1 mfd. and will stand 750 volts. It costs $2.00. + +Connecting Up the Transmitting Apparatus.--From all that has gone +before you have seen that each piece of apparatus is fitted with +terminal, wires, taps or binding posts. To connect up the parts of +this transmitter it is only necessary to make the connections as shown +in the wiring diagram Fig. 78. + +[Illustration: Fig. 78.--5 to 50 Watt C. W. Telegraph Transmitter. +(With Single Oscillation Tube.)] + +A 200 Mile C. W. Telegraph Transmitter.--To make a continuous wave +telegraph transmitter that will cover distances up to 200 miles all +you have to do is to use two 5 watt vacuum tubes in _parallel_, all of +the rest of the apparatus being exactly the same. Connecting the +oscillator tubes up in parallel means that the two filaments are +connected across the leads of the storage battery, the two grids on +the same lead that goes to the aerial and the two plates on the same +lead that goes to the positive pole of the generator. Where two or +more oscillator tubes are used only one storage battery is needed, but +each filament must have its own rheostat. The wiring diagram Fig. 79 +shows how the two tubes are connected up in parallel. + +[Illustration: Fig. 79.--200 Mile C.W. Telegraph Transmitter (With Two +Tubes in Parallel.)] + +A 500 Mile C. W. Telegraph Transmitter.--For sending to distances of +over 200 miles and up to 500 miles you can use either: (1) three or +four 5 watt oscillator tubes in parallel as described above, or (2) +one 50 watt oscillator tube. Much of the apparatus for a 50 watt tube +set is exactly the same as that used for the 5 watt sets. Some of the +parts, however, must be proportionately larger though the design all +the way through remains the same. + +The Apparatus and Connections.--The aerial series condenser, the +blocking condenser, the grid condenser, the telegraph key, the +chopper, the choke coil in the key circuit, the filament voltmeter and +the protective condenser in the power circuit are identical with those +described for the 5 watt transmitting set. + +The 50 Watt Vacuum Tube Oscillator.--This is the size of tube +generally used by amateurs for long distance continuous wave +telegraphy. A single tube will develop 2 to 3 amperes in your aerial. +The filament takes a 10 volt current and a plate potential of 1,000 +volts is needed. One of these tubes is shown in Fig. 80 and the cost +is $30.00. A tube socket to fit it costs $2.50 extra. + +[Illustration: Fig. 80.--50 Watt Oscillator Vacuum Tube.] + +The Aerial Ammeter.--This should read to 5 amperes and the cost is +$6.25. + +The Grid Leak Resistance.--It has the same resistance, namely 5,000 +ohms as the one used with the 5 watt tube transmitter, but it is a +little larger. It is listed at $1.65. + +The Oscillation Choke Coil.--The choke coil in the power circuit is +made of about 260 turns of No. 30 B. & S. cotton covered magnet wire +wound on a spool 2-1/4 inches in diameter and 3-1/4 inches long. + +The Filament Rheostat.--This is made to take care of a 10 volt current +and it costs $10.00. + +The Filament Storage Battery.--This must develop 12 volts and one +having an output of 40 ampere-hours costs about $25.00. + +The Protective Condenser.--This condenser has a capacitance of 1 mfd. +and costs $2.00. + +The Motor-Generator.--Where you use one 50 watt oscillator tube you +will need a motor-generator that develops a plate potential of 1000 +volts and has an output of 200 watts. This machine will stand you +about $100.00. + +The different pieces of apparatus for this set are connected up +exactly the same as shown in the wiring diagram in Fig. 78. + +A 1000 Mile C. W. Telegraph Transmitter.--All of the parts of this +transmitting set are the same as for the 500 mile transmitter just +described except the motor generator and while this develops the same +plate potential, i.e., 1,000 volts, it must have an output of 500 +watts; it will cost you in the neighborhood of $175.00. For this long +distance transmitter you use two 50 watt oscillator tubes in parallel +and all of the parts are connected together exactly the same as for +the 200 mile transmitter shown in the wiring diagram in Fig. 79. + + + + +CHAPTER XVII + +CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH ALTERNATING CURRENT + + +Within the last few years alternating current has largely taken the +place of direct current for light, heat and power purposes in and +around towns and cities and if you have alternating current service in +your home you can install a long distance continuous wave telegraph +transmitter with very little trouble and at a comparatively small +expense. + +A 100 Mile C. W. Telegraph Transmitting Set.--The principal pieces of +apparatus for this transmitter are the same as those used for the _100 +Mile Continuous Wave Telegraph Transmitting Set_ described and +pictured in the preceding chapter which used direct current, except +that an _alternating current power transformer_ is employed instead of +the more costly _motor-generator_. + +The Apparatus Required.--The various pieces of apparatus you will need +for this transmitting set are: (1) one _hot-wire ammeter_ for the +aerial as shown at E in Fig. 75, but which reads to 5 amperes instead +of to 2.5 amperes; (2) one _tuning coil_ as shown at A in Fig. 77; (3) +one aerial condenser as shown at B in Fig. 77; (4) one _grid leak_ as +shown at C in Fig. 77; (5) one _telegraph key_ as shown at G in Fig. +75; (6) one _grid condenser_, made like the aerial condenser but +having only two terminals; (7) one _5 watt oscillator tube_ as shown +at E in Fig. 77; (8) one _.002 mfd. 3,000 volt by-pass condenser_, +made like the aerial and grid condensers; (9) one pair of _choke +coils_ for the high voltage secondary circuit; (10) one +_milli-ammeter_; (11) one A. C. _power transformer_; (12) one +_rheostat_ as shown at I in Fig. 75, and (13) one _panel cut-out_ as +shown at K in Fig. 75. + +The Choke Coils.--Each of these is made by winding about 100 turns of +No. 28, Brown and Sharpe gauge, cotton covered magnet wire on a spool +2 inches in diameter and 2-1/2 inches long, when it will have an +inductance of about 0.5 _millihenry_ [Footnote: A millihenry is +1/1000th part of a henry.] at 1,000 cycles. + +The Milli-ammeter.--This is an alternating current ammeter and reads +from 0 to 250 _milliamperes_; [Footnote: A _milliampere_ is the +1/1000th part of an ampere.] and is used for measuring the secondary +current that energizes the plate of the oscillator tube. It looks like +the aerial ammeter and costs about $7.50. + +The A. C. Power Transformer.--Differing from the motor generator set +the power transformer has no moving parts. For this transmitting set +you need a transformer that has an input of 325 volts. It is made to +work on a 50 to 60 cycle current at 102.5 to 115 volts, which is the +range of voltage of the ordinary alternating lighting current. This +adjustment for voltage is made by means of taps brought out from the +primary coil to a rotary switch. + +The high voltage secondary coil which energizes the plate has an +output of 175 watts and develops a potential of from 350 to 1,100 +volts. The low voltage secondary coil which heats the filament has an +output of 175 watts and develops 7.5 volts. This transformer, which is +shown in Fig. 81, is large enough to take care of from one to four 5 +watt oscillator tubes. It weighs about 15 pounds and sells for $25.00. + +[Illustration: Fig. 81.--Alternation Current Power Transformer. (For +C. W. Telegraphy and Wireless Telephony.)] + +[Illustration: The Transformer and Tuner of the World's Largest Radio +Station. Owned by the Radio Corporation of America at Rocky Point near +Port Jefferson L.I.] + +Connecting Up the Apparatus.--The wiring diagram Fig. 82 shows clearly +how all of the connections are made. It will be observed that a +storage battery is not needed as the secondary coil of the transformer +supplies the current to heat the filament of the oscillator. The +filament voltmeter is connected across the filament secondary coil +terminals, while the plate milli-ammeter is connected to the mid-taps +of the plate secondary coil and the filament secondary coil. + +[Illustration: Fig. 82. Wiring Diagram for 200 to 500 Mile C.W. +Telegraph Transmitting Set. (With Alternating Current)] + +A 200 to 500 Mile C. W. Telegraph Transmitting Set.--Distances of from +200 to 500 miles can be successfully covered with a telegraph +transmitter using two, three or four 5 watt oscillator tubes in +parallel. The apparatus needed is identical with that used for the 100 +mile transmitter just described. The tubes are connected in parallel +as shown in the wiring diagram in Fig. 83. + +[Illustration: Fig. 83.--Wiring Diagram for 500 to 1000 Mile C. W. +Telegraph Transmitter.] + +A 500 to 1,000 Mile C. W. Telegraph Transmitting Set.--With the +apparatus described for the above set and a single 50 watt oscillator +tube a distance of upwards of 500 miles can be covered, while with two +50 watt oscillator tubes in parallel you can cover a distance of 1,000 +miles without difficulty, and nearly 2,000 miles have been covered +with this set. + +The Apparatus Required.--All of the apparatus for this C. W. +telegraph transmitting set is the same as that described for the 100 +and 200 mile sets but you will need: (1) one or two _50 watt +oscillator tubes with sockets;_ (2) one _key condenser_ that has a +capacitance of 1 mfd., and a rated potential of 1,750 volts; (3) one +_0 to 500 milli-ammeter_; (4) one _aerial ammeter_ reading to 5 +amperes, and (5) an _A. C. power transformer_ for one or two 50 watt +tubes. + +[Illustration: Broadcasting Government Reports by Wireless from +Washington. This shows Mr. Gale at work with his set in the Post +Office Department.] + +The Alternating Current Power Transformer.--This power transformer is +made exactly like the one described in connection with the preceding +100 mile transmitter and pictured in Fig. 81, but it is considerably +larger. Like the smaller one, however, it is made to work with a 50 to +60 cycle current at 102.5 to 115 volts and, hence, can be used with +any A. C. lighting current. + +It has an input of 750 volts and the high voltage secondary coil which +energizes the plate has an output of 450 watts and develops 1,500 to +3,000 volts. The low voltage secondary coil which heats the filament +develops 10.5 volts. This transformer will supply current for one or +two 50-watt oscillator tubes and it costs about $40.00. + +Connecting Up the Apparatus.--Where a single oscillator tube is used +the parts are connected as shown in Fig. 82, and where two tubes are +connected in parallel the various pieces of apparatus are wired +together as shown in Fig. 83. The only difference between the 5 watt +tube transmitter and the 50 watt tube transmitter is in the size of +the apparatus with one exception; where one or two 50 watt tubes are +used a second condenser of large capacitance (1 mfd.) is placed in the +grid circuit and the telegraph key is shunted around it as shown in +the diagram Fig. 83. + + + + +CHAPTER XVIII + +WIRELESS TELEPHONE TRANSMITTING SETS WITH DIRECT AND ALTERNATING +CURRENTS + + +In time past the most difficult of all electrical apparatus for the +amateur to make, install and work was the wireless telephone. This was +because it required a _direct current_ of not less than 500 volts to +set up the sustained oscillations and all ordinary direct current for +lighting purposes is usually generated at a potential of 110 volts. + +Now as you know it is easy to _step-up_ a 110 volt alternating current +to any voltage you wish with a power transformer but until within +comparatively recent years an alternating current could not be used +for the production of sustained oscillations for the very good reason +that the state of the art had not advanced that far. In the new order +of things these difficulties have all but vanished and while a +wireless telephone transmitter still requires a high voltage direct +current to operate it this is easily obtained from 110 volt source of +alternating current by means of _vacuum tube rectifiers_. + +The pulsating direct currents are then passed through a filtering +reactance coil, called a _reactor_, and one or more condensers, and +these smooth them out until they approximate a continuous direct +current. The latter is then made to flow through a vacuum tube +oscillator when it is converted into high frequency oscillations and +these are _varied_, or _modulated_, as it is called, by a _microphone +transmitter_ such as is used for ordinary wire telephony. The energy +of these sustained modulated oscillations is then radiated into space +from the aerial in the form of electric waves. + +The distance that can be covered with a wireless telephone transmitter +is about one-fourth as great as that of a wireless telegraph +transmitter having the same input of initial current, but it is long +enough to satisfy the most enthusiastic amateur. For instance with a +wireless telephone transmitter where an amplifier tube is used to set +up the oscillations and which is made for a plate potential of 100 +volts, distances up to 10 or 15 miles can be covered. + +With a single 5 watt oscillator tube energized by a direct current of +350 volts from either a motor-generator or from a power transformer +(after it has been rectified and smoothed out) speech and music can be +transmitted to upwards of 25 miles. Where two 5 watt tubes connected +in parallel are used wireless telephone messages can be transmitted to +distances of 40 or 50 miles. Further, a single 50 watt oscillator tube +will send to distances of 50 to 100 miles while two of these tubes in +parallel will send from 100 to 200 miles. Finally, where four or five +oscillator tubes are connected in parallel proportionately greater +distances can be covered. + +A Short Distance Wireless Telephone Transmitting Set-With 110 Volt +Direct Lighting Current.--For this very simple, short distance +wireless telephone transmitting set you need the same apparatus as +that described and pictured in the beginning of Chapter XVI for a +_Short Distance C. W. Telegraph Transmitter_, except that you use a +_microphone transmitter_ instead of a _telegraph key_. If you have a +110 volt direct lighting current in your home you can put up this +short distance set for very little money and it will be well worth +your while to do so. + +The Apparatus You Need.--For this set you require: (1) one _tuning +coil_ as shown at A and B in Fig. 75; (2) one _aerial ammeter_ as +shown at C in Fig. 75; (3) one _aerial condenser_ as shown at C in +Fig. 75; (4) one _grid, blocking and protective condenser_ as shown at +D in Fig. 75; (5) one _grid leak_ as shown at C in Fig. 77; (6) one +_vacuum tube amplifier_ which is used as an _oscillator_; (7) one _6 +volt storage battery_; (8) one _rheostat_ as shown at I in Fig. 75; +(9) one _oscillation choke coil_; (10) one _panel cut-out_ as shown at +K in Fig. 75 and an ordinary _microphone transmitter_. + +The Microphone Transmitter.--The best kind of a microphone to use with +this and other telephone transmitting sets is a _Western Electric No. +284-W_. [Footnote: Made by the Western Electric Company, Chicago, +Ill.] This is known as a solid back transmitter and is the standard +commercial type used on all long distance Bell telephone lines. It +articulates sharply and distinctly and there are no current variations +to distort the wave form of the voice and it will not buzz or sizzle. +It is shown in Fig. 84 and costs $2.00. Any other good microphone +transmitter can be used if desired. + +[Illustration: Fig. 84.--Standard Microphone Transmitter.] + +Connecting Up the Apparatus.--Begin by connecting the leading-in wire +with one of the terminals of the microphone transmitter, as shown in +the wiring diagram Fig. 85, and the other terminal of this to one end +of the tuning coil. Now connect _clip 1_ of the tuning coil to one of +the posts of the hot-wire ammeter, the other post of this to one end +of aerial condenser and, finally, the other end of the latter with the +water pipe or other ground. The microphone can be connected in the +ground wire and the ammeter in the aerial wire and the results will be +practically the same. + +[Illustration: Fig. 85.--Wiring Diagram of Short Distance Wireless +Telephone Set. (Microphone in Aerial Wire.)] + +Next connect one end of the grid condenser to the post of the tuning +coil that makes connection with the microphone and the other end to +the grid of the tube, and then shunt the grid leak around the +condenser. Connect the + or _positive_ electrode of the storage +battery with one terminal of the filament of the vacuum tube, the +other terminal of the filament with one post of the rheostat and the +other post of this with the - or _negative_ electrode of the battery. +This done, connect _clip 2_ of the tuning coil to the + or _positive_ +electrode of the battery and bring a lead from it to one of the switch +taps of the panel cut-out. + +Now connect _clip 3_ of the tuning coil with one end of the blocking +condenser, the other end of this with one terminal of the choke coil +and the other terminal of the latter with the other switch tap of the +cut-out. Connect the protective condenser across the direct current +feed wires between the panel cut-out and the choke coil. Finally +connect the ends of a lamp cord to the fuse socket taps of the +cut-out, and connect the other ends to a lamp plug and screw it into +the lamp socket of the feed wires. Screw in a pair of 5 ampere _fuse +plugs_, close the switch and you are ready to tune the transmitter and +talk to your friends. + +A 25 to 50 Mile Wireless Telephone Transmitter--With Direct Current +Motor Generator.--Where you have to start with 110 or 220 volt direct +current and you want to transmit to a distance of 25 miles or more you +will have to install a _motor-generator_. To make this transmitter you +will need exactly the same apparatus as that described and pictured +for the _100 Mile C. W. Telegraph Transmitting Set_ in Chapter XVI, +except that you must substitute a _microphone transmitter_ and a +_telephone induction coil_, or a _microphone transformer_, or still +better, a _magnetic modulator_, for the telegraph key and chopper. + +The Apparatus You Need.--To reiterate; the pieces of apparatus you +need are: (1) one _aerial ammeter_ as shown at E in Fig. 75; (2) one +_tuning coil_ as shown at A in Fig. 77; (3) one _aerial condenser_ as +shown at B in Fig. 77; (4) one _grid leak_ as shown at C in Fig. 77; +(5) one _grid, blocking_ and _protective condenser_; (6) one _5 watt +oscillator tube_ as shown at E in Fig. 77; (7) one _rheostat_ as shown +at I in Fig. 75; (8) one _10 volt (5 cell) storage battery_; (9) one +_choke coil_; (10) one _panel cut-out_ as shown at K in Fig. 75, and +(11) a _motor-generator_ having an input of 110 or 220 volts and an +output of 350 volts. + +In addition to the above apparatus you will need: (12) a _microphone +transmitter_ as shown in Fig. 84; (13) a battery of four dry cells or +a 6 volt storage battery, and either (14) a _telephone induction coil_ +as shown in Fig. 86; (15) a _microphone transformer_ as shown in Fig. +87; or a _magnetic modulator_ as shown in Fig. 88. All of these parts +have been described, as said above, in Chapter XVI, except the +microphone modulators. + +[Illustration: Fig. 86.--Telephone Induction Coil. (Used with +Microphone Transmitter.)] + +[Illustration: Fig. 87.--Microphone Transformer. (Used with Microphone +Transmitter.)] + +[Illustration: Fig. 88.--Magnetic Modulator. (Used with Microphone +Transmitter.)] + +The Telephone Induction Coil.--This is a little induction coil that +transforms the 6-volt battery current after it has flowed through and +been modulated by the microphone transmitter into alternating currents +that have a potential of 1,000 volts of more. It consists of a primary +coil of _No. 20 B. and S._ gauge cotton covered magnet wire wound on a +core of soft iron wires while around the primary coil is wound a +secondary coil of _No. 30_ magnet wire. Get a _standard telephone +induction coil_ that has a resistance of 500 or 750 ohms and this will +cost you a couple of dollars. + +The Microphone Transformer.--This device is built on exactly the same +principle as the telephone induction coil just described but it is +more effective because it is designed especially for modulating the +oscillations set up by vacuum tube transmitters. As with the telephone +induction coil, the microphone transmitter is connected in series with +the primary coil and a 6 volt dry or storage battery. + +In the better makes of microphone transformer, there is a third +winding, called a _side tone_ coil, to which a headphone can be +connected so that the operator who is speaking into the microphone can +listen-in and so learn if his transmitter is working up to standard. + +The Magnetic Modulator.--This is a small closed iron core transformer +of peculiar design and having a primary and a secondary coil wound on +it. This device is used to control the variations of the oscillating +currents that are set up by the oscillator tube. It is made in three +sizes and for the transmitter here described you want the smallest +size, which has an output of 1/2 to 1-1/2 amperes. It costs about +$10.00. + +How the Apparatus Is Connected Up.--The different pieces of apparatus +are connected together in exactly the same way as the _100 Mile C. W. +Telegraph Set_ in Chapter XVI except that the microphone transmitter +and microphone modulator (whichever kind you use) is substituted for +the telegraph key and chopper. + +Now there are three different ways that the microphone and its +modulator can be connected in circuit. Two of the best ways are shown +at A and B in Fig. 89. In the first way the secondary terminals of the +modulator are shunted around the grid leak in the grid circuit as at +A, and in the second the secondary terminals are connected in the +aerial as at B. Where an induction coil or a microphone transformer is +used they are shunted around a condenser, but this is not necessary +with the magnetic modulator. Where a second tube is used as in Fig. 90 +then the microphone and its modulator are connected with the grid +circuit and _clip 3_ of the tuning coil. + +[Illustration: Fig. 89.--Wiring Diagram of 25 to 50 Mile Wireless +Telephone. (Microphone Modulator Shunted Around Grid-Leak Condenser.)] + +[Illustration: (B) Fig. 89.--Microphone Modulator Connected in Aerial +Wire.] + +[Illustration: Fig. 90.--Wiring Diagram of 50 to 100 Mile Wireless +Telephone Transmitting Set.] + +A 50 to 100 Mile Wireless Telephone Transmitter--With Direct Current +Motor Generator.--As the initial source of current available is taken +to be a 110 or 220 volt direct current a motor-generator having an +output of 350 volts must be used as before. The only difference +between this transmitter and the preceding one is that: (1) two 5 watt +tubes are used, the first serving as an _oscillator_ and the second as +a _modulator_; (2) an _oscillation choke coil_ is used in the plate +circuit; (3) a _reactance coil_ or _reactor_, is used in the plate +circuit; and (4) a _reactor_ is used in the grid circuit. + +The Oscillation Choke Coil.--You can make this choke coil by winding +about 275 turns of _No. 28 B. and S. gauge_ cotton covered magnet wire +on a spool 2 inches in diameter and 4 inches long. Give it a good +coat of shellac varnish and let it dry thoroughly. + +The Plate and Grid Circuit Reactance Coils.--Where a single tube is +used as an oscillator and a second tube is employed as a modulator, a +_reactor_, which is a coil of wire wound on an iron core, is used in +the plate circuit to keep the high voltage direct current of the +motor-generator the same at all times. Likewise the grid circuit +reactor is used to keep the voltage of the grid at a constant value. +These reactors are made alike and a picture of one of them is shown in +Fig. 91 and each one will cost you $5.75. + +[Illustration: Fig. 91.--Plate and Grid Circuit Reactor.] + +Connecting up the Apparatus.--All of the different pieces of apparatus +are connected up as shown in Fig. 89. One of the ends of the secondary +of the induction coil, or the microphone transformer, or the magnetic +modulator is connected to the grid circuit and the other end to _clip +3_ of the tuning coil. + +A 100 to 200 Mile Wireless Telephone Transmitter--With Direct Current +Motor Generator.--By using the same connections shown in the wiring +diagrams in Fig. 89 and a single 50 watt oscillator tube your +transmitter will then have a range of 100 miles or so, while if you +connect up the apparatus as shown in Fig. 90 and use two 50 watt tubes +you can work up to 200 miles. Much of the apparatus for a 50 watt +oscillator set where either one or two tubes are used is of the same +size and design as that just described for the 5 watt oscillator sets, +but, as in the C. W. telegraph sets, some of the parts must be +proportionately larger. The required parts are (1) the _50 watt tube_; +(2) the _grid leak resistance_; (3) the _filament rheostat_; (4) the +_filament storage battery_; and (5) the _magnetic modulator_. All of +these parts, except the latter, are described in detail under the +heading of a _500 Mile C. W. Telegraph Transmitting Set_ in Chapter +XVI, and are also pictured in that chapter. + +It is not advisable to use an induction coil for the modulator for +this set, but use, instead, either a telephone transformer, or better, +a magnetic modulator of the second size which has an output of from +1-1/2 to 3-1/2 amperes. The magnetic modulator is described and +pictured in this chapter. + +A 50 to 100 Mile Wireless Telephone Transmitting Set--With 110 Volt +Alternating Current.--If you have a 110 volt [Footnote: Alternating +current for lighting purposes ranges from 102.5 volts to 115 volts, so +we take the median and call it 110 volts.] alternating current +available you can use it for the initial source of energy for your +wireless telephone transmitter. The chief difference between a +wireless telephone transmitting set that uses an alternating current +and one that uses a direct current is that: (1) a _power transformer_ +is used for stepping up the voltage instead of a motor-generator, and +(2) a _vacuum tube rectifier_ must be used to convert the alternating +current into direct current. + +The Apparatus You Need.--For this telephone transmitting set you need: +(1) one _aerial ammeter_; (2) one _tuning coil_; (3) one _telephone +modulator_; (4) one _aerial series condenser_; (5) one _4 cell dry +battery_ or a 6 volt storage battery; (6) one _microphone +transmitter_; (7) one _battery switch_; (8) one _grid condenser_; (9) +one _grid leak_; (10) two _5 watt oscillator tubes with sockets_; (11) +one _blocking condenser_; (12) one _oscillation choke coil_; (13) two +_filter condensers_; (14) one _filter reactance coil_; (15) an +_alternating current power transformer_, and (16) two _20 watt +rectifier vacuum tubes_. + +All of the above pieces of apparatus are the same as those described +for the _100 Mile C. W. Telegraph Transmitter_ in Chapter XVII, +except: (a) the _microphone modulator_; (b) the _microphone +transmitter_ and (c) the _dry_ or _storage battery_, all of which are +described in this chapter; and the new parts which are: (d) the +_rectifier vacuum tubes_; (e) the _filter condensers_; and (f) the +_filter reactance coil_; further and finally, the power transformer +has a _third_ secondary coil on it and it is this that feeds the +alternating current to the rectifier tubes, which in turn converts it +into a pulsating direct current. + +The Vacuum Tube Rectifier.--This rectifier has two electrodes, that +is, it has a filament and a plate like the original vacuum tube +detector, The smallest size rectifier tube requires a plate potential +of 550 volts which is developed by one of the secondary coils of the +power transformer. The filament terminal takes a current of 7.5 volts +and this is supplied by another secondary coil of the transformer. +This rectifier tube delivers a direct current of 20 watts at 350 +volts. It looks exactly like the 5 watt oscillator tube which is +pictured at E in Fig. 77. The price is $7.50. + +The Filter Condensers.--These condensers are used in connection with +the reactance coil to smooth out the pulsating direct current after it +has passed through the rectifier tube. They have a capacitance of 1 +mfd. and will stand 750 volts. These condensers cost about $2.00 each. + +The Filter Reactance Coil.--This reactor which is shown in Fig. 92, +has about the same appearance as the power transformer but it is +somewhat smaller. It consists of a coil of wire wound on a soft iron +core and has a large inductance, hence the capacitance of the filter +condensers are proportionately smaller than where a small inductance +is used which has been the general practice. The size you require for +this set has an output of 160 milliamperes and it will supply current +for one to four 5 watt oscillator tubes. This size of reactor costs +$11.50. + +[Illustration: Fig. 92.--Filter Reactor for Smoothing out Rectified +Currents.] + +Connecting Up the Apparatus.--The wiring diagram in Fig. 93 shows how +the various pieces of apparatus for this telephone transmitter are +connected up. You will observe: (1) that the terminals of the power +transformer secondary coil which develops 10 volts are connected to +the filaments of the oscillator tubes; (2) that the terminals of the +other secondary coil which develops 10 volts are connected with the +filaments of the rectifier tubes; (3) that the terminals of the third +secondary coil which develops 550 volts are connected with the plates +of the rectifier tubes; (4) that the pair of filter condensers are +connected in parallel and these are connected to the mid-taps of the +two filament secondary coils; (5) that the reactance coil and the +third filter condenser are connected together in series and these are +shunted across the filter condensers, which are in parallel; and, +finally, (6) a lead connects the mid-tap of the 550-volt secondary +coil of the power transformer with the connection between the reactor +and the third filter condenser. + +[Illustration: Fig 93.--100 to 200 Mile Wireless Telephone +Transmitter.] + +A 100 to 200 Mile Wireless Telephone Transmitting Set--With 110 Volt +Alternating Current.--This telephone transmitter is built up of +exactly the same pieces of apparatus and connected up in precisely the +same way as the one just described and shown in Fig. 93. + +Apparatus Required.--The only differences between this and the +preceding transmitter are: (1) the _magnetic modulator_, if you use +one, should have an output of 3-1/2 to 5 amperes; (2) you will need +two _50 watt oscillator tubes with sockets_; (3) two _150 watt +rectifier tubes with sockets_; (4) an _aerial ammeter_ that reads to +_5 amperes_; (5) three _1 mfd. filter condensers_ in parallel; (6) +_two filter condensers of 1 mfd. capacitance_ that will stand _1750 +volts_; and (6) a _300 milliampere filter reactor_. + +The apparatus is wired up as shown in Fig. 93. + + + + +CHAPTER XIX + +THE OPERATION OF VACUUM TUBE TRANSMITTERS + + +The three foregoing chapters explained in detail the design and +construction of (1) two kinds of C. W. telegraph transmitters, and (2) +two kinds of wireless telephone transmitters, the difference between +them being whether they used (A) a direct current, or (B) an +alternating current as the initial source of energy. Of course there +are other differences between those of like types as, for instance, +the apparatus and connections used (_a_) in the key circuits, and +(_b_) in the microphone circuits. But in all of the transmitters +described of whatever type or kind the same fundamental device is used +for setting up sustained oscillations and this is the _vacuum tube_. + +The Operation of the Vacuum Tube Oscillator.--The operation of the +vacuum tube in producing sustained oscillations depends on (1) the +action of the tube as a valve in setting up the oscillations in the +first place and (2) the action of the grid in amplifying the +oscillations thus set up, both of which we explained in Chapter XIV. +In that chapter it was also pointed out that a very small change in +the grid potential causes a corresponding and larger change in the +amount of current flowing from the plate to the filament; and that if +a vacuum tube is used for the production of oscillations the initial +source of current must have a high voltage, in fact the higher the +plate voltage the more powerful will be the oscillations. + +To understand how oscillations are set up by a vacuum tube when a +direct current is applied to it, take a look at the simple circuits +shown in Fig. 94. Now when you close the switch the voltage from the +battery charges the condenser and keeps it charged until you open it +again; the instant you do this the condenser discharges through the +circuit which includes it and the inductance coil, and the discharge +of a condenser is always oscillatory. + +[Illustration: (A) and (B) Fig. 94. Operation of Vacuum Tube +Oscillators.] + +Where an oscillator tube is included in the circuits as shown at A and +B in Fig. 94, the grid takes the place of the switch and any slight +change in the voltage of either the grid or the plate is sufficient to +start a train of oscillations going. As these oscillations surge +through the tube the positive parts of them flow from the plate to the +filament and these carry more of the direct current with them. + +To make a tube set up powerful oscillations then, it is only necessary +that an oscillation circuit shall be provided which will feed part of +the oscillations set up by the tube back to the grid circuit and when +this is done the oscillations will keep on being amplified until the +tube reaches the limit of its output. + +[Illustration: (C) Fig. 94.--How a Direct Current Sets up +Oscillations.] + +The Operation of C. W. Telegraph Transmitters With Direct +Current--Short Distance C. W. Transmitter.--In the transmitter shown +in the wiring diagram in Fig. 76 the positive part of the 110 volt +direct current is carried down from the lamp socket through one side +of the panel cut-out, thence through the choke coil and to the plate +of the oscillator tube, when the latter is charged to the positive +sign. The negative part of the 110 volt direct current then flows down +the other wire to the filament so that there is a difference of +potential between the plate and the filament of 110 volts. Now when +the 6-volt battery current is switched on the filament is heated to +brilliancy, and the electrons thrown off by it form a conducting path +between it and the plate; the 110 volt current then flows from the +latter to the former. + +Now follow the wiring from the plate over to the blocking condenser, +thence to _clip 3_ of the tuning coil, through the turns of the latter +to _clip 2_ and over to the filament and, when the latter is heated, +you have a _closed oscillation circuit_. The oscillations surging in +the latter set up other and like oscillations in the tuning coil +between the end of which is connected with the grid, the aerial and +the _clip 2_, and these surge through the circuit formed by this +portion of the coil, the grid condenser and the filament; this is the +amplifying circuit and it corresponds to the regenerative circuit of a +receiving set. + +When oscillations are set up in it the grid is alternately charged to +the positive and negative signs. These reversals of voltage set up +stronger and ever stronger oscillations in the plate circuit as before +explained. Not only do the oscillations surge in the closed circuits +but they run to and fro on the aerial wire when their energy is +radiated in the form of electric waves. The oscillations are varied by +means of the telegraph key which is placed in the grid circuit as +shown in Fig. 76. + +The Operation of the Key Circuit.--The effect in a C. W. transmitter +when a telegraph key is connected in series with a buzzer and a +battery and these are shunted around the condenser in the grid +circuit, is to rapidly change the wave form of the sustained +oscillations, and hence, the length of the waves that are sent out. +While no sound can be heard in the headphones at the receiving station +so long as the points of the key are not in contact, when they are in +contact the oscillations are modulated and sounds are heard in the +headphones that correspond to the frequency of the buzzer in the key +circuit. + +The Operation of C. W. Telegraph Transmitters with Direct +Current.--The chief differences between the long distance sets which +use a direct current, i.e., those described in Chapter XVI, and the +short distance transmitting sets are that the former use: (1) a +motor-generator set for changing the low voltage direct current into +high voltage direct current, and (2) a chopper in the key circuit. The +way the motor-generator changes the low- into high-voltage current has +been explained in Chapter XVI. + +The chopper interrupts the oscillations surging through the grid +circuit at a frequency that the ear can hear, that is to say, about +800 to 1,000 times per second. When the key is open, of course, the +sustained oscillations set up in the circuits will send out continuous +waves but when the key is closed these oscillations are broken up and +then they send out discontinuous waves. If a heterodyne receiving set, +see Chapter XV, is being used at the other end you can dispense with +the chopper and the key circuit needed is very much simplified. The +operation of key circuits of the latter kind will be described +presently. + +The Operation of C. W. Telegraph Transmitters with Alternating +Current--With a Single Oscillator Tube.--Where an oscillator tube +telegraph transmitter is operated by a 110 volt alternating current as +the initial source of energy, a buzzer, chopper or other interruptor +is not needed in the key circuit. This is because oscillations are set +up only when the plate is energized with the positive part of the +alternating current and this produces an intermittent musical tone in +the headphones. Hence this kind of a sending set is called a _tone +transmitter_. + +Since oscillations are set up only by the positive part or voltage of +an alternating current it is clear that, as a matter of fact, this +kind of a transmitter does not send out continuous waves and therefore +it is not a C. W. transmitter. This is graphically shown by the curve +of the wave form of the alternating current and the oscillations that +are set up by the positive part of it in Fig. 95. Whenever the +positive half of the alternating current energizes the plate then +oscillations are set up by the tube and, conversely, when the negative +half of the current charges the plate no oscillations are produced. + +[Illustration: Fig. 95.--Positive Voltage only sets up Oscillations.] + +You will also observe that the oscillations set up by the positive +part of the current are not of constant amplitude but start at zero +the instant the positive part begins to energize the plate and they +keep on increasing in amplitude as the current rises in voltage until +the latter reaches its maximum; then as it gradually drops again to +zero the oscillations decrease proportionately in amplitude with it. + +Heating the Filament with Alternating Current.--Where an alternating +current power transformer is used to develop the necessary plate +voltage a second secondary coil is generally provided for heating the +filament of the oscillation tube. This is better than a direct current +for it adds to the life of the filament. When you use an alternating +current to heat the filament keep it at the same voltage rather than +at the same amperage (current strength). To do this you need only to +use a voltmeter across the filament terminals instead of an ammeter in +series with it; then regulate the voltage of the filament with a +rheostat. + +The Operation of C. W. Telegraph Transmitters with Alternating +Current--With Two Oscillator Tubes.--By using two oscillator tubes and +connecting them up with the power transformer and oscillating circuits +as shown in the wiring diagram in Fig. 83 the plates are positively +energized alternately with every reversal of the current and, +consequently, there is no time period between the ending of the +oscillations set up by one tube and the beginning of the oscillations +set up by the other tube. In other words these oscillations are +sustained but as in the case of those of a single tube, their +amplitude rises and falls. This kind of a set is called a _full wave +rectification transmitter_. + +The waves radiated by this transmitter can be received by either a +crystal detector or a plain vacuum-tube detector but the heterodyne +receptor will give you better results than either of the foregoing +types. + +The Operation of Wireless Telephone Transmitters with Direct +Current--Short Distance Transmitter.--The operation of this short +distance wireless telephone transmitter, a wiring diagram of which is +shown in Fig. 85 is exactly the same as that of the _Direct Current +Short Distance C. W. Telegraph Transmitter_ already explained in this +chapter. The only difference in the operation of these sets is the +substitution of the _microphone transmitter_ for the telegraph key. + +The Microphone Transmitter.--The microphone transmitter that is used +to vary, or modulate, the sustained oscillations set up by the +oscillator tube and circuits is shown in Fig. 84. By referring to the +diagram at A in this figure you will readily understand how it +operates. When you speak into the mouthpiece the _sound waves_, which +are waves in the air, impinge upon the diaphragm and these set it into +vibration--that is, they make it move to and fro. + +When the diaphragm moves toward the back of the transmitter it forces +the carbon granules that are in the cup closer together; this lowers +their resistance and allows more current from the battery to flow +through them; when the pressure of the air waves is removed from the +diaphragm it springs back toward the mouth-piece and the carbon +granules loosen up when the resistance offered by them is increased +and less current can flow through them. Where the oscillation current +in the aerial wire is small the transmitter can be connected directly +in series with the latter when the former will surge through it. As +you speak into the microphone transmitter its resistance is varied and +the current strength of the oscillations is varied accordingly. + +The Operation of Wireless Telephone Transmitters with Direct +Current--Long Distance Transmitters.--In the wireless telephone +transmitters for long distance work which were shown and described in +the preceding chapter a battery is used to energize the microphone +transmitter, and these two elements are connected in series with a +_microphone modulator_. This latter device may be either (1) a +_telephone induction coil_, (2) a _microphone transformer_, or (3) a +_magnetic modulator_; the first two of these devices step-up the +voltage of the battery current and the amplified voltage thus +developed is impressed on the oscillations that surge through the +closed oscillation circuit or the aerial wire system according to the +place where you connect it. The third device works on a different +principle and this will be described a little farther along. + +The Operation of Microphone Modulators--The Induction Coil.--This +device is really a miniature transformer, see A in Fig. 86, and its +purpose is to change the 6 volt direct current that flows through the +microphone into 100 volts alternating current; in turn, this is +impressed on the oscillations that are surging in either (1) the grid +circuit as shown at A in Fig. 89, and in Fig. 90, (2) the aerial wire +system, as shown at B in Fig. 89 and Fig. 93. When the current from +the battery flows through the primary coil it magnetizes the soft iron +core and as the microphone varies the strength of the current the high +voltage alternating currents set up in the secondary coil of the +induction coil are likewise varied, when they are impressed upon and +modulate the oscillating currents. + +The Microphone Transformer.--This is an induction coil that is +designed especially for wireless telephone modulation. The iron core +of this transformer is also of the open magnetic circuit type, see A +in Fig. 87, and the _ratio_ of the turns [Footnote: See Chapter VI] of +the primary and the secondary coil is such that when the secondary +current is impressed upon either the grid circuit or the aerial wire +system it controls the oscillations flowing through it with the +greatest efficiency. + +The Magnetic Modulator.--This piece of apparatus is also called a +_magnetic amplifier_. The iron core is formed of very thin plates, or +_laminations_ as they are called, and this permits high-frequency +oscillations to surge in a coil wound on it. In this transformer, see +A in Fig. 88, the current flowing through the microphone varies the +magnetic permeability of the soft iron core by the magnetic saturation +of the latter. Since the microphone current is absolutely distinct +from the oscillating currents surging through the coil of the +transformer a very small direct current flowing through a coil on the +latter will vary or modulate very large oscillating currents surging +through the former. It is shown connected in the aerial wire system +at A in Fig. 88, and in Fig. 93. + +Operation of the Vacuum Tube as a Modulator.--Where a microphone +modulator of the induction coil or microphone transformer type is +connected in the grid circuit or aerial wire system the modulation is +not very effective, but by using a second tube as a _modulator_, as +shown in Fig. 90, an efficient degree of modulation can be had. Now +there are two methods by which a vacuum tube can be used as a +modulator and these are: (1) by the _absorption_ of the energy of the +current set up by the oscillator tube, and (2) by _varying_ the direct +current that energizes the plate of the oscillator tube. + +The first of these two methods is not used because it absorbs the +energy of the oscillating current produced by the tube and it is +therefore wasteful. The second method is an efficient one, as the +direct current is varied before it passes into the oscillator tube. +This is sufficient reason for describing only the second method. The +voltage of the grid of the modulator tube is varied by the secondary +coil of the induction coil or microphone transformer, above described. +In this way the modulator tube acts like a variable resistance but it +amplifies the variations impressed on the oscillations set up by the +oscillator tube. As the magnetic modulator does the same thing a +vacuum tube used as a modulator is not needed where the former is +employed. For this reason a magnetic modulator is the cheapest in the +long run. + +The Operation of Wireless Telephone Transmitters with Alternating +Current.--Where an initial alternating current is used for wireless +telephony, the current must be rectified first and then smoothed out +before passing into the oscillator tube to be converted into +oscillations. Further so that the oscillations will be sustained, two +oscillator tubes must be used, and, finally, in order that the +oscillations may not vary in amplitude the alternating current must be +first changed into direct current by a pair of rectifier vacuum tubes, +as shown in Fig. 93. When this is done the plates will be positively +charged alternately with every reversal of the current in which case +there will be no break in the continuity of the oscillations set up +and therefore in the waves that are sent out. + +The Operation of Rectifier Vacuum Tubes.--The vacuum tube rectifier is +simply a two electrode vacuum tube. The way in which it changes a +commercial alternating current into pulsating direct current is the +same as that in which a two electrode vacuum tube detector changes an +oscillating current into pulsating direct currents and this has been +explained in detail under the heading of _The Operation of a Two +Electrode Vacuum Tube Detector_ in Chapter XII. In the _C. W. +Telegraph Transmitting Sets_ described in Chapter XVII, the oscillator +tubes act as rectifiers as well as oscillators but for wireless +telephony the alternating current must be rectified first so that a +continuous direct current will result. + +The Operation of Reactors and Condensers.--A reactor is a single coil +of wire wound on an iron core, see Fig. 90 and A in Fig. 91, and it +should preferably have a large inductance. The reactor for the plate +and grid circuit of a wireless telephone transmitter where one or more +tubes are used as modulators as shown in the wiring diagram in Fig. +90, and the filter reactor shown in Fig. 92, operate in the same way. + +When an alternating current flows through a coil of wire the reversals +of the current set up a _counter electromotive force_ in it which +opposes, that is _reacts_, on the current, and the _higher_ the +frequency of the current the _greater_ will be the _reactance_. When +the positive half of an alternating current is made to flow through a +large resistance the current is smoothed out but at the same time a +large amount of its energy is used up in producing heat. + +But when the positive half of an alternating current is made to flow +through a large inductance it acts like a large resistance as before +and likewise smooths out the current, but none of its energy is wasted +in heat and so a coil having a large inductance, which is called an +_inductive reactance_, or just _reactor_ for short, is used to smooth +out, or filter, the alternating current after it has been changed into +a pulsating direct current by the rectifier tubes. + +A condenser also has a reactance effect on an alternating current but +different from an induction coil the _lower_ the frequency the +_greater_ will be the reactance. For this reason both a filter reactor +and _filter condensers_ are used to smooth out the pulsating direct +currents. + + + + +CHAPTER XX + +HOW TO MAKE A RECEIVING SET FOR $5.00 OR LESS + + +In the chapters on _Receptors_ you have been told how to build up +high-grade sets. But there are thousands of boys, and, probably, not a +few men, who cannot afford to invest $25.00, more or less, in a +receiving set and would like to experiment in a small way. + +The following set is inexpensive, and with this cheap, little portable +receptor you can get the Morse code from stations a hundred miles +distant and messages and music from broadcasting stations if you do +not live too far away from them. All you need for this set are: (1) a +_crystal detector_, (2) a _tuning coil_ and (3) an _earphone_. You can +make a crystal detector out of a couple of binding posts, a bit of +galena and a piece of brass wire, or, better, you can buy one all +ready to use for 50 cents. + +[Illustration: Wireless Receptor, the size of a Safety Match Box. A +Youthful Genius in the person of Kenneth R. Hinman, Who is only twelve +years old, has made a Wireless Receiving Set that fits neatly into a +Safety Match Box. With this Instrument and a Pair of Ordinary +Receivers, He is able to catch not only Code Messages but the regular +Broadcasting Programs from Stations Twenty and Thirty Miles Distant.] + +The Crystal Detector.--This is known as the _Rasco baby_ detector and +it is made and sold by the _Radio Specialty Company_, 96 Park Place, +New York City. It is shown in Fig. 96. The base is made of black +composition and on it is mounted a standard in which a rod slides and +on one end of this there is fixed a hard rubber adjusting knob while +the other end carries a thin piece of _phosphor-bronze wire_, called a +_cat-whisker_. To secure the galena crystal in the cup you simply +unscrew the knurled cap, place it in the cavity of the post and screw +the cap back on again. The free end of the cat-whisker wire is then +adjusted so that it will rest lightly on the exposed part of the +galena. + +[Illustration: Fig. 96.--Rasco Baby Crystal Detector.] + +The Tuning Coil.--You will have to make this tuning coil, which you +can do at a cost of less than $1.00, as the cheapest tuning coil you +can buy costs at least $3.00, and we need the rest of our $5.00 to +invest in the earphone. Get a cardboard tube, such as is used for +mailing purposes, 2 inches in diameter and 3 inches long, see A in +Fig. 97. Now wind on 250 turns of _No. 40 Brown and Sharpe gauge plain +enameled magnet wire_. You can use _No. 40 double cotton covered +magnet wire_, in which case you will have to shellac the tube and the +wire after you get it on. + +[Illustration: Fig. 97.--How the Tuning Coil is Made.] + +As you wind on the wire take off a tap at every 15th turn, that is, +scrape the wire and solder on a piece about 7 inches long, as shown in +Fig. 99; and do this until you have 6 taps taken off. Instead of +leaving the wires outside of the tube bring them to the inside of it +and then out through one of the open ends. Now buy a _round wood-base +switch_ with 7 contact points on it as shown at B in Fig. 97. This +will cost you 25 or 50 cents. + +The Headphone.--An ordinary Bell telephone receiver is of small use +for wireless work as it is wound to too low a resistance and the +diaphragm is much too thick. If you happen to have a Bell phone you +can rewind it with _No. 40_ single covered silk magnet wire, or +enameled wire of the same size, when its sensitivity will be very +greatly improved. Then you must get a thin diaphragm and this should +_not_ be enameled, as this tends to dampen the vibrations of it. You +can get a diaphragm of the right kind for 5 cents. + +The better way, though, is to buy an earphone made especially for +wireless work. You can get one wound to 1000 ohms resistance for $1.75 +and this price includes a cord. [Footnote: This is Mesco, No. 470 +wireless phone. Sold by the Manhattan Electrical Supply Co., Park +Place, N.Y.C.] For $1.00 extra you can get a head-band for it, and +then your phone will look like the one pictured in Fig. 98. + +[Illustration: Fig. 98.--Mesco 1000 Ohm Head Set.] + +How to Mount the Parts.--Now mount the coil on a wood base, 1/2 or 1 +inch thick, 3-1/2 inches wide and 5-1/2 inches long, and then connect +one end of the coil to one of the end points on the switch, and +connect each succeeding tap to one of the switch points, as shown +schematically in Fig. 99 and diagrammatically in Fig. 100. This done, +screw the switch down to the base. Finally screw the detector to the +base and screw two binding posts in front of the coil. These are for +the earphone. + +[Illustration: Fig. 99.--Schematic Layout of $5.00 Receiving Set.] + +[Illustration: Fig. 100.--Wiring Diagram for $5.00 Receiving Set.] + +The Condenser.--You do not have to connect a condenser across the +earphone but if you do you will improve the receiving qualities of the +receptor. + +How to Connect Up the Receptor.--Now connect up all the parts as shown +in Figs. 99 and 100, then connect the leading-in wire of the aerial +with the lever of the switch; and connect the free end of the tuning +coil with the _ground_. If you have no aerial wire try hooking it up +to a rain pipe that is _not grounded_ or the steel frame of an +umbrella. For a _ground_ you can use a water pipe, an iron pipe driven +into the ground, or a hydrant. Put on your headphone, adjust the +detector and move the lever over the switch contacts until it is in +adjustment and then, if all your connections are properly made, you +should be able to pick up messages. + +[Illustration: Wireless Set made into a Ring, designed by Alfred G. +Rinehart, of Elizabeth, New Jersey. This little Receptor is a +Practical Set; it will receive Messages, Concerts, etc., Measures 1" +by 5/8" by 7/8". An ordinary Umbrella is used as an Aerial.] + + + + +APPENDIX + + +USEFUL INFORMATION + +ABBREVIATIONS OF UNITS + +Unit Abbreviation + +ampere amp. +ampere-hours amp.-hr. +centimeter cm. +centimeter-gram-second c.g.s. +cubic centimeters cm.^3 +cubic inches cu. in. +cycles per second ~ +degrees Centigrade °C. +degrees Fahrenheit °F. +feet ft. +foot-pounds ft.-lb. +grams g. +henries h. +inches in. +kilograms kg. +kilometers km. +kilowatts kw. +kilowatt-hours kw.-hr. +kilovolt-amperes kv.-a. +meters m. +microfarads [Greek: mu]f. +micromicrofarads [Greek: mu mu]f. +millihenries mh. +millimeters mm. +pounds lb. +seconds sec. +square centimeters cm.^2 +square inches sq. in. +volts v. +watts w. + +PREFIXES USED WITH METRIC SYSTEM UNITS + +Prefix Abbreviation Meaning + +micro [Greek: mu]. 1 millionth +milli m. 1 thousandth +centi c. 1 hundredth +deci d. 1 tenth +deka dk. 10 +hekto h. 1 hundred +kilo k. 1 thousand +mega m. 1 million + + + + +SYMBOLS USED FOR VARIOUS QUANTITIES + + +Quantity Symbol + +capacitance C + +conductance g + +coupling co-efficient k + +current, instantaneous i + +current, effective value I + +decrement [Greek: delta] + +dielectric constant [Greek: alpha] + +electric field intensity [Greek: epsilon] + +electromotive force, +instantaneous value E + +electromotive force, +effective value F + +energy W + +force F + +frequency f + +frequency x 2[Greek: pi] [Greek: omega] + +impedance Z + +inductance, self L + +inductance, mutual M + +magnetic field intensity A + +magnetic flux [Greek: Phi] + +magnetic induction B + +period of a complete +oscillation T + +potential difference V + +quantity of electricity Q + +ratio of the +circumference of a +circle to its diameter +=3.1416 [Greek: pi] + +reactance X + +resistance R + +time t + +velocity v + +velocity of light c + +wave length [Greek: lambda] + +wave length in meters [Greek: lambda]m + +work W + +permeability [Greek: mu] + +Square root [Math: square root] + + + + +TABLE OF ENAMELED WIRE + + No. of Turns Turns Ohms per + Wire, per per Cubic Inch + B.& S. Linear Square of + Gauge Inch Inch Winding + + 20 30 885 .748 + + 22 37 1400 1.88 + + 24 46 2160 4.61 + + 26 58 3460 11.80 + + 28 73 5400 29.20 + + 30 91 8260 70.90 + + 32 116 21,000 7547.00 + + 34 145 13,430 2968.00 + + 36 178 31,820 1098.00 + + 38 232 54,080 456.00 + + 40 294 86,500 183.00 + + + + +TABLE OF FREQUENCY AND WAVE LENGTHS + + + W. L.--Wave Lengths in Meters. + F.--Number of Oscillations per Second. + O. or square root L. C. is called Oscillation Constant. + C.--Capacity in Microfarads. + L.--Inductance in Centimeters. + 1000 Centimeters = 1 Microhenry. + + + W.L. F O L.C. + 50 6,000,000 .839 .7039 + 100 3,000,000 1.68 2.82 + 150 2,000,000 2.52 6.35 + 200 1,500,000 3.36 11.29 + 250 1,200,000 4.19 17.55 + 300 1,000,000 5.05 25.30 + 350 857,100 5.87 34.46 + 400 750,000 6.71 45.03 + 450 666,700 7.55 57.00 + 500 600,000 8.39 70.39 + 550 545,400 9.23 85.19 + 600 500,000 10.07 101.41 + 700 428,600 11.74 137.83 + 800 375,000 13.42 180.10 + 900 333,300 15.10 228.01 + 1,000 300,000 16.78 281.57 + 1,100 272,730 18.45 340.40 + 1,200 250,000 20.13 405.20 + 1,300 230,760 21.81 475.70 + 1,400 214,380 23.49 551.80 + 1,500 200,000 25.17 633.50 + 1,600 187,500 26.84 720.40 + 1,700 176,460 28.52 813.40 + 1,800 166,670 30.20 912.00 + 1,900 157,800 31.88 1,016.40 + 2,000 150,000 33.55 1,125.60 + 2,100 142,850 35.23 1,241.20 + 2,200 136,360 36.91 1,362.40 + 2,300 130,430 38.59 1,489.30 + 2,400 125,000 40.27 1,621.80 + 2,500 120,000 41.95 1,759.70 + 2,600 115,380 43.62 1,902.60 + 2,700 111,110 45.30 2,052.00 + 2,800 107,140 46.89 2,207.00 + 2,900 103,450 48.66 2,366.30 + 3,000 100,000 50.33 2,533.20 + 4,000 75,000 67.11 4,504.00 + 5,000 60,000 83.89 7,038.00 + 6,000 50,000 100.7 10,130.00 + 7,000 41,800 117.3 13,630.00 + 8,000 37,500 134.1 18,000.00 + 9,000 33,300 151.0 22,820.00 + 10,000 30,000 167.9 28,150.00 + 11,000 27,300 184.8 34,150.00 + 12,000 25,000 201.5 40,600.00 + 13,000 23,100 218.3 47,600.00 + 14,000 21,400 235.0 55,200.00 + 15,000 20,000 252.0 63,500.00 + 16,000 18,750 269.0 72,300.00 + + + + +PRONUNCIATION OF GREEK LETTERS + + +Many of the physical quantities use Greek letters for symbols. The +following is the Greek alphabet with the way the letters are +pronounced: + + a alpha + b beta + g gamma + d delta + e epsilon + z zeta + ae eta + th theta + i iota + k kappa + l lambda + m mu + n nu + x Xi(Zi) + o omicron + p pi + r rho + s sigma + t tau + u upsilon + ph phi + ch chi + ps psi + o omega + + + + +TABLE OF SPARKING DISTANCES + +In Air for Various Voltages between Needle Points + + + Volts Distance + Inches Centimeter + 5,000 .225 .57 + 10,000 .470 1.19 + 15,000 .725 1.84 + 20,000 1.000 2.54 + 25,000 1.300 3.30 + 30,000 1.625 4.10 + 35,000 2.000 5.10 + 40,000 2.450 6.20 + 45,000 2.95 7.50 + 50,000 3.55 9.90 + 60,000 4.65 11.8 + 70,000 5.85 14.9 + 80,000 7.10 18.0 + 90,000 8.35 21.2 + 100,000 9.60 24.4 + 110,000 10.75 27.3 + 120,000 11.85 30.1 + 130,000 12.95 32.9 + 140,000 13.95 35.4 + 150,000 15.00 38.1 + + +FEET PER POUND OF INSULATED MAGNET WIRE + + No. of Single Double Single Double + B.& S. Cotton, Cotton, Silk, Silk, Enamel + Gauge 4-Mils 8-Mils 1-3/4-Mils 4-Mils + + 20 311 298 319 312 320 + 21 389 370 408 389 404 + 22 488 461 503 498 509 + 23 612 584 636 631 642 + 24 762 745 800 779 810 + 25 957 903 1,005 966 1,019 + 26 1,192 1,118 1,265 1,202 1,286 + 27 1,488 1,422 1,590 1,543 1,620 + 28 1,852 1,759 1,972 1,917 2,042 + 29 2,375 2,207 2,570 2,435 2,570 + 30 2,860 2,534 3,145 2,900 3,240 + 31 3,800 2,768 3,943 3,683 4,082 + 32 4,375 3,737 4,950 4,654 5,132 + 33 5,590 4,697 6,180 5,689 6,445 + 34 6,500 6,168 7,740 7,111 8,093 + 35 8,050 6,737 9,600 8,584 10,197 + 36 9,820 7,877 12,000 10,039 12,813 + 37 11,860 9,309 15,000 10,666 16,110 + 38 14,300 10,636 18,660 14,222 20,274 + 39 17,130 11,907 23,150 16,516 25,519 + 40 21,590 14,222 28,700 21,333 32,107 + + + + +INTERNATIONAL MORSE CODE AND CONVENTIONAL SIGNALS + +TO BE USED FOR ALL GENERAL PUBLIC SERVICE RADIO COMMUNICATION + + +1. A dash is equal to three dots. + +2. The space between parts of the same letter is equal to one dot. + +3. The space between two letters is equal to three dots. + +4. The space between two words is equal to five dots. + +[Note: period denotes Morse dot, hyphen denotes Morse dash] + +A .- + +B -... + +C -.-. + +D -.. + +E . + +F ..-. + +G --. + +H .... + +I .. + +J .--- + +K -.- + +L .-.. + +M -- + +N -. + +O --- + +P .--. + +Q --.- + +R .-. + +S ... + +T - + +U ..- + +V ...- + +W .-- + +X -..- + +Y -.-- + +Z --.. + +Ä (German) .-.- + +Á or Å (Spanish-Scandinavian) .--.- + +CH (German-Spanish) ---- + +É (French) ..-.. + +Ñ (Spanish) --.-- + +Ö (German) ---. + +Ü (German) ..-- + +1 .---- + +2 ..--- + +3 ...-- + +4 ....- + +5 ..... + +6 -.... + +7 --... + +8 ---.. + +9 ----. + +0 ----- + +Period .. .. .. + +Semicolon -.-.-. + +Comma -.-.-. + +Colon ---... + +Interrogation ..--.. + +Exclamation point --..-- + +Apostrophe .----. + +Hyphen -....- + +Bar indicating fraction -..-. + +Parenthesis -.--.- + +Inverted commas .-..-. + +Underline ..--.- + +Double dash -...- + +Distress Call ...---... + +Attention call to precede every transmission -.-.- + +General inquiry call -.-. --.- + +From (de) -.. . + +Invitation to transmit (go ahead) -.- + +Warning--high power --..-- + +Question (please repeat after ...)--interrupting long messages ..--.. + +Wait .-... + +Break (Bk.) (double dash) -...- + +Understand ...-. + +Error ........ + +Received (O.K.) .-. + +Position report (to precede all position messages) - .-. + +End of each message (cross) .-.-. + +Transmission finished (end of work) (conclusion of correspondence) ...-.- + + + + +INTERNATIONAL RADIOTELEGRAPHIC CONVENTION + +LIST OF ABBREVIATIONS TO BE USED IN RADIO COMMUNICATION + +ABBREVIATION QUESTION ANSWER OR REPLY + +PRB Do you wish to communicate I wish to communicate by means + by means of the International of the International Signal Code. + Signal Code? + +QRA What ship or coast station is This is.... + that? + +QRB What is your distance? My distance is.... + +QRC What is your true bearing? My true bearing is.... + +QRD Where are you bound for? I am bound for.... + +QRF Where are you bound from? I am bound from.... + +QRG What line do you belong to? I belong to the ... Line. + +QRH What is your wave length in My wave length is ... meters. + meters? + +QRJ How many words have you to send? I have ... words to send. + +QRK How do you receive me? I am receiving well. + +QRL Are you receiving badly? I am receiving badly. Please + Shall I send 20? send 20. + ...-. ...-. + for adjustment? for adjustment. + +QRM Are you being interfered with? I am being interfered with. + +QRN Are the atmospherics strong? Atmospherics are very strong. + +QRO Shall I increase power? Increase power. + +QRP Shall I decrease power? Decrease power. + +QRQ Shall I send faster? Send faster. + +QRS Shall I send slower? Send slower. + +QRT Shall I stop sending? Stop sending. + +QRU Have you anything for me? I have nothing for you. + +QRV Are you ready? I am ready. All right now. + +QRW Are you busy? I am busy (or: I am busy with...). + Please do not interfere. + +QRX Shall I stand by? Stand by. I will call you when + required. + +QRY When will be my turn? Your turn will be No.... + +QRZ Are my signals weak? You signals are weak. + +QSA Are my signals strong? You signals are strong. + +QSB Is my tone bad? The tone is bad. + Is my spark bad? The spark is bad. + +QSC Is my spacing bad? Your spacing is bad. + +QSD What is your time? My time is.... + +QSF Is transmission to be in Transmission will be in + alternate order or in series? alternate order. + +QSG Transmission will be in a + series of 5 messages. + +QSH Transmission will be in a + series of 10 messages. + +QSJ What rate shall I collect for...? Collect.... + +QSK Is the last radiogram canceled? The last radiogram is canceled. + +QSL Did you get my receipt? Please acknowledge. + +QSM What is your true course? My true course is...degrees. + +QSN Are you in communication with land? I am not in communication with land. + +QSO Are you in communication with I am in communication with... + any ship or station (through...). + (or: with...)? + +QSP Shall I inform...that you are Inform...that I am calling him. + calling him? + +QSQ Is...calling me? You are being called by.... + +QSR Will you forward the radiogram? I will forward the radiogram. + +QST Have you received the general General call to all stations. + call? + +QSU Please call me when you have Will call when I have finished. + finished (or: at...o'clock)? + +QSV Is public correspondence being Public correspondence is being + handled? handled. Please do not interfere. + +[Footnote: Public correspondence is any radio work, official or +private, handled on commercial wave lengths.] + +QSW Shall I increase my spark Increase your spark frequency. + frequency? + +QSX Shall I decrease my spark Decrease your spark frequency. + frequency? + +QSY Shall I send on a wavelength Let us change to the wave length + of ... meters? of ... meters. + +QSZ Send each word twice. I have + difficulty in receiving you. + +QTA Repeat the last radiogram. + + +When an abbreviation is followed by a mark of interrogation, it refers +to the question indicated for that abbreviation. + + + + +Useful Information + +Symbols Used For Apparatus + +alternator + +ammeter + +aerial + +arc + +battery + +buzzer + +condenser + +variable condenser + +connection of wires + +no connection + +coupled coils + +variable coupling + +detector + +gap, plain + +gap, quenched + +ground + +hot wire ammeter + +inductor + +variable inductor + +key + +resistor + +variable resistor + +switch s.p.s.t. + +" s.p.d.t. + +" d.p.s.t. + +" d.p.d.t. + +" reversing + +phone receiver + +" transmitter + +thermoelement + +transformer + +vacuum tube + +voltmeter + +choke coil + + + + +DEFINITIONS OF ELECTRIC AND MAGNETIC UNITS + + +The _ohm_ is the resistance of a thread of mercury at the temperature +of melting ice, 14.4521 grams in mass, of uniform cross-section and a +length of 106.300 centimeters. + +The _ampere_ is the current which when passed through a solution of +nitrate of silver in water according to certain specifications, +deposits silver at the rate of 0.00111800 of a gram per second. + +The _volt_ is the electromotive force which produces a current of 1 +ampere when steadily applied to a conductor the resistance of which is +1 ohm. + +The _coulomb_ is the quantity of electricity transferred by a current +of 1 ampere in 1 second. + +The _ampere-hour_ is the quantity of electricity transferred by a +current of 1 ampere in 1 hour and is, therefore, equal to 3600 +coulombs. + +The _farad_ is the capacitance of a condenser in which a potential +difference of 1 volt causes it to have a charge of 1 coulomb of +electricity. + +The _henry_ is the inductance in a circuit in which the electromotive +force induced is 1 volt when the inducing current varies at the rate +of 1 ampere per second. + +The _watt_ is the power spent by a current of 1 ampere in a resistance +of 1 ohm. + +The _joule_ is the energy spent in I second by a flow of 1 ampere in 1 +ohm. + +The _horse-power_ is used in rating steam machinery. It is equal to +746 watts. + +The _kilowatt_ is 1,000 watts. + +The units of capacitance actually used in wireless work are the +_microfarad_, which is the millionth part of a farad, because the +farad is too large a unit; and the _C. G. S. electrostatic unit of +capacitance_, which is often called the _centimeter of capacitance_, +which is about equal to 1.11 microfarads. + +The units of inductance commonly used in radio work are the +_millihenry_, which is the thousandth part of a henry; and the +_centimeter of inductance_, which is one one-thousandth part of a +microhenry. + +Note.--For further information about electric and magnetic units get +the _Bureau of Standards Circular No. 60_, called _Electric Units and +Standards_, the price of which is 15 cents; also get _Scientific Paper +No. 292_, called _International System of Electric and Magnetic +Units_, price 10 cents. These and other informative papers can be had +from the _Superintendent of Documents, Government Printing Office_, +Washington, D. C. + + + + +WIRELESS BOOKS + + +The Admiralty Manual of Wireless Telegraphy. 1920. Published by His +Majesty's Stationery Office, London. + +Ralph E. Batcher.--Prepared Radio Measurements. 1921. Wireless Press, +Inc., New York City. + +Elmer E. Bucher.--Practical Wireless Telegraphy. 1918. Wireless +Press, Inc., New York City. + +Elmer E. Bucher.--Vacuum Tubes in Wireless Communication. 1919. +Wireless Press, Inc., New York City. + +Elmer E. Bucher.--The Wireless Experimenter's Manual. 1920. Wireless +Press, Inc., New York City. + +A. Frederick Collins.--Wireless Telegraphy, Its History, Theory, and +Practice. 1905. McGraw Pub. Co., New York City. + +J. H. Dellinger.--Principles Underlying Radio Communication. 1921. +Signal Corps, U. S. Army, Washington, D. C. + +H. M. Dorsett.--Wireless Telegraphy and Telephony. 1920. Wireless +Press, Ltd., London. + +J. A. Fleming.--Principles of Electric Wave Telegraphy. 1919. +Longmans, Green and Co., London. + +Charles B. Hayward.--How to Become a Wireless Operator. 1918. +American Technical Society, Chicago, Ill. + +G. D. Robinson.--Manual of Radio Telegraphy and Telephony. 1920. +United States Naval Institute, Annapolis, Md. + +Rupert Stanley.--Textbook of Wireless Telegraphy. 1919. Longmans, +Green and Co., London. + +E. W. Stone.--Elements of Radio Telegraphy. 1919. D, Van Nostrand Co., +New York City. + +L. B. Turner.--Wireless Telegraphy and Telephony. 1921. Cambridge +University Press. Cambridge, England. + +Send to the _Superintendent of Documents, Government Printing Office_, +Washington, D. C., for a copy of _Price List No. 64_ which lists the +Government's books and pamphlets on wireless. It will be sent to you +free of charge. + +The Government publishes; (1) _A List of Commercial Government and +Special Wireless Stations_, every year, price 15 cents; (2) _A List of +Amateur Wireless Stations_, yearly, price 15 cents; (3) _A Wireless +Service Bulletin_ is published monthly, price 5 cents a copy, or 25 +cents yearly; and (4) _Wireless Communication Laws of the United +States_, the _International Wireless Telegraphic Convention and +Regulations Governing Wireless Operators and the Use of Wireless on +Ships and Land Stations_, price 15 cents a copy. Orders for the above +publications should be addressed to the _Superintendent of Documents, +Government Printing Office, Washington, D. C._ + + + + +Manufacturers and Dealers in Wireless Apparatus and Supplies: + +Adams-Morgan Co., Upper Montclair, N. J. + +American Hard Rubber Co., 11 Mercer Street, New York City. + +American Radio and Research Corporation, Medford Hillside, Mass. + +Brach (L. S.) Mfg. Co., 127 Sussex Ave., Newark, N. J. + +Brandes (C.) Inc., 237 Lafayette St., New York City. + +Bunnell (J. H.) Company, Park Place, New York City. + +Burgess Battery Company, Harris Trust Co. Bldg., Chicago, Ill. + +Clapp-Eastman Co., 120 Main St., Cambridge, Mass. + +Connecticut Telephone and Telegraph Co., Meriden, Conn. + +Continental Fiber Co., Newark, Del. + +Coto-Coil Co., Providence, R. I. + +Crosley Mfg. Co., Cincinnati, Ohio. + +Doolittle (F. M.), 817 Chapel St., New Haven, Conn. + +Edelman (Philip E.), 9 Cortlandt St., New York City. + +Edison Storage Battery Co., Orange, N. J. + +Electric Specialty Co., Stamford, Conn. + +Electrose Mfg. Co., 60 Washington St., Brooklyn, N. Y. + +General Electric Co., Schenectady, N. Y. + +Grebe (A. H.) and Co., Inc., Richmond Hill, N. Y. C. + +International Brass and Electric Co., 176 Beekman St., New York City. + +International Insulating Co., 25 West 45th St., New York City. + +King Amplitone Co., 82 Church St., New York City. + +Kennedy (Colin B.) Co., Rialto Bldg., San Francisco, Cal. + +Magnavox Co., Oakland, Cal. + +Manhattan Electrical Supply Co., Park Place, N. Y. + +Marshall-Gerken Co., Toledo, Ohio. + +Michigan Paper Tube and Can Co., 2536 Grand River Ave., Detroit, Mich. + +Murdock (Wm. J.) Co., Chelsea, Mass. + +National Carbon Co., Inc., Long Island City, N. Y. + +Pittsburgh Radio and Appliance Co., 112 Diamond St., Pittsburgh, Pa, + +Radio Corporation of America, 233 Broadway, New York City. + +Riley-Klotz Mfg. Co., 17-19 Mulberry St., Newark, N. J. + +Radio Specialty Co., 96 Park Place, New York City. + +Roller-Smith Co., 15 Barclay St., New York City. + +Tuska (C. D.) Co., Hartford, Conn. + +Western Electric Co., Chicago, Ill. + +Westinghouse Electric Co., Pittsburgh, Pa. + +Weston Electrical Instrument Co., 173 Weston Ave., Newark, N. J. + +Westfield Machine Co., Westfield, Mass. + + + + +ABBREVIATIONS OF COMMON TERMS + + +A. ..............Aerial + +A.C. ............Alternating Current + +A.F. ............Audio Frequency + +B. and S. .......Brown & Sharpe Wire Gauge + +C. ..............Capacity or Capacitance + +C.G.S. ..........Centimeter-Grain-Second + +Cond. ...........Condenser + +Coup. ...........Coupler + +C.W. ............Continuous Waves + +D.C. ............Direct Current + +D.P.D.T. ........Double Point Double Throw + +D.P.S.T. ........Double Point Single Throw + +D.X. ............Distance + +E. ..............Short for Electromotive Force (Volt) + +E.M.F. ..........Electromotive Force + +F. ..............Filament or Frequency + +G. ..............Grid + +Gnd. ............Ground + +I. ..............Current Strength (Ampere) + +I.C.W. ..........Interrupted Continuous Waves + +KW. .............Kilowatt + +L. ..............Inductance + +L.C. ............Loose Coupler + +Litz. ...........Litzendraht + +Mfd. ............Microfarad + +Neg. ............Negative + +O.T. ............Oscillation Transformer + +P. ..............Plate + +Prim. ...........Primary + +Pos. ............Positive + +R. ..............Resistance + +R.F. ............Radio Frequency + +Sec. ............Secondary + +S.P.D.T. ........Single Point Double Throw + +S.P.S.T. ........Single Point Single Throw + +S.R. ............Self Rectifying + +T. ..............Telephone or Period (time) of Complete + Oscillation + +Tick. ...........Tickler + +V. ..............Potential Difference + +Var. ............Variometer + +Var. Cond. ......Variable Condenser + +V.T. ............Vacuum Tube + +W.L. ............Wave Length + +X. ..............Reactance + + + + +GLOSSARY + + +A BATTERY.--See Battery A. + +ABBREVIATIONS, CODE.--Abbreviations of questions and answers used in +wireless communication. The abbreviation _of a question_ is usually in +three letters of which the first is Q. Thus Q R B is the code +abbreviation of "_what is your distance?_" and the answer "_My +distance is_..." See Page 306 [Appendix: List of Abbreviations]. + +ABBREVIATIONS, UNITS.--Abbreviations of various units used in wireless +electricity. These abbreviations are usually lower case letters of the +Roman alphabet, but occasionally Greek letters are used and other +signs. Thus _amperes_ is abbreviated _amp., micro_, which means _one +millionth_, [Greek: mu], etc. See Page 301 [Appendix: Useful +Abbreviations]. + +ABBREVIATIONS OF WORDS AND TERMS.--Letters used instead of words and +terms for shortening them up where there is a constant repetition of +them, as _A.C._ for _alternating current; C.W._ for _continuous waves; +V.T._ for _vacuum tube_, etc. See Page 312 [Appendix: Abbreviations of +Common Terms]. + +AERIAL.--Also called _antenna_. An aerial wire. One or more wires +suspended in the air and insulated from its supports. It is the aerial +that sends out the waves and receives them. + +AERIAL, AMATEUR.--An aerial suitable for sending out 200 meter wave +lengths. Such an aerial wire system must not exceed 120 feet in length +from the ground up to the aerial switch and from this through the +leading-in wire to the end of the aerial. + +AERIAL AMMETER.--See _Ammeter, Hot Wire_. + +AERIAL, BED-SPRINGS.--Where an outdoor aerial is not practicable +_bed-springs_ are often made to serve the purpose. + +AERIAL CAPACITY.--See _Capacity, Aerial._ + +AERIAL COUNTERPOISE.--Where it is not possible to get a good ground an +_aerial counterpoise_ or _earth capacity_ can be used to advantage. +The counterpoise is made like the aerial and is supported directly +under it close to the ground but insulated from it. + +AERIAL, DIRECTIONAL.--A flat-top or other aerial that will transmit +and receive over greater distances to and from one direction than to +and from another. + +AERIAL, GROUND.--Signals can be received on a single long wire when it +is placed on or buried in the earth or immersed in water. It is also +called a _ground antenna_ and an _underground aerial._ + +AERIAL, LOOP.--Also called a _coil aerial, coil antenna, loop aerial, +loop antenna_ and when used for the purpose a _direction finder_. A +coil of wire wound on a vertical frame. + +AERIAL RESISTANCE.--See _Resistance, Aerial._ + +AERIAL SWITCH.--See _Switch Aerial._ + +AERIAL WIRE.--(1) A wire or wires that form the aerial. (2) Wire that +is used for aerials; this is usually copper or copper alloy. + +AERIAL WIRE SYSTEM.--An aerial and ground wire and that part of the +inductance coil which connects them. The open oscillation circuit of +a sending or a receiving station. + +AIR CORE TRANSFORMER.--See _Transformer, Air Core._ + +AMATEUR AERIAL OR ANTENNA.--See _Aerial, Amateur._ + +ALTERNATOR.--An electric machine that generates alternating current. + +ALPHABET, INTERNATIONAL CODE.--A modified Morse alphabet of dots and +dashes originally used in Continental Europe and, hence, called the +_Continental Code_. It is now used for all general public service +wireless communication all over the world and, hence, it is called the +_International Code_. See page 305 [Appendix: International Morse +Code]. + +ALTERNATING CURRENT (_A.C._)--See _Current._ + +ALTERNATING CURRENT TRANSFORMER.--See _Transformer_. + +AMATEUR GROUND.--See _Ground, Amateur_. + +AMMETER.--An instrument used for measuring the current strength, in +terms of amperes, that flows in a circuit. Ammeters used for measuring +direct and alternating currents make use of the _magnetic effects_ of +the currents. High frequency currents make use of the _heating +effects_ of the currents. + +AMMETER, HOT-WIRE.--High frequency currents are usually measured by +means of an instrument which depends on heating a wire or metal strip +by the oscillations. Such an instrument is often called a _thermal +ammeter_, _radio ammeter_ and _aerial ammeter_. + +AMMETER, AERIAL.--See _Ammeter, Hot Wire_. + +AMMETER, RADIO.--See _Ammeter, Hot Wire_. + +AMPERE.--The current which when passed through a solution of nitrate +of silver in water according to certain specifications, deposits +silver at the rate of 0.00111800 of a gram per second. + +AMPERE-HOUR.--The quantity of electricity transferred by a current of +1 ampere in 1 hour and is, therefore, equal to 3600 coulombs. + +AMPERE-TURNS.--When a coil is wound up with a number of turns of wire +and a current is made to flow through it, it behaves like a magnet. B +The strength of the magnetic field inside of the coil depends on (1) +the strength of the current and (2) the number of turns of wire on the +coil. Thus a feeble current flowing through a large number of turns +will produce as strong a magnetic field as a strong current flowing +through a few turns of wire. This product of the current in amperes +times the number of turns of wire on the coil is called the +_ampere-turns_. + +AMPLIFICATION, AUDIO FREQUENCY.--A current of audio frequency that is +amplified by an amplifier tube or other means. + +AMPLIFICATION, CASCADE.--See _Cascade Amplification_. + +AMPLIFICATION, RADIO FREQUENCY.--A current of radio frequency that is +amplified by an amplifier tube or other means before it reaches the +detector. + +AMPLIFICATION, REGENERATIVE.--A scheme that uses a third circuit to +feed back part of the oscillations through a vacuum tube and which +increases its sensitiveness when used as a detector and multiplies its +action as an amplifier and an oscillator. + +AMPLIFIER, AUDIO FREQUENCY.--A vacuum tube or other device that +amplifies the signals after passing through the detector. + +AMPLIFIER, MAGNETIC.--A device used for controlling radio frequency +currents either by means of a telegraph key or a microphone +transmitter. The controlling current flows through a separate circuit +from that of the radio current and a fraction of an ampere will +control several amperes in the aerial wire. + +AMPLIFIERS, MULTI-STAGE.--A receiving set using two or more +amplifiers. Also called _cascade amplification_. + +AMPLIFIER, VACUUM TUBE.--A vacuum tube that is used either to amplify +the radio frequency currents or the audio frequency currents. + +AMPLITUDE OF WAVE.--The greatest distance that a point moves from its +position of rest. + +AMPLIFYING TRANSFORMER, AUDIO.--See _Transformer, Audio Amplifying_. + +AMPLIFYING MODULATOR VACUUM TUBE.--See _Vacuum Tube, Amplifying +Modulator_. + +AMPLIFYING TRANSFORMER RADIO.--See _Transformer, Radio Amplifying_. + +ANTENNA, AMATEUR.--See _Aerial, Amateur_. + +ANTENNA SWITCH.--See _Switch, Aerial_. + +APPARATUS SYMBOLS.--See _Symbols, Apparatus_. + +ARMSTRONG CIRCUIT.--See _Circuit, Armstrong_. + +ATMOSPHERICS.--Same as _Static_, which see. + +ATTENUATION.--In Sending wireless telegraph and telephone messages the +amplitude of the electric waves is damped out as the distance +increases. This is called _attenuation_ and it increases as the +frequency is increased. This is the reason why short wave lengths +will not carry as far as long wave lengths. + +AUDIO FREQUENCY AMPLIFIER.--See _Amplifier, Audio Frequency_. + +AUDIO FREQUENCY AMPLIFICATION.--See _Amplification, Audio Frequency_. + +AUDIBILITY METER.--See _Meter, Audibility_. + +AUDIO FREQUENCY.--See _Frequency, Audio_. + +AUDIO FREQUENCY CURRENT.--See _Current, Audio Frequency_. + +AUDION.--An early trade name given to the vacuum tube detector. + +AUTODYNE RECEPTOR.--See _Receptor, Autodyne_. + +AUTO TRANSFORMER.--See _Transformer, Auto_. + +BAKELITE.--A manufactured insulating compound. + +B BATTERY.--See _Battery B_. + +BAND, WAVE LENGTH.--See _Wave Length Band_. + +BASKET WOUND COILS.--See _Coils, Inductance_. + +BATTERY, A.--The 6-volt storage battery used to heat the filament of a +vacuum tube, detector or amplifier. + +BATTERY, B.--The 22-1/2-volt dry cell battery used to energize the +plate of a vacuum tube detector or amplifier. + +BATTERY, BOOSTER.--This is the battery that is connected in series +with the crystal detector. + +BATTERY, C.--A small dry cell battery sometimes used to give the grid +of a vacuum tube detector a bias potential. + +BATTERY, EDISON STORAGE.--A storage battery in which the elements are +made of nickel and iron and immersed in an alkaline +_electrolyte_. + +BATTERY, LEAD STORAGE.--A storage battery in which the elements are +made of lead and immersed in an acid electrolyte. + +BATTERY POLES.--See _Poles, Battery_. + +BATTERY, PRIMARY.--A battery that generates current by chemical +action. + +BATTERY, STORAGE.--A battery that develops a current after it has been +charged. + +BEAT RECEPTION.--See _Heterodyne Reception_. + +BED SPRINGS AERIAL.--See _Aerial, Bed Springs_. + +BLUB BLUB.--Over modulation in wireless telephony. + +BROAD WAVE.--See _Wave, Broad_. + +BRUSH DISCHARGE.--See _Discharge_. + +BUZZER MODULATION.--See _Modulation, Buzzer_. + +BLUE GLOW DISCHARGE.--See _Discharge_. + +BOOSTER BATTERY.--See _Battery, Booster_. + +BROADCASTING.--Sending out intelligence and music from a central +station for the benefit of all who live within range of it and who +have receiving sets. + +CAPACITANCE.--Also called by the older name of _capacity_. The +capacity of a condenser, inductance coil or other device capable of +retaining a charge of electricity. Capacitance is measured in terms +of the _microfarad_. + +CAPACITIVE COUPLING.--See _Coupling, Capacitive_. + +CAPACITY.--Any object that will retain a charge of electricity; hence +an aerial wire, a condenser or a metal plate is sometimes called a +_capacity_. + +CAPACITY, AERIAL.--The amount to which an aerial wire system can be +charged. The _capacitance_ of a small amateur aerial is from +0.0002 to 0.0005 microfarad. + +CAPACITY, DISTRIBUTED.--A coil of wire not only has inductance, but +also a certain small capacitance. Coils wound with their turns +parallel and having a number of layers have a _bunched capacitance_ +which produces untoward effects in oscillation circuits. In honeycomb +and other stagger wound coils the capacitance is more evenly +distributed. + +CAPACITY REACTANCE.--See _Reactance, Capacity_. + +CAPACITY UNIT.--See _Farad_. + +CARBON RHEOSTATS.--See _Rheostat, Carbon_. + +CARBORUNDUM DETECTOR.--See _Detector_. + +CARRIER CURRENT TELEPHONY.--See _Wired-Wireless_. + +CARRIER FREQUENCY.--See _Frequency, Carrier_. + +CARRIER FREQUENCY TELEPHONY.--See _Wired-Wireless_. + +CASCADE AMPLIFICATION.--Two or more amplifying tubes hooked up in a +receiving set. + +CAT WHISKER CONTACT.--A long, thin wire which makes contact with the +crystal of a detector. + +CENTIMETER OF CAPACITANCE.--Equal to 1.11 _microfarads_. + +CENTIMETER OF INDUCTANCE.--Equal to one one-thousandth part of a +_microhenry_. + +CELLULAR COILS.--See _Coils, Inductance_. + +C.G.S. ELECTROSTATIC UNIT OF CAPACITANCE.--See _Centimeter of +Capacitance_. + +CHARACTERISTICS.--The special behavior of a device, such as an aerial, +a detector tube, etc. + +CHARACTERISTICS, GRID.--See _Grid Characteristics_. + +CHOKE COILS.--Coils that prevent the high voltage oscillations from +surging back into the transformer and breaking down the insulation. + +CHOPPER MODULATION.--See _Modulation, Chopper_. + +CIRCUIT.--Any electrical conductor through which a current can flow. A +low voltage current requires a loop of wire or other conductor both +ends of which are connected to the source of current before it can +flow. A high frequency current will surge in a wire which is open at +both ends like the aerial. + +Closed Circuit.--A circuit that is continuous. + +Open Circuit.--A conductor that is not continuous. + +Coupled Circuits.--Open and closed circuits connected together +by inductance coils, condensers or resistances. See _coupling_. + +Close Coupled Circuits.--Open and closed circuits connected +directly together with a single inductance coil. + +Loose Coupled Circuits.--Opened and closed currents connected +together inductively by means of a transformer. + +Stand-by Circuits.--Also called _pick-up_ circuits. When listening-in +for possible calls from a number of stations, a receiver is used which +will respond to a wide band of wave lengths. + +Armstrong Circuits.--The regenerative circuit invented by Major E. H. +Armstrong. + +CLOSE COUPLED CIRCUITS.--See _Currents, Close Coupled_. + +CLOSED CIRCUIT.--See _Circuit, Closed_. + +CLOSED CORE TRANSFORMER.--See _Transformer, Closed Core_. + +CODE.-- + +Continental.--Same as _International_. + +International.--On the continent of Europe land lines use the +_Continental Morse_ alphabetic code. This code has come to be used +throughout the world for wireless telegraphy and hence it is now +called the _International code_. It is given on Page 305. [Appendix: +International Morse Code]. + +Morse.--The code devised by Samuel F. B. Morse and which is used on +the land lines in the U. S. + +National Electric.--A set of rules and requirements devised by the +_National Board of Fire Underwriters_ for the electrical installations +in buildings on which insurance companies carry risks. This code also +covers the requirements for wireless installations. A copy may be had +from the _National Board of Fire Underwriters_, New York City, or from +your insurance agent. + +National Electric Safety.--The Bureau of Standards, Washington, D. C., +have investigated the precautions which should be taken for the safe +operation of all electric equipment. A copy of the _Bureau of +Standards Handbook No. 3_ can be had for 40 cents from the +_Superintendent of Documents_. + +COEFFICIENT OF COUPLING.--See _Coupling, Coefficient of_. + +COIL AERIAL.--See _Aerial, Loop_. + +COIL ANTENNA.--See _Aerial, Loop_. + +COIL, INDUCTION.--An apparatus for changing low voltage direct +currents into high voltage, low frequency alternating currents. When +fitted with a spark gap the high voltage, low frequency currents are +converted into high voltage, high frequency currents. It is then also +called a _spark coil_ and a _Ruhmkorff coil_. + +COIL, LOADING.--A coil connected in the aerial or closed oscillation +circuit so that longer wave lengths can be received. + +COIL, REPEATING.--See _Repeating Coil_. + +COIL, ROTATING.--One which rotates on a shaft instead of sliding as in +a _loose coupler_. The rotor of a _variometer_ or _variocoupler_ is a +_rotating coil_. + +COILS, INDUCTANCE.--These are the tuning coils used for sending and +receiving sets. For sending sets they are formed of one and two coils, +a single sending coil is generally called a _tuning inductance coil_, +while a two-coil tuner is called an _oscillation transformer_. +Receiving tuning coils are made with a single layer, single coil, or a +pair of coils, when it is called an oscillation _transformer_. Some +tuning inductance coils have more than one layer, they are then called +_lattice wound_, _cellular_, _basket wound_, _honeycomb_, +_duo-lateral_, _stagger wound_, _spider-web_ and _slab_ coils. + +COMMERCIAL FREQUENCY.--See _Frequency, Commercial_. + +CONDENSER, AERIAL SERIES.--A condenser placed in the aerial wire +system to cut down the wave length. + +CONDENSER, VERNIER.--A small variable condenser used for receiving +continuous waves where very sharp tuning is desired. + +CONDENSER.--All conducting objects with their insulation form +capacities, but a _condenser_ is understood to mean two sheets or +plates of metal placed closely together but separated by some +insulating material. + +Adjustable Condenser.--Where two or more condensers can be coupled +together by means of plugs, switches or other devices. + +Aerial Condenser.--A condenser connected in the aerial. + +Air Condenser.--Where air only separates the sheets of metal. + +By-Pass Condenser.--A condenser connected in the transmitting currents +so that the high frequency currents cannot flow back through the power +circuit. + +Filter Condenser.--A condenser of large capacitance used in +combination with a filter reactor for smoothing out the pulsating +direct currents as they come from the rectifier. + +Fixed Condenser.--Where the plates are fixed relatively to one +another. + +Grid Condenser.--A condenser connected in series with the grid lead. + +Leyden Jar Condenser.--Where glass jars are used. + +Mica Condenser.--Where mica is used. + +Oil Condenser.--Where the plates are immersed in oil. + +Paper Condenser.--Where paper is used as the insulating material. + +Protective.--A condenser of large capacity connected across the low +voltage supply circuit of a transmitter to form a by-path of kick-back +oscillations. + +Variable Condenser.--Where alternate plates can be moved and so made +to interleave more or less with a set of fixed plates. + +Vernier.--A small condenser with a vernier on it so that it can be +very accurately varied. It is connected in parallel with the variable +condenser used in the primary circuit and is used for the reception of +continuous waves where sharp tuning is essential. + +CONDENSITE.--A manufactured insulating compound. + +CONDUCTIVITY.--The conductance of a given length of wire of uniform +cross section. The reciprocal of _resistivity_. + +CONTACT DETECTORS.--See _Detectors, Contact_. + +CONTINENTAL CODE.--See _Code, Continental_. + +COULOMB.--The quantity of electricity transferred by a current of 1 +ampere in 1 second. + +CONVECTIVE DISCHARGE.--See _Discharge_. + +CONVENTIONAL SIGNALS.--See _Signals, Conventional_. + +COUNTER ELECTROMOTIVE FORCE.--See _Electromotive Force, Counter_. + +COUNTERPOISE. A duplicate of the aerial wire that is raised a few feet +above the earth and insulated from it. Usually no connection is made +with the earth itself. + +COUPLED CIRCUITS.--See _Circuit, Coupled_. + +COUPLING.--When two oscillation circuits are connected together either +by the magnetic field of an inductance coil, or by the electrostatic +field of a condenser. + +COUPLING, CAPACITIVE.--Oscillation circuits when connected together by +condensers instead of inductance coils. + +COUPLING, COEFFICIENT OF.--The measure of the closeness of the +coupling between two coils. + +COUPLING, INDUCTIVE.--Oscillation circuits when connected together by +inductance coils. + +COUPLING, RESISTANCE.--Oscillation circuits connected together by a +resistance. + +CRYSTAL RECTIFIER.--A crystal detector. + +CURRENT, ALTERNATING (A.C.).--A low frequency current that surges to +and fro in a circuit. + +CURRENT, AUDIO FREQUENCY.--A current whose frequency is low enough to +be heard in a telephone receiver. Such a current usually has a +frequency of between 200 and 2,000 cycles per second. + +CURRENT, PLATE.--The current which flows between the filament and the +plate of a vacuum tube. + +CURRENT, PULSATING.--A direct current whose voltage varies from moment +to moment. + +CURRENT, RADIO FREQUENCY.--A current whose frequency is so high it +cannot be heard in a telephone receiver. Such a current may have a +frequency of from 20,000 to 10,000,000 per second. + +CURRENTS, HIGH FREQUENCY.--(1) Currents that oscillate from 10,000 to +300,000,000 times per second. (2) Electric oscillations. + +CURRENTS, HIGH POTENTIAL.--(1) Currents that have a potential of more +than 10,000 volts. (2) High voltage currents. + +CYCLE.--(1) A series of changes which when completed are again at the +starting point. (2) A period of time at the end of which an +alternating or oscillating current repeats its original direction of +flow. + +DAMPING.--The degree to which the energy of an electric oscillation is +reduced. In an open circuit the energy of an oscillation set up by a +spark gap is damped out in a few swings, while in a closed circuit it +is greatly prolonged, the current oscillating 20 times or more before +the energy is dissipated by the sum of the resistances of the circuit. + +DECREMENT.--The act or process of gradually becoming less. + +DETECTOR.--Any device that will (1) change the oscillations set up by +the incoming waves into direct current, that is which will rectify +them, or (2) that will act as a relay. + +Carborundum.--One that uses a _carborundum_ crystal for the sensitive +element. Carborundum is a crystalline silicon carbide formed in the +electric furnace. + +Cat Whisker Contact.--See _Cat Whisker Contact_. + +Chalcopyrite.--Copper pyrites. A brass colored mineral used as a +crystal for detectors. See _Zincite_. + +Contact.--A crystal detector. Any kind of a detector in which two +dissimilar but suitable solids make contact. + +Ferron.--A detector in which iron pyrites are used as the sensitive +element. + +Galena.--A detector that uses a galena crystal for the rectifying +element. + +Iron Pyrites.--A detector that uses a crystal of iron pyrites for its +sensitive element. + +Molybdenite.--A detector that uses a crystal of _sulphide of +molybdenum_ for the sensitive element. + +Perikon.--A detector in which a _bornite_ crystal makes contact with a +_zincite_ crystal. + +Silicon.--A detector that uses a crystal of silicon for its sensitive +element. + +Vacuum Tube.--A vacuum tube (which see) used as a detector. + +Zincite.--A detector in which a crystal of _zincite_ is used as the +sensitive element. + +DE TUNING.--A method of signaling by sustained oscillations in which +the key when pressed down cuts out either some of the inductance or +some of the capacity and hence greatly changes the wave length. + +DIELECTRIC.--An insulating material between two electrically charged +plates in which there is set up an _electric strain_, or displacement. + +DIELECTRIC STRAIN.--The electric displacement in a dielectric. + +DIRECTIONAL AERIAL.--See _Aerial, Directional_. + +DIRECTION FINDER.--See _Aerial, Loop_. + +DISCHARGE.--(1) A faintly luminous discharge that takes place from the +positive pointed terminal of an induction coil, or other high +potential apparatus; is termed a _brush discharge_. (2) A continuous +discharge between the terminals of a high potential apparatus is +termed a _convective discharge_. (3) The sudden breaking-down of the +air between the balls forming the spark gap is termed a _disruptive +discharge_; also called an _electric spark_, or just _spark_ for +short. (4) When a tube has a poor vacuum, or too large a battery +voltage, it glows with a blue light and this is called a _blue glow +discharge_. + +DISRUPTIVE DISCHARGE.--See _Discharge_. + +DISTRESS CALL. [Morse code:] ...---... (SOS). + +DISTRIBUTED CAPACITY.--See _Capacity, Distributed_. + +DOUBLE HUMP RESONANCE CURVE.--A resonance curve that has two peaks or +humps which show that the oscillating currents which are set up when +the primary and secondary of a tuning coil are closely coupled have +two frequencies. + +DUO-LATERAL COILS.--See _Coils, Inductance_. + +DUPLEX COMMUNICATION.--A wireless telephone system with which it is +possible to talk between both stations in either direction without the +use of switches. This is known as the _duplex system_. + +EARTH CAPACITY.--An aerial counterpoise. + +EARTH CONNECTION.--Metal plates or wires buried in the ground or +immersed in water. Any kind of means by which the sending and +receiving apparatus can be connected with the earth. + +EDISON STORAGE BATTERY.--See _Storage Battery, Edison_. + +ELECTRIC ENERGY.--The power of an electric current. + +ELECTRIC OSCILLATIONS.--See _Oscillations, Electric_. + +ELECTRIC SPARK.--See _Discharge, Spark_. + +ELECTRICITY, NEGATIVE.--The opposite of _positive electricity_. +Negative electricity is formed of negative electrons which make up the +outside particles of an atom. + +ELECTRICITY, POSITIVE.--The opposite of _negative electricity_. +Positive electricity is formed of positive electrons which make up the +inside particles of an atom. + +ELECTRODES.--Usually the parts of an apparatus which dip into a liquid +and carry a current. The electrodes of a dry battery are the zinc and +carbon elements. The electrodes of an Edison storage battery are the +iron and nickel elements, and the electrodes of a lead storage battery +are the lead elements. + +ELECTROLYTES.--The acid or alkaline solutions used in batteries. + +ELECTROMAGNETIC WAVES.--See _Waves, Electric_. + +ELECTROMOTIVE FORCE.--Abbreviated _emf_. The force that drives an +electric current along a conductor. Also loosely called +_voltage_. + +ELECTROMOTIVE FORCE, COUNTER.--The emf. that is set up in a direction +opposite to that in which the current is flowing in a conductor. + +ELECTRON.--(1) A negative particle of electricity that is detached +from an atom. (2) A negative particle of electricity thrown off from +the incandescent filament of a vacuum tube. + +ELECTRON FLOW.--The passage of electrons between the incandescent +filament and the cold positively charged plate of a vacuum tube. + +ELECTRON RELAY.--See _Relay, Electron_. + +ELECTRON TUBE.--A vacuum tube or a gas-content tube used for any +purpose in wireless work. See _Vacuum Tube_. + +ELECTROSE INSULATORS.--Insulators made of a composition material the +trade name of which is _Electrose_. + +ENERGY, ELECTRIC.--See _Electric Energy_. + +ENERGY UNIT.--The _joule_, which see, Page 308 [Appendix: Definitions +of Electric and Magnetic Units]. + +FADING.--The sudden variation in strength of signals received from a +transmitting station when all the adjustments of both sending and +receiving apparatus remain the same. Also called _swinging_. + +FARAD.--The capacitance of a condenser in which a potential difference +of 1 volt causes it to have a charge of 1 coulomb of electricity. + +FEED-BACK ACTION.--Feeding back the oscillating currents in a vacuum +tube to amplify its power. Also called _regenerative action_. + +FERROMAGNETIC CONTROL.--See _Magnetic Amplifier_. + +FILAMENT.--The wire in a vacuum tube that is heated to incandescence +and which throws off electrons. + +FILAMENT RHEOSTAT.--See _Rheostat, Filament_. + +FILTER.--Inductance coils or condensers or both which (1) prevent +troublesome voltages from acting on the different circuits, and (2) +smooth out alternating currents after they have been rectified. + +FILTER REACTOR.--See _Reactor, Filter_. + +FIRE UNDERWRITERS.--See _Code, National Electric_. + +FIXED GAP.--See _Gap_. + +FLEMING VALVE.--A two-electrode vacuum tube. + +FORCED OSCILLATIONS.--See _Oscillations, Forced_. + +FREE OSCILLATIONS.--See _Oscillations, Free_. + +FREQUENCY, AUDIO.--(1) An alternating current whose frequency is low +enough to operate a telephone receiver and, hence, which can be heard +by the ear. (2) Audio frequencies are usually around 500 or 1,000 +cycles per second, but may be as low as 200 and as high as 10,000 +cycles per second. + +Carrier.--A radio frequency wave modulated by an audio frequency wave +which results in setting of _three_ radio frequency waves. The +principal radio frequency is called the carrier frequency, since it +carries or transmits the audio frequency wave. + +Commercial.--(1) Alternating current that is used for commercial +purposes, namely, light, heat and power. (2) Commercial frequencies +now in general use are from 25 to 50 cycles per second. + +Natural.--The pendulum and vibrating spring have a _natural frequency_ +which depends on the size, material of which it is made, and the +friction which it has to overcome. Likewise an oscillation circuit has +a natural frequency which depends upon its _inductance_, _capacitance_ +and _resistance_. + +Radio.--(1) An oscillating current whose frequency is too high to +affect a telephone receiver and, hence, cannot be heard by the ear. +(2) Radio frequencies are usually between 20,000 and 2,000,000 cycles +per second but may be as low as 10,000 and as high as 300,000,000 +cycles per second. + +Spark.--The number of sparks per second produced by the discharge of a +condenser. + +GAP, FIXED.--One with fixed electrodes. + +GAP, NON-SYNCHRONOUS.--A rotary spark gap run by a separate motor +which may be widely different from that of the speed of the +alternator. + +GAP, QUENCHED.--(1) A spark gap for the impulse production of +oscillating currents. (2) This method can be likened to one where a +spring is struck a single sharp blow and then continues to set up +vibrations. + +GAP, ROTARY.--One having fixed and rotating electrodes. + +GAP, SYNCHRONOUS.--A rotary spark gap run at the same speed as the +alternator which supplies the power transformer. Such a gap usually +has as many teeth as there are poles on the generator. Hence one spark +occurs per half cycle. + +GAS-CONTENT TUBE.--See _Vacuum Tube._ + +GENERATOR TUBE.--A vacuum tube used to set up oscillations. As a +matter of fact it does not _generate_ oscillations, but changes the +initial low voltage current that flows through it into oscillations. +Also called an _oscillator tube_ and a _power tube._ + +GRID BATTERY.--See _Battery C._ + +GRID CHARACTERISTICS.--The various relations that could exist between +the voltages and currents of the grid of a vacuum tube, and the values +which do exist between them when the tube is in operation. These +characteristics are generally shown by curves. + +GRID CONDENSER.--See _Condenser, Grid._ + +GRID LEAK.--A high resistance unit connected in the grid lead of both +sending and receiving sets. In a sending set it keeps the voltage of +the grid at a constant value and so controls the output of the aerial. +In a receiving set it controls the current flowing between the plate +and filament. + +GRID MODULATION.--See _Modulation, Grid._ + +GRID POTENTIAL.--The negative or positive voltage of the grid of a +vacuum tube. + +GRID VOLTAGE.--See _Grid Potential._ + +GRINDERS.--The most common form of _Static,_ which see. They make a +grinding noise in the headphones. + +GROUND.--See _Earth Connection._ + +GROUND, AMATEUR.--A water-pipe ground. + +GROUND, WATERPIPE.--A common method of grounding by amateurs is to use +the waterpipe, gaspipe or radiator. + +GUIDED WAVE TELEPHONY.--See _Wired Wireless._ + +HARD TUBE.--A vacuum tube in which the vacuum is _high,_ that is, +exhausted to a high degree. + +HELIX.--(1) Any coil of wire. (2) Specifically a transmitter tuning +inductance coil. + +HENRY.--The inductance in a circuit in which the electromotive force +induced is 1 volt when the inducing current varies at the rate of 1 +ampere per second. + +HETERODYNE RECEPTION.--(1) Receiving by the _beat_ method. (2) +Receiving by means of superposing oscillations generated at the +receiving station on the oscillations set up in the aerial by the +incoming waves. + +HETERODYNE RECEPTOR.--See _Receptor, Heterodyne._ + +HIGH FREQUENCY CURRENTS.--See _Currents, High Frequency._ + +HIGH FREQUENCY RESISTANCE.--See _Resistance, High Frequency._ + +HIGH POTENTIAL CURRENTS.--See _Currents, High Potential._ + +HIGH VOLTAGE CURRENTS.--See _Currents, High Potential._ + +HONEYCOMB COILS.--See _Coils, Inductance._ + +HORSE-POWER.--Used in rating steam machinery. It is equal to 746 +watts. + +HOT WIRE AMMETER.--See _Ammeter, Hot Wire._ + +HOWLING.--Where more than three stages of radio amplification, or more +than two stages of audio amplification, are used howling noises are +apt to occur in the telephone receivers. + +IMPEDANCE.--An oscillation circuit has _reactance_ and also +_resistance,_ and when these are combined the total opposition to the +current is called _impedance._ + +INDUCTANCE COILS.--See _Coils, Inductance._ + +INDUCTANCE COIL, LOADING.--See _Coil, Loading Inductance._ + +INDUCTIVE COUPLING.--See _Coupling, Inductive._ + +INDUCTIVE REACTANCE.--See _Reactance, Inductive._ + +INDUCTION COIL.--See _Coil, Induction._ + +INDUCTION, MUTUAL.--Induction produced between two circuits or coils +close to each other by the mutual interaction of their magnetic +fields. + +INSULATION.--Materials used on and around wires and other conductors +to keep the current from leaking away. + +INSPECTOR, RADIO.--A U. S. inspector whose business it is to issue +both station and operators' licenses in the district of which he is in +charge. + +INTERFERENCE.--The crossing or superposing of two sets of electric +waves of the same or slightly different lengths which tend to oppose +each other. It is the untoward interference between electric waves +from different stations that makes selective signaling so difficult a +problem. + +INTERMEDIATE WAVES.--See _Waves._ + +IONIC TUBES.--See _Vacuum Tubes._ + +INTERNATIONAL CODE.--See Code, International. + +JAMMING.--Waves that are of such length and strength that when they +interfere with incoming waves they drown them out. + +JOULE.--The energy spent in 1 second by a flow of 1 ampere in 1 ohm. + +JOULE'S LAW.--The relation between the heat produced in seconds to the +resistance of the circuit, to the current flowing in it. + +KENOTRON.--The trade name of a vacuum tube rectifier made by the +_Radio Corporation of America._ + +KICK-BACK.--Oscillating currents that rise in voltage and tend to flow +back through the circuit that is supplying the transmitter with low +voltage current. + +KICK-BACK PREVENTION.--See _Prevention, Kick-Back._ + +KILOWATT.--1,000 watts. + +LAMBDA.--See Pages 301, 302. [Appendix: Useful Abbreviations]. + +LATTICE WOUND COILS.--See _Coils, Inductance._ + +LIGHTNING SWITCH.--See _Switch, Lightning._ + +LINE RADIO COMMUNICATION.--See _Wired Wireless._ + +LINE RADIO TELEPHONY.--See _Telephony, Line Radio._ + +LITZENDRAHT.--A conductor formed of a number of fine copper wires +either twisted or braided together. It is used to reduce the _skin +effect._ See _Resistance, High Frequency._ + +LOAD FLICKER.--The flickering of electric lights on lines that supply +wireless transmitting sets due to variations of the voltage on opening +and closing the key. + +LOADING COIL.--See _Coil, Loading._ + +LONG WAVES.--See _Waves._ + +LOOP AERIAL.--See _Aerial, Loop._ + +LOOSE COUPLED CIRCUITS.--See _Circuits, Loose Coupled._ + +LOUD SPEAKER.--A telephone receiver connected to a horn, or a +specially made one, that reproduces the incoming signals, words or +music loud enough to be heard by a room or an auditorium full of +people, or by large crowds out-doors. + +MAGNETIC POLES.--See _Poles, Magnetic._ + +MEGOHM.--One million ohms. + +METER, AUDIBILITY.--An instrument for measuring the loudness of a +signal by comparison with another signal. It consists of a pair of +headphones and a variable resistance which have been calibrated. + +MHO.--The unit of conductance. As conductance is the reciprocal of +resistance it is measured by the _reciprocal ohm_ or _mho._ + +MICA.--A transparent mineral having a high insulating value and which +can be split into very thin sheets. It is largely used in making +condensers both for transmitting and receiving sets. + +MICROFARAD.--The millionth part of a _farad._ + +MICROHENRY.--The millionth part of a _farad._ + +MICROMICROFARAD.--The millionth part of a _microfarad._ + +MICROHM.--The millionth part of an _ohm._ + +MICROPHONE TRANSFORMER.--See _Transformer, Microphone._ + +MICROPHONE TRANSMITTER.--See _Transmitter, Microphone._ + +MILLI-AMMETER.--An ammeter that measures a current by the +one-thousandth of an ampere. + +MODULATION.--(1) Inflection or varying the voice. (2) Varying the +amplitude of oscillations by means of the voice. + +MODULATION, BUZZER.--The modulation of radio frequency oscillations by +a buzzer which breaks up the sustained oscillations of a transmitter +into audio frequency impulses. + +MILLIHENRY.--The thousandth part of a _henry._ + +MODULATION, CHOPPER.--The modulation of radio frequency oscillations +by a chopper which breaks up the sustained oscillations of a +transmitter into audio frequency impulses. + +MODULATION, GRID.--The scheme of modulating an oscillator tube by +connecting the secondary of a transformer, the primary of which is +connected with a battery and a microphone transmitter, in the grid +lead. + +MODULATION, OVER.--See _Blub Blub._ + +MODULATION, PLATE.--Modulating the oscillations set up by a vacuum +tube by varying the current impressed on the plate. + +MODULATOR TUBE.--A vacuum tube used as a modulator. + +MOTION, WAVE.--(1) The to and fro motion of water at sea. (2) Waves +transmitted by, in and through the air, or sound waves. (3) Waves +transmitted by, in and through the _ether,_ or _electromagnetic +waves,_ or _electric waves_ for short. + +MOTOR-GENERATOR.--A motor and a dynamo built to run at the same speed +and mounted on a common base, the shafts being coupled together. In +wireless it is used for changing commercial direct current into direct +current of higher voltages for energizing the plate of a vacuum tube +oscillator. + +MULTI-STAGE AMPLIFIERS.--See _Amplifiers, Multi-Stage._ + +MUTUAL INDUCTION.--See _Induction, Mutual._ + +MUSH.--Irregular intermediate frequencies set up by arc transmitters +which interfere with the fundamental wave lengths. + +MUSHY NOTE.--A note that is not clear cut, and hence hard to read, +which is received by the _heterodyne method_ when damped waves or +modulated continuous waves are being received. + +NATIONAL ELECTRIC CODE.--See _Code, National Electric._ + +NATIONAL ELECTRIC SAFETY CODE.--See _Code, National Electric +Safety._ + +NEGATIVE ELECTRICITY.--See _Electricity, Negative._ + +NON-SYNCHRONOUS GAP.--See _Gap, Non-Synchronous._ + +OHM.--The resistance of a thread of mercury at the temperature of +melting ice, 14.4521 grams in mass, of uniform cross-section and a +length of 106.300 centimeters. + +OHM'S LAW.--The important fixed relation between the electric current, +its electromotive force and the resistance of the conductor in which +it flows. + +OPEN CIRCUIT.--See _Circuit, Open._ + +OPEN CORE TRANSFORMER.--See _Transformer, Open Core._ + +OSCILLATION TRANSFORMER.--See _Transformer, Oscillation._ + +OSCILLATIONS, ELECTRIC.--A current of high frequency that surges +through an open or a closed circuit. (1) Electric oscillations may be +set up by a spark gap, electric arc or a vacuum tube, when they have +not only a high frequency but a high potential, or voltage. (2) When +electric waves impinge on an aerial wire they are transformed into +electric oscillations of a frequency equal to those which emitted the +waves, but since a very small amount of energy is received their +potential or voltage is likewise very small. + +Sustained.--Oscillations in which the damping factor is small. + +Damped.--Oscillations in which the damping factor is large. + +Free.--When a condenser discharges through an oscillation circuit, +where there is no outside electromotive force acting on it, the +oscillations are said to be _free._ + +Forced.--Oscillations that are made to surge in a circuit whose +natural period is different from that of the oscillations set up in +it. + +OSCILLATION TRANSFORMER.--See _Transformer._ + +OSCILLATION VALVE.--See _Vacuum Tube._ + +OSCILLATOR TUBE.--A vacuum tube which is used to produce electric +oscillations. + +OVER MODULATION.--See _Blub Blub._ + +PANCAKE OSCILLATION TRANSFORMER.--Disk-shaped coils that are used for +receiving tuning inductances. + +PERMEABILITY, MAGNETIC.--The degree to which a substance can be +magnetized. Iron has a greater magnetic permeability than air. + +PHASE.--A characteristic aspect or appearance that takes place at the +same point or part of a cycle. + +PICK-UP CIRCUITS.--See _Circuits, Stand-by._ + +PLATE CIRCUIT REACTOR.--See _Reactor, Plate Circuit._ + +PLATE CURRENT.--See _Current, Plate._ + +PLATE MODULATION.--See _Modulation, Plate._ + +PLATE VOLTAGE.--See _Foliage, Plate._ + +POLES, BATTERY.--The positive and negative terminals of the elements +of a battery. On a storage battery these poles are marked + and - +respectively. + +POLES, MAGNETIC.--The ends of a magnet. + +POSITIVE ELECTRICITY.--See _Electricity, Positive._ + +POTENTIAL DIFFERENCE.--The electric pressure between two charged +conductors or surfaces. + +POTENTIOMETER.--A variable resistance used for subdividing the voltage +of a current. A _voltage divider._ + +POWER TRANSFORMER.--See _Transformer, Power._ + +POWER TUBE.--See _Generator Tube._ + +PRIMARY BATTERY.--See _Battery, Primary._ + +PREVENTION, KICK-BACK.--A choke coil placed in the power circuit to +prevent the high frequency currents from getting into the transformer +and breaking down the insulation. + +Q S T.--An abbreviation used in wireless communication for (1) the +question "Have you received the general call?" and (2) the notice, +"General call to all stations." + +QUENCHED GAP.--See _Gap, Quenched._ + +RADIATION.--The emission, or throwing off, of electric waves by an +aerial wire system. + +RADIO AMMETER.--See _Ammeter, Hot Wire._ + +RADIO FREQUENCY.--See _Frequency, Radio._ + +RADIO FREQUENCY AMPLIFICATION.--See _Amplification, Radio Frequency._ + +RADIO FREQUENCY CURRENT.--See _Current, Radio Frequency._ + +RADIO INSPECTOR.--See _Inspector, Radio_. + +RADIOTRON.--The trade name of vacuum tube detectors, amplifiers, +oscillators and modulators made by the _Radio Corporation of America_. + +RADIO WAVES.--See _Waves, Radio_. + +REACTANCE.--When a circuit has inductance and the current changes in +value, it is opposed by the voltage induced by the variation of the +current. + +REACTANCE, CAPACITY.--The capacity reactance is the opposition offered +to a current by a capacity. It is measured as a resistance, that is, +in _ohms_. + +RECEIVING TUNING COILS.--See _Coils, Inductance_. + +RECEIVER, LOUD SPEAKING.--See _Loud Speakers_. + +RECEIVER, WATCH CASE.--A compact telephone receiver used for wireless +reception. + +REACTANCE, INDUCTIVE.--The inductive reactance is the opposition +offered to the current by an inductance coil. It is measured as a +resistance, that is, in _ohms_. + +REACTOR, FILTER.--A reactance coil for smoothing out the pulsating +direct currents as they come from the rectifier. + +REACTOR, PLATE CIRCUIT.--A reactance coil used in the plate circuit of +a wireless telephone to keep the direct current supply at a constant +voltage. + +RECEIVER.--(1) A telephone receiver. (2) An apparatus for receiving +signals, speech or music. (3) Better called a _receptor_ to +distinguish it from a telephone receiver. + +RECTIFIER.--(1) An apparatus for changing alternating current into +pulsating direct current. (2) Specifically in wireless (_a_) a +crystal or vacuum tube detector, and (_b_) a two-electrode vacuum +tube used for changing commercial alternating current into direct +current for wireless telephony. + +REGENERATIVE AMPLIFICATION.--See _Amplification, Regenerative_. + +RECEPTOR.--A receiving set. + +RECEPTOR, AUTODYNE.--A receptor that has a regenerative circuit and +the same tube is used as a detector and as a generator of local +oscillations. + +RECEPTOR, BEAT.--A heterodyne receptor. + +RECEPTOR, HETERODYNE.--A receiving set that uses a separate vacuum +tube to set up the second series of waves for beat reception. + +REGENERATIVE ACTION.--See _Feed-Back Action._ + +REGENERATIVE AMPLIFICATION.--See _Amplification, Regenerative._ + +RELAY, ELECTRON.--A vacuum tube when used as a detector or an +amplifier. + +REPEATING COIL.--A transformer used in connecting up a wireless +receiver with a wire transmitter. + +RESISTANCE.--The opposition offered by a wire or other conductor to +the passage of a current. + +RESISTANCE, AERIAL.--The resistance of the aerial wire to oscillating +currents. This is greater than its ordinary ohmic resistance due to +the skin effect. See _Resistance, High Frequency._ + +RESISTANCE BOX.--See _Resistor._ + +RESISTANCE COUPLING.--See _Coupling, Resistance._ + +RESISTANCE, HIGH FREQUENCY.--When a high frequency current oscillates +on a wire two things take place that are different than when a direct +or alternating current flows through it, and these are (1) the current +inside of the wire lags behind that of the current on the surface, and +(2) the amplitude of the current is largest on the surface and grows +smaller as the center of the wire is reached. This uneven distribution +of the current is known as the _skin effect_ and it amounts to the +same thing as reducing the size of the wire, hence the resistance is +increased. + +RESISTIVITY.--The resistance of a given length of wire of uniform +cross section. The reciprocal of _conductivity._ + +RESISTOR.--A fixed or variable resistance unit or a group of such +units. Variable resistors are also called _resistance boxes_ and more +often _rheostats._ + +RESONANCE.--(1) Simple resonance of sound is its increase set up by +one body by the sympathetic vibration of a second body. (2) By +extension the increase in the amplitude of electric oscillations when +the circuit in which they surge has a _natural_ period that is the +same, or nearly the same, as the period of the first oscillation +circuit. + +RHEOSTAT.--A variable resistance unit. See _Resistor._ + +RHEOSTAT, CARBON.--A carbon rod, or carbon plates or blocks, when used +as variable resistances. + +RHEOSTAT, FILAMENT.--A variable resistance used for keeping the +current of the storage battery which heats the filament of a vacuum +tube at a constant voltage. + +ROTATING COIL.--See _Coil._ + +ROTARY GAP.--See _Gap._ + +ROTOR.--The rotating coil of a variometer or a variocoupler. + +RUHMKORFF COIL.--See _Coil, Induction._ + +SATURATION.--The maximum plate current that a vacuum tube will take. + +SENSITIVE SPOTS.--Spots on detector crystals that are sensitive to the +action of electric oscillations. + +SHORT WAVES.--See _Waves._ + +SIDE WAVES.--See _Wave Length Band._ + +SIGNALS, CONVENTIONAL.--(1) The International Morse alphabet and +numeral code, punctuation marks, and a few important abbreviations +used in wireless telegraphy. (2) Dot and dash signals for distress +call, invitation to transmit, etc. Now used for all general public +service wireless communication. + +SKIN EFFECT.--See _Resistance, High Frequency._ + +SOFT TUBE.--A vacuum tube in which the vacuum is low, that is, it is +not highly exhausted. + +SPACE CHARGE EFFECT.--The electric field intensity due to the pressure +of the negative electrons in the space between the filament and plate +which at last equals and neutralizes that due to the positive +potential of the plate so that there is no force acting on the +electrons near the filament. + +SPARK.--See _Discharge._ + +SPARK COIL.--See _Coil, Induction._ + +SPARK DISCHARGE.--See _Spark, Electric._ + +SPARK FREQUENCY.--See _Frequency, Spark._ + +SPARK GAP.--(1) A _spark gap,_ without the hyphen, means the apparatus +in which sparks take place; it is also called a _spark discharger._ +(2) _Spark-gap,_ with the hyphen, means the air-gap between the +opposed faces of the electrodes in which sparks are produced. + +Plain.--A spark gap with fixed electrodes. + +Rotary.--A spark gap with a pair of fixed electrodes and a number of +electrodes mounted on a rotating element. + +Quenched.--A spark gap formed of a number of metal plates placed +closely together and insulated from each other. + +SPIDER WEB INDUCTANCE COIL.--See _Coil, Spider Web Inductance._ + +SPREADER.--A stick of wood, or spar, that holds the wires of the +aerial apart. + +STAGGER WOUND COILS.--See _Coils, Inductance._ + +STAND-BY CIRCUITS.--See _Circuits, Stand-By._ + +STATIC.--Also called _atmospherics, grinders, strays, X's,_ and, when +bad enough, by other names. It is an electrical disturbance in the +atmosphere which makes noises in the telephone receiver. + +STATOR.--The fixed or stationary coil of a variometer or a +variocoupler. + +STORAGE BATTERY.--See _Battery, Storage._ + +STRAY ELIMINATION.--A method for increasing the strength of the +signals as against the strength of the strays. See _Static._ + +STRAYS.--See _Static_. + +STRANDED WIRE.--See _Wire, Stranded_. + +SUPER-HETERODYNE RECEPTOR.--See _Heterodyne, Super_. + +SWINGING.--See _Fading_. + +SWITCH, AERIAL.--A switch used to change over from the sending to the +receiving set, and the other way about, and connect them with the +aerial. + +SWITCH, LIGHTNING.--The switch that connects the aerial with the +outside ground when the apparatus is not in use. + +SYMBOLS, APPARATUS.--Also called _conventional symbols_. These are +diagrammatic lines representing various parts of apparatus so that +when a wiring diagram of a transmitter or a receptor is to be made it +is only necessary to connect them together. They are easy to make and +easy to read. See Page 307 [Appendix: Symbols Used for Apparatus]. + +SYNCHRONOUS GAP.--See _Gap, Synchronous_. + +TELEPHONY, LINE RADIO.--See _Wired Wireless_. + +THERMAL AMMETER.--See _Ammeter, Hot Wire_. + +THREE ELECTRODE VACUUM TUBE.--_See Vacuum Tube, Three Electrode_. + +TIKKER.--A slipping contact device that breaks up the sustained +oscillations at the receiving end into groups so that the signals can +be heard in the head phones. The device usually consists of a fine +steel or gold wire slipping in the smooth groove of a rotating brass +wheel. + +TRANSFORMER.--A primary and a secondary coil for stepping up or down a +primary alternating or oscillating current. + +A. C.--See _Power Transformer_. + +Air Cooled.--A transformer in which the coils are exposed to the air. + +Air Core.--With high frequency currents it is the general practice not +to use iron cores as these tend to choke off the oscillations. Hence +the core consists of the air inside of the coils. + +Auto.--A single coil of wire in which one part forms the primary and +the other part the secondary by bringing out an intermediate tap. + +Audio Amplifying.--This is a transformer with an iron core and is used +for frequencies up to say 3,000. + +Closed Core.--A transformer in which the path of the magnetic flux is +entirely through iron. Power transformers have closed cores. + +Microphone.--A small transformer for modulating the oscillations set +up by an arc or a vacuum tube oscillator. + +Oil Cooled.--A transformer in which the coils are immersed in oil. + +Open Core.--A transformer in which the path of the magnetic flux is +partly through iron and partly through air. Induction coils have open +cores. + +Oscillation.--A coil or coils for transforming or stepping down or up +oscillating currents. Oscillation transformers usually have no iron +cores when they are also called _air core transformers._ + +Power.--A transformer for stepping down a commercial alternating +current for lighting and heating the filament and for stepping up the +commercial a.c., for charging the plate of a vacuum tube oscillator. + +Radio Amplifying.--This is a transformer with an air core. It does not +in itself amplify but is so called because it is used in connection +with an amplifying tube. + +TRANSMITTER, MICROPHONE.--A telephone transmitter of the kind that is +used in the Bell telephone system. + +TRANSMITTING TUNING COILS.--See _Coils, Inductance._ + +TUNING.--When the open and closed oscillation circuits of a +transmitter or a receptor are adjusted so that both of the former will +permit electric oscillations to surge through them with the same +frequency, they are said to be tuned. Likewise, when the sending and +receiving stations are adjusted to the same wave length they are said +to be _tuned._ + +Coarse Tuning.--The first adjustment in the tuning oscillation +circuits of a receptor is made with the inductance coil and this tunes +them coarse, or roughly. + +Fine Tuning.--After the oscillation circuits have been roughly tuned +with the inductance coil the exact adjustment is obtained with the +variable condenser and this is _fine tuning._ + +Sharp.--When a sending set will transmit or a receiving set will +receive a wave of given length only it is said to be sharply tuned. +The smaller the decrement the sharper the tuning. + +TUNING COILS.--See _Coils, Inductance._ + +TWO ELECTRODE VACUUM TUBE.--See _Vacuum Tube, Two Electrode._ + +VACUUM TUBE.--A tube with two or three electrodes from which the air +has been exhausted, or which is filled with an inert gas, and used as +a detector, an amplifier, an oscillator or a modulator in wireless +telegraphy and telephony. + +Amplifier.--See _Amplifier, Vacuum Tube._ + +Amplifying Modulator.--A vacuum tube used for modulating and +amplifying the oscillations set up by the sending set. + +Gas Content.--A tube made like a vacuum tube and used as a detector +but which contains an inert gas instead of being exhausted. + +Hard.--See _Hard Tube._ + +Rectifier.--(1) A vacuum tube detector. (2) a two-electrode vacuum +tube used for changing commercial alternating current into direct +current for wireless telephony. + +Soft.--See _Soft Tube._ + +Three Electrode.--A vacuum tube with three electrodes, namely a +filament, a grid and a plate. + +Two Electrode.--A vacuum tube with two electrodes, namely the filament +and the plate. + +VALVE.--See _Vacuum Tube._ + +VALVE, FLEMING.--See _Fleming Valve._ + +VARIABLE CONDENSER.--See _Condenser, Variable._ + +VARIABLE INDUCTANCE.--See _Inductance, Variable._ + +VARIABLE RESISTANCE.--See _Resistance, Variable._ + +VARIOCOUPLER.--A tuning device for varying the inductance of the +receiving oscillation circuits. It consists of a fixed and a rotatable +coil whose windings are not connected with each other. + +VARIOMETER.--A tuning device for varying the inductance of the +receiving oscillation currents. It consists of a fixed and a rotatable +coil with the coils connected in series. + +VERNIER CONDENSER.--See _Condenser, Vernier._ + +VOLT.--The electromotive force which produces a current of 1 ampere +when steadily applied to a conductor the resistance of which is one +ohm. + +VOLTAGE DIVIDER.--See _Potentiometer._ + +VOLTAGE, PLATE.--The voltage of the current that is used to energize +the plate of a vacuum tube. + +VOLTMETER.--An instrument for measuring the voltage of an electric +current. + +WATCH CASE RECEIVER.--See _Receiver, Watch Case._ + +WATER-PIPE GROUND.--See _Ground, Water-Pipe._ + +WATT.--The power spent by a current of 1 ampere in a resistance of 1 +ohm. + +WAVE, BROAD.--A wave having a high decrement, when the strength of the +signals is nearly the same over a wide range of wave lengths. + +WAVE LENGTH.--Every wave of whatever kind has a length. The wave +length is usually taken to mean the distance between the crests of two +successive waves. + +WAVE LENGTH BAND.--In wireless reception when continuous waves are +being sent out and these are modulated by a microphone transmitter the +different audio frequencies set up corresponding radio frequencies and +the energy of these are emitted by the aerial; this results in waves +of different lengths, or a band of waves as it is called. + +WAVE METER.--An apparatus for measuring the lengths of electric waves +set up in the oscillation circuits of sending and receiving sets. + +WAVE MOTION.--Disturbances set up in the surrounding medium as water +waves in and on the water, sound waves in the air and electric waves +in the ether. + +WAVES.--See _Wave Motion_. + +WAVES, ELECTRIC.--Electromagnetic waves set up in and transmitted by +and through the ether. + +Continuous. Abbreviated C.W.--Waves that are emitted without a break +from the aerial. Also called _undamped waves_. + +Discontinuous.--Waves that are emitted periodically from the aerial. +Also called _damped waves_. Damped.--See _Discontinuous Waves_. + +Intermediate.--Waves from 600 to 2,000 meters in length. + +Long.--Waves over 2,000 meters in length. + +Radio.--Electric waves used in wireless telegraphy and telephony. + +Short.--Waves up to 600 meters in length. + +Wireless.--Electric waves used in wireless telegraphy and telephony. + +Undamped.--See _Continuous Waves_. + +WIRELESS TELEGRAPH CODE.--See _Code, International_. + +WIRE, ENAMELLED.--Wire that is given a thin coat of enamel which +insulates it. + +WIRE, PHOSPHOR BRONZE.--A very strong wire made of an alloy of copper +and containing a trace of phosphorus. + +WIRED WIRELESS.--Continuous waves of high frequency that are sent over +telephone wires instead of through space. Also called _line radio +communication; carrier frequency telephony, carrier current telephony; +guided wave telephony_ and _wired wireless._ + +X'S.--See _Static._ + +ZINCITE.--See _Detector._ + + + + +WIRELESS DON'TS + +AERIAL WIRE DON'TS + +_Don't_ use iron wire for your aerial. + +_Don't_ fail to insulate it well at both ends. + +_Don't_ have it longer than 75 feet for sending out a 200-meter wave. + +_Don't_ fail to use a lightning arrester, or better, a lightning +switch, for your receiving set. + +_Don't_ fail to use a lightning switch with your transmitting set. + +_Don't_ forget you must have an outside ground. + +_Don't_ fail to have the resistance of your aerial as small as +possible. Use stranded wire. + +_Don't_ fail to solder the leading-in wire to the aerial. + +_Don't_ fail to properly insulate the leading-in wire where it goes +through the window or wall. + +_Don't_ let your aerial or leading-in wire touch trees or other +objects. + +_Don't_ let your aerial come too close to overhead wires of any kind. + +_Don't_ run your aerial directly under, or over, or parallel with +electric light or other wires. + +_Don't_ fail to make a good ground connection with the water pipe +inside. + +TRANSMITTING DON'TS + +_Don't_ attempt to send until you get your license. + +_Don't_ fail to live up to every rule and regulation. + +_Don't_ use an input of more than 1/2 a kilowatt if you live within 5 +nautical miles of a naval station. + +_Don't_ send on more than a 200-meter wave if you have a restricted or +general amateur license. + +_Don't_ use spark gap electrodes that are too small or they will get +hot. + +_Don't_ use too long or too short a spark gap. The right length can be +found by trying it out. + +_Don't_ fail to use a safety spark gap between the grid and the +filament terminals where the plate potential is above 2,000 volts. + +_Don't_ buy a motor-generator set if you have commercial alternating +current in your home. + +_Don't_ overload an oscillation vacuum tube as it will greatly shorten +its life. Use two in parallel. + +_Don't_ operate a transmitting set without a hot-wire ammeter in the +aerial. + +_Don't_ use solid wire for connecting up the parts of transmitters. +Use stranded or braided wire. + +_Don't_ fail to solder each connection. + +_Don't_ use soldering fluid, use rosin. + +_Don't_ think that all of the energy of an oscillation tube cannot be +used for wave lengths of 200 meters and under. It can be if the +transmitting set and aerial are properly designed. + +_Don't_ run the wires of oscillation circuits too close together. + +_Don't_ cross the wires of oscillation circuits except at right +angles. + +_Don't_ set the transformer of a transmitting set nearer than 3 feet +to the condenser and tuning coil. + +_Don't_ use a rotary gap in which the wheel runs out of true. + +RECEIVING DON'TS + +_Don't_ expect to get as good results with a crystal detector as with +a vacuum tube detector. + +_Don't_ be discouraged if you fail to hit the sensitive spot of a +crystal detector the first time--or several times thereafter. + +_Don't_ use a wire larger than _No. 80_ for the wire electrode of a +crystal detector. + +_Don't_ try to use a loud speaker with a crystal detector receiving +set. + +_Don't_ expect a loop aerial to give worthwhile results with a crystal +detector. + +_Don't_ handle crystals with your fingers as this destroys their +sensitivity. Use tweezers or a cloth. + +_Don't_ imbed the crystal in solder as the heat destroys its +sensitivity. Use _Wood's metal,_ or some other alloy which melts at or +near the temperature of boiling water. + +_Don't_ forget that strong static and strong signals sometimes destroy +the sensitivity of crystals. + +_Don't_ heat the filament of a vacuum tube to greater brilliancy than +is necessary to secure the sensitiveness required. + +_Don't_ use a plate voltage that is less or more than it is rated for. + +_Don't_ connect the filament to a lighting circuit. + +_Don't_ use dry cells for heating the filament except in a pinch. + +_Don't_ use a constant current to heat the filament, use a constant +voltage. + +_Don't_ use a vacuum tube in a horizontal position unless it is made +to be so used. + +_Don't_ fail to properly insulate the grid and plate leads. + +_Don't_ use more than 1/3 of the rated voltage on the filament and on +the plate when trying it out for the first time. + +_Don't_ fail to use alternating current for heating the filament where +this is possible. + +_Don't_ fail to use a voltmeter to find the proper temperature of the +filament. + +_Don't_ expect to get results with a loud speaker when using a single +vacuum tube. + +_Don't_ fail to protect your vacuum tubes from mechanical shocks and +vibration. + +_Don't_ fail to cut off the A battery entirely from the filament when +you are through receiving. + +_Don't_ switch on the A battery current all at once through the +filament when you start to receive. + +_Don't_ expect to get the best results with a gas-content detector +tube without using a potentiometer. + +_Don't_ connect a potentiometer across the B battery or it will +speedily run down. + +_Don't_ expect to get as good results with a single coil tuner as you +would with a loose coupler. + +_Don't_ expect to get as good results with a two-coil tuner as with +one having a third, or _tickler_, coil. + +_Don't_ think you have to use a regenerative circuit, that is, one +with a tickler coil, to receive with a vacuum tube detector. + +_Don't_ think you are the only amateur who is troubled with static. + +_Don't_ expect to eliminate interference if the amateurs around you +are sending with spark sets. + +_Don't_ lay out or assemble your set on a panel first. Connect it up +on a board and find out if everything is right. + +_Don't_ try to connect up your set without a wiring diagram in front +of you. + +_Don't_ fail to shield radio frequency amplifiers. + +_Don't_ set the axes of the cores of radio frequency transformers in a +line. Set them at right angles to each other. + +_Don't_ use wire smaller than _No. 14_ for connecting up the various +parts. + +_Don't_ fail to adjust the B battery after putting in a fresh vacuum +tube, as its sensitivity depends largely on the voltage. + +_Don't_ fail to properly space the parts where you use variometers. + +_Don't_ fail to put a copper shield between the variometer and the +variocoupler. + +_Don't_ fail to keep the leads to the vacuum tube as short as +possible. + +_Don't_ throw your receiving set out of the window if it _howls_. Try +placing the audio-frequency transformers farther apart and the cores +of them at right angles to each other. + +_Don't_ use condensers with paper dielectrics for an amplifier +receiving set or it will be noisy. + +_Don't_ expect as good results with a loop aerial, or when using the +bed springs, as an out-door aerial will give you. + +_Don't_ use an amplifier having a plate potential of less than 100 +volts for the last step where a loud speaker is to be used. + +_Don't_ try to assemble a set if you don't know the difference between +a binding post and a blue print. Buy a set ready to use. + +_Don't_ expect to get Arlington time signals and the big cableless +stations if your receiver is made for short wave lengths. + +_Don't_ take your headphones apart. You are just as apt to spoil them +as you would a watch. + +_Don't_ expect to get results with a Bell telephone receiver. + +_Don't_ forget that there are other operators using the ether besides +yourself. + +_Don't_ let your B battery get damp and don't let it freeze. + +_Don't_ try to recharge your B battery unless it is constructed for +the purpose. + +STORAGE BATTERY DON'TS + +_Don't_ connect a source of alternating current direct to your storage +battery. You have to use a rectifier. + +_Don't_ connect the positive lead of the charging circuit with the +negative terminal of your storage battery. + +_Don't_ let the electrolyte get lower than the tops of the plates of +your storage battery. + +_Don't_ fail to look after the condition of your storage battery once +in a while. + +_Don't_ buy a storage battery that gives less than 6 volts for heating +the filament. + +_Don't_ fail to keep the specific gravity of the electrolyte of your +storage battery between 1.225 and 1.300 Baume. This you can do with a +hydrometer. + +_Don't_ fail to recharge your storage battery when the hydrometer +shows that the specific gravity of the electrolyte is close to 1.225. + +_Don't_ keep charging the battery after the hydrometer shows that the +specific gravity is 1.285. + +_Don't_ let the storage battery freeze. + +_Don't_ let it stand for longer than a month without using unless you +charge it. + +_Don't_ monkey with the storage battery except to add a little +sulphuric acid to the electrolyte from time to time. If anything goes +wrong with it better take it to a service station and let the expert +do it. + +EXTRA DON'TS + +_Don't_ think you have an up-to-date transmitting station unless you +are using C.W. + +_Don't_ use a wire from your lightning switch down to the outside +ground that is smaller than No. _4_. + +_Don't_ try to operate your spark coil with 110-volt direct lighting +current without connecting in a rheostat. + +_Don't_ try to operate your spark coil with 110-volt alternating +lighting current without connecting in an electrolytic interrupter. + +_Don't_ try to operate an alternating current power transformer with +110-volt direct current without connecting in an electrolytic +interruptor. + +_Don't_--no never--connect one side of the spark gap to the aerial +wire and the other side of the spark gap to the ground. The Government +won't have it--that's all. + +_Don't_ try to tune your transmitter to send out waves of given length +by guesswork. Use a wavemeter. + +_Don't_ use _hard fiber_ for panels. It is a very poor insulator where +high frequency currents are used. + +_Don't_ think you are the only one who doesn't know all about +wireless. Wireless is a very complex art and there are many things +that those experienced have still to learn. + + + + +THE END. + + + + +*** END OF THE PROJECT GUTENBERG EBOOK, THE RADIO AMATEUR'S HAND BOOK *** + +This file should be named 6935.txt or 6935.zip + +Project Gutenberg eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the US +unless a copyright notice is included. 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