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The Radio Amateur's Hand Book
by A. Frederick Collins
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THE RADIO AMATEUR'S HAND BOOK



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.)



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.



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.

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