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POPULAR EDITION

THE STANDARD

RADIOGUIDE

How to Enjoy Radio at HorneHow to Listen -In What You Can HearHowMuch to Pay How to MakeYour

for Your Set Own Setc

Bashed hy Popular Science Monthly Rice 50 Cents

ABC UNITS come to you complete inevery detail and ready -to -operate. The firstUNIT of the series, shown above, is an en-tirely practical receiving outfit which willrespond to wireless telephone 25 to 35 milesand wireless telegraph much farther. Phones,aerial, in fact every item of accessory equip-ment is included. Just put up a simple twoor four wire aerial, make an easy ground con-nection and you are ready to listen in. Thereis no danger, no current, no technical adjust-ments.

Start with an ABC UNIT and when youwant to add to your set later, as you surelywill, you have all the advantages of the ex-clusive UNIT system. (See inside backcover.)

Jewett Manufacturing CorporationCanadian Pacific Building

Madison Ave., and 44th St. New York City

THE STANDARD

RADIOGUIDE

Wireless Explained in Simple LanguageWith Pictures, Diagrams, Radio Map

and Complete Directions forUsing Receiving Outfits

Popular Edition

Published by

POPULAR SCIENCE MONTHLY225 West 39th Street

New York City

Copyright. 1922. by the

Modern Publishing Company

Printed in United States of America

TABLE OF CONTENTS

Chapter PageI What You Can Hear with a Radio Set 5

A description of the types of broadcasted entertain-ments now available to all owners of radio receivingsets

II How Wireless Speech Is Possible 9A simple explanation of the way voices and musicare sent through the air and received

III A Picture Story of Radio 12The various parts of a sending and receiving set, illus-trated and explained

IV Radio Equipment You Will Need 14Describing sets costing from $15 to $200, and explainingwhat broadcasts each will bring you

V How to Assemble Your Receiving Set 26Simplifying what seems to many a difficult task.Learn what troubles to look for, before they are met

VI How to "Tune" Your Set 32With these instructions the procedure of "tuning in"is made so simple that success is assured

VII What Radio Stations You Can Hear 49The range of typical receiving sets explained, and illus-trated with a broadcasting chart of the United States

VIII How to Make a Crystal Detector Set 52Full directions for laying out and constructing a set athome, using a minimum of purchased articles

IX How to Make a Vacuum Tube Set 56This set has actually been built, and gives excellentresults. Costing $30, it equals a $100 set in receivingrange

X A Few Facts about Transmitting Sets 61An outline of the status of amateur sending stations,with some data on the expense of conducting broad-casting stations

XI Important Tips and "Trouble Spots" 64The experimenter may discover that one of these dia-grams will add miles in receiving range to his set

XII Glossary of Radio Terms 67The principal terms encountered in radio literatureexplained in words understandable by all

3

The owner -of a simple radio outfit can "listen in" upon the greatevents of the world. Exciting news, sporting events describedpia i by play, as well as concerts and great speeches can be picked

up from the air

4

The Standard

RADIO GUIDE

CHAPTER 1

What You Can Hear with a Radio Set

OVER all the United States, to -day, the air is throb-bing with the songs of famous soloists, with instru-mental music played by concert orchestras andpopular jazz bands, with humorous talks by noted

entertainers, with lectures, sermons, and bits of vaude-ville, with news bulletins, business information, educa-tional talks, friendly gossip, market reports, weather fore-casts, and important political speeches.

The ether has become one vast concert hall, offering afree selection of every variety of entertainment.

And all that is necessary to make the silence of thenight speak to you with a thousand voices is to own oneof the magic little radio receiving outfits, which you your-self can make at small cost, or purchase.

The purpose of this booklet is to tell you what sort ofradio entertainment you can enjoy; to explain in simpleterms the secrets of radio about which everybody wantsto know; to tell you what sort of wireless sets to buy, justhow to install them, and how to get the very best resultsfrom them; and, finally, to describe simply, step by step,how easy it is to build your own radio set, if you prefer.

Over a score of powerful radio broadcasting stations arenightly flinging music to the air. One or another of themcan be heard in almost every part of the country. Boston,New York, Pittsburgh, Detroit, Washington, Omaha,Denver, Kansas City, Seattle, San Francisco, Los Angeles

5

THE STANDARD RADIO GUIDE

-each of these cities, to mention only a few, is a broad-casting center, and many of their programs are enjoyedby amateurs a thousand miles away. Most readers ofthis book live so near to some broadcasting station thatthey can hear its programs with a low-priced receivingset; while with a somewhat better equipment they canenjoy the magic thrill of listening nightly to noted mentalking, or to vaudeville entertainers singing in some cityhalf a continent away.

A Typical Radio ProgramIN some cities the newspapers give special types of pro-gram; in others the state universities broadcast music,news, and educational talks; while in numberless' others,smaller stations send out varied musical programs. Butthe following is a typical daily schedule of any one of thescore or more powerful stations that have suddenly be-come national institutions:

11 A. M. -News and music, government weatherforecast.

12 M. -News and music, government weatherforecast, agricultural report.

12:30 P. M.-Music.1:00 P. M.-News and music.2:05 P. M.-Shipping news.3:00 P. M.-News and music.4:00 P. M.-News and music.5:00 P. M.-News and music, government weather

forecast.6:00 P. M.-News and music, agricultural report.7:30 P. M.-Children's bedtime stories.7:45 P. M.-Special news, market, weather, and

Stock Exchange reports.8:00 P. M.-Talk on business conditions.8:30 P. M. to 9:45 P. M.-Concert and entertainment

by musical comedy stars.9:55 P. M.-Arlington time signals.

Such week -day programs as the above are varied onSundays with sermons by noted preachers, and withselections of music and choral singing. The programs

6

WHAT YOU CAN HEAR WITH A RADIO SET

This picture shows how a duet is sent out from a broad-casting station. The small cylinder suspended fromthe frame at the right contains the transmitter. Theman at the left is signaling the generator room, where

the energy is controlled

that are offered the radio listener are as varied as theregions covered. Often on the same evening, the for-tunately located expert listener can, by turning a knobback and forth, hear a concert from one town, pick up alecture from another, get the latest news from a third,catch a bit of wireless chat between two amateurs, hearconversations between two ships at sea, and wind up hisevening of adventure in the ether by getting the correcttime and weather forecast from Washington.

These broadcasting programs are being heard simul-taneously by the plantation worker in Cuba and thelumberjack in a lonely North Woods hut. They arebringing the remotest corners of the land into touch withcivilization. News of the world that otherwise would beweeks old before it reached some of these spots is spreadby the radiotelephone with the speed of light from Canadato Cuba, from ships in the Atlantic to other vessels

7


many days out from the Golden Gate, and from theUnited States to her farthest possessions.

It is in this great drama of world-wide intercommuni-cation that you can share when you install a radio set inyour own home. Before long, every American will feelit as much a part of his duty to share in it as he now feelsit his duty to read the papers and visit the voting boothat election time. For the government sees itself as thelogical broadcasting agency. With 61 governmental ex-perimental stations, and 40 state universities as a nucleusof a national broadcasting system, the scope of govern-ment broadcasting will surely be increased until everysquare mile of the country is daily in direct vocal touchwith the seat of government. Health advice in times ofepidemics; warnings of floods; short talks on rural im-provements; speeches by high officials; and the more pro-saic, but equally important, weather, news, and marketreports-the broadcasting of these and many other itemswill be considered a normal function to be performed bythe government for its citizens. But on the shoulders ofthe private corporations will continue to fall the pleasingburden of entertaining the great mass of people with con-certs, operas, and music in all its forms.

8

CHAPTER II

How Wireless Speech Is Possible

EVERYBODY whose fancy is caught by the magic ofradio, and every purchaser of a radio set, wants firstof all to try to visualize just what is happening in

the sending and receiving sets, to make the miracle ofwireless speech possible. A few simple steps towardunderstanding the fundamentals of radio will make yourenjoyment and success with it infinitely greater.

If you plunge a stick vertically into a sheet of still waterat regular intervals, a series of small waves will start fromthe stick and gradually widen in circles across the water,until they diminish in size and disappear.

The radiotelephone transmits speech by starting similarwaves in the air. The human voice is produced by vi-brations of the cords in the throat. These vibrations,varying in frequency from 4000 to 10,000 a second, setup sound waves in the air. Now if these waves arechanged into electric vibrations, instead of sound vibra-tions, they can be sent broadcast over great distances inmuch the same way that the water waves traveled on thewater's surface. The sounds are easily converted intoelectrical waves by a small device called the vacuum tube.This tube, when fed with electric current, commences tovibrate, or, as it is technically termed, oscillate. Thewaves that it sends out do not vary in intensity until avoice, speaking into an ordinary telephone transmitter, isimpinged upon the current passing through the tube,when the sound vibrations will be added to the normalvibrations of the tube, and the ether or air waves will

9


j Radwfrequenfy4 I

Waves u

How the modulated waves corresponding to sound arecarried through the air on a "carrier wave" of highfrequency. These high frequency radio waves act as a

support for the speech waves

vary with the sound vibrations. Once the sounds havethus been converted into electric waves, some methodmust be adopted at the receiving stations to convert theelectric waves back into sound waves, so that the manlistening at the phones will have the words translated forhim in the sender's own voice.

This is accomplished by devices almost identical withthose of the sending station, except that the instrumentsare in reverse order. First, there is the aerial wire, orantenna, connected with which are the coils used for ad-justment. Next there is a small instrument called thedetector, which does the actual converting of the waves.And finally comes a pair of telephone receivers, throughwhich the listener hears the sounds.

When a singer or an orchestra at the transmitting sta-tion sends its sound waves into the transmitter, and thelatter translates them into electrical waves, they race tothe antenna and generate the waves in the air, or ether.These waves travel in every direction at the rate of 186,300miles a second. The distance at which they may be re-ceived will depend on the power behind the waves, theland over which they travel, and the receiving set which

10

HOW WIRELESS SPEECH IS POSSIBLE

tries to pick them up. In reality, the waves might passcompletely around the earth, but at the end of that jour-ney they would be so weak as to make detection impossible.

Thus, while the radio waves from any given broadcast-ing station travel enormous distances almost instantly,the purchaser of a receiving outfit may find that it is notsensitive enough to pick up the concerts he wishes to hear.What stations you are likely to hear in your vicinity, andwhat type of set you will require to do so is explained onpage 49 of this book.

The broadcasting chart published on page 50 is a sim-plified copy of the elaborate national broadcasting mapof the United States compiled by POPULAR SCIENCEMONTHLY, and showing in great detail all the most im-portant stations in the country, together with their rangefor various types of receiving sets, their call letters, ad-dresses, etc. The map is invaluable, both to the pros-pective purchaser of a radio set, who cannot wisely deter-mine how expensive an apparatus to buy, without con-sulting it, and to the owner of an outfit, who will be ableto locate from it the stations he picks up.

The map is procurable from POPULAR SCIENCEMONTHLY. See page 73 for further description.

11

CHAPTER

A Picture Story of

TRANSMITTING AERI-AL-Transmitting stations

I must have aerials of four ormore wires. The aerial is

only one half of the electric circuit, theother half being the ground.

INDUCTANCE-Change in the lengthof wires in the aerial is effected by using a

2 larger or smaller number of wires on theinductance, a cylinder 10 inches or morein diameter.

VACUUM TUBE-Sound currents fromthe voice entering the transmitter passthrough this tube, where they meet a high

3 frequency, powerful wave already beinggenerated. The sound waves combinewith the tube waves and ride on the latterto their destination.

TRANSFORMER -A transformer be-comes necessary, to raise the voltage of

4 the impulses after they have been pro-duced in the phone circuit by the action ofthe sound on the diaphragm.

TRANSMITTER -The phone used forsending out radio broadcasts is not unlikethe ordinary desk transmitter. It con-sists of a mouthpiece to catch and directthe sound wave, a flexible metal diaphragmand two carbon buttons, between which

5 are placed a quantity of fine carbon gran-ules. One of the carbon buttons is sta-tionary, but the other is connected withthe diaphragm. When the diaphragm vi-brates, the carbon granules are alternatelypacked more tightly and more loosely to-gether, thus providing a better electricalcircuit and varying the amount of cur-rent.

STORAGE BATTERY-When radiotele-phone messages are to be carried only a

6 short distance, one or more storage bat-teries may be used. The larger stationsare connected with huge direct currentgenerators, instead.

12

THREE ReceivingAerial

How Radio Sets Work

NOTE-Each part bears itssymbol as used in diagrams.

VARIOCOUPLER - The variocouplersupplies the means for altering the amountof wire in the aerial. This is called tuning,and on it depend the strength and clear-ness of the signals received.

VARIOMETER -Sometimes a variom-eter is used to make accurate changes inthe wave length of the aerial. A variom-eter consists of two coils of wire con-nected by a flexible cord, the inner coilrotating inside the larger.

VACUUM TUBE -Radio waves vibratetoo rapidly to actuate ordinary phone re-ceivers. The vacuum tube is employedto alter the frequency without distortingthe sound. The vacuum tube is an in-candescent bulb containing a filament, ametal plate and a network of fine wires.

STORAGE BATTERY-A storage bat-tery, which is required to heat the filamentof the vacuum tube, is the most reliablesource of constant current.

A second variometer is sometimesadded, when by so doing the signals maybe strengthened."B" BATTERY-The voltage on theplate of the vacuum tube is supplied by adry battery, usually known as the "B"battery.HEAD PHONES-The electric impulsesreceived from the aerial and altered inform and frequency by the vacuum tubes,pass through sensitive magnets in thephone receivers and vibrate the diaphragmin agreement with the electric wave. Themovement of the diaphragm producessound waves that are translated by theear into speech.VARIABLE CONDENSER -A variablecondenser consists of two series of alumi-num or brass plates, with one series sta- 15tionary and the other rotatable, so that itmay be revolved inside or outside thestationary plates.

13

CHAPTER IV ,

What Radio Equipment You Will Need

NOTE: Reference from this and following chapters backto the preceding chapter, "A Picture Story of Radio," willmake all the terms, parts mentioned, and wiring descrip-tion more quickly intelligible to the non -technical reader.

THOUSANDS of persons-men, women, and chil-dren-suddenly aroused to enthusiasm toward thescience of the radiotelephone, are asking the same

question: "What kind of equipment do I need, to hearthese concerts, operas, and other broadcasts?" Theanswer depends, in part, on the location of the house. Ifit is situated close to a broadcasting station, nothing wouldbe gained by installing one of the more expensive outfits;but if the home is several hundred miles away, then careshould be exercised in purchasing a receiving set and aerialof proper design. If this is not done at the start, the re-sults will be exceedingly disappointing. Even if the houseis only 25 miles distant from a broadcasting station, thepurchaser should realize that every additional dollar hespends for an outfit, up to $200, will improve the regu-larity and clearness of the sounds received and lessen thepossibility of interference.

One of the first questions asked by a customer at a radiostore is, "How far will this set receive?" The salesmanmay name a distance based on the success of some otherowner of the same type of outfit. If the figure is 50 miles,the purchaser buys the set with the fixed impression thatit will receive up to 50 miles. As a matter of fact, he may

14

WHAT RADIO EQUIPMENT YOU WILL NEED

This is a typical lowpriced crystal detec-tor set. Unbelievableranges have been cov-ered with such outfits,but in a general waythey should not beinstalled if the ama-teur is more than 15to 25 miles away fromthe broadcasting sta-tion. In, a crowdedcity, where there aremany interferences,the crystal set is sel-

dom satisfactory

find when he has finished the installation that it will"listen in" on a phone station 100 miles away, or he mayfind that a broadcasting station only 25 miles away can-not be heard even during the clear, crisp nights of fall andearly winter, when radiotelephone transmission is at itsbest. Mysterious atmospheric and geographical condi-tions, unsolved even by experts, are responsible for thisanomaly.

However, among the different classes of radio sets dis-cussed in the following paragraphs, there is one or anotherwhich will probably be the best for you to start with; andfrom this description you should familiarize yourself withthe sets and their possibilities, before going to the dealerto make your purchase; for radio stores are so busy thatthe purchaser who knows nothing about the apparatus islikely to be at a disadvantage.

15

The Lowest Price Radio SetsSets selling for about $15 are of the simplest practicable

sort, consisting of a small inductance coil for tuning pur-poses, a fixed condenser, a crystal detector, and a single phoneto hold to the ear. With an aerial or antenna, consistingof one copper wire strung from a tree 100 feet or moreaway from the house, an outfit of this type shouldpick up the broadcasting concerts 10 miles from the sta-tion. The wire you should ask for is No. 14 gage. Evenat this distance, the sounds may sometimes be so low inintensity that any interference from other wireless sta-tions will garble or obliterate them, while on the otherhand these sets have been known to receive over muchgreater distances. The simple tuning coil of this set doesnot permit of selective tuning; that is, if other stations aresending at the same time, whether in telegraphic code orvocal sounds, it will be impossible to separate the soundsproduced by their waves from the sounds of the stationyou are trying to hear. Nevertheless, these $15 sets areexcellent as beginners' low-priced outfits, and many ama-teurs continue to use them for knockabout purposes, evenafter they have installed better sets.

Simple Definitions of Radio TermsBefore going further into the details of typical sets,

many readers will want simple definitions of the variousparts mentioned above. The antenna or aerial for receiv-ing purposes does not need to be the elaborate type sooften seen on roof tops. A single wire of copper or phos-phor bronze, of almost any size between No. 10 and No. 16may be used. This can be bought at any electrical supplystore. Great height is not necessary. An aerial with oneend 40 feet in the air will be sufficient. A 75 -foot aerialmight be considered as ideal, but is not always attainable,except at much expense. It is not essential that the wire

16


used be bare. Insulated wire is just as satisfactory, sincewireless waves pass through anything, but the addedweight of insulated wire requires heavier fastenings at thepoint of support. Complete working directions for theerection of the aerial will be found on page 26.

You can obtain a clear understanding of the other partsof typical sets by studying them in the order they are en-countered by the radio waves passing down through thisaerial and the lead in wire, which connects it with yourreceiving box.

The Tuning CoilThe first piece is the inductance or tuning coil. This is

merely a number of turns-varying from 25 to 200-ofinsulated wire, about No. 22 gage, wound closely around afiber or cardboard tube. At every 5 or 10 turns a con-nection is taken off and carried to a small switch withrotating handle, or knob. By turning this handle, con-tact may be made with the different points, so that agreater or lesser number of turns of the coil are connectedwith the aerial. The purpose of this tuning coil is tomake it possible for the listener -in to increase or diminishthe length of wire used in receiving the signals, so that thelatter will be heard at their loudest. The secret of tuning,which you hear so frequently mentioned, simply lies inthis adjustment of the length of your receiving wire, sothat it will bring you only the radio waves you want tohear.

Next to the tuning coil is the fixed condenser. This isa part seldom seen, and never touched. Often it is notin evidence, being buried in the base of the detector. Itis made up of alternate sheets of tinfoil and waxed paper,and functions in the same way that Benjamin Franklin'sLeyden jar performed. It receives the minute charges ofelectricity from the air and stores them up until there areenough to make an impression on the telephone receiver.

17


The detector in the less expensive sets consists of thecrystal, on which rests the point of a fine wire or catwhisker.Sometimes the crystal is silicon, but in general it is galena,the ore from which lead is obtained. In operation, thepoint of the catwhisker is swung around on the surface ofthe crystal until, by the sound of the signals received, it isknown that a "sensitive" spot has been located. Afterthat, the adjustment is not touched, unless by accidentthe set is jarred.

Because of the low selling price of some sets it is notpossible to supply a complete pair of telephone receiversor head phones and only one is sold with the instruments.This is usually a receiver of the "watchcase" type and isinefficient when compared with the special high resist-ance phones designed for radio.

Describing Some of the Moderate Priced Sets

Without doubtmore sets costingaround $25 are inactual use thansets of all otherprices combined,and yet they aresuitable only forstations within 15miles of the radio-telephone broad-casting stations.Their principaladvantages overthe less expensive

A crystal -detectorset in the classcosting about $25

is


sets are in the greater range of the tuner and in the ad-dition of a complete pair of head phones of correct design.By correct design is meant those phones having a highresistance of 2000 to 3000 ohms.

The phrase "greater range of tuner" does not necessarilymean that the distance over which a station can be heardis lengthened, but rather that the number of stations of allkinds that can be picked up is increased.

If a radio receiving set is being purchased for the pur-pose of rendering music and concerts loud enough for thefamily to hear, this will necessitate a loudspeaking deviceand none of the sets so far mentioned is suitable for thiswork.

Sets of Greater Refinement

The radio sets costing about $75 contain an audiondetector, which takes the place of the crystal detector inthe lower priced outfits. A $75 set is made up of a vario-coupler or similar tuning device; a condenser, generallyfixed but sometimes variable; an audion or vacuum tubewith accompanying dry batteries; a storage battery, andthe resistancecoil or rheostatto control theamount of cur-rent sent throughthe little filamentin the vacuumtube.

This vacuum tubeoutfit is from 10 to100 times as sensi-tive as the crystaldetector. It hasthe added advan-tage that it is posi-tive in operation

19

r titRESISTANCE


Since the vacuum tube will be mentioned frequently inthe pages that follow, it will be well to describe it here.The other devices referred to in the preceding paragraphwill be described in detail in the chapters devoted to theadjustment of sets.

The vacuum tube is a glass bulb shaped like an incan-descent lamp but, unlike the lamp, having in addition toa filament two other metallic elements called the grid andthe plate.

The filament, generally of tungsten, gives off, whenheated by the current from the storage battery, a multi-tude of electrons or minute negative charges of electricity.

The grid, of nickel or molybdenum' in the form of a per-forated sheet or a network of fine wires, is connected withthe aerial.

The plate, also of nickel or molybdenum, is merely a

close the filament and grid. As everybody understands,an electric circuit must have a positive and negative ter-minal to be complete. In the vacuum tube the filamentsupplies the negative while the plate is arranged to pre-sent a positive surface. It is connected with the positivepole of the dry battery.

How the Vacuum Tube WorksTo best understand the working of a vacuum tube,

consider the filament as being located at one side of thetube and the plate at the other, with the grid between.When the filament is heated by electric current from thebattery, the little electrons fly off toward the plate, butin so doing they are forced to pass through the grid. Thegrid acts like a traffic policeman. The waves coming intothe grid from the aerial are first positive and then nega-tive, like the alternating current in the home. When thenegative half of the wave comes to the grid, it holds up a"stop" sign to the stream of negative electrons from the

20


A typical vacuum tube, in three stages of construction.A vacuum tube contains three elements: The filamentgenerates electrons, the plate receives them and the

grid controls their flow

filament and refuses to let them pass. An instant later,when the positive half appears on the grid, the electronsare given the "go" sign and they pass to the plate with anadded impetus, because the waves on the grid are addedto those coming from the filament.

During all this procedure the plate is connected througha dry battery to the head phones and every time the elec-trons are allowed to pass from filament to plate, theyproduce an impulse in the phones. These impulses beingcontrolled by the grid, coincide with the wireless waveson the grid and the sound in the phones must therefore

- agree with those sent out by the transmitting station.g. In slightly less technical terms the audion or vacuum

tube may be considered as a very sensitive valve whichworks like a gun trigger. The incoming waves being weakcannot operate the phones, but they are able to trip a

21


trigger, which in turn allows plenty of current from abattery to pass through to work the phones.

In sets around the $75 price there is often included aninstrument marked tickler. A tickler is an auxiliary coilof wire wound on or near the tuning coil and is used onlywith circuits known as regenerative. A regenerative cir-cuit is a particular way of connecting the devices com-prising a receiving set which makes it possible for signalsto be amplified or strengthened in the same tube wherethey are detected. This is accomplished by making someof the current from the plate pass around toward theaerial, through the tickler and back to the grid, adding itsstrength to the weak incoming impulses.

When properly installed and operated, these $75 setswill receive long-distance broadcasts. Records up to 750miles have been reported, but in general their range shouldnot be considered over 75 miles. Although the wave-length range is limited to less than 1000 meters, it is pos-sible, by adding a suitable loading coil, to increase thisrange sufficiently to permit reception of broadcasts fromstations using higher wave lengths. A loading coil ismerely a tuning coil containing a large number of turnsof wire which, when inserted in the wire leading in fromthe aerial, has the effect of adding many feet of wire tothe antenna circuit.

The Ideal Radio Outfit

The receiving outfits in the general class costing some-thing under or over $200 cannot easily be improved upon.With almost any aerial and at great distances fromsending stations, they will pick up the broadcasts andamplify the weak signals to a strength sufficient to oper-ate a loudspeaking device-thus allowing an entire groupto enjoy the concert at once. The tuning facilities insurea minimum of interference from other stations. The sets

22


make a fine appearance and most of them are well builtso that once installed they will last for years, or untilobsolete.

Assuming that the aerial is a normal one of from 60 to70 feet in height and 125 feet in length, these sets shouldpermit the owner to listen in on stations 750 miles away.

This type of set consists of a tuning unit used in con-junction with a detector and two special vacuum tubes.Every tube added to the set in this manner is said to addone stage of amplification. Even though the electricalcircuit employed is complicated to the layman, engineershave simplified matters, and usually the binding postsare plainly marked to enable the beginner to set up theoutfit without expert assistance.

Another feature of this "ideal" set is the readiness

TUNING DEVICEFOR RECEIVING l'T,STACTEBROADCASTS AMPLIFIER

2" STAGEAMPLIFIER

"7 DETECTOR -4 \

SWITCH TO CHANGEWAVE LENGTH

1

VARIABLE CONDENSERS la '"RHEOSTATS TO(ON 1 h'01. I IL'.WREENT

NER

The higher priced set shown above will receive wavelengths from 200 to 20,000 meters. A special tuningdevice brings in broadcasts with unusual clearness.

Note loudspeaker at right23


with which it may be improved by the simple addition ofamplifying units. At the start of the amateur's interest,the two stages of amplification will be sufficient, but manyof the more adventurous will want to widen their contactwith the world by reaching out for the foreign stations

4k

At the upper right of this set are three honeycomb coils,which make it possible to tune in any station by sub-stituting the proper coil. Sets of this quality cannot

be bettered for the advanced amateur

and the broadcasting stations at the opposite side of thecontinent. To operate a station with more than twostages of amplification requires experience, for amplifiersare not particular what they amplify. Not only do theyincrease the strength of signals, but they treat other soundsin the same way. Static, amateur interference, spark ortelegraphic code stations-all are given the same amountof amplification.

Even the tubes themselves are not free from blame.A vacuum tube, when so minded, can produce in the mostmysterious way a weird medley of groans, growls, and

24


howls. All this must be anticipated by the station ownerwho seeks to "step up" the strength of his signals byadditional stages of amplification. During the trans-atlantic tests by the Amateur Radio Relay League thereceiving station made use of ten stages of amplification.Six stages are frequently hooked up, but the beginnershould forswear intricate sets until he has thoroughlyfamiliarized himself with the peculiarities of the simpleroutfits.

25

CHAPTER V

How to Assemble Your Receiving Set

WHEN the science of radiotelephony has advanceda few years, it will not be necessary to erect anoutside aerial. Of course it is possible to do this

now with certain types of outfits, but for the beginner it isnot to be recommended.

Loop aerials, consisting of 10 turns of No. 16 insulatedwire wound around the outside of a boxlike frame, withthe turns VI inch apart, will produce results with severalstages of amplification. Indoor aerials formed by layingseveral strands of insulated wire behind the picture mold-ing in the room are also frequently found to give satis-factory returns. But the beginner in radio who wantsto be more certain of success should leave these odditiesalone and, for the time being at least, put up with theappearance of an outside wire aerial.

In placing the receiving set in the house, the locationof the outside aerial will be the deciding factor. It ispossible to place the set anywhere and carry the wire fromthe aerial to it; but if the distance between aerial and re-ceiving set is great, the leakage of high frequency cur-rents will cut down somewhat the operating efficiency ofthe instruments. In consequence, it is best to place theset near the lower end of the aerial.

Erection of Aerial

The aerial or antenna for receiving purposes is a simpleaffair to erect. It can be placed in position in an hour's time.

26

B.

HOW TO ASSEMBLE YOUR RECEIVING SET

Determine on the location of the upper or farther endof the aerial and pace off the distance on the ground inorder to arrive at a rough estimate of the length of wirerequired. Buy a coil of wire of the necessary length, andtwo small electrose insulators. The kind of wire to buywas described on page 16. Fasten one end of the wirethrough an eye in the insulator and pull through a 10 -inchlength.

Beginning at a point about 1 inch away from the eye,hold the long length of wire firmly and twist the shortend round and round in such a way that the turns lie closetogether. This will make the neatest and strongest splice.Then, with a short piece of the same kind of wire, make asimilar splice through the other eye of the insulator andcarry the wire to the tree, building, or pole that is to beone terminus of the aerial. With end securely hitched,the coil of wire can now be unrolled until the lower end ofthe aerial-the end nearest the receiving set-is reached.

There are two methods of fastening this nearer end.The aerial wire can be cut off short at the insulator and anew wire soldered on for a wire to lead in to the set or,better still, the wire can be passed through the insulator,twisted back on itself several times to prevent wear byfriction in the eye of the insulator and then carried directinto the house. By following the latter method there isno need to make soldered joints anywhere in the aerial,since both the aerial and lead-in wires are of one piece.

Simple Lightning Protection

Up to the present few cities have fire regulations govern-ing the erection of aerials for receiving purposes. Butthe Board of Fire Underwriters, whose authority is recog-nized throughout the land, have suggested that the aerial,house, and instruments can best be protected from light-ning discharges by placing a simple air -gap (see accom-

27


(Insulator

One of the best ways to erect an 1006/40aerial. A single wire is best for thereceiving set. Many other methods of suspension may

be used, providing the wire is insulated from all objects

panying illustration) near where the aerial enters thebuilding. One side of this gap should be carried straightdown into the ground by means of a heavy copper wire ofabout the size of a pencil. The gap makes it possible forthe waves to pass down the aerial and into the instru-ments without becoming grounded, while if lightningpasses down the same aerial, it will choose to hurdle thegap and surge into the ground instead of taking the longerpath through the wireless set and then into the ground.For those who can afford it, an outside switch is neverthe-less a good addition to the equipment for the security itgives, if for no other reason. Its only drawback is thefact that it must be thrown to make connection with theground before the shower arrives-and owners are apt toforget this. In contrast with this, the gap, while not sosure a safeguard, is always on the job and cannot beforgotten.

If possible, the lead-in wire should be brought into the28


house through a hole drilled into a pane of glass. or elsethrough one of the entrance tubes made for the purpose.

Ground ConnectionNext to the aerial in importance ranks the ground con-

' nection. If a water -supply pipe passes near where theset will be located, it can be used. A radiator makes asecond-class ground, but can nevertheless be used withfair success. The large number of pipe joints in heatingsystems makes them less desirable for radio grounds thanthe cold -water pipes. The ground connection is made bycarrying a wire of No. 10 gage from the set to the pipeand wrapping several feet of the bare wire around a placescraped on the pipe. If the binding can be soldered, theground will be improved.

If neither of these pipes is available, a ground will haveto be prepared by driving a 6 -foot pipe into the earthoutside the house or by burying a section of wire nettingseveral feet deep. The area of the netting will dependon the moisture in the soil. If the soil is dry, an area ofat least 100 square feet will be needed. Any buriedground will be improved by embedding it in charcoal,which has the property of attracting moisture, thusmaking the'soil damp at all seasons of the year.

If a driven pipe is used as a ground, scrape a place nearthe top for a ground clamp, which is a flexible metal bandwith patented devices for tightening it about the pipe.The clamp should be soldered in position or protectedthoroughly by many layers of tape, otherwise corrosionwill render the ground useless.

ITo Avoid Near -by Interferences

Almost all communities are in a sense a maze of wires,carrying electric current for house and factory lighting.In many neighborhoods high-tension transmission lines

29


'!

/mulator,'

-Rope

/4 Bore Copper

If the amateur is limited to a short aerial, the additionof an extra wire, as here shown, will improve the receiv-ing powers of his station

are common. These seemingly innocent wires can causea great deal of trouble to the amateur unless he considersand makes arrangements to circumvent them.

In laying out the aerial, the ground should be lookedover for such sources of interference and if possible theaerial should be arranged to run at right angles to thecourse of these lines. When the aerial is suspended inthis way, induction from the other wires-that unseentrouble -making electric force-has least effect. On theother hand, if the aerial runs parallel to the high-tensionwires, the phones of the receiving station will be con-stantly assailed by a continuous buzz known as "inductivehum."

Whether or not near -by trolley tracks will have a badeffect on the receiving set can never be foretold. Duringwet nights there may be some annoyance, but if there areno leaking insulators or bad rail joints, the cars will rarelybother in good weather.

In the suburban districts, where plenty of open spacesabound, there will be no trouble in finding a spot for theaerial, but in crowded city districts the beginner's ingenu-ity is taxed to arrange for the anchorages of an aerial ofsufficient length. It sometimes becomes necessary to

30


string the wire vertically from the building top, down theside wall, with poles projecting from the building to' keepthe wires away from the walls. Signals can be heardwith an aerial of this type, but they will invariably beweaker. Where no other location is possible, the vertical

a wire will give passable service.Finally there is the amateur who can neither arrange

with his landlord for an aerial on the roof nor secure apermit to hang one outside. His aerial must then be ofthe indoor type-one of the various forms of "loops."

Probably the most useful inside aerial will be one madeby laying three or four strands of wire behind the picturemolding of a room. Specially made separators should bepurchased to keep the wires about 341 inch apart. Thewire should be No. 18 single cotton covered. This aerialcan be used with or without a ground attachment, but theground should be used if possible. If the ground is neg-lected, the owner will require the special hook-up de-scribed on page 65.

The second type of loop aerial is similar to the radiocompasses used by vessels to obtain bearings at sea orin foggy weather. Its construction was described onpage 26.

31

CHAPTER VI

How to Adjust Your Set for Signals

NOTE: Consult, on page 50, broadcasting chart and de-scription of the range of various sets, to obtain full infor-mation as to what you should receive with the outfitsdescribed in these pages.

THE motions which must be gone through in tuning-in a receiving set are similar with both elementaryand more intricate types of outfits; but for the sake

of clarity the simple crystal detector set will be taken upfirst.

Crystal Detector Set

It is assumed that the aerial has been erected accordingto the instructions of Chapter V and that a ground wireof about No. 10 B. & S. gage has been carried from theroom where the set will be used to a water pipe or outsideground, and that the connection between the ground wireand the ground has been well made and tightly soldered.The station is now ready to operate.

If the set is one of the types lately improved, the bind-ing posts will be plainly marked. To begin with, takethe wire leading in from the aerial, brighten it with knifeor sandpaper and insert it in the binding post marked"Aerial" or "A." Place the ground wire on the postmarked "Ground" or "Grd." Take the two nickeled tipsof the phone receiver and insert them in the binding postsmarked "Tel." Place the phones on the head to be pre-

32

HOW TO ADJUST YOUR SET FOR SIGNALS

pared for any signals. The next thing is to adjust thetuning coil and set the detector.

Most of the compact receiving sets have a tuning coiladjusted by a circular switch. Set this switch at its mid-point and leave it there for the minute. See that thecrystal is in the detector. Whether it is a galena or asilicon detector, the mineral will have the appearance offreshly cut lead. Another crystal or a piece of fine wiremay be connected in the other part of the detector. Withthe handle on the latter, place the fine wire on the galenaso that it touches lightly. If nothing is heard, move thehandle of the tuner and in the new position manipulatethe detector. If there are signals or radiotelephone broad-casts in the air, a point will soon be found where they areheard. When they are noticed, leave the detector aloneand turn the tuner handle slowly until the signals comein loudest. When this point has been found, experiment

On some crystals there are many such spots, while othershave only a few sensitive places. Once the tuner anddetector have been accurately adjusted they should beleft alone, unless the set is jarred.

Some crystal detector sets are equipped with a tuningdevice called the loose coupler and another called the

The sensitiveness of a crystaldetector is seriously affectedby dust, dirt and oil. The in-teresting detector at the leftis made with a glass coveringover the crystal, to protect itfrom these substances. Thenormal receiving range of sucha set, properly installed andunder favorable conditions, is

about 10 to 25 miles

33


This shows the construction of a vari-able condenser, which consists of twosets of brass or aluminum plates -oneof the sets being stationary and theother movable. The movable platesrotate inside the stationary plates with-out touching them, thus varying the

electrical capacity of the circuit

variable condenser. A loose coupler consists of two tele-scoping tubes, both wound with one layer of insulatedwire. The outer coil, called the primary, has a pathscraped bare along its entire length on which a slidingcontact rests. The inner coil, called the secondary, isentirely separate from the primary. Sometimes the in-dividual turns of the secondary winding are brought out-side by means of flexible wires and connected with a cir-cular "switch having many contact points, but more fre-quently the secondary is wound without taps. A circularswitch consists of a short, narrow strip of metal held by a

This diagram shows asimple way to test theadjustment of your crys-tal set. These sets mustbe frequently tested forsensitiveness. A buzzercircuit arranged accord-ing to this diagram, asdescribed in the text,provides a method bywhich the most sensitivespot on the crystal canbe found and maintained

Run Wire for1272/onOicleAerial or Ground Wire.Separate I.?

--Buzzer

DryBaffery

I I

`Push &lion

34


pivoting screw at one end and with the other end free to

move in a circular path. Along this circular path and

separated so that they do not touch one another are anumber of flat headed screws. Each screw is connectedin order with a tap from the coil winding so that by rotat-

ing the switch the number of turns used can be varied.

Tuning is accomplished with the loose coupler by slidingthe inner or secondary coil about halfway out and then

\BuzzerPush &Mon

A complete receiving layout, as fully described in the text35


moving the slider on the outer or primary coil until signalsare heard. The secondary is then moved in or out untilthe signals are loudest. The new position of the innercoil may require a second adjustment of the primary be-fore the point of greatest signal strength is located.

A variable condenser consists of a series of stationaryand movable brass or aluminum plates so arranged thatthe movable plates may slide between the stationary ones.All of the latter or permanent plates are connected,as are also those that rotate. When one set of platesis all within the others, the capacity (see Glossary formeaning of term) is at its maximum; when the movingplates are all outside, the capacity is zero.

The variable condenser is set at zero until the tuninghas been made clear and sharp by means of the loosecoupler. Then the condenser is rotated to the pointwhere signal strength is greatest.

The Buzzer Test

It will be apparent that any method of searching forthe sensitive spot on the crystal, without knowing whgnit has been found, unless signals happen to be in the airat the time, could be improved upon. There is a simpleattachment by which the detector can be adjusted withcertainty and the entire attention given to tuning. Allthat is necessary is a buzzer, a pushbutton, and a drycell. Connect the buzzer with the pushbutton and bat-tery as in any bell circuit. Then connect a second wirewith the left-hand binding post or the vibrating point ofthe buzzer and run this wire alongside the aerial wire fora foot or two. When this has been done, it will be noticedthat if the pushbutton is pressed when the detector isadjusted, a clear note will be heard in the phones. Thus,when operating the set, the buzzer can be used to tellwhen the most sensitive spot on the crystal is touched.

36


No harm can come to the coils of the outfit through usingthis simple test, as the waves are produced by inductionfrom the wire running alongside the aerial wire.

What to Look for if Nothing Is Heard

If no signals of any sort-either radiotelephone or tele-graph code-are heard, try out the buzzer test to makesure the detector is properly adjusted. If no sounds areheard even then, the trouble lies somewhere in the setitself. Look over all connections and see that the wiresare bright and firmly attached. Be sure that you haveplaced the different wires in their proper places. Lookover the phones, but do not remove the caps. If there istrouble with the fine magnets inside the phone cases, theyshould be returned to the manufacturer. All you can dois to see that the tips of the cord have not dropped out ofthe holes in the receivers.

It is not always a sure test to touch the phone terminalsto a battery circuit. Often they will respond to theseheavy currents and refuse any action whatsoever whenin a radio circuit. If there is an experienced radio ama-teur near you, have him try out your phones with his ownset, to check up on their sensitiveness. If the trouble doesnot exist in the phones, then it is hidden somewhere in thecoils and the set should be .returned to the store.

If the detector will not remain in adjustment, it maybe due to too much or too little pressure on it. The sur-f ace of galena is quite soft and heavy pressure will flakeaway the sensitive spot. On the other hand, a pressurethat is too light will not hold the fine wire or catwhiskerin position, and at every slight jar the wire will move.

If the signals suddenly stop and then start again, re-peating the action frequently, there is a bad connectionsomewhere in the set, probably in the aerial or ground,although a loose phone terminal might cause the trouble.

37


A Variocoupler -The wire -wound ball inside the outertube of the variocouplerchanges its position by rota-tion. This action is necessaryto tune the wave length of thereceiving station with that ofthe sending station. There isno connection between the

two coils

How to Tune the Audion Set

The perfecting of the vacuum tube and the develop-ments that have taken place since its advent have openedup a wealth of possibilities. The tube is used in a hun-dred different ways and with a thousand varieties of hook-ups. So varied are these that in a handbook of this na-ture it would be impossible to discuss them in detail. Theowner of a receiving set consisting of one or more stagesof amplification must study the instruction books just asa motor -car owner studies automobile treatises. Ourtreatment of the "v. t." sets will be confined to outfitsusing only the tube as a detector.

There are two principal types of vacuum -tube detectorsets, the most common being those employing the "straightaudion circuit." The second class makes use, by permis-sion, of the patented "regenerative circuit," so called.

In the straight audion circuit the tuning facilities areprovided by a simple tuning coil, a loose coupler, a vario-coupler or a variometer. It is also possible to use two ormore of these devices together, as will be noted in thechapter on hook-ups.

A variocoupler consists of two coils, the smaller swing-ing on a pivot inside the larger. Both are wound with

38


Broadcast Variocoupler -Some sets are not designedto tune -in the broadcastedentertainments. For theseoutfits a device such as theone at the left is added tothe set for this purpose. Itconsists of a tube with a ro-

tating coil at each end

wire, about No. 18 B. & S., but the only connection be-tween them is by magnetic induction. The two coils inreality constitute a fraiNformer, except that the vario-coupler "secondary" (the inner rotating part) is able tochange its position with respect to the outer coil and yetmaintain a short distance between the two coils of wire.This feature is essential to obtain close tuning and highreceiving efficiency.

In general, the primary is wound with "contacts" takenoff every half dozen turns. These contacts are carried toa circular switch so that the number of turns used maybe varied according to the wave length of the stationbeing received. The secondary is seldom, tapped. Thevariation there is secured by rotation.

A variometer appears much like a variocoupler. Ithas one coil that swings inside the larger one. The prin-cipal difference lies in the fact that the variometer coilsare connected so that the current goes first through theouter coil, then passes through a short flexible wire to thesecond coil. When the two coils are parallel, the effectis practically the same as if all the wire had been woundon one coil. But if the inner coil is swung slightly, theinductive force commences to have an effect. The cur-rent induced in the inner coil tends to obstruct the passageof the current in the circuit. When the inner coil hasbeen swung one half turn, the induced current will com-pletely obstruct or "buck" the flow of current in the cir-

39


cuit. By altering this "bucking effect," the induction inthe circuit is changed to supply the exact amount requiredto give the receiving set the desired natural wave length.

With every audion set, whatever its characteristics, astorage battery of 6 volts, a low -voltage resistance andone or more cells of 22 -volt dry batteries, generallycalled B batteries, must be used. The storage battery isused to heat the filament of the tube. The resistance, orrheostat, controls the current passing through the filamentand the dry cells supply the voltage in the plate and phonecircuit.

In this connection it should be clearly understood thatthe vacuum tube will not detect unless the plate is con-

A Variometer - Variometersprovide an additional tuningdevice with fine graduations.In this instrument the innerand outer coils of wire are con-

nected by a flexible cable

netted with the positive pole of the 22 .!-volt B battery.An easy way to remember this is to consider the two p's(plate and positive) as going together. It is advisable tomake certain that the filament is properly connected also,although a difference in the polarity will not entirelyeliminate the signals. The grid is always connected withthe wire leading from the tuning device.

The procedure to employ in tuning an audion set isreally simpler than in the case of the crystal detector set.In order to protect the tube many firms advise connectingthe aerial with the ground just before connecting theaerial with the receiving set. This carries off any heavy

40


charge that may have accumulated on the aerial during itsperiod of inaction.

The first thing to do is to see that the filament rheostatis at its "zero" position before connecting the storage bat-tery, otherwise the rush of current through the filamentwould surely burn it out.

Don't Burn Vacuum Tube Too Brightly

"Light up" the filament slowly by rotating the rheostathandle. Do not let it burn brightly. This is not neces-sary to get good results. Place the phones on the headand adjust the tuner. If you have arranged the buzzertesting equipment, this should be tried to see that thevacuum tube is functioning. When this has been triedand proved, no further attention need be paid to the tube.Simply move the tuning device until the signals arebrought in at their loudest.

Sometimes stations sending telegraphic code can bereadily picked up, but no radiotelephone broadcasts. Ifthis is the case, first make sure that some station whichyou should hear is on schedule. Listen for it at the low-est point on the tuning coil. If nothing can be heard, itis probable that the wave length of your station is toohigh. Many broadcasts are sent on 360 meters and ifyour set will not tune down below 400, it is certain thatyou would hear nothing. All that is required to correctthis fault is the insertion of a variable condenser in thewire leading to the ground. Cut the ground wire andplace the cut ends on the variable condenser. By throw-ing out the plates and then gradually swinging them in,the broadcasts will finally be heard.

If it is ever desired to listen in on a station of consider-ably longer wave length, the same variable condenser canbe used, but its location should be around the primaryof the tuning coil.

41


Troubles with an Audion Set

After you have learned the ways of radio you will nothesitate to speak of "oscillations" in the vacuum tube.But as they are neither heard nor seen, it is not alwayseasy for a beginner to determine if his tube is doing itsduty. There are many kinks used by experienced oper-ators. One is to wet the finger and press firmly on thebulb. If the tube is oscillating, it will buzz angrily in thephones. But the best and most reliable method is tohook up a simple buzzer as described above in this chapterand note whether the tube responds to local signals.

If the tube will not function, look first to the connec-tions of the A (storage) battery and B (dry) battery.See that the positive terminal, marked +, of the B bat-tery is connected with the plate of the vacuum tube.Trace out the storage battery wires and make sure thatthe positive wire is connected with the binding post onthe tube socket or cabinet marked +. If there is morethan one cell in the B battery, look over the connectionsto see that the cells are not bucking one another as wouldhappen if the plus terminals were not connected with theminus posts.

With all the connections checked, there is still the pos-sibility that the voltages of the batteries may not be upto normal. The one and only way to prove this is bymeans of a low voltage voltmeter, an instrument thatshould be in the tool kit of every owner of v. t. stations.

Assuming that all these possibilities have been traceddown without result, the trouble lies either in the im-proper manipulation of the tube circuit or in a faultytube. If you are in the habit of burning your tube athigh brilliancy, try it at cherry red; or if you have refusedto shorten the life of your tube by burning the filamentat white heat, try it out at that current density. It maybe that the tube is one that demands full voltage.

42


Vacuum tubes are wonderful devices, but they have morewhims than all other apparatus combined, and it is onlyby careful, thoughtful experimentation that a stationowner learns how to get the most from his outfit.

A Test for Vacuum Tubes

And, lastly, if none of the foregoing suggestions bringsresults, take your tube to a radio store where broad-casts are being received and have it substituted for oneof the tubes in .the demonstration set. This method willdetect faults instantly.

All vacuum tube sets must be sensitively controlled.Remember that you are dealing with electrons-the small-est possible particle of electricity-and that it requiresbut little external force to send them on the wrong path.A crystal set can be roughly handled without lasting re-sults, but a vacuum tube must be nursed along duringits entire life, which under proper supervision should beover 1000 hours. Turn on the filament current slowly.When through with the set, don't disconnect the batteryuntil the filament rheostat has been turned back to zero.The possibility of trouble does not lie in cutting off thecurrent suddenly, but rather in the chance that when thestation is next opened the position of the rheostat will beoverlooked and the full 6 volts thrown into the filament.

Many of the audion sets now sold in cabinet form havethe unusual Armstrong regenerative circuit, named afterits inventor, Mr. E. H. Armstrong, and licensed by himfor amateur use.

In the regenerative circuit, as mentioned previously,the potential on the plate of the tube is led around andfed back to the grid. As the plate potential depends onthe grid potential, it will be seen that the regenerativecircuit does what its name implies, viz., feeds back andregenerates or strengthens the incoming signals. The

43


advantage of the regenerative circuit is computed to beequal to one stage of amplification. Thus a regenerativecircuit with one stage of amplification would be the equiv-alent in actual signal strength of a non -regenerative outfitwith two stages.

In regenerative circuits there will be found a coil termedthe tickler. Many station owners are using a tickler todaywithout knowing its functions or how it is placed in theset. This is not important, but an understanding willenable the operator to produce better results.

The tickler is a small coil entirely separate in mostcases from the primary and secondary of loose coupler orvariocoupler and placed near one end of these tuningdevices. In sets receiving only the short waves frombroadcasting stations, the tickler coil is about the samesize as the secondary of the coupler. This coil picks upsome of the magnetic lines of force and adds the potentialthus induced to that of the plate.

Manipulation of Dials

In adjusting a regenerative set, the tickler is held atzero until after the signals are brought in as loud as pos-sible with the other tuning devices and then varied untilthe regeneration is at its maximum. When this has beenreached, it may be necessary to tune still finer with thevariable condenser and sometimes with the loose coupleror variocoupler.

For the benefit of those to whom the inside of a receiv-ing set is a complete mystery and who are principallyconcerned with "making the thing talk," the differentsteps in setting up and adjusting a vacuum tube receiv-ing set consisting of a regenerative circuit with two stagesof amplification, will now be discussed.

The tuning knobs and dials will be found at the extremeleft of most sets. There will be notations under them:

44


"Tuner," "Vernier" and "Tickler." Follow the direc-tions with the set as regards the connections from the Aand B batteries to the cabinets. If a loudspeaker is used,connect it with the terminals marked "Second Stage."Do not plug the phones into the terminals except at thedetector, unless you wish to pick up distant signals andare sure that no local station of high power is transmit-ting. The danger is not to the instruments but to theeardrums.

To Control Current in Tubes

At some place on the detector cabinet will be found aknob or dial marked "Fil. Rheo.," or with the words,"Increase -Decrease." These terms, or any variation ofthem, refer to the resistance coils controlling the amountof current through the several vacuum tubes.

When the set is ready, turn the filament rheostats fromthe zero point slowly and watch the vacuum tubes throughthe porthole in the cabinet. Do not turn "full on," buttry it first at the three-quarters point. Sometimes onedial controls both tubes in a two -stage outfit; this simpli-fies operation, but for general work the separate rheostaton each tube will permit of closer control.

When the detector tube and the two amplifying tubeshave been brought to three -quart 3rs brilliance, leave themfor the moment and give attention to the tuning cabinet.

Set the tuner so that the pointer is at the center of thescale. This applies to short-wave sets only. Leave thevernier at zero. Listen closely and if no sounds are heard,turn the tuner slowly, first toward one terminus and thentoward the other. If you are testing out your set duringthe evening, when there are broadcasting stations in oper-ation, a point will be found where signals, perhaps faint,

wk, will be heard. Adjust the dial until these sounds areJogdest. Move the dial marked "Vernier" until the

45


signals reach their maximum and then do the same withthe tickler. A great difference in the signals will now be

noticed. When the sounds have been brought to theirhighest intensity, go back to the vacuum tubes and care-fully manipulate the rheostats until the signals are clearcut and the words or music well toned. Make a note ofthe settings of all dials and knobs. A knowledge of thiswill help you in tuning thereafter.

The foregoing detailed description of the procedurewill, of course, vary somewhat with every set, as the dif-ferent circuits employed make use of a variety of instru-ments, but in general the order to be followed is the same.As has been stated so often before in these pages, it isonly by constant experimentation that the fine points ofa set can be learned.

Loudspeaking Devices

When broadcasted concerts, musical programs, and

speeches can be sufficiently amplified to permit it, theradio amateur's equipment, to be complete, will include

a loudspeaking device. The loudspeaker delivers thesounds loudly enough for all those assembled in the roomto hear. It is particularly well suited for halls and audi-toriums and for dancing in private homes. There aremany such devices on the market varying in price from$5 to $100 or more. None will work with a crystal detector.

The simplest loudspeaker consists of a simple mega-phone horn shaped with a special attachment in the baseto take a phone receiver. Two stages of amplificationwill increase the intensity to a point where the phone inthe base will vibrate loudly and the sounds passing throughthe tone chamber of the horn are further increased in vol-

ume. These horns find their greatest application where

it is desired to entertain a small roomful of listeners.Unless many stages of amplification are added, it would

46


be inadequate for dancing or for auditoriums, for whichpurposes other models are used.

Loudspeakers delivering the sound in greater volumework on an entirely different principle. The electricwave impulses are strengthened and made to vibrate adelicate diaphragm suspended between two magnet coils.The movement of this diaphragm is communicated to alarger diaphragm by means of a series of levers. Thelevers magnify an infinitesimal movement of the delicatediaphragm many times. Between these two extremes ofloudspeakers are a score of others using the principle ofone or the other or in combination.

Pertinent Suggestions

In fairness to the industry as well as to the individualpurchaser of radio equipment, there are several pointsconnected with the merchandizing of radio receiving setsthat should be borne in mind.

Nine out of every ten beginners ask the salesman thispertinent question, "How far will this set receive?" Inreply the salesman frequently says: "A man living 150miles away from KDKA (or other broadcasting station)is using one of these sets and gets all the broadcasts."

Such a statement should not be taken literally. Be-c,a,use one man is able to hear 150 miles with a particularset, it does not signify that another can do it. As a mat-ter of fact, the receiving range of a set is not a fixed quantity.Once in a while an amateur hears POZ-the powerfulGerman station at Nauen-and does it all with a crystaldetector. Others less fortunately situated cannot coverelk 50 miles with a similar set.

It is easy to learn how far a set ought to receive andbase the purchase on that, but there is no surety, andnone can be given, that a set in itself will perform over aspecified number of miles. For, remember: the trans-

47


mitting station has a great deal to do with it, also thecountry over which the signals must travel. As one con-crete example: A well known broadcasting station is reg-ularly heard in Canada -400 miles away-but in a city60 miles distant only the most sensitive sets are able topick it up. Why this is has not yet been satisfactorilyexplained. It may be due to metal deposits in the groundthat filter off the waves, or it may be caused by naturalscreens of a type so far unrecognized.

Don't expect too much of a loud speaking device.Many give excellent results, but a vacuum tube set withtwo stages of amplification is generally necessary.

There is one safe rule to follow in determining the type

of set to install. It is, "Learn what others in the vicinity

are using." Find an amateur near by and visit his sta-

tion. Learn from him at first hand what instrumentsare needed to receive broadcasts. Listen in on his equip-ment and decide for yourself whether you would be satis-fied with a station as good as his or would need a better

one.Among all radio enthusiasts there is a strong link of

friendship and courtesy and it is seldom that one meetsan amateur who is unwilling to help his brothers in everypossible way. With the assistance now available in every

state from coast to coast there is no reason why the be-ginner should not capitalize it. In doing so he practi-cally assures himself of success.

48

CHAPTER VII

What Radio Stations You Can HearTHE information on this page, and reference

to the map on the following page will giveyou an idea of what great broadcasting

services cover your vicinity, and what sort ofradio set you should purchase to hear them.

If your aerial is properly erected, your setefficiently installed, and atmospheric conditionsfavorable, you should be able to hear:

10 miles with a crystal detector outfit, costing about$15 to $25

50 miles with a vacuum tube set, costing about $60to $80

200 miles with a two -stage set, costing about $130to $175

500 miles with sets costing $250 and overAny one of these sets may prove to have a much

greater range than indicated.

Leading Broadcasting CentersSome of the leading broadcasting stations shown on

the map (page 50) together with their call letters, arethe following:KDKA-Westinghouse Elec. & Mfg. Co., E. Pittsburg, Pa.WJZ -Westinghouse Elec. & Mfg. Co., Newark, N. J.WBZ -Westinghouse Elec. & Mfg. Co., Springfield, Mass.WWZ -John Wanamaker's Store, New York, N. Y.WVP -Signal Corps, Fort Wood, Bedloe's Island, N. Y.WGY -General Electric Company, Schenectady, N. Y.WGI -American Radio & Research Corp., Medford Hillsides, Mass.NoF -Government Station, Anacostia, D. C.KYW -Westinghouse Elec. & Mfg. Co., Chicago, Ill.WHA -University of Wisconsin, Madison, Wis.9YA -University of Iowa, Iowa City, Ia.WOQ -Western Radio Co., Kansas City, Mo.9YY -University of Nebraska, Lincoln, Nebr.\VRR -City of Dallas Station, Dallas, Texas.5ZU -State University, Austin, Texas.

(Concluded on page 51)

49

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d 51

WHAT RADIO STATIONS YOU CAN HEAR

(Concluded from page 49)

WRW -Tarrytown, N. Y.WWJ -Detroit News, Detroit, Mich.WLB -University of Minnesota, Minneapolis. Minn.KZY -A -P Radio Supplies Co., Rockridge, Oakland, Cal.

On this broadcasting map the average range of eachstation, under normal conditions, is indicated by thecircles. The small inner circle represents a 25 -mileradius, the limiting distance of a good crystal set. Theshaded circle, with its 100 -mile radius, denotes the ter-ritory that can be covered by a single vacuum tube set.The large outer circle of the 500 -mile radius representsthe receiving range of outfits costing around $200.

The Standard Broadcasting MapA larger broadcasting map, giving more complete

details, has been prepared by POPULAR SCIENCEMONTHLY for amateurs who wish to maintain a recordof radio stations heard. This map shows the outlinesof the states in size large enough to permit the use oftacks to indicate the location of stations. The priceis 25 cents.

Further information regarding this map, or any ofthe broadcasting stations, can be obtained from theInformation Department, Popular Science Monthly,225 West 39th St., New York, N. Y.

51

CHAPTER VIII

How to Make a Crystal Detector Set

NOTE-The symbols used in the wiring diagrams in thisand following chapters will be made clear to the beginnerby reference to pages 12 and 13.

LL who have read carefully the foregoing chapterswill realize at once that this set is suitable only foramateurs living within 15 miles of the broadcasting

stations. If the aerial to which it is connected is betterthan the average, a crystal detector set of this type canoften be made to pick up concerts and other phone broad-casts 20 or 25 miles away, but the chances are against it.

The crystal detector does not admit of so many varia-tions in hook-ups as the audion, but in the circuit aboutto be described the detector has been inserted in thetuning circuit in a manner that makes possible extremelysharp tuning.

To begin with, secure two pieces of cardboard tubing,one piece 3 inches in diameter and 2 inches long, and

ONE TURNOF TAPE

TAPE CUTCLOSE TOWINDING

WINDING

(7

WIRE TO BEWOUND ON

' END OFWIRE

Fig. 1This diagram willaid in winding thecoils for the crystaldetector receivingset described in

the text

52

HOW TO MAKE A CRYSTAL DETECTOR SET

Fig. 2The tuning coil for thisset is unique and simple lf:T:tiT1to construct, in that thesecondary does not ro-tate inside the primary, in7.""

but beside it

tousyla:Vt.U0 Non

aratr, ,peA r.VMS'0 va,91,:q

INMS 1U311.0

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the other 2 2 inches in diameter and 1,2 inches long.Wind with short strips of tape as illustrated in Figure 1.The idea of the tape is to make the coil winding easier byproviding a yielding surface to grip the wire.

Buy 16 pound of No. 26 double cotton covered magnetwire. The same size is used on both coils. On the largertube, marked Li in the drawings, wind 105 turns, tak-ing taps off at the twentieth, fortieth, and sixtieth.These taps can be best taken off by using a small 'gimletto punch a hole in the tube through which a loop of thewire is led. In this way the tap can be taken off withoutcutting the wire. A simple method of anchoring the wireat the start and finish is shown in Figure 1. It consistsin making three small holes in a row and drawing thewire down and up through the openings, thus clinchingthem rigidly.

SCALEs-44.-- 6.-.- 3':--1

7._1_

0 3"

11

.P., PRIMARY COND. SECONDARY COND

I PRI. IND. I, ;Ao

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T3.

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I 1 TU. ING 0 ----4-STOPPINGS'S CONDENSER

1Gi FLAT c.SHARP

o -41/v4PSAI

Vii_Ar2. -t-7144

Fig. 3-One type of layout for the panel front53


The secondary coil, L2, is formed by winding 60 turnswith taps taken off at the fifteenth, thirtieth, and forty-fifth turns. When completed, the secondary is attachedto a special suspension, which allows it to be rotated byits coupling knob. The distance between the primaryand secondary coils has been selected so that when rota-ted at right angles the coil L2 will pass slightly within theopening to Lt.

The detail of the detector is sufficiently plain withoutgoing into further instructions. The base may be made

BRASS CUPCRYSTAL SET IN

ViRO WOMB METALCAT WHISKER OF/MANDOLIN STRINGWIRE(SILVER-PLATED STEEL)

SWIVEL

1111100-iLlatJOINT

SPRINGWASHER,

RETAINING--

FIG.4II N 3ISSPRING

A simple crystal detector that can bemade with familiar tools found in any

home workshop

of wood or any of the composition boards on the market.The VI inch square brass supports will need some machinework for the swivels, but if this is difficult to obtain, thenovice should understand that a deviation from the detailswill not affect the operation of the set as a whole.

For the detector crystal, either galena, silicon, radio -cite, or the double crystals-zincite and chalcopyrite-may be used. The crystal is held in a small metal cupby Wood's metal or any other low melting solder. Bymeans of the knob the cup may be turned in any positionand held there by the set screw.

54

HOW TO MAKE A CRYSTAL DETECTOR SET

GROUND

TELEPHONE RECEIVERS20,000 OHMS IMPEDANCEAT 1000 CYCLES A SEC.OR 2000 OHMS RESISTANCE

CRYSTALDETECTOR

STOPP NG CONDENSER

(002 MED200 MICR(i MICROFARADS

Fig. 5-Wiring diagram of crystal de-tector set described in this chapter. Its

receiving range is limited to 25 miles

The catwhisker is adjusted by turning the handle orsliding the rod through the support. The brass spring isfastened to the support and presses on the catwhisker rodso that it will stay put in any position. The rod is alsocapable of swinging on the swivel, which is made to stayin any desired position by the spring washer.

By purchasing two switch knobs and four switch con-tacts for each knob, the taps that were taken off fromprimary and secondary coils can be led to the rotaryswitches and the tuning controlled from the panel. Withthis done it is necessary to purchase two variable air con-densers of .00075 microfarad capacity each, to completethe set.

Figure 5 shows a diagram of connections. It will beseen that the detector, instead of being connected directlyacross the secondary, as is generally done, is placed acrossonly a portion of it. This feature lifts the set from theordinary and gives it a selectivity that can be improvedonly by a well adjusted vacuum tube outfit.

55

CHAPTER IX

How to Make a Vacuum Tube Set at Home

ALTHOUGH the inherent sensitiveness of the vac-uum tube detector is greater than that of the crystaldetector, this difference is not considered as having

as great weight as the fact that the vacuum tube outfitcan be expanded by adding parts until it is as sensitiveand selective a set as one could wish. Expressed in per-centages, the vacuum Eube may be 50 per cent more sen-sitive than a galena detector, but the signal strength fromthe latter is fixed and can be but slightly improved, whilethe impulses from a vacuum tube can be "stepped up"repeatedly by adding stages of amplification.

This set was designed to be made in the home work-shop. The types of coils have been selected because theycan be wound at home and mounted out of odds and endsalready at hand. The wire, the vacuum tube, the storageand the dry batteries must be purchased, but the totalcost of these parts will not exceed $30. When finished,the set will equal those on the market costing $100.

To begin with, buy pound No. 22 single cotton cov-ered magnet wire. The same wire is used on all the coils.Procure a cardboard or fiber tube 15 inches long and 4inches in diameter and cut it into three equal sections.In addition, you will need a 9 -inch length of 31A -inch

t"tubing, cut as before in three sections. fTake one of the large tubes and beginning at a point

1 inch from the end, wind on the wire in one layer untilyou have 50 turns. At the start take off a tap every turn Vfor 10 turns and thereafter only at every tenth turn. The

56

HOW TO MAKE A VACUUM TUBE SET AT HOME

%TURNS A20 WCIRCULAR BASECOPPER WIRE IINSIOETUBE 10 TURNS IS TURIN 3

0 9 1) o

r 1

FIGI FIG 2 FiG 3BACK V ENV

Back view of vacuum tube set, showing thevariocoupler and two variometers in place

best way to take off taps is to punch two holes under thewire, then push through a loop, bringing the loop up againthrough the other hole. Leave about 4 inches of the loopoutside for attaching to the switch.

The taps from the first 10 turns ire carried to a switchcalled the "units switch." The taps from the other turnsare connected with a "tens switch." Thus, if it is desiredto use 46 turns on the primary coil, the "tens switch"would be placed on the fourth point and the "units switch"on its sixth point. This arrangement permits of closetuning.

When the primary has been completed, take one of thesmall coils and, commencing about inch from the edge,wind on 15 turns, then fasten the wire solid by passing itdown and up through two holes, but do not cut the wire.Leave 1A inch, then carry the wire across the gap thus

GR DCONDENSER

TOP VIEW AND LEAK UNIT

View of the vacuum tube set, lookingdown upon the apparatus

57


left and wind on 15 more turns. The gap is for the brassrod that passes through both primary and secondarycoils. When both coils have been completed, insert an8/32 -inch threaded brass rod, slipping on nuts to hold thesecondary firmly to it. On one end of the rod attach aknob of some sort so that the secondary may be revolved.This completes the variocoupler. The next items are thetwo variometers, both alike and without taps.

On the large tubes wind 20 turns of the wire, 10 turnson each side of the swivel rod. On the small tubes windthe same as for the variocoupler. Insert the brass rodsand connect one end of each larger coil to its correspond-ing small coil, making one continuous winding. All thatis now necessary to finish the set are the vacuum tube,the grid condenser, and the batteries. The most expen-sive of these is the storage battery, but often it is possibleto use a 6 -volt storage battery from the automobile.

A vacuum tube requires about one ampere. Thismeans that a storage battery of 80 -ampere hour capacity

STATIONARY VARIOMETERCOILS

STATIONARY GRID CONDENSERCOIL AND LEAK UNIT'

Wiring diagram for the vacuum tube outfit

should operate a tube for 80 hours on one charge. Thebest dry cells are those sold especially for radio under thename of B batteries. The voltage required is about 22.

Although it is not necessary, a panel on which theswitches and knobs are mounted improves the appearance

58

HOW TO MAKE A VACUUM SET AT HOME

A suggestion forlaying out thefront of the receiv-ing panel in thevacuum tube set

COUPLINGKNOB

SINGLE GRID PLATETURNSWITCH VARIOMETER KNOB VARIOMETER KNOS

ACUUM TUBE u3LE

L BINDING -POSTS FOR RECEIVERSGo FOR 20 -VOLT BATTERY

o 0..--** ss-wo 9. ,9 9.I 1

FRONT VIEW BINDING -POSTS FOR4 -VOLT BATTERY

of a set. The panel may be of hard wood, fiber, hardrubber, or any of the patented compositions on sale atradio shops. Plan out the appearance of the front andthen bore holes for the rods. When completed, the panelwill look like the sketch above.

The diagram of connections for this set is shown onpage 58 and the method of setting up the set and adjust-ing it may be copied from Chapters V. and VI.

Observe These Warnings for SuccessIn conclusion, it would be well to heed the following

warnings:Don't try to hook the filament of the vacuum tube tothe house -lighting circuit, even when a toy transformeris used.Don't expect to throw the parts together and still getgood results. Professional workmanship is not essen-tial, but the outfit will reflect the intelligence used inassembling it.Don't be afraid to use solder when making connections.The vacuum tube will notify you of all bad connectionsby a persistent series of groans and squeaks.Don't expect to hear 500 miles with the set. You willneed several stages of amplification to do that. Masterthis simple set first.Don't stint your aerial on your ground. The higherand longer an aerial can be made, the better and farther

59

THE STANDARD RADIO GUIDEyou will receive. A ground can never be quite goodenough unless you have access to a deep well and candrop a wire into the water without a long run.

Careful study of this entire guide will make it apparentthat the task of constructing your own set is not so dif-ficult as may seem at first glance. If, however, anyreader encounters problems that he cannot solve, aclearly worded letter to the Information Department ofPOPULAR SCIENCE MONTHLY will bring him all helpwithin the editor's power to give, while in the columns ofthe magazine itself he will find much additional informa-tion of prime value to all interested in radio.

Vital Help in Making a VacuumTube Set

COMPLETE working drawings of an efficientradio set, with two stages of amplification,

normally having a possible receiving range ofseveral hundred miles, have been prepared inblueprint form by the radio experts of POPULARSCIENCE MONTHLY. This sheet, containing billof materials, dimensions in detail, and othernecessary helps to the beginner, is obtainablefrom the Blueprint Editor of POPULAR SCIENCEMONTHLY. Send 25 cents and ask for Blue-print for Vacuum Tube Set.

No matter how helpful a textbook may be tothe new radio fan, individual problems oftenarise that require special attention from an ex-pert. The Information Department of POPULARSCIENCE MONTHLY stands ready at all times togive help along these lines to readers.

60

CHAPTER X

A Few Facts about Transmitting Sets

ACERTAIN percentage of amateurs will not be sat-isfied with possessing only a receiving station, butwill feel that the cycle of their enthusiasm must be

completed by adding a transmitting set. This certainpercentage is sure to be pretty well scattered over thecountry and, lest the attempts of these amateurs to trans-mit interfere with the broadcasting activities of the com-mercial companies, the government will no doubt find itnecessary to step in with strict regulations governing thedesign and operation of sending outfits.

What an amateur music broadcasting station lookslike. The horn conveys the sounds to the sensitive

transmitter and vacuum tube(1

Get this Blue Print and Make

$125 Set for $40This blue print presents a two -stage regenerative re-

ceiving set complete with working drawings, instructions,and bill of materials, that a professional would be proudto own; it is the equal of any on the market. It com-prises an Armstrong variocoupler and two-variometer-re-generative tuning circuit coupled, if desired, with twostages of audio frequency amplification. The tuningcoils have been selected because of the ease with whichthey may be constructed at home.

In this set have been incorporated the best features ofseveral types of outfits. It will tune from 180 metersto about 600 meters. It should hear for 500 miles.

Price 25 Cents, PostpaidPopular Science Monthly, 225 W. 39th St., New York

Needed with Every Radio Set !Popular Science Monthly's Standard

BROADCASTING MAPof the United States

You need it before and after buying a radio set, because:It shows just what radio programs can be heard in your

region; it explains the kind of receiving set you must buyto hear them.

It shows you all the big broadcasting stations youshould try to "tune in" on; it gives you their call letters;it gives you their addresses, so you may write for com-plete programs; it helps identify the new stations youpick up by chance.

Every owner of a radio receiving set discovers sooneror later that the Standard Broadcasting Map of theUnited States is a necessary part of his equipment.

You can get yours NOW by writing for it to PopularScience Monthly, 225 West 39th Street, New York City,enclosing 25 cents.

62

A FEW FACTS ABOUT TRANSMITTING SETS

One fact is quite certain and that is that if amateursare allowed to broadcast telephonic material, they will berestricted to the lowest possible wave length-somewherebetween 100 and 200 meters. Such a law would workautomatically to discourage them, since resources andability would be taxed to keep the wave at this low figure.

Admittedly, a transmitting station is a worthy adjunctto a good receiving station, but the cost of installationand the later cost of upkeep and operation will deter mostamateurs from attempting it.

A commercial broadcasting station costs about $10,000to install and about twice that amount in yearly expenses,not including the small fortunes paid to artists whosetalents are sent out on the air.

An amateur transmitting station with a range of 75miles costs approximately $1000, and the replacementsof power vacuum tubes added to the current cost, if thestation is much used, would consume an equal amountyearly.

For the present, while the science is developing so rap-idly and the regulations of both amateur and commercialstations are in a state of flux, it would seem undesirablefor the average beginner to think of adding a transmittingset. Prudence suggests that he leave the important workof supplying entertainment to those companies able todo it best. The amateur in his own way can make radio-telephony more valuable to the world by extending thebenefits of his receiving set to others who are not sofortunate as to possess the necessary apparatus.

63

CHAPTER XI

Important Tricks and "Trouble Spots" in Radio

ONCE you have been using a radio receiving set fora short time, you will find that there are numerousvariations in the layout of the set that may make

it serve you more satisfactorily. You will learn, also, ofmany "trouble spots" to watch over especially, and willdiscover little tricks that insure better reception or doaway with some of the minor troubles that frequentlyplague the beginner.

The diagram on page 65 will help you, as you becomemore familiar with the pastime, to experiment with sev-eral of the most effective "hook-ups," while the followingparagraphs in this chapter will prove of assistance intracing the cause of unsatisfactory reception, or in get-ting the maximum of enjoyment out of the radio outfit,with a clearer understanding of the principles involved.

The Aerial

THEaerial must not touch a tree, building, metal roof,

drainpipe, or other wire. Dry wood is a fairly goodinsulator, but if the lead-in wire comes within a few inchesof a metal plate that is grounded, the loss of signal strengthwill be marked.

ARE your aerial and ground wires attached to the properbinding posts on the receiving cabinet? In many setsthese wires can be interchanged without affecting theoperation, but in others it is necessary to follow the de -

64

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signer's plan, and beginners frequently make the wrongconnection.

How to Get the Longer WavesTHE prompt action of the Federal authorities in in-

quiring into the conditions of the ether caused by theradiotelephone broadcasting system has done a great dealto place the new form of entertainment on a sound basis.

One of the important results of the conference, how-ever, is the desire it has created in the army of radionovices to listen to long -wave stations.

In a general way, there is only one means of doing it, andthat is by the use of loading coils. Loading coils aresimply coils of wire, similar in every way to ordinarytuning coils. They add a certain amount of wire in con-densed form to the aerial wire, thus increasing the totalamount of inductance in the tuning circuit.

In the first place, if you are using a simple crystal de-tector with a single coil, it is a simple matter to put ahoneycomb coil in the aerial circuit in series with theusual tuning coil. In this case the honeycomb coil willhave to have sufficient inductance to make up for thedifference between the normal wave -length range of thereceiving set and the wave length of the station you wishto listen to. Consult a dealer.

In the case of the more elaborate sets using vacuumtubes, it is not so easy to decide just where the loadingcoils should go, but it is a pretty safe bet that you will getthe desired results if you load up the aerial, as in thesimple sets just described, but with the addition, also, ofa similar coil in the plate circuit. In the latter case itwill be necessary to experiment until just the right posi-tion between the primary loading coil and the plate load-ing coil has been obtained, because a regenerative actiontakes place between them. Here, again, an expert's per-sonal advice will be helpful.

66

CHAPTER XII

GLOSSARY OF RADIO TERMSAmpere-The term used to indicate the volume of current

flowing through an electric circuit. Corresponds tothe quantity of water in a pipe line.

Capacity-A property of electricity, varied in receivingsets by means of the condenser.

C. W.-Continuous wave. This is the wave form gen-erated by a properly controlled vacuum tube circuit.The length of a C. W. is definite, making it possiblefor a larger number of C. W. stations to use the air atone time without undue interference.

Damped wave-A wave whose oscillations decrease rap-idly in amplitude.

Electron-The smallest electrical particle known. Elec-trons are given off whenever a filament is heated byan electric current. They are always negative.

Fleming valve-One variety of vacuum tube having afilament and plate but no grid.

Formica-A patented composition suited by its electricalproperties as a material for wireless insulation.

Honeycomb coil-Tuning coils wound in compact shapewith the wires crossing and recrossing each other.Also called duo -lateral coils.

I. C. W.-Interrupted Continuous Wave. The type ofwave used to broadcast radiotelephone programs. Itis produced by cutting up into short trains of wave thepure wave of the vacuum tube circuit. A C. W.cannot be picked up by a crystal detector, but anI. C. W. has no such limitation.

Inductance-One of the two electrical properties-theother being capacity-which must be properlybalanced in a receiving set to bring in a wireless wave

67


of a certain length. The tuning coil is the apparatusused to vary inductance.

Microfarad-Usually shortened to mfd.-the term usedto measure capacity.

Microhenry-The term used to measure inductance.Ohm-The unit of resistance. A circuit is said to have one

ohm resistance when a pressure of one volt is requiredto send a current of one ampere through it.

Rheostat-A coil of resistance wire used to control theflow of current in a circuit.

Tickler-See page 44. A coil used in the tuning circuitto make regeneration of signals possible.

Vernier-A supplementary device used principally withcondensers to permit of minute changes in capacity.

Volt-The term used in an electric current to denote theforce that causes the current to flow. Corresponds tothe pressure of water in a pipe line.

Wave length-The distance usually expressed in metersfrom crest to crest of the wave propagated by thetransmitting station. It has nothing whatsoever todo with the receiving distance of a station. A meteris equal to 39.37 inches.

68

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69

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70

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71

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Address73

Brandes 'Phones RestOn Wise Heads

The

The experienced radioman knows that a goodpair of sensitive 'phonesis half of the receivingoutfit. You may havea good aerial, a goodtuning coil and a perfectdetector but what hap-pens after your signalsor music reaches the'phones? Doyour'phones make the mostof the weak currentsthat pass through them?

experienced radio man knows that hecannot depend upon appearance; he wantsperformance. That is the reason he insistson Brandes Matched -Tone* Headsets. They"nurse" in that long distance "stuff" that youcannot get with ordinary 'phones. Be sure thatyou start right with Brandes.

Standard Since 1908Used as standard equipment by the leading

manufacturers.

C. BRANDES, Inc.,237 Lafayette Street, New York, N. Y.

Chicago office: 33 South Clinton Street.

*Trade mark registered U. S. Pat. Office.

74

"What Do I Needand What Will

it Cost?"Let

t ---01151t11Solve this problem!

AT each of the SORSI\( offices there are thor-oughly trained professional radio men whoknow from experience the past performance

of each piece of apparatus.Backed by the most complete stocks of the lead-

ing lines, these men can advise and help you ininvesting your money in radio equipment to yourbest advantage. It is well worth your while totake advantage of this service, and-it costs nomore to buy from SORSINC.

\Ve have just prepared an interesting little book-let illustrating the best apparatus on the markettoday. Send 6 cents in stamps for your copy.

RADIO SERVICE INC.

80 Washington Street, New York, N. Y.

"THE LARGEST RADIO CHAIN STORE SYSTEMIN THE WORLD"

.'

i/P OTUVR

75

C. G. Conn, Ltd.,National Radiophone Concerts

As world's largest band instrumentmanufacturers, Conn, Ltd., has againproved its leadership.

We have arranged a series of nation-wide radiophone concerts, broadcastedfrom the great sending stations.Watch for local announcements ofdates and programs.

Dance to the music of America'smost famous orchestras -Isham Jones'of Chicago; Joseph Smith's, New York;

Benson's, Chicago; HalNichol's, Denver; Rose -brook's, San Francisco; andothers to be announced.

The World'sFinest Saxophone

Hear solos by stars on thesaxophone, trombone, cornet aswell as vocalists of note.

America's greatest artists.who choose Conn instrumentsbecause of their superior tone.tune and mechanism, are co-operating with Conn in pro-viding these extraordinary treatsfor radiophone enthusiasts.

Conn Dealers every-where are entertain-ing with radiophoneconcerts. Get in touchwith your local dealer

and be his guest.

C. G. CONN, Ltd.,Dept. 32 Conn Bldg. Elkhart, Indiana

World's Largest Manufacturers of HighGrade Band and Orchestra Instruments.

76

MURDOCK REAL RADIO RE-CEIVERS have delivered com-plete satisfaction, on a "money -

back" basis for 14 years. Those yearsof experience have so simplified andperfected our production that there aretoday no receivers quite so good at solow a price.

Many of the complete receiving setsnow on the market include MurdockPhones as standard equipment. If theset you buy does not, be sure to get aset of Murdock receivers to completeyour station. Go to your radio dealerand convince yourself of the qualityof Murdock receivers by actual exami-nation before you buy. Prices $5.00 to$6.00. Wm. J. Murdock Co., Dept. S,Chelsea, Mass.

The Correct AnswerTo the "B" Battery Problem

50 VOLTS

2 VOLT

STEPS154W.LAKE ST.CMiCACCI.ILL.

EASILY

CHARGED

LONG LIFE

THE BIESMANN "B" Fully GuaranteedCombination Detector and Amplifier Battery24 cells. individually tapped, permitting use of any voltagefrom 2 to 50 volts in steps of two volts each. Provides a noise-less circuit for the receivers. The electrolyte is a semi -solid;cannot spill or- leak. One piece cast "Rub -Tex" Indestructocase, of which the individual cells are a part. Highly polishedand neat in appearance. Pasted type plates especially developedfor Radio service. Can be re -charged at any Battery ServiceStation, or on any type of vibrating rectifier by using the circuitprovided with the battery. Complete instructions with eachbattery. Contacts between cells easily accessible. Over-alldimensions: 9 inches long, 4'z inches wide, 4! inches high.

THE "BIG SIX" A -BATTERYA FEW FACTS BRIEFLY STATED

Semi -solid electrolyte which cannot spill-No injurious sulphation-Plates will not buckle-Highest electrical efficiency and voltage main-tenance-Quickly and easily re -charged - Can stand idle indefinitelywithout injury-Superior physical-properties-Hard wood case.

THE "BIG SIX" IS FULLY GUARANTEED AS TO LIFE, CAPACITY,ELECTRICAL EFFICIENCY, DESIGN AND WORKMANSHIP

Manufactured byGeneral Battery and

Supply Co.,Chicago, Illinois

JOBBERSWrite For Our Interesting Sales Proposition

SOLE DISTRIBUTOR

HERBERT H. FROST, 154 West Lake Street, CHICAGO, ILLINOIS

7ti

ALL loud speakers require vacuum tubeamplification. The heart of the ampli-

fier is the transformer.

ACME TRANSFORMERShave been brought to a high degree of effici-ency through years of specialization on thisone product. They amplify wireless tele-phone without detracting from the originaltone value.

ACME transformers are for sale separatelyand are also incorporated in complete Acmevacuum tube detector and amplifier instru-ments designed to hook on to your presentreceiving equipment.

The ACMEFONE, illustrated below, is acomplete long range installation. It includesin one handsome cabinet, the tuner for se-lecting the particular station you want tohear, the equipment for three vacuum tubesto amplify (or magnify) the sounds, and aloud speaker which sends the voice and musicclearly all over the room. The price is only$80.00. The work of installation has beenreduced to the minimum. Just put up asimple aerial, insert tubes, hook on batteriesand you are ready to listen.

ACME apparatus is for sale at all radiodealers.

ACME APPARATUS CO.Cambridge, Mash.

Transformers and RadioEngineers and Manufacturers

clueRadio parat s

79

Ask YourDealer

Confucius has said:"The accomplish-

ment of great thingsconsists in doingsmall things well."

Perfection of detailmakes the GREBERADIONELLE whatit is.

Licensed underArmstrong U. S- Patent,

No. 1113149.

The practical radio -talking machine with whichyou may entertain a room full of friends withyour favorite disc records and the fascinatingradio broadcasts.

A. H. Grebe & Co., Inc., Richmond Hill, N. Y.

,6aliIllluuwBuild your Station

on the Sectional SystemABC UNITS are built on the sectional plan,

just like a sectional bookcase. You can grad-ually add to your outfit without discarding anickel's worth of your previous equipment.

The first UNIT of the four UNIT combina-tion shown above is a complete crystal detectoroutfit.

For longer range and louder signals, add thesecond UNIT.

To receive still farther and amplify your signalsstill more, add the third UNIT.

When you have these three UNITS, you canadd the ABC "Clation" Loud Speaker whicheliminates the use of head phones by throwingthe voice and music clearly all over the room.

Go to your radio or electrical supplies dealerand ask him about the exclusive sectional featureof ABC UNITS.

Jewett Manufacturing CorporationCanadian Pacific Building

Madison Ave., and 44th St. New York City

THE S NDARD

R. 1.D IVIDE

How to Enjoy Radio at HomeHow to Listen -In What You Can HearHowMuch to Pay How to MakeYour

for Your Set Own Set

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