ProjectGutenberg'sTheRadioAmateur'sHandBook,byA.FrederickCollins

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Title:TheRadioAmateur'sHandBook

Author:A.FrederickCollins

PostingDate:March21,2013[EBook#6934]

ReleaseDate:November,2004

FirstPosted:February13,2003

Language:English

***STARTOFTHISPROJECTGUTENBERGEBOOKTHERADIOAMATEUR'SHANDBOOK***

ProducedbyAlanMillarandtheOnlineDistributedProofreadingTeam.

THERADIOAMATEUR'SHANDBOOK

PhotographunavailableA.FrederickCollins,InventoroftheWirelessTelephone,1899.AwardedGoldMedalforsame,

AlaskaYukonPacificExposition,1909.

THERADIOAMATEUR'SHANDBOOKAComplete,AuthenticandInformativeWorkonWirelessTelegraphyandTelephony

BYFREDERICKCOLLINS

InventoroftheWirelessTelephone1899;HistorianofWireless1901-1910;Authorof"WirelessTelegraphy"1905

1922

TOWILLIAMMARCONI

INVENTOROFTHEWIRELESSTELEGRAPH

INTRODUCTION

Beforedelvingintothemysteriesofreceivingandsendingmessageswithoutwires,awordastothehistoryoftheartanditspresentdayapplicationsmaybeofservice.Whilepopularinterestinthesubjecthasgoneforwardbyleapsandboundswithinthelasttwoorthreeyears,ithasbeenamatterofscientificexperimentformorethanaquarterofacentury.

ThewirelesstelegraphwasinventedbyWilliamMarconi,atBologna,Italy,in1896,andinhisfirstexperimentshesentdotanddashsignalstoadistanceof200or300feet.ThewirelesstelephonewasinventedbytheauthorofthisbookatNarberth,Penn.,in1899,andinhisfirstexperimentsthehumanvoicewastransmittedtoadistanceofthreeblocks.

ThefirstvitalexperimentsthatleduptotheinventionofthewirelesstelegraphweremadebyHeinrichHertz,ofGermany,in1888whenheshowedthatthesparkofaninductioncoilsetupelectricoscillationsinanopencircuit,andthattheenergyofthesewaveswas,inturn,sentoutintheformofelectricwaves.Healsoshowedhowtheycouldbereceivedatadistancebymeansofaringdetector,whichhecalledaresonator.

In1890,EdwardBranly,ofFrance,showedthatmetalfilingsinatubecoheredwhenelectricwavesactedonthem,andthisdevicehetermedaradioconductor;thiswasimproveduponbySirOliverLodge,whocalleditacoherer.In1895,AlexanderPopoff,ofRussia,constructedareceivingsetforthestudyofatmosphericelectricity,andthisarrangementwastheearliestonrecordoftheuseofadetectorconnectedwithanaerialandtheearth.

Marconiwasthefirsttoconnectanaerialtoonesideofasparkgapandagroundtotheothersideofit.Heusedaninductioncoiltoenergizethesparkgap,andatelegraphkeyintheprimarycircuittobreakupthecurrentintosignals.AddingaMorseregister,whichprintedthedotanddashmessagesonatape,tothePopoffreceptorheproducedthefirstsystemforsendingandreceivingwirelesstelegraphmessages.

PhotographunavailableCollins'WirelessTelephoneExhibitedattheMadisonSquareGarden,October1908.

AfterMarconihadshowntheworldhowtotelegraphwithoutconnectingwiresitwouldseem,onfirstthought,tobeaneasymattertotelephonewithoutwires,butnotso,fortheelectricsparksetsupdampedandperiodicoscillationsandthesecannotbeusedfortransmittingspeech.Instead,theoscillationsmustbeofconstantamplitudeandcontinuous.ThatadirectcurrentarclighttransformsapartofitsenergyintoelectricoscillationswasshownbyFirthandRogers,ofEngland,in1893.

Theauthorwasthefirsttoconnectanarclampwithanaerialandaground,andtouseamicrophonetransmittertomodulatethesustainedoscillationssosetup.Thereceivingapparatusconsistedofavariablecontact,knownasapill-boxdetector,whichSirOliverLodgehaddevised,andtothiswasconnectedanEricssontelephonereceiver,thenthemostsensitivemade.Alaterimprovementforsettingupsustainedoscillationswastheauthor'srotatingoscillationarc.

Sincethosememorabledaysofmorethantwodecadesago,wonderfuladvanceshavebeenmadein

bothofthesemethodsoftransmittingintelligence,andtheendisasyetnowhereinsight.Twelveorfifteenyearsagotheboysbegantogetfunoutoflistening-intowhattheshipandshorestationsweresendingand,further,theybegantodoalittlesendingontheirownaccount.Theseyoungsters,whocausedtheprofessionaloperatorsmanyapang,werethefirstwirelessamateurs,andamongthemexpertsweredevelopedwhoareforemostinthepracticeofthearttoday.

Awaybackthere,thesparkcoilandthearclampweretheonlyknownmeansforsettinguposcillationsatthesendingend,whiletheelectrolyticandcrystaldetectorsweretheonlyavailablemeansfortheamateurtoreceivethem.Asitwasnexttoimpossibleforaboytogetacurrenthavingahighenoughvoltageforoperatinganoscillationarclamp,wirelesstelephonywasoutofthequestionforhim,sohehadtosticktothesparkcoiltransmitterwhichneededonlyabatterycurrenttoenergizeit,andthis,ofcourse,limitedhimtosendingMorsesignals.Astheelectrolyticdetectorwascumbersomeandrequiredaliquid,thecrystaldetectorwhichcameintobeingshortlyafterwasjustassensitiveandsoondisplacedtheformer,evenasthishaddisplacedthecoherer.

Afewyearsaheadoftheseamateurs,thatistosayin1905,J.A.Fleming,ofEngland,inventedthevacuumtubedetector,buttenmoreyearselapsedbeforeitwasperfectedtoapointwhereitcouldcompetewiththecrystaldetector.Thenitsusebecamegeneralandworkerseverywheresoughtto,anddidimproveit.Further,theyfoundthatthevacuumtubewouldnotonlyactasadetector,butthatifenergizedbyadirectcurrentofhighvoltageitwouldsetupsustainedoscillationslikethearclamp,andthevalueofsustainedoscillationsforwirelesstelegraphyaswellaswirelesstelephonyhadalreadybeendiscovered.

Thefactthatthevacuumtubeoscillatorrequiresnoadjustmentofitselements,thatitsinitialcostismuchlessthantheoscillationarc,besidesotherconsiderations,isthereasonthatitpopularizedwirelesstelephony;andbecausecontinuouswaveshavemanyadvantagesoverperiodicoscillationsisthereasonthevacuumtubeoscillatorisreplacingthesparkcoilasawirelesstelegraphtransmitter.Moreover,byusinganumberoflargetubesinparallel,powerfuloscillationscanbesetupand,hence,thewavessentoutareradiatedtoenormousdistances.

WhileoscillatortubeswerebeingexperimentedwithintheresearchlaboratoriesoftheGeneralElectric,theWestinghouse,theRadioCorporationofAmerica,andotherbigcompanies,alltheyouthfulamateursinthecountryhadlearnedthatbyusingavacuumtubeasadetectortheycouldeasilygetmessages500milesaway.Theuseofthesetubesasamplifiersalsomadeitpossibletoemployaloudspeaker,sothataroom,ahall,oranout-of-dooraudiencecouldhearclearlyanddistinctlyeverythingthatwasbeingsentout.

Theboyamateurhadonlytoletfatherormotherlisten-in,andtheyweredulyimpressedwhenhetoldthemtheyweregettingitfromKDKA(thePittsburghstationoftheWestinghouseCo.),forwasnotPittsburgh500milesaway!Andsothey,too,becameenthusiasticwirelessamateurs.Thisnewinterestofthegrown-upswasatoncemetnotonlybythemanufacturersofapparatuswithcompletereceivingandsendingsets,butalsobythebigcompanieswhichbeganbroadcastingregularprogramsconsistingofmusicandtalksonallsortsofinterestingsubjects.

Thisisthewireless,orradio,astheaverageamateurknowsittoday.Butitisbynomeansthelimitofitspossibilities.Onthecontrary,wearejustbeginningtorealizewhatitmaymeantothehumanrace.TheGovernmentisnowutilizingittosendoutweather,cropandmarketreports.Foreigntradeconditionsarebeingreported.TheNavalObservatoryatArlingtoniswirelessingtimesignals.

Departmentstoresarebeginningtoissueprogramsandadvertisebyradio!Citiesarealsotakingupsuchprograms,andtheywilldoubtlessbeincludedsoonamongtheregularprivilegesofthetax-payers.Politiciansaddresstheirconstituents.Preachersreachthestay-at-homes.Greatsingersthrillthousandsinsteadofhundreds.Soonitwillbepossibletohearthefinestmusicalprograms,entertainers,andorators,withoutbudgingfromone'seasychair.

IntheWorldWarwirelessprovedofinestimablevalue.Airplanes,insteadofflyingaimlessly,keptinconstanttouchwithheadquarters.Bodiesoftroopsmovedalertlyandintelligently.Shipsatseatalkedfreely,overhundredsofmiles.Scoutsreported.Everywhereitsinvisibleaidwasinvoked.

Intimeofpeace,however,ithasprovedandwillprovethegreatestservantofmankind.Wirelessmessagesnowgodailyfromcontinenttocontinent,andsoonwillgoaroundtheworldwiththesamefacility.Shipsindistressatseacansummonaid.Vesselseverywheregettheday'snews,eventobaseballscores.Dailynewtasksarebeingassignedthistireless,wirelessmessenger.

Messageshavebeensentandreceivedbymovingtrains,theLackawannaandtheRockIslandrailroadsbeingpioneersinthisfield.Messageshavealsobeenreceivedbyautomobiles,andoneinventorhassuccessfullydemonstratedamotorcarcontrolledentirelybywireless.Thismethodofcommunicationisbeingemployedmoreandmorebynewspapers.Itisalsoofgreatserviceinreportingforestfires.

Collegesarebeginningtotakeupthesubject,someofthefirstbeingTuftsCollege,HunterCollege,Princeton,Yale,Harvard,andColumbia,whichhaveregularlyorganizeddepartmentsforstudentsinwireless.

Insteadoftheunwieldyandformidablelookingapparatusofashorttimeago,experimentersarenowvyingwitheachotherinmakingsmallornovelequipment.Portablesetsofallsortsarebeingfashioned,fromonewhichwillgointoanordinarysuitcase,toonesosmallitwilleasilyslipintoaBrowniecamera.Onereceiverdepictedinanewspaperwasoneinchsquare!Anotherwasaringforthefinger,withasettingoneinchbyfive-eighthsofaninch,andanumbrellaasa"ground."Walkingsetswithreceiversfastenedtoone'sbeltarealsocommon.Dailynewnoveltiesandmarvelsareannounced.

Meanwhile,theradioamateurtowhomthisbookisaddressedmayhavehisshareinthejoysofwireless.Togetallofthesegoodthingsoutoftheetheronedoesnotneedarodoragun--onlyacopperwiremadefastateitherendandareceivingsetofsomekind.Ifyouareasheerbeginner,thenyoumustbeverycarefulinbuyingyourapparatus,forsincethegreatwaveofpopularityhaswashedwirelessintotheheartsofthepeople,numerouscompanieshavesprungupandsomeofthesearesellingtheveriestkindsofjunk.

Andhow,youmayask,areyougoingtobeabletoknowthegoodfromtheindifferentandbadsets?Bybuyingamakeofafirmwithanestablishedreputation.Ihavegivenafewoffhandattheendofthisbook.Obviouslytherearemanyothersofmerit--somany,indeed,thatitwouldbequiteimpossibletogetthemallinsuchalist,butthesewillserveasaguideuntilyoucanchooseintelligentlyforyourself.

F.C.

CONTENTS

CHAPTER

I.HOWTOBEGINWIRELESS

KindsofWirelessSystems--PartsofaWirelessSystem--TheEasiestWaytoStart--AboutAerialWireSystems--AbouttheReceivingApparatus--AboutTransmittingStations--KindsofTransmitters--TheSparkGapWirelessTelegraphTransmitter--TheVacuumTableTelegraphTransmitter--TheWirelessTelephoneTransmitter.

II.PUTTINGUPYOURAERIAL

KindsofAerialWireSystems--HowtoPutUpaCheapReceivingAerial--ATwo-wireAerial--ConnectingintheGround--HowtoPutupaGoodAerial--AnInexpensiveGoodAerial--TheBestAerialThatCanbeMade--AssemblingtheAerial--MakingaGoodGround.

III.SIMPLETELEGRAPHANDTELEPHONERECEIVINGSETS

AssembledWirelessReceivingSets--AssemblingYourOwnReceivingSet--TheCrystalDetector--TheTuningCoil--TheLooseCoupledTuningCoil--FixedandVariableCondensers--AboutTelephoneReceivers--ConnectingUptheParts--ReceivingSetNo.2--AdjustingtheNo.1Set--TheTuningCoil--AdjustingtheNo.2Set.

IV.SIMPLETELEGRAPHSENDINGSETS

ACheapTransmittingSet(No.1)--TheSparkCoil--TheBattery--TheTelegraphKey--TheSparkGap--TheTuningCoil--TheHigh-tensionCondenser--ABetterTransmittingSet(No.2)--TheAlternatingCurrentTransformer--TheWirelessKey--TheSparkGap--TheHigh-tensionCondenser--TheOscillationTransformer--ConnectingUptheApparatus--ForDirectCurrent--HowtoAdjustYourTransmitter.TurningWithaHotWireAmmeter--ToSendOuta200-meterWaveLength--TheUseoftheAerialSwitch--AerialSwitchforaCompleteSendingandReceivingSet--ConnectingintheLightningSwitch.

V.ELECTRICITYSIMPLYEXPLAINED

ElectricityatRestandinMotion--TheElectricCurrentanditsCircuit--CurrentandtheAmpere--ResistanceandtheOhm--WhatOhm'sLawIs--WhattheWattandKilowattAre--ElectromagneticInduction--MutualInduction--High-frequencyCurrents--ConstantsofanOscillationCircuit--WhatCapacitanceIs--WhatInductanceIs--WhatResistanceIs--TheEffectofCapacitance.

VI.HOWTHETRANSMITTINGANDRECEIVINGSETSWORK

HowTransmittingSetNo.1Works--TheBatteryandSparkCoilCircuit--ChangingthePrimary

SparkCoilCurrentIntoSecondaryCurrents--WhatRatioofTransformationMeans--TheSecondarySparkCoilCircuit--TheClosedOscillationCircuit--HowTransmittingSetNo.2Works-WithAlternatingCurrent--WithDirectCurrent--TheRotarySparkGap--TheQuenchedSparkGap--TheOscillationTransformer--HowReceivingSetNo.1Works--HowReceivingSetNo.2Works.

VII.MECHANICALANDELECTRICALTUNING

DampedandSustainedMechanicalVibrations--DampedandSustainedOscillations--AboutMechanicalTuning--AboutElectricTuning.

VIII.ASIMPLEVACUUMTUBEDETECTORRECEIVINGSET

AssembledVacuumTubeReceivingSet--ASimpleVacuumTubeReceivingSet--TheVacuumTubeDetector--ThreeElectrodeVacuumTubeDetector--TheDryCellandStorageBatteries--TheFilamentRheostat--AssemblingtheParts--ConnectingUptheParts--AdjustingtheVacuumTubeDetectorReceivingSet.

IX.VACUUMTUBEAMPLIFIERRECEIVINGSETS

AGridLeakAmplifierReceivingSet.WithCrystalDetector--TheFixedResistanceUnit,orGridLeak--AssemblingthePartsforaCrystalDetectorSet--ConnectingupthePartsforaCrystalDetector--AGridLeakAmplifyingReceivingSetWithVacuumTubeDetector--ARadioFrequencyTransformerAmplifyingReceivingSet--AnAudioFrequencyTransformerAmplifyingReceivingSet--ASixStepAmplifierReceivingSetwithaLoopAerial--HowtoPreventHowling.

X.REGENERATIVEAMPLIFICATIONRECEIVINGSETS

TheSimplestTypeofRegenerativeReceivingSet--WithLooseCoupledTuningCoil--ConnectingUptheParts--AnEfficientRegenerativeReceivingSet.WithThreeCoilLooseCoupler--TheABatteryPotentiometer--ThePartsandHowtoConnectThemUp--ARegenerativeAudioFrequencyAmplifier--ThePartsandHowtoConnectThemUp.

XI.SHORTWAVEREGENERATIVERECEIVINGSETS

AShortWaveRegenerativeReceiver,withOneVariometerandThreeVariableCondensers--TheVariocoupler--TheVariometer--ConnectingUptheParts--ShortWaveRegenerativeReceiverwithTwoVariometersandTwoVariableCondensers--ThePartsandHowtoConnectThemUp.

XII.INTERMEDIATEANDLONGWAVEREGENERATIVERECEIVINGSETS

IntermediateWaveReceivingSets--IntermediateWaveSetWithLoadingCoils--ThePartsandHowtoConnectThemUp--AnIntermediateWaveSetwithVariocouplerInductanceCoils--ThePartsandHowtoConnectThemUp--ALongWaveReceivingSet--ThePartsandHowtoConnectThemUp.

XIII.HETERODYNEORBEATLONGWAVETELEGRAPHRECEIVINGSET

WhattheHeterodyneorBeatMethodIs--TheAutodyneorSelf-heterodyneLongWaveReceivingSet--ThePartsandConnectionsofanAutodyneorSelf-heterodyne,ReceivingSet--TheSeparateHeterodyneLongWaveReceivingSet--ThePartsandConnectionsofaSeparateHeterodyneLongWaveReceivingSet.

XIV.HEADPHONESANDLOUDSPEAKERS

WirelessHeadphones--HowaBellTelephoneReceiverisMade--HowaWirelessHeadphoneisMade--AboutResistance,TurnsofWireandSensitivityofHeadphones--TheImpedanceofHeadphones--HowtheHeadphonesWork--AboutLoudSpeakers--TheSimplestTypeofLoudSpeaker--AnotherSimpleKindofLoudSpeaker--AThirdKindofSimpleLoudSpeaker--ASuperLoudSpeaker.

XV.OPERATIONOFVACUUMTUBERECEPTORS

WhatisMeantbyIonization--HowElectronsareSeparatedfromAtoms--ActionoftheTwoElectrodeVacuumTube--HowtheTwoElectrodeTubeActsasaDetector--HowtheThreeElectrodeTubeActsasaDetector--HowtheVacuumTubeActsasanAmplifier--TheOperationofaSimpleVacuumTubeReceivingSet--OperationofaRegenerativeVacuumTubeReceivingSet--OperationofAutodyneandHeterodyneReceivingSets--TheAutodyne,orSelf-HeterodyneReceivingSet--TheSeparateHeterodyneReceivingSet.

XVI.CONTINUOUSWAVETELEGRAPHTRANSMITTINGSETSWITHDIRECTCURRENT

SourcesofCurrentforTelegraphTransmittingSets--AnExperimentalContinuousWaveTelegraphTransmitter--TheApparatusYouNeed--TheTuningCoil--TheCondensers--TheAerialAmmeter--TheBuzzerandDryCell--TheTelegraphKey--TheVacuumTubeOscillator--TheStorageBattery--TheBatteryRheostat--TheOscillationChokeCoil--TransmitterConnectors--ThePanelCutout--ConnectingUptheTransmittingApparatus--A100-mileC.W.TelegraphTransmitter--TheApparatusYouNeed--TheTuningCoil--TheAerialCondenser--TheAerialAmmeter--TheGridandBlockingCondensers--TheKeyCircuitApparatus--The5WattOscillatorVacuumTube--TheStorageBatteryandRheostat--TheFilamentVoltmeter--TheOscillationChokeCoil--TheMotor-generatorSet--ThePanelCut-out--TheProtectiveCondenser--ConnectingUptheTransmittingApparatus--A200-mileC.W.TelegraphTransmitter--A500-mileC.W.TelegraphTransmitter--TheApparatusandConnections--The50-wattVacuumTubeOscillator--TheAerialAmmeter--TheGridLeakResistance--TheOscillationChokeCoil--TheFilamentRheostat--TheFilamentStorageBattery--TheProtectiveCondenser--TheMotor-generator--A1000-mileC.W.TelegraphTransmitter.

XVII.CONTINUOUSWAVETELEGRAPHTRANSMITTINGSETSWITHALTERNATINGCURRENT

A100-mileC.W.TelegraphTransmittingSet--TheApparatusRequired--TheChokeCoils--TheMilli-ammeter--TheA.C.PowerTransformer--ConnectingUptheApparatus--A200-to500-mileC.W.TelegraphTransmittingSet-A500-to1000-mileC.W.TelegraphTransmittingSet--TheApparatusRequired--TheAlternatingCurrentPowerTransformer-ConnectingUptheApparatus.

XVIII.WIRELESSTELEPHONETRANSMITTINGSETSWITHDIRECTANDALTERNATINGCURRENTS

AShortDistanceWirelessTelephoneTransmittingSet--With110-voltDirectLightingCurrent--TheApparatusYouNeed--TheMicrophoneTransmitter--ConnectingUptheApparatus--A25-to50-mileWirelessTelephoneTransmitter--WithDirectCurrentMotorGenerator--TheApparatusYouNeed--TheTelephoneInductionCoil--TheMicrophoneTransformer--TheMagneticModulator--HowtheApparatusisConnectedUp--A50-to100-mileWirelessTelephoneTransmitter--WithDirectCurrentMotorGenerator--TheOscillationChokeCoil--ThePlateandGridCircuitReactanceCoils--ConnectinguptheApparatus--A100-to200-mileWirelessTelephoneTransmitter--WithDirectCurrentMotorGenerator--A50-to100-mileWirelessTelephoneTransmittingSet--With100-voltAlternatingCurrent--TheApparatusYouNeed--TheVacuumTubeRectifier--TheFilterCondensers--TheFilterReactanceCoil--ConnectingUptheApparatus--A100-to200-mileWirelessTelephoneTransmittingSet--With110-voltAlternatingCurrent--ApparatusRequired.

XIX.THEOPERATIONOFVACUUMTUBETRANSMITTERS

TheOperationoftheVacuumTubeOscillator--TheOperationofC.W.TelegraphTransmitterswithDirectCurrent--ShortDistanceC.W.Transmitter--TheOperationoftheKeyCircuit--TheOperationofC.W.TelegraphTransmittingwithDirectCurrent--TheOperationofC.W.TelegraphTransmitterswithAlternatingCurrent--WithaSingleOscillatorTube--HeatingtheFilamentwithAlternatingCurrent--TheOperationofC.W.TelegraphTransmitterswithAlternatingCurrent--WithTwoOscillatorTubes--TheOperationofWirelessTelephoneTransmitterswithDirectCurrent--ShortDistanceTransmitter--TheMicrophoneTransmitter--TheOperationofWirelessTelephoneTransmitterswithDirectCurrent--LongDistanceTransmitters--TheOperationofMicrophoneModulators--TheInductionCoil--TheMicrophoneTransformer--TheMagneticModulator--OperationoftheVacuumTubeasaModulator--TheOperationofWirelessTelephoneTransmitterswithAlternatingCurrent--TheOperationofRectifierVacuumTubes--TheOperationofReactorsandCondensers.

XX.HOWTOMAKEARECEIVINGSETFOR$5.00ORLESS.

TheCrystalDetector--TheTuningCoil--TheHeadphone--HowtoMounttheParts--TheCondenser--HowtoConnectUptheReceptor.

APPENDIX

UsefulInformation--Glossary--WirelessDon'ts.

LISTOFFIGURES

Fig.1.--SimpleReceivingSetFig.2.--SimpleTransmittingSet(A)Fig.3.--FlatTop,orHorizontalAerial(B)Fig.3.--InclinedAerial(A)Fig.4.--InvertedLAerial(B)Fig.4.--TAerialFig.5.--MaterialforaSimpleAerialWireSystem(A)Fig.6.--SingleWireAerialforReceiving(B)Fig.6.--ReceivingAerialwithSparkGapLightningArrester(C)Fig.6.--AerialwithLightningSwitchFig.7.--Two-wireAerial(A)Fig.8.--PartofaGoodAerial(B)Fig.8.--TheSpreaders(A)Fig.9.--TheMiddleSpreader(B)Fig.9.--OneEndofAerialComplete(C)Fig.9.--TheLeadinginSpreader(A)Fig.10.--CrossSectionofCrystalDetector(B)Fig.10.--TheCrystalDetectorComplete(A)Fig.11.--SchematicDiagramofaDoubleSlideTuningCoil(B)Fig.11.--DoubleSlideTuningCoilComplete(A)Fig.12.--SchematicDiagramofaLooseCoupler(B)Fig.12.--LooseCouplerComplete(A)Fig.13.--HowaFixedReceivingCondenserisBuiltup(B)Fig.13.--TheFixedCondenserComplete(C)and(D)Fig.13.--VariableRotaryCondenserFig.14.--PairofWirelessHeadphones(A)Fig.15.--TopViewofApparatusLayoutforReceivingSetNo.1(B)Fig.15.--WiringDiagramforReceivingSetNo.1(A)Fig.16.--TopViewofApparatusLayoutforReceivingSetNo.2(B)Fig.16.--WiringDiagramforReceivingSetNo.2Fig.17.--AdjustingtheReceivingSet(A)and(B)Fig.18.--TypesofSparkCoilsforSetNo.1(C)Fig.18.--WiringDiagramofSparkCoilFig.19.--OtherPartsforTransmittingSetNo.1(A)Fig.20.--TopViewofApparatusLayoutforSendingSetNo.1(B)Fig.20.--WiringofDiagramforSendingSetNo.1Fig.21.--PartsforTransmittingSetNo.2(A)Fig.22.--TopViewofApparatusLayoutforSendingSetNo.2(B)Fig.22.--WiringDiagramforSendingSetNo.2Fig.23.--Usinga110-voltDirectCurrentwithanAlternatingcurrentTransformerFig.24.--PrincipleoftheHotWireAmmeterFig.25.--KindsofAerialSwitchesFig.26.--WiringDiagramforaCompleteSendingandReceivingSetNo.1

Fig.27.--WiringDiagramforCompleteSendingandReceivingSetNo.2Fig.28.--WaterAnalogueforElectricPressureFig.29.--WaterAnaloguesforDirectandAlternatingCurrentsFig.30.--HowtheAmmeterandVoltmeterareUsedFig.31.--WaterValveAnalogueofElectricResistance(A)and(B)Fig.32.--HowanElectricCurrentisChangedintoMagneticLinesofForceandTheseintoanElectricCurrent(C)and(D)Fig.32.--HowanElectricCurrentSetsupaMagneticFieldFig.33.--TheEffectofResistanceontheDischargeofanElectricCurrentFig.34.--DampedandSustainedMechanicalVibrationsFig.35.--DampedandSustainedElectricOscillationsFig.36.--SoundWaveandElectricWaveTunedSendersandReceptorsFig.37.--TwoElectrodeVacuumTubeDetectorsFig.38.--ThreeElectrodeVacuumTubeDetectorandBatteryConnectionsFig.39.--AandBBatteriesforVacuumTubeDetectorsFig.40.--RheostatfortheAorStorage-batteryCurrent(A)Fig.41.--TopViewofApparatusLayoutforVacuumTubeDetectorReceivingSet(B)Fig.41.--WiringDiagramofaSimpleVacuumTubeReceivingSetFig.42.--GridLeaksandHowtoConnectthemUpFig.43.--CrystalDetectorReceivingSetwithVacuumTubeAmplifier(ResistanceCoupled)(A)Fig.44.--VacuumTubeDetectorReceivingSetwithOneStepAmplifier(ResistanceCoupled)(B)Fig.44.--WiringDiagramforUsingOneAorStorageBatterywithanAmplifierandaDetectorTube(A)Fig.45.--WiringDiagramforRadioFrequencyTransformerAmplifyingReceivingSet(B)Fig.45.--RadioFrequencyTransformer(A)Fig.46.--AudioFrequencyTransformer(B)Fig.46.--WiringDiagramforAudioFrequencyTransformerAmplifyingReceivingSet.(WithVacuumTubeDetectorandTwoStepAmplifierTubes)(A)Fig.47.--SixStepAmplifierwithLoopAerial(B)Fig.47.--EfficientRegenerativeReceivingSet(WithThreeCoilLooseCouplerTuner)Fig.48.--SimpleRegenerativeReceivingSet(WithLooseCouplerTuner)(A)Fig.49.--DiagramofThreeCoilLooseCoupler(B)Fig.49.--ThreeCoilLooseCouplerTunerFig.50.--HoneycombInductanceCoilFig.51.--TheUseofthePotentiometerFig.52.--RegenerativeAudioFrequencyAmplifierReceivingSetFig.53.--HowtheVarioCouplerisMadeandWorksFig.54.--HowtheVariometerisMadeandWorksFig.55.--ShortWaveRegenerativeReceivingSet(OneVariometerandThreeVariableCondensers)Fig.56.--ShortWaveRegenerativeReceivingSet(TwoVariometerandTwoVariableCondensers)Fig.57.--WiringDiagramShowingFixedLoadingCoilsforIntermediateWaveSetFig.58.--WiringDigramofIntermediateWaveReceptorwithOneVarioCouplerand12SectionBank-woundInductanceCoilFig.59.--WiringDiagramShowingLongWaveReceptorwithVarioCouplersand8Bank-

woundInductanceCoilsFig.60.--WiringDiagramofLongWaveAutodyne,orSelf-heterodyneReceptor(ComparewithFig.77)Fig.61.--WiringDiagramofLongWaveSeparateHeterodyneReceivingSetFig.62.--CrossSectionofBellTelephoneReceiverFig.63.--CrossSectionofWirelessHeadphoneFig.64.--TheWirelessHeadphoneFig.65.--ArkayLoudSpeakerFig.66.--AmplitoneLoudSpeakerFig.67.--AmplitronLoudSpeakerFig.68.--MagnavoxLoudSpeakerFig.69.--SchematicDiagramofanAtomFig.70.--ActionofTwo-electrodeVacuumTube(A)and(B)Fig.71.--HowaTwo-electrodeTubeActsasRelayoraDetector(C)Fig.71.--OnlythePositivePartofOscillationsGoesthroughtheTube(A)and(B)Fig.72.--HowthePositiveandNegativeVoltagesoftheOscillationsActontheElectrons(C)Fig.72.--HowtheThree-electrodeTubeActsasDetectorandAmplifier(D)Fig.72.--HowtheOscillationsControltheFlowoftheBatteryCurrentthroughtheTubeFig.73.--HowtheHeterodyneReceptorWorksFig.74.--SeparateHeterodyneOscillator(A)Fig.75.--ApparatusforExperimentalC.W.TelegraphTransmitter.(B)Fig.75.--ApparatusforExperimentalC.W.TelegraphTransmitter.Fig.76.--ExperimentalC.W.TelegraphTransmitterFig.77.--Apparatusof100-mileC.W.TelegraphTransmitterFig.78.--5-to50-wattC.W.TelegraphTransmitter(withaSingleOscillationTube)Fig.79.--200-mileC.W.TelegraphTransmitter(withTwoTubesinParallel)Fig.80.--50-wattOscillatorVacuumTubeFig.81.--AlternatingCurrentPowerTransformer(forC.W.TelegraphyandWirelessTelephony)Fig.82.--WiringDiagramfor200-to500-mileC.W.TelegraphTransmittingSet.(WithAlternatingCurrent.)Fig.83.--WiringDiagramfor500-to1000-mileC.W.TelegraphTransmitterFig.84.--StandardMicrophoneTransmitterFig.85.--WiringDiagramofShortDistanceWirelessTelephoneSet.(MicrophoneinAerialWire.)Fig.86.--TelephoneInductionCoil(usedwithMicrophoneTransmitter).Fig.87.--MicrophoneTransformerUsedwithMicrophoneTransmitterFig.88.--MagneticModulatorUsedwithMicrophoneTransmitter(A)Fig.89.--WiringDiagramof25--to50-mileWirelessTelephone.(MicrophoneModulatorShuntedAroundGrid-leakCondenser)(B)Fig.89.--MicrophoneModulatorConnectedinAerialWireFig.90.--WiringDiagramof50-to100-mileWirelessTelephoneTransmittingSetFig.91.--PlateandGridCircuitReactorFig.92.--FilterReactorforSmoothingOutRectifiedCurrentsFig.93.--100-to200-mileWirelessTelephoneTransmitter(A)and(B)Fig.94.--OperationofVacuumTubeOscillators

(C)Fig.94.--HowaDirectCurrentSetsupOscillationsFig.95.--PositiveVoltageOnlySetsupOscillationsFig.96.--RascoBabyCrystalDetectorFig.97.--HowtheTuningCoilisMadeFig.98.--Mescoloop-ohmHeadSetFig.99.--SchematicLayoutofthe$5.00ReceivingSetFig.100.--WiringDiagramforthe$5.00ReceivingSet

LISTOFILLUSTRATIONS

FrederickCollins,InventoroftheWirelessTelephone,1899.AwardedGoldMedalforsame,AlaskaYukonPacificExposition,1909Collins'WirelessTelephoneExhibitedattheMadisonSquareGarden,October,1908GeneralPershing"Listening-in"TheWorld'sLargestRadioReceivingStation.OwnedbytheRadioCorporationofAmericaatRockyPointnearPortJefferson,L.I.FirstWirelessCollegeintheWorld,atTuftsCollege,MassAlexanderGrahamBell,InventoroftheTelephone,nowanardentRadioEnthusiastWorld'sLargestLoudSpeakerevermade.InstalledinLytlePark,Cincinnati,Ohio,topermitPresidentHarding'sAddressatPointPleasant,Ohio,duringtheGrantCentenaryCelebrationtobeheardwithinaradiusofonesquareUnitedStatesNavalHighPowerStation,Arlington,Va.GeneralviewofPowerRoom.AttheleftcanbeseentheControlSwitchboards,andoverhead,thegreat30K.W.ArcTransmitterwithAccessoriesTheTransformerandTuneroftheWorld'sLargestRadioStation.OwnedbytheRadioCorporationofAmericaatRockyPointnearPortJefferson,L.I.BroadcastingGovernmentReportsbyWirelessfromWashington.ThisshowsMr.GaleatworkwithhissetinthePostOfficeDepartmentWirelessReceptor,thesizeofaSafetyMatchBox.AYouthfulGeniusinthepersonofKennethR.Hinman,whoisonlytwelveyearsold,hasmadeaWirelessReceivingSetthatfitsneatlyintoaSafetyMatchBox.WiththisInstrumentandaPairofOrdinaryReceivers,heisabletocatchnotonlyCodeMessagesbuttheregularBroadcastingProgramsfromStationsTwentyandThirtyMilesDistantWirelessSetmadeintoaRing,designedbyAlfredG.Rinehart,ofElizabeth,NewJersey.ThislittleReceptorisaPracticalSet;itwillreceiveMessages,Concerts,etc.,measures1"by5/8"by7/8".AnordinaryUmbrellaisusedasanAerial

CHAPTERI

HOWTOBEGINWIRELESS

Inwritingthisbookitistakenforgrantedthatyouare:first,oneoftheseveralhundredthousandpersonsintheUnitedStateswhoareinterestedinwirelesstelegraphyandtelephony;second,thatyouwouldliketoinstallanapparatusinyourhome,andthird,thatitisallnewtoyou.

Nowifyouliveinacityortownlargeenoughtosupportanelectricalsupplystore,thereyouwillfindthenecessaryapparatusonsale,andsomeonewhocantellyouwhatyouwanttoknowaboutitandhowitworks.Ifyouliveawayfromthemartsandhivesofindustryyoucansendtovariousmakersofwirelessapparatus[Footnote:AlistofmakersofwirelessapparatuswillbefoundintheAppendix.]fortheircataloguesandprice-listsandthesewillgiveyoumuchusefulinformation.Butineithercaseitisthebetterplanforyoutoknowbeforeyoustartintobuyanoutfitexactlywhatapparatusyouneedtoproducetheresultyouhaveinmind,andthisyoucangainineasystepsbyreadingthisbook.

KindsofWirelessSystems.--Therearetwodistinctkindsofwirelesssystemsandtheseare:thewirelesstelegraphsystem,andthewirelesstelephonesystem.Thedifferencebetweenthewirelesstelegraphandthewirelesstelephoneisthattheformertransmitsmessagesbymeansofatelegraphkey,andthelattertransmitsconversationandmusicbymeansofamicrophonetransmitter.Inotherwords,thesamedifferenceexistsbetweentheminthisrespectasbetweentheMorsetelegraphandtheBelltelephone.

PartsofaWirelessSystem.--Everycompletewirelessstation,whethertelegraphortelephone,consistsofthreechiefseparateanddistinctpartsandtheseare:(a)theaerialwiresystem,orantennaasitisoftencalled,(b)thetransmitter,orsender,and(c)thereceiver,or,moreproperly,thereceptor.Theaerialwireispreciselythesameforeitherwirelesstelegraphyorwirelesstelephony.Thetransmitterofawirelesstelegraphsetgenerallyusesasparkgapforsettinguptheelectricoscillations,whileusuallyforwirelesstelephonyavacuumtubeisemployedforthispurpose.Thereceptorforwirelesstelegraphyandtelephonyisthesameandmayincludeeitheracrystaldetectororavacuumtubedetector,aswillbeexplainedpresently.

TheEasiestWaytoStart.--Firstofallyoumustobtainagovernmentlicensetooperateasendingset,butyoudonotneedalicensetoputupanduseareceivingset,thoughyouarerequiredbylawtokeepsecretanymessageswhichyoumayoverhear.Sincenolicenseisneededforareceivingsettheeasiestwaytobreakintothewirelessgameistoputupanaerialandhookupareceivingsettoit;youcanthenlisten-inandhearwhatisgoingonintheall-pervadingetheraroundyou,andyouwillsoonfindenoughtomakethingshighlyentertaining.

Nearlyallthebigwirelesscompanieshavegreatstationsfittedwithpowerfultelephonetransmittersandatgivenhoursofthedayandnighttheysendoutsongsbypopularsingers,dancemusicbyjazzorchestras,fashiontalksbyandfortheladies,agriculturalreports,governmentweatherforecastsandotherinterestingfeatures.Thenbysimplyshiftingtheslideonyourtuningcoilyoucanoftentune-insomeonewhoissendingMorse,thatis,messagesinthedotanddashcode,or,perhapsafriendwhohasawirelesstelephonetransmitterandistalking.Ofcourse,ifyouwanttotalkbackyoumusthave

awirelesstransmitter,eithertelegraphicortelephonic,andthisisamuchmoreexpensivepartoftheapparatusthanthereceptor,bothinitsinitialcostandinitsoperation.Awirelesstelegraphtransmitterislesscostlythanawirelesstelephonetransmitteranditisaverygoodschemeforyoutolearntosendandreceivetelegraphicmessages.

Atthepresenttime,however,therearefifteenamateurreceivingstationsintheUnitedStatestoeverysendingstation,soyoucanseethatthemajorityofwirelessfolkscaremoreforlisteningintothebroadcastingofnewsandmusicthantosendingoutmessagesontheirownaccount.Theeasiestwaytobeginwireless,then,istoputupanaerialandhookupareceivingsettoit.

AboutAerialWireSystems.--Tothebeginnerwhowantstoinstallawirelessstationtheaerialwiresystemusuallyloomsupasthebiggestobstacleofall,andespeciallyisthistrueifhishouseiswithoutaflagpole,orotherelevationfromwhichtheaerialwirecanbeconvenientlysuspended.

Ifyouliveinthecongestedpartofabigcitywheretherearenoyardsand,particularly,ifyouliveinaflatbuildingoranapartmenthouse,youwillhavetostringyouraerialwireontheroof,andtodothisyoushouldgettheowner's,oragent's,permission.Thisisusuallyaneasythingtodowhereyouonlyintendtoreceivemessages,foroneortwothinwiressupportedateitherendofthebuildingareallthatareneeded.Ifforanyreasonyoucannotputyouraerialontheroofthenrunawirealongthebuildingoutsideofyourapartment,and,finally,ifthisisnotfeasible,connectyourreceivertoawirestrungupinyourroom,oreventoanironorabrassbed,andyoucanstillgetthenear-bystations.

Animportantpartoftheaerialwiresystemistheground,thatis,yourreceivingsetmustnotonlybeconnectedwiththeaerialwire,butwithawirethatleadstoandmakesgoodcontactwiththemoistearthoftheground.Whereahouseorabuildingispipedforgas,waterorsteam,itiseasytomakeagroundconnection,forallyouhavetodoistofastenthewiretooneofthepipeswithaclamp.[Footnote:Pipesareofteninsulatedfromtheground,whichmakesthemuselessforthispurpose.]Wherethehouseisisolatedthenalotofwiresorasheetofcopperorofzincmustbeburiedinthegroundatasufficientdepthtoinsuretheirbeingkeptmoist.

AbouttheReceivingApparatus.--Youcaneitherbuythepartsofthereceivingapparatusseparateandhookthemupyourself,oryoucanbuytheapparatusalreadyassembledinasetwhichis,inthebeginning,perhaps,thebetterway.

Thesimplestreceivingsetconsistsof(1)adetector,(2)atuningcoil,and(3)atelephonereceiverandthesethreepiecesofapparatusare,ofcourse,connectedtogetherandarealsoconnectedtotheaerialandgroundasthediagraminFig.1clearlyshows.Therearetwochiefkindsofdetectorsusedatthepresenttimeandtheseare:(a)thecrystaldetector,and(b)thevacuumtubedetector.Thecrystaldetectoristhecheapestandsimplest,butitisnotassensitiveasthevacuumtubedetectoranditrequiresfrequentadjustment.Acrystaldetectorcanbeusedwithorwithoutabatterywhilethevacuumtubedetectorrequirestwosmallbatteries.

Atuningcoilofthesimplestkindconsistsofasinglelayerofcopperwirewoundonacylinderwithanadjustable,orsliding,contact,butforsharptuningyouneedaloosecoupledtuningcoil.Whereasinglecoiltunerisusedafixedcondensershouldbeconnectedaroundthetelephonereceivers.Wherealoosecoupledtunerisemployedyoushouldhaveavariablecondenserconnectedacrosstheclosedoscillationcircuitandafixedcondenseracrossthetelephonereceivers.

Whenlistening-intodistantstationstheenergyofthereceivedwirelesswavesisoftensoveryfeeblethatinordertoheardistinctlyanamplifiermustbeused.Toamplifytheincomingsoundsavacuumtubemadelikeadetectorisusedandsometimesasmanyashalf-a-dozenofthesetubesareconnectedinthereceivingcircuit,orincascade,asitiscalled,whenthesoundsareamplified,thatismagnified,manyhundredsoftimes.

Thetelephonereceiverofareceivingsetisequallyasimportantasthedetector.Asinglereceivercanbeusedbutapairofreceiversconnectedwithahead-bandgivesfarbetterresults.Thenagainthehighertheresistanceofthereceiversthemoresensitivetheyoftenareandthosewoundtoashigharesistanceas3,200ohmsaremadeforusewiththebestsets.Tomaketheincomingsignals,conversationormusic,audibletoaroomfullofpeopleinsteadoftojustyourselfyoumustusewhatiscalledaloudspeaker.Initssimplestformthisconsistsofametalconelikeamegaphonetowhichisfittedatelephonereceiver.

AboutTransmittingStations--GettingYourLicense.--Ifyouaregoingtoinstallawirelesssendingapparatus,eithertelegraphicortelephonic,youwillhavetosecureagovernmentlicenseforwhichnofeeorchargeofanykindismade.Therearethreeclassesoflicensesissuedtoamateurswhowanttooperatetransmittingstationsandtheseare:(1)therestrictedamateurlicense,(2)thegeneralamateurlicense,and(3)thespecialamateurlicense.

Ifyouaregoingtosetupatransmitterwithinfivenauticalmilesofanynavalwirelessstationthenyouwillhavetogetarestrictedamateurlicensewhichlimitsthecurrentyouusetohalfakilowatt[Footnote:AKilowattis1,000watts.Thereare746wattsinahorsepower.]andthewavelengthyousendoutto200meters.Shouldyouliveoutsideofthefive-milerangeofanavystationthenyoucangetageneralamateurlicenseandthispermitsyoutouseacurrentof1kilowatt,butyouarelikewiselimitedtoawavelengthof200meters.Butifyoucanshowthatyouaredoingsomespecialkindof

wirelessworkandnotusingyoursendingstationforthemerepleasureyouaregettingoutofityoumaybeabletogetaspecialamateurlicensewhichgivesyoutherighttosendoutwavelengthsupto375meters.

WhenyouarereadytoapplyforyourlicensewritetotheRadioInspectorofwhicheveroneofthefollowingdistrictsyoulivein:

FirstDistrict..............Boston,Mass.

Second"..............NewYorkCity

Third"..............Baltimore,Md.

Fourth"..............Norfolk,Va.

Fifth"..............NewOrleans,La.

Sixth".............SanFrancisco,Cal.

Seventh".............Seattle,Wash.

Eighth".............Detroit,Mich.

Ninth"..............Chicago,Ill.

KindsofTransmitters.--Therearetwogeneraltypesoftransmittersusedforsendingoutwirelessmessagesandtheseare:(1)wirelesstelegraphtransmitters,and(2)wirelesstelephonetransmitters.Telegraphtransmittersmayuseeither:(a)ajump-spark,(b)anelectricarc,or(c)avacuumtubeapparatusforsendingoutdotanddashmessages,whiletelephonetransmittersmayuseeither,(a)anelectricarc,or(b)avacuumtubeforsendingoutvocalandmusicalsounds.Amateursgenerallyuseajump-sparkforsendingwirelesstelegraphmessagesandthevacuumtubeforsendingwirelesstelephonemessages.

TheSparkGapWirelessTelegraphTransmitter.--Thesimplestkindofawirelesstelegraphtransmitterconsistsof:(1)asourceofdirectoralternatingcurrent,(2)atelegraphkey,(3)aspark-coiloratransformer,(4)asparkgap,(5)anadjustablecondenserand(6)anoscillationtransformer.Wheredrycellsorastoragebatterymustbeusedtosupplythecurrentforenergizingthetransmitteraspark-coilcanbeemployedandthesemaybehadinvarioussizesfromalittlefellowwhichgives1/4-inchsparkuptoalargeronewhichgivesa6-inchspark.Wheremoreenergyisneededitisbetterpracticetouseatransformerandthiscanbeworkedonanalternatingcurrentof110volts,orifonlya110voltdirectcurrentisavailablethenanelectrolyticinterruptermustbeusedtomakeandbreakthecurrent.AsimpletransmittingsetwithaninductioncoilisshowninFig.2.

Awirelesskeyismadelikeanordinarytelegraphkeyexceptthatwherelargecurrentsaretobeuseditissomewhatheavierandisprovidedwithlargesilvercontactpoints.Sparkgapsforamateurworkareusuallyof:(1)theplainorstationarytype,(2)therotatingtype,and(3)thequenchedgaptype.Theplainspark-gapismoresuitableforsmallspark-coilsets,anditisnotsoapttobreakdownthetransformerandcondenserofthelargersetsastherotarygap.Therotarygapontheotherhandtendstopreventarcingandsothebreakisquickerandthereislessdraggingofthespark.Thequenchedgapismoreefficientthaneithertheplainorrotarygapandmoreoveritisnoiseless.

CondensersforsparktelegraphtransmitterscanbeordinaryLeydenjarsorglassplatescoatedwithtinorcopperfoilandsetintoaframe,ortheycanbebuiltupofmicaandsheetmetalembeddedinaninsulatingcomposition.Theglassplatecondensersarethecheapestandwillserveyourpurposewell,especiallyiftheyareimmersedinoil.Tuningcoils,sometimescalledtransmittinginductancesandoscillationtransformers,areofvarioustypes.Thesimplestkindisatransmittinginductancewhichconsistsof25or30turnsofcopperwirewoundonaninsulatingtubeorframe.Anoscillationtransformerisaloosecoupledtuningcoilanditconsistsofaprimarycoilformedofanumberofturnsofcopperwirewoundonafixedinsulatingsupport,andasecondarycoilofabouttwicethenumberofturnsofcopperwirewhichislikewisefixedinaninsulatingsupport,butthecoilsarerelativelymovable.Anoscillationtransformer(insteadofatuningcoil),isrequiredbygovernmentregulationsunlessinductivelycoupled.

TheVacuumTubeTelegraphTransmitter.--Thisconsistsof:(1)asourceofdirectoralternatingcurrent,(2)atelegraphkey,(3)avacuumtubeoscillator,(4)atuningcoil,and(5)acondenser.Thiskindofatransmittersetsupsustainedoscillationsinsteadofperiodicoscillationswhichareproduced

byasparkgapset.TheadvantagesofthiskindofasystemwillbefoundexplainedinChapterXVI.

TheWirelessTelephoneTransmitter.--Becauseajump-sparksetsupperiodicoscillations,thatis,theoscillationsarediscontinuous,itcannotbeusedforwirelesstelephony.Anelectricarcoravacuumtubesetsupsustainedoscillations,thatis,oscillationswhicharecontinuous.Asitisfareasiertokeeptheoscillationsgoingwithavacuumtubethanitiswithanarctheformermeanshasallbutsupplantedthelatterforwirelesstelephonetransmitters.Theapparatusrequiredandtheconnectionsusedforwirelesstelephonesetswillbedescribedinlaterchapters.

UsefulInformation.--ItwouldbewiseforthereadertoturntotheAppendix,beginningwithpage301ofthisbook,andfamiliarizehimselfwiththeinformationtheresetdownintabularandgraphicform.Forexample,thefirsttablegivesabbreviationsofelectricaltermswhichareingeneraluseinallworksdealingwiththesubject.Youwillalsofindtherebriefdefinitionsofelectricandmagneticunits,whichitwouldbewelltocommittomemory;or,atleast,tomakesothoroughlyyourownthatwhenanyofthesetermsismentioned,youwillknowinstantlywhatisbeingtalkedabout.

CHAPTERII

PUTTINGUPYOURAERIAL

Asinferredinthefirstchapter,anaerialforreceivingdoesnothavetobenearlyaswellmadeorputupasoneforsending.Butthisdoesnotmeanthatyoucanslipshodtheconstructionandinstallationofit,forhoweversimpleitis,thejobmustbedonerightandinthiscaseitisaseasytodoitrightaswrong.

Tosendwirelesstelegraphandtelephonemessagestothegreatestdistancesandtoreceivethemasdistinctlyaspossiblefromthegreatestdistancesyoumustuseforyouraerial(1)copperoraluminumwire,(2)twoormorewires,(3)havethemtheproperlength,(4)havethemashighintheairasyoucan,(5)havethemwellapartfromeachother,and(6)havethemwellinsulatedfromtheirsupports.Ifyouliveinaflatbuildingoranapartmenthouseyoucanstringyouraerialwiresfromoneedgeoftherooftotheotherandsupportthembywoodenstaysashighaboveitasmaybeconvenient.

Shouldyouliveinadetachedhouseinthecityyoucanusuallygetyournext-doorneighbortoletyoufastenoneendoftheaerialtohishouseandthiswillgiveyouagoodstretchandafairlyhighaerial.Inthecountryyoucanstretchyourwiresbetweenthehouseandbarnorthewindmill.Fromthisyouwillseethatnomatterwhereyouliveyoucannearlyalwaysfindwaysandmeansofputtingupanaerialthatwillserveyourneedswithoutgoingtotheexpenseoferectingamast.

KindsofAerialWireSystems.--Anamateurwirelessaerialcanbeanywherefrom25feetto100feetlongandifyoucangetastretchofthelatterlengthandaheightoffrom30to75feetyouwillhaveonewithwhichyoucanreceiveathousandmilesormoreandsendoutasmuchenergyasthegovernmentwillallowyoutosend.

Thekindofanaerialthatgivesthebestresultsisonewhosewire,orwires,arehorizontal,thatis,parallelwiththeearthunderitasshownatAinFig.3.Ifonlyoneendcanbefixedtosomeelevatedsupportthenyoucansecuretheotherendtoapostintheground,buttheslopeoftheaerialshouldnotbemorethan30or35degreesfromthehorizontalatmostasshownatB.

Theleading-inwire,thatis,thewirethatleadsfromandjoinstheaerialwirewithyoursendingand

receivingset,canbeconnectedtotheaerialanywhereitismostconvenienttodoso,butthebestresultsarehadwhenitisconnectedtooneendasshownatAinFig.4,inwhichcaseitiscalledaninvertedLaerial,orwhenitisconnectedtoitatthemiddleasshownatB,whenitiscalledaTaerial.Theleading-inwiremustbecarefullyinsulatedfromtheoutsideofthebuildingandalsowhereitpassesthroughittotheinside.Thisisdonebymeansofaninsulatingtubeknownasaleading-ininsulator,orbulkheadinsulatorasitissometimescalled.

Asaprotectionagainstlightningburningoutyourinstrumentsyoucanuseeither:(1)anair-gaplightningarrester,(2)avacuumtubeprotector,or(3)alightningswitch,whichisbetter.Whicheverofthesedevicesisuseditisconnectedinbetweentheaerialandanoutsidegroundwiresothatadirectcircuittotheearthwillbeprovidedatalltimesexceptwhenyouaresendingorreceiving.Soyouraerialinsteadofbeingamenacereallyactsduringanelectricalstormlikealightningrodanditisthereforearealprotection.Theair-gapandvacuumtubelightningarrestersarelittledevicesthatcanbeusedonlywhereyouaregoingtoreceive,whilethelightningswitchmustbeusedwhereyouaregoingtosend;indeed,insomelocalitiestheFireUnderwritersrequirealargelightningswitchtobeusedforreceivingsetsaswellassendingsets.

HowtoPutUpaCheapReceivingAerial.--Thekindofanaerialwiresystemyouputupwilldepend,chiefly,ontwothings,andtheseare:(1)yourpocketbook,and(2)theplacewhereyoulive.

ASingleWireAerial.--Thisisthesimplestandcheapestkindofareceivingaerialthatcanbeputup.Thefirstthingtodoistofindoutthelengthofwireyouneedbymeasuringthespanbetweenthetwopointsofsupport;thenaddasufficientlengthfortheleading-inwireandenoughmoretoconnectyourreceivingsetwiththeradiatororwaterpipe.

YoucanuseanysizeofcopperoraluminumwirethatisnotsmallerthanNo.16BrownandSharpegauge.Whenyoubuythewiregetalsothefollowingmaterial:(1)twoporcelaininsulatorsasshownatAinFig.5;(2)threeorfourporcelainknobinsulators,seeB;(3)either(a)anairgaplightningarrester,seeC,or(b)alightningswitchseeD;(4)aleading-inporcelaintubeinsulator,seeE,and(5)agroundclamp,seeF.

Tomaketheaerialslipeachendofthewirethroughaholeineachinsulatorandtwistitfast;nextcutoffandsliptwomorepiecesofwirethroughtheotherholesintheinsulatorsandtwistthemfastandthensecurethesetothesupportsattheendsofthebuilding.Takethepieceyouaregoingtousefortheleading-inwire,twistitaroundtheaerialwireandsolderittherewhenitwilllooklikeAinFig.6.Nowifyouintendtousetheairgaplightningarresterfastenittothewallofthebuildingoutsideofyourwindow,andbringtheleading-inwirefromtheaerialtothetopbindingpostofyourarresterandkeepitclearofeverythingasshownatB.Ifyouraerialisontheroofandyouhavetobringtheleading-inwireoverthecorniceoraroundacornerfixaporcelainknobinsulatortotheoneortheotherandfastenthewiretoit.

Nextboreaholethroughtheframeofthewindowatapointnearestyourreceivingsetandpusha

porcelaintube5/8inchindiameterand5or6incheslong,throughit.Connectalengthofwiretothetoppostofthearresterorjustaboveittothewire,runthisthroughtheleading-ininsulatorandconnectittothesliderofyourtuningcoil.Screwtheendofapieceofheavycopperwiretothelowerpostofthearresterandrunittotheground,onporcelainknobsifnecessary,andsolderittoanironrodorpipewhichyouhavedrivenintotheearth.FinallyconnectthefixedterminalofyourtuningcoilwiththewaterpipeorradiatorinsideofthehousebymeansofthegroundclampasshowninthediagrammaticsketchatBinFig.6andyouarereadytotunein.

Ifyouwanttousealightningswitchinsteadoftheair-gaparresterthenfastenittotheoutsidewallinsteadofthelatterandscrewthefreeendoftheleading-inwirefromtheaerialtothemiddlepostofitasshownatCinFig.6.Runawirefromthetoppostthroughtheleading-ininsulatorandconnectitwiththesliderofyourtuningcoil.Nextscrewoneendofalengthofheavycopperwiretothelowerpostoftheaerialswitchandrunittoanironpipeinthegroundasdescribedaboveinconnectionwiththespark-gaplightningarrester;thenconnectthefixedterminalofyourtuningcoilwiththeradiatororwaterpipeandyouraerialwiresystemwillbecompleteasshownatCinFig.6.

ATwo-wireAerial.--Anaerialwithtwowireswillgivebetterresultsthanasinglewireandthreewiresarebetterthantwo,butyoumustkeepthemwellapart.Toputupatwo-wireaerialget(1)enoughNo.16,orpreferablyNo.14,solidorstrandedcopperoraluminumwire,(2)fourporcelaininsulators,seeBinFig.5,and(3)twosticksabout1inchthick,3incheswideand3or4feetlong,forthespreaders,andbore1/8-inchholethrougheachendofeachone.Nowtwisttheendsofthewirestotheinsulatorsandthencutofffourpiecesofwireabout6feetlongandrunthemthroughtheholesinthewoodspreaders.Finallytwisttheendsofeachpairofshortwirestothefreeendsoftheinsulatorsandthentwistthefreeendsofthewirestogether.

Fortheleading-inwirethatgoestothelightningswitchtaketwolengthsofwireandtwistoneendofeachonearoundtheaerialwiresandsolderthemthere.TwisttheshortwirearoundthelongwireandsolderthisjointalsowhentheaerialwilllooklikeFig.7.Bringthefreeendoftheleading-inwiredowntothemiddlepostofthelightningswitchandfastenitthereandconnectupthereceivertoitandthegroundasdescribedunderthecaptionofASingleWireAerial.

ConnectingintheGround.--Ifthereisagasorwatersystemorasteam-heatingplantinyourhouseyoucanmakeyourgroundconnectionbyclampingagroundclamptothenearestpipeashasbeenpreviouslydescribed.Connectalengthofbareorinsulatedcopperwirewithitandbringthisupto

thetableonwhichyouhaveyourreceivingset.Iftherearenogroundedpipesavailablethenyouwillhavetomakeagoodgroundwhichweshalldescribepresentlyandleadthegroundwirefromyourreceivingsetoutofthewindowanddowntoit.

HowtoPutUpaGoodAerial.--Whileyoucanusethecheapaerialalreadydescribedforasmallspark-coilsendingsetyoushouldhaveabetterinsulatedonefora1/2ora1kilowatttransformerset.Thecostforthematerialsforagoodaerialissmallandwhenproperlymadeandwellinsulateditwillgiveresultsthatarealloutofproportiontothecostofit.

AnInexpensiveGoodAerial.--Afarbetteraerial,becauseitismorehighlyinsulated,canbemadebyusingmidgetinsulatorsinsteadoftheporcelaininsulatorsdescribedunderthecaptionofASingleWireAerialandusingasmallelectroseleading-ininsulatorinsteadoftheporcelainbushing.Thismakesagoodsendingaerialforsmallsetsaswellasagoodreceivingaerial.

TheBestAerialthatCanBeMade.--Tomakethisaerialgetthefollowingmaterialtogether:(1)enoughstrandedorbraidedwireforthreeorfourlengthsofparallelwires,accordingtothenumberyouwanttouse(2)sixoreightelectroseballinsulators,seeB,Fig.8;(3)two5-inchor10-inchelectrosestraininsulators,seeC;(4)sixoreightS-hooks,seeD;onelargewithewithoneeyeformiddleofendspreader,seeE;(6)twosmallerwitheswithoneeyeeachforendspreader,seeE;(7)twostillsmallerwithes,withtwoeyeseachfortheendsoftheendspreaders,seeE(8)twothimbles,seeF,for1/4-inchwirecable;(9)sixoreighthardrubbertubesorbushingsasshownatG;and(10)twoendspreaders,seeH;onemiddlespreader,seeI;andoneleading-inspreader,seeJ.

Forthisaerialanyoneofanumberofkindsofwirecanbeusedandamongtheseare(a)strandedcopperwire;(b)braidedcopperwire;(c)strandedsiliconbronzewire,and(d)strandedphosphorbronzewire.Strandedandbraidedcopperwireisveryflexibleasitisformedofsevenstrandsoffinewiretwistedorbraidedtogetheranditisverygoodforshortandlightaerials.Siliconbronzewireisstrongerthancopperwireandshouldbeusedwhereaerialsaremorethan100feetlong,whilephosphorbronzewireisthestrongestaerialwiremadeandisusedforhighgradeaerialsbythecommercialcompaniesandtheGovernmentfortheirhigh-powerstations.

Thespreadersshouldbemadeofspruce,andshouldbe4feet10incheslongforathree-wireaerialand7feet1inchlongforafour-wireaerialasthedistancebetweenthewiresshouldbeabout27inches.Theendspreaderscanbeturnedcylindricallybutitmakesabetterlookingjobiftheytaperfromthemiddletotheends.Theyshouldbe2-1/4inchesindiameteratthemiddleand1-3/4inchesattheends.Themiddlespreadercanbecylindricaland2inchesindiameter.Itmusthaveholesboredthroughitatequidistantpointsforthehardrubbertubes;eachoftheseshouldbe5/8inchindiameterandhaveahole5/32inchindiameterthroughitfortheaerialwire.Theleading-inspreaderisalsomadeofspruceandis1-1/2inchessquareand26incheslong.Borethreeorfour5/8-inchholesatequidistantpointsthroughthisspreaderandinserthardrubbertubesinthemaswiththemiddlespreader.

AssemblingtheAerial.--Beginbymeasuringoffthelengthofeachwiretobeusedandseetoitthatallofthemareofexactlythesamelength.NowpushthehardrubberinsulatorsthroughtheholesinthemiddlespreaderandthreadthewiresthroughtheholesintheinsulatorsasshownatAinFig9.

Nexttwisttheendsofeachwiretotheringsoftheballinsulatorsandthenputthelargewithesonthemiddleofeachoftheendspreaders;fixtheotherwithesonthespreaderssothattheywillbe27inchesapartandfastentheballinsulatorstotheeyesinthewitheswiththeS-hooks.Nowslipathimblethroughtheeyeofoneofthelongstraininsulators,threadalengthofstrandedsteelwire1/4inchindiameterthroughitandfastentheendsofittotheeyesinthewithesontheendsofthespreaders.

Finallyfastena40-inchlengthofsteelstrandedwiretoeachoftheeyesofthewithesonthemiddleofeachofthespreaders,looptheotherendoverthethimbleandthenwraptheendaroundthewiresthatarefixedtotheendsofthespreaders.OneendoftheaerialisshowncompleteatBinFig.9,andfromthisyoucanseeexactlyhowitisassembled.Nowcutoffthreeorfourpiecesofwire15or20feetlongandtwistandsoldereachonetooneoftheaerialwires;thenslipthemthroughthehardrubbertubesintheleading-inspreader,bringtheirfreeendstogetherasatCandtwistandsolderthemtoalengthofwirelongenoughtoreachtoyourlightningswitchorinstruments.

MakingaGoodGround.--Whereyouhavetomakeagroundyoucandosoeitherby(1)buryingsheetsofzincorcopperinthemoistearth;(2)buryinganumberofwiresinthemoistearth,or(3)usingacounterpoise.Tomakeagroundofthefirstkindtakehalfadozenlargesheetsofcopperorzinc,cutthemintostripsafootwide,solderthemalltogetherwithotherstripsandburythemdeeplyintheground.

Itiseasiertomakeawireground,sayofasmanyormorewiresasyouhaveinyouraerialandconnectthemtogetherwithcrosswires.Toputsuchagroundintheearthyouwillhavetouseaplowtomakethefurrowsdeepenoughtoinsurethemalwaysbeingmoist.Inthecounterpoisegroundyoumakeupasystemofwiresexactlylikeyouraerial,thatis,youinsulatethemjustascarefully;thenyousupportthemsothattheywillbeasclosetothegroundaspossibleandyetnottouchitoranythingelse.Thisandtheothertwogroundsjustdescribedshouldbeplaceddirectlyundertheaerialwireifthebestresultsaretobehad.Inusingacounterpoiseyoumustbringthewirefromituptoandthroughanotherleading-ininsulatortoyourinstruments.

CHAPTERIII

SIMPLETELEGRAPHANDTELEPHONERECEIVINGSETS

Withacrystaldetectorreceivingsetyoucanreceiveeithertelegraphicdotsanddashesortelephonicspeechandmusic.Youcanbuyareceivingsetalreadyassembledoryoucanbuythedifferentpartsandassemblethemyourself.Anassembledsetislessbotherinthebeginningbutifyouliketoexperimentyoucanhookup,thatis,connecttheseparatepartstogetheryourselfanditisperhapsalittlecheapertodoitthisway.Thenagain,bysodoingyougetalotofvaluableexperienceinwirelessworkandanunderstandingoftheworkingsofwirelessthatyoucannotgetinanyotherway.

AssembledWirelessReceivingSets.--Thecheapestassembledreceivingset[Footnote:TheMarvel,madebytheRadioMfg.Co.,NewYorkCity.]advertisedisoneinwhichthedetectorandtuningcoilismountedinabox.Itcosts$15.00,andcanbeboughtofdealersinelectricsuppliesgenerally.

Thispricealsoincludesacrystaldetector,anadjustabletuningcoil,asingletelephonereceiverwithhead-bandandthewire,porcelaininsulators,lightningswitchandgroundclampfortheaerialwiresystem.Itwillreceivewirelesstelegraphandtelephonemessagesoverarangeoffrom10to25miles.

Anothercheapunitreceptor,thatis,acompletewirelessreceivingsetalreadymountedwhichcanbeusedwithasingleaerialissoldfor$25.00.[Footnote:TheAeriolaJr.,madebytheWestinghouseCompany,Pittsburgh,Pa.]Thissetincludesacrystaldetector,avariabletuningcoil,afixedcondenserandapairofheadtelephonereceivers.Itcanalsobeusedtoreceiveeithertelegraphortelephonemessagesfromdistancesupto25miles.Theaerialequipmentisnotincludedinthisprice,butitcanbeboughtforabout$2.50extra.

AssemblingYourOwnReceivingSet.--Inthischapterweshallgoonlyintotheapparatususedfortwosimplereceivingsets,bothofwhichhaveacrystaldetector.Thefirstsetincludesadouble-slidetuningcoilandthesecondsetemploysaloose-coupledtuningcoil,orloosecoupler,asitiscalledforshort.Foreithersetyoucanuseapairof2,000-or3,000-ohmheadphones.

Photographunavailableoriginal©UnderwoodandUnderwood.

GeneralPershingListeningIn.

TheCrystalDetector.--Acrystaldetectorconsistsof:(1)theframe,(2)thecrystal,and(3)thewirepoint.Thereareanynumberofdifferentdesignsforframes,theideabeingtoprovideadevicethatwill(a)holdthesensitivecrystalfirmlyinplace,andyetpermitofitsremoval,(b)topermitthewirepoint,orelectrode,tobemovedinanydirectionsothatthefreepointofitcanmakecontactwiththemostsensitivespotonthecrystaland(c)tovarythepressureofthewireonthecrystal.

Asimpledetectorframeisshowninthecross-sectionatAinFig.10;thecrystal,whichmaybegalena,siliconorironpyrites,isheldsecurelyinaholderwhilethephosphor-bronzewirepointwhichmakescontactwithit,isfixedtooneendofathreadedrodontheotherendofwhichisaknob.

Thisrodscrewsintoandthroughasleevefixedtoaballthatsetsbetweentwobrassstandardsandthispermitsanupanddownorasidetosideadjustmentofthemetalpointwhilethepressureofitonthecrystalisregulatedbythescrew.

Acrystalofthiskindisoftenenclosedinaglasscylinderandthismakesitretainitssensitivenessforamuchlongertimethanifitwereexposedtodustandmoisture.Anuprighttypeofthisdetectorcanbeboughtfor$2.25,whileahorizontaltype,asshownatB,canbeboughtfor$2.75.Galenaisthecrystalthatisgenerallyused,for,whileitisnotquiteassensitiveassiliconandironpyrites,itiseasiertoobtainasensitivepiece.

TheTuningCoil.--Itiswiththetuningcoilthatyoutuneinandtuneoutdifferentstationsandthisyoudobyslidingthecontactstoandfroovertheturnsofwire;inthiswayyouvarytheinductanceandcapacitance,thatis,theconstantsofthereceivingcircuitsandsomakethemreceiveelectricwaves,thatis,wirelesswaves,ofdifferentlengths.

TheDoubleSlideTuningCoil.--Withthistuningcoilyoucanreceivewavesfromanystationupto1,000metersinlength.OneoftheendsofthecoilofwireconnectswiththebindingpostmarkedainFig.11,andtheotherendconnectswiththeotherbindingpostmarkedb,whileoneoftheslidingcontactsisconnectedtothebindingpostc,andtheotherslidingcontactisconnectedwiththebindingpostd.

Whenconnectinginthetuningcoil,onlythepostaorthepostbisusedasmaybemostconvenient,

buttheotherendofthewirewhichisconnectedtoapostisleftfree;justbearthispointinmindwhenyoucometoconnectthetuningcoilupwiththeotherpartsofyourreceivingset.ThetuningcoilisshowncompleteatBanditcosts$3.00or$4.00.Atripleslidetuningcoilconstructedlikethedoubleslidetunerjustdescribed,onlywithmoreturnsofwireonit,makesitpossibletoreceivewavelengthsupto1,500meters.Itcostsabout$6.00.

TheLooseCoupledTuningCoil.--Withaloosecoupler,asthiskindofatuningcoiliscalledforshort,veryselectivetuningispossible,whichmeansthatyoucantuneinastationverysharply,anditwillreceiveanywavelengthsaccordingtosizeofcoils.Theprimarycoiliswoundonafixedcylinderanditsinductanceisvariedbymeansofaslidingcontactlikethedoubleslidetuningcoildescribedabove.Thesecondarycoiliswoundonacylinderthatslidesinandoutoftheprimarycoil.Theinductanceofthiscoilisvariedbymeansofaswitchthatmakescontactwiththefixedpoints,eachofwhichisconnectedwitheverytwentiethturnofwireasshowninthediagramAinFig.12.Theloosecoupler,whichisshowncompleteatB,costsintheneighborhoodof$8.00or$10.00.

FixedandVariableCondensers.--Youdonotrequireacondenserforasimplereceivingset,butifyouwillconnectafixedcondenseracrossyourheadphonesyouwillgetbetterresults,whileavariablecondenserconnectedintheclosedcircuitofadirectcoupledreceivingset,thatis,onewhereadoubleslidetuningcoilisused,makesiteasytotuneverymuchmoresharply;avariablecondenserisabsolutelynecessarywherethecircuitsareinductivelycoupled,thatis,wherealoosecoupledtunerisused.

Afixedcondenserconsistsofanumberofsheetsofpaperwithleavesoftin-foilinbetweenthemandsobuiltupthatoneendofeveryotherleafoftin-foilprojectsfromtheoppositeendofthepaperasshownatAinFig.13.Thepaperandtin-foilarethenpressedtogetherandimpregnatedwithaninsulatingcompound.Afixedcondenseroftheexactcapacitancerequiredforconnectingacrosstheheadphonesismountedinabasefittedwithbindingposts,asshownatB,andcosts75cents.(Paperones25cents.)

Avariablecondenser,seeC,oftherotatingtypeisformedofasetoffixedsemi-circularmetalplateswhichareslightlyseparatedfromeachotherandbetweentheseasimilarsetofmovablesemi-circularmetalplatesismadetointerleave;thelatteraresecuredtoashaftonthetopendofwhichisaknobandbyturningitthecapacitanceofthecondenser,and,hence,ofthecircuitinwhichitisconnected,isvaried.Thiscondenser,whichisshownatD,ismadeintwosizes,thesmalleronebeinglargeenoughforallordinarywavelengthswhilethelargeroneisforproportionatelylongerwavelengths.Thesecondenserscost$4.00and$5.00respectively.

AboutTelephoneReceivers.--Thereareanumberofmakesofheadtelephonereceiversonthemarketthataredesignedespeciallyforwirelesswork.Thesephonesarewoundtoresistancesoffrom75ohmsto8,000ohms,andcostfrom$1.25forareceiverwithoutacordorheadbandto$15.00forapairofphoneswithacordandheadband.Youcangetareceiverwoundtoanyresistanceinbetweentheabovevaluesbutforeitherofthesimplereceivingsetssuchasdescribedinthischapteryououghttohaveapairwoundtoatleast2,000ohmsandthesewillcostyouabout$5.00.ApairofheadphonesofthistypeisshowninFig.14.

ConnectingUptheParts--ReceivingSetNo.1.--Forthissetget(1)acrystaldetector,(2)atwo-slidetuningcoil,(3)afixedcondenser,and(4)apairof2,000ohmheadphones.Mountthedetectorontheright-handsideofaboardandthetuningcoilontheleft-handside.ScrewintwobindingpostsforthecordendsofthetelephonereceiversataandbasshownatAinFig.15.Thisdoneconnectoneoftheendbindingpostsofthetuningcoilwiththegroundwireandapostofoneofthecontactslideswiththelightningarresterorswitchwhichleadstotheaerialwire.

Nowconnectthepostoftheothercontactslidetooneofthepostsofthedetectorandtheotherpostofthelatterwiththebindingposta,thenconnectthebindingpostbtothegroundwireandsolderthejoint.Nextconnecttheendsofthetelephonereceivercordtothepostsaandbandconnectafixedcondenseralsowiththeseposts,allofwhichareshowninthewiringdiagramatB,andyouarereadytoadjustthesetforreceiving.

ReceivingSetNo.2.--UsethesamekindofadetectorandpairofheadphonesasforSetNo.1,butget(1)aloosecoupledtuningcoil,and(2)avariablecondenser.Mounttheloosecoupleratthebackofaboardontheleft-handsideandthevariablecondenserontheright-handside.Thenmountthedetectorinfrontofthevariablecondenserandscrewtwobindingposts,aandb,infrontofthetuningcoilasshownatAinFig.16.

Nowconnectthepostoftheslidingcontactoftheloosecouplerwiththewirethatrunstothelightningswitchandthencetotheaerial;connectthepostoftheprimarycoil,whichistheoutsidecoil,withthegroundwire;thenconnectthebindingpostleadingtotheswitchofthesecondarycoil,whichistheinsidecoil,withoneofthepostsofthevariablecondenser,andfinally,connectthepostthatisjoinedtooneendofthesecondarycoilwiththeotherpostofthevariablecondenser.

Thisdone,connectoneofthepostsofthecondenserwithoneofthepostsofthedetector,theotherpostofthedetectorwiththebindingposta,andthepostbtotheotherpostofthevariablecondenser.Nextconnectafixedcondensertothebindingpostsaandbandthenconnectthetelephonereceiverstothesesameposts,allofwhichisshowninthewiringdiagramatB.Youarenowreadytoadjusttheinstruments.InmakingtheconnectionsuseNo.16or18insulatedcopperwireandscrapetheendscleanwheretheygointothebindingposts.See,also,thatalloftheconnectionsaretightandwhereyouhavetocrossthewireskeepthemapartbyaninchorsoandalwayscrossthematrightangles.

AdjustingtheNo.1Set--TheDetector.--Thefirstthingtodoistotestthedetectorinordertofindoutifthepointofthecontactwireisonasensitivespotofthecrystal.Todothisyouneedabuzzer,aswitchandadrycell.Anelectricbellfromwhichthegonghasbeenremovedwilldoforthebuzzer,butyoucangetonethatismadespeciallyforthepurpose,for75cents,whichgivesoutaclear,high-pitchednotethatsoundslikeahigh-powerstation.

Connectoneofthebindingpostsofthebuzzerwithonepostoftheswitch,theotherpostofthelatterwiththezincpostofthedrycellandthecarbonpostofthistotheotherpostofthebuzzer.Thenconnectthepostofthebuzzerthatisjoinedtothevibrator,tothegroundwireasshowninthewiringdiagram,Fig.17.Nowclosetheswitchofthebuzzercircuit,putonyourheadphones,andmovethewirepointofthedetectortovariousspotsonthecrystaluntilyouhearthesparksmadebythebuzzer

inyourphones.

Thenvarythepressureofthepointonthecrystaluntilyouhearthesparksasloudaspossible.Afteryouhavemadetheadjustmentopentheswitchanddisconnectthebuzzerwirefromthegroundwireofyourset.Thisdone,beverycarefulnottojarthedetectororyouwillthrowitoutofadjustmentandthenyouwillhavetodoitalloveragain.Youarenowreadytotunethesetwiththetuningcoilandlistenin.

TheTuningCoil.--TotunethissetmovetheslideAofthedouble-slidetuner,seeBinFig.15,overtotheendofthecoilthatisconnectedwiththegroundwireandtheslideBneartheoppositeendofthecoil,thatis,theonethathasthefreeend.NowmovetheslideAtowardtheBslideandwhenyouhearthedotsanddashes,orspeechormusic,thatiscominginasloudasyoucanmovetheBslidetowardtheAslideuntilyouhearstillmoreloudly.Averyfewtrialsonyourpartandyouwillbeabletotuneinortuneoutanystationyoucanhear,ifnottoocloseorpowerful.

Photographunavailableoriginal©UnderwoodandUnderwood.

TheWorld'sLargestRadioReceivingStation.OwnedbytheRadioCorporationofAmericaatRocky

PointnearPointJefferson,L.I.

AdjustingtheNo.2Set.--FirstadjustthecrystaldetectorwiththebuzzersetasdescribedabovewithSetNo.1,thenturntheknobofyourvariablecondensersothatthemovableplatesarejusthalf-wayin,pullthesecondarycoilofyourloose-coupledtunerhalfwayout;turntheswitchleveronituntilitmakesacontactwiththemiddlecontactpointandsettheslideroftheprimarycoilhalfwaybetweentheends.

Nowlisteninfortelegraphicsignalsortelephonicspeechormusic;whenyouhearoneortheotherslidethesecondarycoilinandoutoftheprimarycoiluntilthesoundsareloudest;nowmovethecontactswitchoverthepointsforthandbackuntilthesoundsarestilllouder,thenmovetheslidertoandfrountilthesoundsareyetlouderand,finally,turntheknobofthecondenseruntilthesoundsareclearandcrisp.Whenyouhavedoneallofthesethingsyouhave,intheparlanceofthewirelessoperator,tunedinandyouarereadytoreceivewhateverisbeingsent.

CHAPTERIV

SIMPLETELEGRAPHSENDINGSETS

Awirelesstelegraphtransmittingsetcanbeinstalledforaverysmallamountofmoneyprovidedyouarecontentwithonethathasalimitedrange.Largerandbetterinstrumentscan,ofcourse,behadformoremoney,buthowevermuchyouarewillingtospendstillyouarelimitedinyoursendingradiusbytheGovernment'srulesandregulations.Thebestway,andthecheapestintheend,toinstallatelegraphsetistobuytheseparatepartsandhookthemupyourself.

Theusualtypeofwirelesstelegraphtransmitteremploysadisruptivedischarge,orspark,asitiscalled,forsettinguptheoscillatingcurrentsintheaerialwiresystemandthisisthetypeofapparatusdescribedinthischapter.Therearetwowaystosetupthesparksandtheseare:(1)withaninductioncoil,orspark-coil,asitiscommonlycalled,and(2)withanalternatingcurrenttransformer,orpowertransformer,asitissometimescalled.Whereyouhavetogeneratethecurrentwithabatteryyoumustuseasparkcoil,butifyouhavea110-voltdirectoralternatinglightingcurrentinyourhomeyoucanuseatransformerwhichwillgiveyoumorepower.

ACheapTransmittingSet(No.1).--Forthissetyouwillneed:(1)aspark-coil,(2)abatteryofdrycells,(3)atelegraphkey,(4)asparkgap,(5)ahigh-tensioncondenser,and(6)anoscillationtransformer.Therearemanydifferentmakesandstylesofthesepartsbutinthelastanalysisallofthemarebuiltonthesameunderlyingbasesandworkonthesamefundamentalprinciples.

TheSpark-Coil.--Sparkcoilsforwirelessworkaremadetogivesparksfrom1/4inchinlengthupto6inchesinlength,butasasparkcoilthatgiveslessthana1-inchsparkhasaverylimitedoutputitisbesttogetacoilthatgivesatleasta1-inchspark,asthisonlycostsabout$8.00,andifyoucangeta2-ora4-inchsparkcoilsomuchthebetter.TherearetwogeneralstylesofsparkcoilsusedforwirelessandtheseareshownatAandBinFig.18.

Asparkcoilofeitherstyleconsistsof(a)asoftironcoreonwhichiswound(b)acoupleoflayersofheavyinsulatedwireandthisiscalledtheprimarycoil,(c)whileoverthis,butinsulatedfromit,iswoundalargenumberofturnsofveryfineinsulatedcopperwirecalledthesecondarycoil;(d)aninterrupter,orvibrator,asitiscommonlycalled,and,finally,(e)acondenser.Thecore,primaryandsecondarycoilsformaunitandthesearesetinaboxormountedontopofahollowwoodenbase.Thecondenserisplacedinthebottomofthebox,oronthebase,whilethevibratorismountedononeendoftheboxorontopofthebase,anditistheonlypartofthecoilthatneedsadjusting.

Thevibratorconsistsofastiff,flatspringfixedatoneendtotheboxorbasewhileitcarriesapieceofsoftironcalledanarmatureonitsfreeendandthissetsclosetooneendofthesoftironcore.Insulatedfromthisspringisastandardthatcarriesanadjustingscrewonthesmallendofwhichisaplatinumpointandthismakescontactwithasmallplatinumdiskfixedtothespring.ThecondenserisformedofalternatesheetsofpaperandtinfoilbuiltupinthesamefashionasthereceivingcondenserdescribedunderthecaptionofFixedandVariableCondensers,inChapterIII.

ThewiringdiagramCshowshowthesparkcoiliswiredup.Oneofthebatterybindingpostsisconnectedwithoneendoftheprimarycoilwhiletheotherendofthelatterwhichiswoundonthesoftironcoreconnectswiththespringofthevibrator.Theotherbatterybindingpostconnectswiththestandardthatsupportstheadjustingscrew.Thecondenserisshuntedacrossthevibrator,thatis,oneendofthecondenserisconnectedwiththespringandtheotherendofthecondenserisconnectedwiththeadjustingscrewstandard.Theendsofthesecondarycoilleadtotwobindingposts,whichareusuallyplacedontopofthesparkcoilanditistothesethatthesparkgapisconnected.

TheBattery.--Thiscanbeformedofdrycellsoryoucanuseastoragebatterytoenergizeyourcoil.Forallcoilsthatgivelessthana1-inchsparkyoushoulduse5drycells;for1-and2-inchsparkcoilsuse6or8drycells,andfor3to4-inchsparkcoilsuse8to10drycells.Thewaythedrycellsareconnectedtogethertoformabatterywillbeshownpresently.AdrycellisshownatAinFig,19.

TheTelegraphKey.--YoucanuseanordinaryMorsetelegraphkeyforthesendingsetandyoucangetonewithajapannedironbasefor$1.50(orbetter,onemadeofbrassandwhichhas1/8-inchsilvercontactpointsfor$3.00.AkeyofthelatterkindisshownatB).

TheSparkgap.--Itisinthesparkgapthatthehightensionsparktakesplace.Theapparatusinwhichthesparktakesplaceisalsocalledthesparkgap.Itconsistsofapairofzincplugs,calledelectrodes,fixedtotheendsofapairofthreadedrods,withknobsontheotherends,andthesescrewintoandthroughapairofstandardsasshownatc.Thisiscalledafixed,orstationarysparkgapandcostsabout$1.00.

TheTuningCoil.--Thetransmittinginductance,orsendingtuningcoil,consistsof20to30turnsofNo.8or9harddrawncopperwirewoundonaslottedinsulatedformandmountedonawoodenbase.Itisprovidedwithclipssothatyoucancutinandcutoutasmanyturnsofwireasyouwishandsotunethesendingcircuitstosendoutwhateverwavelengthyoudesire.Itisshownatd,andcostsabout$5.00.SeealsoOscillationTransformer,page63[ChapterIV].

TheHighTensionCondenser.--Hightensioncondensers,thatis,condenserswhichwillstandupunderhighpotentials,orelectricpressures,canbeboughtinunitsorsections.Thesecondensersaremadeupofthinbrassplatesinsulatedwithaspecialcompoundandpressedintoacompactform.Thecapacitance[Footnote:Thisisthecapacityofthecondenser.]ofonesectionisenoughforatransmittingsetusingasparkcoilthatgivesa2inchsparkorlessandtwosectionsconnectedtogethershouldbeusedforcoilsgivingfrom2to4inchsparks.Itisshownate.

ConnectingUptheApparatus.--Yoursendingsetshouldbemountedonatable,orabench,whereitneednotbemoved.Placethekeyinaboutthemiddleofthetableanddowninfront,andthesparkcoiltotheleftandwelltothebackbutsothatthevibratorendwillbetotheright,asthiswillenableyoutoadjustiteasily.Placethebatterybackofthesparkcoilandthetuningcoil(oscillationtransformer)totherightofthesparkcoilandbackofthekey,allofwhichisshowninthelayoutatAinFig.20.

Forthelowvoltagecircuit,thatisthebatterycircuit,useNo.12or14insulatedcopperwire.Connectallofthedrycellstogetherinseries,thatis,connectthezincofonecellwiththecarbonofthenextandsoonuntilallofthemareconnectedup.Thenconnectthecarbonoftheendcellwithoneofthe

postsofthekey,thezincoftheotherendcellwithoneoftheprimarypostsofthesparkcoilandtheotherprimarypostofthesparkcoilwiththeotherpostofthekey,whentheprimarycircuitwillbecomplete.

Forthehightensioncircuits,thatis,theoscillationcircuits,youmayuseeitherbareorinsulatedcopperwirebutyoumustbecarefulthattheydonottouchthetable,eachother,oranypartoftheapparatus,except,ofcourse,thepoststheyareconnectedwith.Connectoneofthepostsofthesecondarycoilofthesparkcoilwithoneofthepostsofthesparkgap,andtheotherpostwithoneofthepostsofthecondenser;thenconnecttheotherpostofthecondenserwiththelowerspringclipofthetuningcoilandalsoconnectthisclipwiththeground.Thisdone,connectthemiddlespringclipwithoneofthepostsofthesparkgap,and,finally,connectthetopclipwiththeaerialwireandyourtransmittingsetisreadytobetuned.AwiringdiagramoftheconnectionsisshownatB.AsthissetistunedinthesamewayasSetNo.2whichfollows,youarereferredtotheendofthischapter.

ABetterTransmittingSet(No.2).--Theapparatusforthissetincludes:(1)analternatingcurrenttransformer,(2)awirelesstelegraphkey,(3)afixed,arotary,oraquenchedsparkgap,(4)acondenser,and(5)anoscillationtransformer.Ifyouhavea110voltdirectlightingcurrentinyourhomeinsteadof110voltalternatingcurrent,thenyouwillalsoneed(6)anelectrolyticinterrupter,forinthiscasetheprimarycircuitofthetransformermustbemadeandbrokenrapidlyinordertosetupalternatingcurrentsinthesecondarycoil.

TheAlternatingCurrentTransformer.--Analternatingcurrent,orpower,transformerismadeonthesameprincipleasasparkcoil,thatis,ithasasoftironcore,aprimarycoilformedofacoupleoflayersofheavywire,andasecondarycoilwoundupofalargenumberofturnsofveryfinewire.Unlikethesparkcoil,however,whichhasanopenmagneticcoreandwhosesecondarycoiliswoundontheprimarycoil,thetransformerhasaclosedmagneticcore,withtheprimarycoilwoundononeofthelegsofthecoreandthesecondarywoundontheotherleg.Ithasneitheravibratornoracondenser.AplaintransformerisshownatAinFig.21.

Atransformerofthiskindcanbeboughteither(a)unmounted,thatis,justthebaretransformer,or(b)fullymounted,thatis,fittedwithanironstand,mountedonaninsulatingbaseonwhichareapairofprimarybindingposts,whilethesecondaryisprovidedwithasafetysparkgap.Therearethreesizesoftransformersofthiskindmadeandtheyareratedat1/4,1/2and1kilowatt,respectively,theydeliverasecondarycurrentof9,000,11,000and25,000volts,accordingtosize,andcost$16.00,$22.00and$33.00whenfullymounted;areductionof$3.00,$4.00and$5.00ismadewhentheyareunmounted.Allofthesetransformersoperateon110volt,60cyclecurrentandcanbeconnecteddirectlytothesourceofalternatingcurrent.

TheWirelessKey.--ForthistransmittingsetastandardwirelesskeyshouldbeusedasshownatB.Itismadeaboutthesameasaregulartelegraphkeybutitismuchheavier,thecontactpointsarelargerandinsteadofthecurrentbeingledthroughthebearingsasinanordinarykey,itiscarriedbyheavyconductorsdirectlytothecontactpoints.Thiskeyismadeinthreesizesandthefirstwillcarryacurrentof5amperes[Footnote:SeeAppendixfordefinition.]andcosts$4.00,thesecondwillcarryacurrentof10amperesandcosts$6.50,whilethethirdwillcarryacurrentof20amperesandcosts$7.50.

TheSparkGap.--Eitherafixed,arotary,oraquenchedsparkgapcanbeusedwiththisset,buttheformerisseldomusedexceptwithspark-coilsets,asitisveryhardtokeepthesparksfromarcingwhenlargecurrentsareused.Arotarysparkgapcomprisesawheel,drivenbyasmallelectricmotor,withprojectingplugs,orelectrodes,onitandapairofstationaryplugsoneachsideofthewheelas

shownatC.Thenumberofsparkspersecondcanbevariedbychangingthespeedofthewheelandwhenitisrotatedrapidlyitsendsoutsignalsofahighpitchwhichareeasytoreadatthereceivingend.Arotarygapwitha110-voltmotorcostsabout$25.00.

Aquenchedsparkgapnotonlyeliminatesthenoiseoftheordinarygapbut,whenproperlydesigned,itincreasestherangeofaninductioncoilsetsome200percent.A1/4kilowattquenchedgapcosts$10.00.[Footnote:SeeAppendixfordefinition.]

TheHighTensionCondenser.--Since,ifyouareanamateur,youcanonlysendoutwavesthatare200metersinlength,youcanonlyuseacondenserthathasacapacitanceof.007microfarad.[Footnote:SeeAppendixfordefinition.]AsectionalhightensioncondenserliketheonedescribedinconnectionwithSetNo.1canbeusedwiththissetbutitmusthaveacapacitanceofnotmorethan.007microfarad.Acondenserofthisvaluefora1/4-kilowatttransformercosts$7.00;fora1/2-kilowatttransformer$14.00,andfora1-kilowatttransformer$21.00.SeeE,Fig.19.

TheOscillationTransformer.--Withanoscillationtransformeryoucantunemuchmoresharplythanwithasingleinductancecoiltuner.Theprimarycoilisformedof6turnsofcopperstrip,orNo.9copperwire,andthesecondaryisformedof9turnsofstrip,orwire.Theprimarycoil,whichistheoutsidecoil,ishingedtothebaseandcanberaisedorloweredlikethelidofabox.Whenitisloweredtheprimaryandsecondarycoilsareinthesameplaneandwhenitisraisedthecoilssetatanangletoeachother.ItisshownatDandcosts$5.00.

ConnectingUptheApparatus.ForAlternatingCurrent.--Screwthekeytothetableaboutthemiddleofitandnearthefrontedge;placethehightensioncondenserbackofitandtheoscillationtransformerbackofthelatter;setthealternatingcurrenttransformertotheleftoftheoscillationtransformerandplacetherotaryorquenchedsparkgapinfrontofit.

NowbringapairofNo.12or14insulatedwiresfromthe110voltlightingleadsandconnectthemwithasingle-throw,double-poleswitch;connectonepoleoftheswitchwithoneofthepostsoftheprimarycoilofthealternatingpowertransformerandconnecttheotherpostofthelatterwithoneofthepostsofyourkey,andtheotherpostofthiswiththeotherpoleoftheswitch.Nowconnectthemotoroftherotarysparkgaptothepowercircuitandputasingle-pole,single-throwswitchinthemotorcircuit,allofwhichisshownatAinFig.22.

Nextconnectthepostsofthesecondarycoiltothepostsoftherotaryorquenchedsparkgapandconnectonepostofthelattertoonepostofthecondenser,theotherpostofthistothepostoftheprimarycoiloftheoscillationtransformer,whichistheinsidecoil,andtheclipoftheprimarycoiltotheothersparkgappost.Thiscompletestheclosedoscillationcircuit.Finallyconnectthepostofthesecondarycoiloftheoscillationtransformertothegroundandtheclipofittothewireleadingtotheaerialwhenyouarereadytotunetheset.AwiringdiagramoftheconnectionsisshownatB.

ForDirectCurrent.--Whereyouhave110voltdirectcurrentyoumustconnectinanelectrolyticinterrupter.Thisinterrupter,whichisshownatAandBinFig.23,consistsof(1)ajarfilledwithasolutionof1partofsulphuricacidand9partsofwater,(2)aleadelectrodehavingalargesurfacefastenedtothecoverofsurfacethatsetsinaporcelainsleeveandwhoseendrestsonthebottomofthejar.

Whentheseelectrodesareconnectedinserieswiththeprimaryofalargesparkcoiloranalternatingcurrenttransformer,seeC,andadirectcurrentoffrom40to110voltsismadetopassthroughit,thecurrentismadeandbrokenfrom1,000to10,000timesaminute.Byraisingorloweringthesleeve,thusexposingmoreorlessoftheplatinum,oralloypoint,thenumberofinterruptionsperminutecanbevariedatwill.Astheelectrolyticinterrupterwillonlyoperateinonedirection,youmustconnectitwithitsplatinum,oralloyanode,tothe+orpositivepowerleadandtheleadcathodetothe-ornegativepowerlead.Youcanfindoutwhichiswhichbyconnectingintheinterrupterandtryingit,oryoucanuseapolarityindicator.Anelectrolyticinterruptercanbeboughtforaslittleas$3.00.

HowtoAdjustYourTransmitter.TuningWithaHotWireAmmeter.--Atransmittercanbetunedintwodifferentwaysandtheseare:(1)byadjustingthelengthofthesparkgapandthetuningcoilsothatthegreatestamountofenergyissetupintheoscillatingcircuits,and(2)byadjustingtheapparatussothatitwillsendoutwavesofagivenlength.

Toadjustthetransmittersothatthecircuitswillbeintuneyoushouldhaveahotwireammeter,orradiationammeter,asitiscalled,whichisshowninFig.24.Itconsistsofathinplatinumwire

throughwhichthehigh-frequencycurrentssurgeandtheseheatit;theexpansionandcontractionofthewiremovesaneedleoverascalemarkedoffintofractionsofanampere.Whenthesparkgapandtuningcoilofyoursetareproperlyadjusted,theneedlewillswingfarthesttotherightoverthescaleandyouwillthenknowthattheaerialwiresystem,oropenoscillationcircuit,andtheclosedoscillationcircuitareintuneandradiatingthegreatestamountofenergy.

ToSendOuta200MeterWaveLength.--Ifyouareusingacondenserhavingacapacitanceof.007microfarad,whichisthelargestcapacityvaluethattheGovernmentwillallowanamateurtouse,thenifyouhaveahotwireammeterinyouraerialandtunetheinductancecoilorcoilsuntiltheammetershowsthelargestamountofenergyflowingthroughityouwillknowthatyourtransmitteristunedandthattheaerialissendingoutwaveswhoselengthis200meters.Totunetodifferentwavelengthsyoumusthaveawave-meter.

TheUseoftheAerialSwitch.--Whereyouintendtoinstallbothatransmitterandareceptoryouwillneedathrowoverswitch,oraerialswitch,asitiscalled.Anordinarydouble-pole,double-throwswitch,asshownatAinFig.25,canbeused,oraswitchmadeespeciallyforthepurposeasatBishandierbecausethearcofthethrowismuchless.

AerialSwitchforaCompleteSendingandReceivingSet.--Youcanbuyadouble-pole,double-throwswitchmountedonaporcelainbaseforabout75centsandthiswillserveforSetNo.1.Screwthisswitchonyourtablebetweenthesendingandreceivingsetsandthenconnectoneofthemiddlepostsofitwiththegroundwireandtheothermiddlepostwiththelightningswitchwhichconnectswiththeaerial.Connectthepostofthetuningcoilwithoneoftheendpostsoftheswitchandtheclipofthetuningcoilwiththeotherandcomplementarypostoftheswitch.Thisdone,connectoneoftheoppositeendpostsoftheswitchtothepostofthereceivingtuningcoilandconnecttheslidingcontactofthelatterwiththeotherandcomplementarypostoftheswitchasshowninFig.26.

ConnectingintheLightningSwitch.--Theaerialwireconnectswiththemiddlepostofthelightningswitch,whileoneoftheendpostsleadtooneofthemiddlepostsoftheaerialswitch.Theotherendpostofthelightningswitchleadstoaseparategroundoutsidethebuilding,asthewiringdiagramsFigs.26and27show.

CHAPTERV

ELECTRICITYSIMPLYEXPLAINED

Itiseasytounderstandhowelectricitybehavesandwhatitdoesifyougettherightideaofitatthestart.Inthefirstplace,ifyouwillthinkofelectricityasbeingafluidlikewateritsfundamentalactionswillbegreatlysimplified.Bothwaterandelectricitymaybeatrestorinmotion.Whenatrest,undercertainconditions,eitheronewilldeveloppressure,andthispressurewhenreleasedwillcausethemtoflowthroughtheirrespectiveconductorsandthusproduceacurrent.

ElectricityatRestandinMotion.--Anywireoraconductorofanykindcanbechargedwithelectricity,butaLeydenjar,orothercondenser,isgenerallyusedtoholdanelectricchargebecauseithasamuchlargercapacitance,asitscapacityiscalled,thanawire.Asasimpleanalogueofacondenser,supposeyouhaveatankofwaterraisedaboveasecondtankandthattheseareconnectedtogetherbymeansofapipewithavalveinit,asshownatAinFig.28.

Photographunavailableoriginal©UnderwoodandUnderwood.

FirstWirelessCollegeintheWorld,atTuftsCollege,Mass.

Nowifyoufilltheuppertankwithwaterandthevalveisturnedoff,nowatercanflowintothelowertankbutthereisadifferenceofpressurebetweenthem,andthemomentyouturnthevalveonacurrentofwaterwillflowthroughthepipe.Inverymuchthesamewaywhenyouhaveacondenserchargedwithelectricitythelatterwillbeunderpressure,thatis,adifferenceofpotentialwillbesetup,foroneofthesheetsofmetalwillbechargedpositivelyandtheotherone,whichisinsulatedfromit,willbechargednegatively,asshownatB.Onclosingtheswitchtheoppositechargesrushtogetherandformacurrentwhichflowstoandfrobetweenthemetalplates.[Footnote:Strictlyspeakingitisthedifferenceofpotentialthatsetsuptheelectromotiveforce.]

TheElectricCurrentandItsCircuit.--Justaswaterflowingthroughapipehasquantityandpressure

backofitandthepipeoffersfrictiontoitwhichtendstoholdbackthewater,so,likewise,doeselectricityflowinginacircuithave:(1)quantity,orcurrentstrength,orjustcurrent,asitiscalledforshort,oramperage,and(2)pressure,orpotentialdifference,orelectromotiveforce,orvoltage,asitisvariouslycalled,andthewire,orcircuit,inwhichthecurrentisflowinghas(3)resistancewhichtendstoholdbackthecurrent.

Adefiniterelationexistsbetweenthecurrentanditselectromotiveforceandalsobetweenthecurrent,electromotiveforceandtheresistanceofthecircuit;andifyouwillgetthisrelationshipclearlyinyourmindyouwillhaveaverygoodinsightintohowdirectandalternatingcurrentsact.Tokeepaquantityofwaterflowinginaloopofpipe,whichwewillcallthecircuit,pressuremustbeappliedtoitandthismaybedonebyarotarypumpasshownatAinFig.29;inthesameway,tokeepaquantityofelectricityflowinginaloopofwire,orcircuit,abattery,orothermeansforgeneratingelectricpressuremustbeused,asshownatB.

Ifyouhaveaclosedpipeconnectedwithapistonpump,asatC,asthepistonmovestoandfrothewaterinthepipewillmovefirstonewayandthentheother.Soalsowhenanalternatingcurrentgeneratorisconnectedtoawirecircuit,asatD,thecurrentwillflowfirstinonedirectionandthenintheother,andthisiswhatiscalledanalternatingcurrent.

CurrentandtheAmpere.--Theamountofwaterflowinginaclosedpipeisthesameatallpartsofitandthisisalsotrueofanelectriccurrent,inthatthereisexactlythesamequantityofelectricityatonepointofthecircuitasthereisatanyother.

Theamountofelectricity,orcurrent,flowinginacircuitinasecondismeasuredbyaunitcalledtheampere,[Footnote:FordefinitionofampereseeAppendix.]anditisexpressedbythesymbolI.[Footnote:ThisisbecausetheletterCisusedforthesymbolofcapacitance]Justtogiveyouanideaofthequantityofcurrentanampereiswewillsaythatadrycellwhenfreshgivesacurrentofabout20amperes.Tomeasurethecurrentinamperesaninstrumentcalledanammeterisused,asshownatAinFig.30,andthisisalwaysconnectedinserieswiththeline,asshownatB.

ElectromotiveForceandtheVolt.--Whenyouhaveapipefilledwithwateroracircuitchargedwithelectricityandyouwanttomakethemflowyoumustuseapumpinthefirstcaseandabatteryoradynamointhesecondcase.Itisthebatteryordynamothatsetsuptheelectricpressureasthecircuititselfisalwayschargedwithelectricity.

Themorecellsyouconnecttogetherinseriesthegreaterwillbetheelectricpressuredevelopedandthemorecurrentitwillmovealongjustastheamountofwaterflowinginapipecanbeincreasedbyincreasingthepressureofthepump.Theunitofelectromotiveforceisthevolt,andthisistheelectricpressurewhichwillforceacurrentof1amperethrougharesistanceof1ohm;itisexpressedbythesymbolE.Afreshdrycellwilldeliveracurrentofabout1.5volts.Tomeasurethepressureofacurrentinvoltsaninstrumentcalledavoltmeterisused,asshownatCinFig.30,andthisisalwaysconnectedacrossthecircuit,asshownatD.

ResistanceandtheOhm.--Justasawaterpipeoffersacertainamountofresistancetotheflowofwaterthroughit,soacircuitopposestheflowofelectricityinitandthisiscalledresistance.Further,inthesamewaythatasmallpipewillnotallowalargeamountofwatertoflowthroughit,so,too,athinwirelimitstheflowofthecurrentinit.

Ifyouconnectaresistancecoilinacircuititactsinthesamewayaspartlyclosingthevalveinapipe,asshownatAandBinFig.31.Theresistanceofacircuitismeasuredbyaunitcalledtheohm,anditisexpressedbythesymbolR.ANo.10,BrownandSharpegaugesoftcopperwire,1,000feetlong,hasaresistanceofabout1ohm.Tomeasuretheresistanceofacircuitanapparatuscalledaresistancebridgeisused.Theresistanceofacircuitcan,however,beeasilycalculated,asthefollowingshows.

WhatOhm'sLawIs.--If,now,(1)youknowwhatthecurrentflowinginacircuitisinamperes,andtheelectromotiveforce,orpressure,isinvolts,youcantheneasilyfindwhattheresistanceisinohmsofthecircuitinwhichthecurrentisflowingbythisformula:

VoltsE

---------=Ohms,or---=R

AmperesI

Thatis,ifyoudividethecurrentinamperesbytheelectromotiveforceinvoltsthequotientwillgiveyoutheresistanceinohms.

Or(2)ifyouknowwhattheelectromotiveforceofthecurrentisinvoltsandtheresistanceofthecircuitisinohmsthenyoucanfindwhatthecurrentflowinginthecircuitisinamperes,thus:

VoltsE

-----=Amperes,or---=I

OhmsR

Thatis,bydividingtheresistanceofthecircuitinohms,bytheelectromotiveforceofthecurrentyouwillgettheamperesflowinginthecircuit.

Finally(3)ifyouknowwhattheresistanceofthecircuitisinohmsandthecurrentisinamperesthenyoucanfindwhattheelectromotiveforceisinvoltssince:

OhmsxAmperes=Volts,orRxI=E

Thatis,ifyoumultiplytheresistanceofthecircuitinohmsbythecurrentinamperestheresultwillgiveyoutheelectromotiveforceinvolts.

Fromthisyouwillseethatifyouknowthevalueofanytwooftheconstantsyoucanfindthevalueoftheunknownconstantbyasimplearithmeticalprocess.ThisrelationbetweenthesethreeconstantsisknownasOhm'sLawandastheyareveryimportantyoushouldmemorizethem.

WhattheWattandKilowattAre.--JustashorsepowerorH.P.,istheunitofworkthatsteamhasdoneorcando,sothewattistheunitofworkthatanelectriccurrenthasdoneorcando.Tofindthewattsacurrentdevelopsyouneedonlytomultiplytheamperesbythevolts.Thereare746wattsto1horsepower,and1,000wattsareequalto1kilowatt.

ElectromagneticInduction.--Toshowthatacurrentofelectricitysetsupamagneticfieldaroundityouhaveonlytoholdacompassoverawirewhoseendsareconnectedwithabatterywhentheneedlewillswingatrightanglestothelengthofthewire.Bywindinganinsulatedwireintoacoilandconnectingtheendsofthelatterwithabatteryyouwillfind,ifyoutestitwithacompass,thatthecoilismagnetic.

ThisisduetothefactthattheenergyofanelectriccurrentflowinginthewireispartlychangedintomagneticlinesofforcewhichrotateatrightanglesaboutitasshownatAinFig.32.Themagneticfieldproducedbythecurrentflowinginthecoilispreciselythesameasthatsetupbyapermanentsteelmagnet.Conversely,whenamagneticlineofforceissetupapartofitsenergygoestomakeupelectriccurrentswhichwhirlaboutinalikemanner,asshownatB.

Self-inductionorInductance.--Whenacurrentismadetoflowinacoilofwirethemagneticlinesofforceproducedareconcentrated,asatC,justasalensconcentratesraysoflight,andthisformsanintensemagneticfield,asitiscalled.Nowifabarofsoftironisbroughtclosetooneendofthecoilofwire,or,betterstill,ifitispushedintothecoil,itwillbemagnetizedbyelectromagneticinduction,seeD,anditwillremainamagnetuntilthecurrentiscutoff.

MutualInduction.--Whentwoloopsofwire,orbetter,twocoilsofwire,areplacedclosetogethertheelectromagneticinductionbetweenthemisreactive,thatis,whenacurrentismadetoflowthroughoneofthecoilsclosedmagneticlinesofforcearesetupandwhenthesecuttheotherlooporturnsofwireoftheothercoil,theyinturnproduceelectriccurrentsinit.

Itisthemutualinductionthattakesplacebetweentwocoilsofwirewhichmakesitpossibletotransformlowvoltagecurrentsfromabatteryora110voltsourceofcurrentintohighpressurecurrents,orhighpotentialcurrents,astheyarecalled,bymeansofasparkcoiloratransformer,aswellastostepupandstepdownthepotentialofthehighfrequencycurrentsthataresetupinsendingandreceivingoscillationtransformers.Softironcoresarenotusedinoscillationinductancecoilsandoscillationtransformersforthereasonthatthefrequencyofthecurrentissohightheironwouldnothavetimetomagnetizeanddemagnetizeandsowouldnothelpalongthemutualinductiontoanyappreciableextent.

High-FrequencyCurrents.--Highfrequencycurrents,orelectricoscillationsastheyarecalled,arecurrentsofelectricitythatsurgetoandfroinacircuitamilliontimes,moreorless,persecond.Currentsofsuchhighfrequencieswilloscillate,thatis,surgetoandfro,inanopencircuit,suchasanaerialwiresystem,aswellasinaclosedcircuit.

Nowthereisonlyonemethodbywhichcurrentsofhighfrequency,orradio-frequency,astheyaretermed,canbesetupbysparktransmitters,andthisisbydischargingachargedcondenserthroughacircuithavingasmallresistance.Tochargeacondenserasparkcoiloratransformerisusedandtheendsofthesecondarycoil,whichdeliversthehighpotentialalternatingcurrent,areconnectedwiththecondenser.Todischargethecondenserautomaticallyaspark,oranarc,ortheflowofelectronsinavacuumtube,isemployed.

ConstantsofanOscillationCircuit.--Anoscillationcircuit,aspointedoutbefore,isoneinwhichhighfrequencycurrentssurgeoroscillate.Nowthenumberoftimesahighfrequencycurrentwillsurgeforthandbackinacircuitdependsuponthreefactorsofthelatterandthesearecalledtheconstantsofthecircuit,namely:(1)itscapacitance,(2)itsinductanceand(3)itsresistance.

WhatCapacitanceIs.--Thewordcapacitancemeanstheelectrostaticcapacityofacondenseroracircuit.Thecapacitanceofacondenseroracircuitisthequantityofelectricitywhichwillraiseitspressure,orpotential,toagivenamount.Thecapacitanceofacondenseroracircuitdependsonitssizeandformandthevoltageofthecurrentthatischargingit.

Thecapacitanceofacondenseroracircuitisdirectlyproportionaltothequantityofelectricitythatwillkeepthechargeatagivenpotential.Thefarad,whosesymbolisM,istheunitofcapacitanceandacondenseroracircuittohaveacapacitanceofonefaradmustbeofsuchsizethatonecoulomb,whichistheunitofelectricalquantity,willraiseitschargetoapotentialofonevolt.Sincethefaradisfartoolargeforpracticalpurposesamillionthofafarad,ormicrofarad,whosesymbolismfd.,isused.

WhatInductanceIs.--Underthesub-captionofSelf-inductionandInductanceinthebeginningofthischapteritwasshownthatitwastheinductanceofacoilthatmakesacurrentflowingthroughitproduceastrongmagneticfield,andhere,asoneoftheconstantsofanoscillationcircuit,itmakesahigh-frequencycurrentactasthoughitpossessedinertia.

Inertiaisthatpropertyofamaterialbodythatrequirestimeandenergytosetinmotion,orstop.Inductanceisthatpropertyofanoscillationcircuitthatmakesanelectriccurrenttaketimetostartandtimetostop.Becauseoftheinductance,whenacurrentflowsthroughacircuititcausestheelectricenergytobeabsorbedandchangesalargepartofitintomagneticlinesofforce.Wherehighfrequencycurrentssurgeinacircuittheinductanceofitbecomesapowerfulfactor.ThepracticalunitofinductanceisthehenryanditisrepresentedbythesymbolL.

WhatResistanceIs.--Theresistanceofacircuittohigh-frequencycurrentsisdifferentfromthatforlowvoltagedirectoralternatingcurrents,astheformerdonotsinkintotheconductortonearlysogreatanextent;infact,theystickpracticallytothesurfaceofit,andhencetheirflowisopposedtoaverymuchgreaterextent.Theresistanceofacircuittohighfrequencycurrentsisgenerallyfoundinthesparkgap,arcgap,orthespacebetweentheelectrodesofavacuumtube.Theunitofresistanceis,asstated,theohm,anditssymbolisR.

TheEffectofCapacitance,InductanceandResistanceonElectricOscillations.--Ifanoscillationcircuitinwhichhighfrequencycurrentssurgehasalargeresistance,itwillsoopposetheflowofthecurrentsthattheywillbedampedoutandreachzerogradually,asshownatAinFig.33.Butiftheresistanceofthecircuitissmall,andinwirelesscircuitsitisusuallysosmallastobenegligible,thecurrentswilloscillate,untiltheirenergyisdampedoutbyradiationandotherlosses,asshownatB.

Asthecapacitanceandtheinductanceofthecircuit,whichmaybemadeofanyvalue,thatisamount,youwish,determinesthetimeperiod,thatis,thelengthoftimeforacurrenttomakeonecompleteoscillation,itmustbeclearthatbyvaryingthevaluesofthecondenserandtheinductancecoilyoucanmakethehighfrequencycurrentoscillateasfastorasslowasyouwishwithincertainlimits.Wheretheelectricoscillationsthataresetupareveryfast,thewavessentoutbytheaerialwillbeshort,and,conversely,wheretheoscillationsareslowthewavesemittedwillbelong.

CHAPTERVI

HOWTHETRANSMITTINGANDRECEIVINGSETSWORK

Theeasiestwaytogetaclearconceptionofhowawirelesstransmittersendsoutelectricwavesandhowawirelessreceptorreceivesthemistotakeeachoneseparatelyandfollow:(1)inthecaseofthetransmitter,thetransformationofthelowvoltagedirect,oralternatingcurrentintohighpotentialalternatingcurrents;thenfindouthowthesechargethecondenser,howthisisdischargedbythesparkgapandsetsuphigh-frequencycurrentsintheoscillationcircuits;then(2)inthecaseofthereceptor,tofollowthehighfrequencycurrentsthataresetupintheaerialwireandlearnhowtheyaretransformedintooscillationsoflowerpotentialwhentheyhavealargercurrentstrength,howtheseareconvertedintointermittentdirectcurrentsbythedetectorandwhichthenflowintoandoperatethetelephonereceiver.

HowTransmittingSetNo.1Works.TheBatteryandSparkCoilCircuit.--Whenyoupressdownontheknobofthekeythesilverpointsofitmakecontactandthisclosesthecircuit;thelowvoltagedirectcurrentfromthebatterynowflowsthroughtheprimarycoilofthesparkcoilandthismagnetizesthesoftironcore.Theinstantitbecomesmagneticitpullsthespringofthevibratorovertoitandthisbreaksthecircuit;whenthistakesplacethecurrentstopsflowingthroughtheprimarycoil;thiscausesthecoretoloseitsmagnetismwhenthevibratorspringfliesbackandagainmakescontactwiththeadjustingscrew;thenthecycleofoperationsisrepeated.

Acondenserisconnectedacrossthecontactpointsofthevibratorsincethisgivesamuchhighervoltageattheendsofthesecondarycoilthanwherethecoilisusedwithoutit;thisisbecause:(1)theself-inductionoftheprimarycoilmakesthepressureofthecurrentriseandwhenthecontactpointsclosethecircuitagainitdischargesthroughtheprimarycoil,and(2)whenthebreaktakesplacethecurrentflowsintothecondenserinsteadofarcingacrossthecontactpoints.

ChangingthePrimarySparkCoilCurrentIntoSecondaryCurrents.--Noweverytimethevibratorcontactpointsclosetheprimarycircuittheelectriccurrentintheprimarycoilischangedintoclosedmagneticlinesofforceandasthesecutthroughthesecondarycoiltheysetupinitamomentarycurrentinonedirection.Thentheinstantthevibratorpointsbreakaparttheprimarycircuitisopenedandtheclosedmagneticlinesofforcecontractandastheydosotheycuttheturnsofwireinthesecondarycoilintheoppositedirectionandthissetsupanothermomentarycurrentinthesecondarycoilintheotherdirection.Theresultisthatthelowvoltagedirectcurrentofthebatteryischangedintoalternatingcurrentswhosefrequencyispreciselythatofthespringvibrator,butwhilethefrequencyofthecurrentsislowtheirpotential,orvoltage,isenormouslyincreased.

WhatRatioofTransformationMeans.--Tomakeasparkcoilstepupthelowvoltagedirectcurrentintohighpotentialalternatingcurrenttheprimarycoiliswoundwithacoupleoflayersofthickinsulatedcopperwireandthesecondaryiswoundwithathousand,moreorless,numberofturnswithveryfineinsulatedcopperwire.Iftheprimaryandsecondarycoilswerewoundwiththesamenumberofturnsofwirethenthepressure,orvoltage,ofthesecondarycoilatitsterminalswouldbethesameasthatofthecurrentwhichflowedthroughtheprimarycoil.Undertheseconditionstheratiooftransformation,asitiscalled,wouldbeunity.

Theratiooftransformationisdirectlyproportionaltothenumberofturnsofwireontheprimaryandsecondarycoilsand,sincethisisthecase,ifyouwind10turnsofwireontheprimarycoiland1,000turnsofwireonthesecondarycoilthenyouwillget100timesashighapressure,orvoltage,attheterminalsofthesecondaryasthatwhichyoucausedtoflowthroughtheprimarycoil,but,naturally,thecurrentstrength,oramperage,willbeproportionatelydecreased.

TheSecondarySparkCoilCircuit.--Thisincludesthesecondarycoilandthesparkgapwhichareconnectedtogether.Whenthealternating,buthighpotential,currentswhicharedevelopedbythesecondarycoil,reachtheballs,orelectrodes,ofthesparkgapthelatterarealternatelychargedpositivelyandnegatively.

Nowtakeagiveninstantwhenoneelectrodeischargedpositivelyandtheotheroneischargednegatively,thenwhentheyarechargedtoahighenoughpotentialtheelectricstrainbreaksdowntheairgapbetweenthemandthetwochargesrushtogetherasdescribedinthechapterbeforethisoneinconnectionwiththedischargeofacondenser.Whenthechargesrushtogethertheyformacurrentwhichburnsouttheairinthegapandthisgivesrisetothespark,andastheheatedgapbetweenthetwoelectrodesisaverygoodconductortheelectriccurrentsurgesforthandbackwithhighfrequency,perhapsadozentimes,beforetheairreplacesthatwhichhasburnedout.Itistheinrushingairtofillthevacuumofthegapthatmakesthecracklingnoisewhichaccompaniesthedischargeoftheelectricspark.

Inthiswaythenelectricoscillationsoftheorderofamillion,moreorless,areproducedandifanaerialandagroundwireareconnectedtothesparkballs,orelectrodes,theoscillationswillsurgeupanddownitandtheenergyoftheseinturn,arechangedintoelectricwaveswhichtraveloutintospace.Anopencircuittransmitterofthiskindwillsendoutwavesthatarefourtimesaslongastheaerialitself,butasthewavesitsendsoutarestronglydampedtheGovernmentwillnotpermitittobeused.

TheClosedOscillationCircuit.--Byusingaclosedoscillationcircuitthetransmittercanbetunedtosendoutwavesofagivenlengthandwhilethewavesarenotsostronglydampedmorecurrentcanbesentintotheaerialwiresystem.Theclosedoscillationcircuitconsistsof:(1)asparkgap,(2)acondenserand(3)anoscillationtransformer.Thehighpotentialalternatingcurrentdeliveredbythesecondarycoilnotonlychargesthesparkgapelectrodeswhichnecessarilyhaveaverysmallcapacitance,butitchargesthecondenserwhichhasalargecapacitanceandthevalueofwhichcanbechangedatwill.

Nowwhenthecondenserisfullychargeditdischargesthroughthesparkgapandthentheelectricoscillationssetupsurgetoandfrothroughtheclosedcircuit.Asaclosedcircuitisaverypoorradiatorofenergy,thatis,theelectricoscillationsarenotfreelyconvertedintoelectricwavesbyit,theysurgeupto,andthroughtheaerialwire;nowastheaerialwireisagoodradiatornearlyalloftheenergyoftheelectricoscillationswhichsurgethroughitareconvertedintoelectricwaves.

HowTransmittingSetNo.2Works.WithAlternatingCurrent.Theoperationofatransmittingsetthatusesanalternatingcurrenttransformer,orpowertransformer,asitissometimescalled,isevenmoresimplethanoneusingasparkcoil.Thetransformerneedsnovibratorwhenusedwithalternatingcurrent.Thecurrentfromageneratorflowsthroughtheprimarycoilofthetransformerandthealternationsoftheusuallightingcurrentis60cyclespersecond.Thiscurrentsetsupanalternatingmagneticfieldinthecoreofthetransformerandasthesemagneticlinesofforceexpandandcontract

theysetupalternatingcurrentsofthesamefrequencybutofmuchhighervoltageattheterminalsofthesecondarycoilaccordingtotheratiooftheprimaryandsecondaryturnsofwireasexplainedunderthesub-captionofRatioofTransformation.

WithDirectCurrent.--Whena110voltdirectcurrentisusedtoenergizethepowertransformeranelectrolyticinterruptorisneededtomakeandbreaktheprimarycircuit,justasavibratorisneededforthesamepurposewithasparkcoil.Whentheelectrodesareconnectedinserieswiththeprimarycoilofatransformerandasourceofdirectcurrenthavingapotentialof40to110volts,bubblesofgasareformedontheendoftheplatinum,oralloyanode,whichpreventthecurrentfromflowinguntilthebubblesbreakandthenthecurrentflowsagain,inthiswaythecurrentisrapidlymadeandbrokenandthebreakisverysharp.

Wherethistypeofinterrupterisemployedthecondenserthatisusuallyshuntedaroundthebreakisnotnecessaryastheinterrupteritselfhasacertaininherentcapacitance,duetoelectrolyticaction,andwhichiscalleditselectrolyticcapacitance,andthisislargeenoughtobalancetheself-inductionofthecircuitsincethegreaterthenumberofbreaksperminutethesmallerthecapacitancerequired.

TheRotarySparkGap.--Inthistypeofsparkgapthetwofixedelectrodesareconnectedwiththeterminalsofthesecondarycoilofthepowertransformerandalsowiththecondenserandprimaryoftheoscillationtransformer.Nowwheneveranypairofelectrodesontherotatingdiskareinalinewiththepairoffixedelectrodesasparkwilltakeplace,hencethepitchofthenotedependsonthespeedofthemotordrivingthedisk.Thiskindofarotaryspark-gapiscallednon-synchronousanditisgenerallyusedwherea60cyclealternatingcurrentisavailablebutitwillworkwithotherhigherfrequencies.

TheQuenchedSparkGap.--Ifyoustrikeapianostringasinglequickblowitwillcontinuetovibrateaccordingtoitsnaturalperiod.Thisisverymuchthewayinwhichaquenchedsparkgapsetsuposcillationsinacoupledclosedandopencircuit.Theoscillationssetupintheprimarycircuitbyaquenchedsparkmakeonlythreeorfoursharpswingsandinsodoingtransferalloftheirenergyovertothesecondarycircuit,whereitwilloscillatesomefiftytimesormorebeforeitisdampedout,becausethehighfrequencycurrentsarenotforced,butsimplyoscillatetothenaturalfrequencyofthecircuit.Forthisreasontheradiatedwavesapproachsomewhattheconditionofcontinuouswaves,andsosharpertuningispossible.

TheOscillationTransformer.--InthissetthecondenserintheclosedcircuitischargedanddischargedandsetsuposcillationsthatsurgethroughtheclosedcircuitasinSetNo.1.Inthisset,however,anoscillationtransformerisusedandastheprimarycoilofitisincludedintheclosedcircuittheoscillationssetupinitproducestrongoscillatingmagneticlinesofforce.Themagneticfieldthusproducedsetsupinturnelectricoscillationsinthesecondarycoiloftheoscillationtransformerandthesesurgethroughtheaerialwiresystemwheretheirenergyisradiatedintheformofelectricwaves.

Thegreatadvantageofusinganoscillationtransformerinsteadofasimpleinductancecoilisthatthecapacitanceoftheclosedcircuitcanbeverymuchlargerthanthatoftheaerialwiresystem.Thispermitsmoreenergytobestoredupbythecondenserandthisisimpressedontheaerialwhenitisradiatedaselectricwaves.

HowReceivingSetNo.IWorks.--Whentheelectricwavesfromadistantsendingstationimpingeon

thewireofareceivingaerialtheirenergyischangedintoelectricoscillationsthatareofexactlythesamefrequency(assumingthereceptoristunedtothetransmitter)butwhosecurrentstrength(amperage)andpotential(voltage)areverysmall.Theseelectricwavessurgethroughtheclosedcircuitbutwhentheyreachthecrystaldetectorthecontactofthemetalpointonthecrystalpermitsmorecurrenttoflowthroughitinonedirectionthanitwillallowtopassintheotherdirection.Forthisreasonacrystaldetectorissometimescalledarectifier,whichitreallyis.

Thusthehighfrequencycurrentswhichthesteelmagnetcoresofthetelephonereceiverwouldchokeoffarechangedbythedetectorintointermittentdirectcurrentswhichcanflowthroughthemagnetcoilsofthetelephonereceiver.Sincethetelephonereceiverchokesofftheoscillations,asmallcondensercanbeshuntedarounditsothatacompleteclosedoscillationcircuitisformedandthisgivesbetterresults.

Whentheintermittentrectifiedcurrentflowsthroughthecoilsofthetelephonereceiveritenergizesthemagnetaslongasitlasts,whenitisde-energized;thiscausesthesoftirondisk,ordiaphragmasitiscalled,whichsetsclosetotheendsofthepolesofthemagnet,tovibrate;andthisinturngivesforthsoundssuchasdotsanddashes,speechormusic,accordingtothenatureoftheelectricwavesthatsentthemoutatthedistantstation.

HowReceivingSetNo.2Works.--Whentheelectricoscillationsthataresetupbytheincomingelectricwavesontheaerialwiresurgethroughtheprimarycoiloftheoscillationtransformertheyproduceamagneticfieldandasthelinesofforceofthelattercutthesecondarycoil,oscillationsofthesamefrequencyaresetupinit.Thepotential(voltage)oftheseoscillationsare,however,steppeddowninthesecondarycoiland,hence,theircurrentstrength(amperes)isincreased.

TheoscillationsthenflowthroughtheclosedcircuitwheretheyarerectifiedbythecrystaldetectorandtransformedintosoundwavesbythetelephonereceiverasdescribedinconnectionwithSetNo.1.Thevariablecondensershuntedacrosstheclosedcircuitpermitsfinersecondarytuningtobedonethanispossiblewithoutit.Whereyouarereceivingcontinuouswavesfromawirelesstelephonetransmitter(speechormusic)youhavetotunesharperthanispossiblewiththetuningcoilaloneandtodothisavariablecondenserconnectedinparallelwiththesecondarycoilisnecessary.

CHAPTERVII

MECHANICALANDELECTRICALTUNING

Thereisastrikinglycloseresemblancebetweensoundwavesandthewaytheyaresetupintheairbyamechanicallyvibratingbody,suchasasteelspringoratuningfork,andelectricwavesandthewaytheyaresetupintheetherbyacurrentoscillatinginacircuit.Asitiseasytograspthewaythatsoundwavesareproducedandbehavesomethingwillbetoldabouttheminthischapterandalsoanexplanationofhowelectricwavesareproducedandbehaveandthusyouwillbeabletogetaclearunderstandingofthemandoftuningingeneral.

DampedandSustainedMechanicalVibrations.--IfyouwillplaceoneendofaflatsteelspringinaviceandscrewituptightasshownatAinFig.34,andthenpullthefreeendoverandletitgoitwillvibratetoandfrowithdecreasingamplitudeuntilitcomestorestasshownatB.Whenyoupullthespringoveryoustoreupenergyinitandwhenyouletitgothestoredupenergyischangedintoenergyofmotionandthespringmovesforthandback,orvibratesaswecallit,untilallofitsstoredupenergyisspent.

Ifitwerenotfortheairsurroundingitandotherfrictionallosses,thespringwouldvibrateforaverylongtimeasthestoredupenergyandtheenergyofmotionwouldpracticallyoffseteachotherandsotheenergywouldnotbeusedup.Butasthespringbeatstheairthelatterissentoutinimpulsesandtheconversionofthevibrationsofthespringintowavesintheairsoonusesuptheenergyyouhaveimpartedtoitanditcomestorest.

Inordertosendoutcontinuouswavesintheairinsteadofdampedwavesaswithaflatsteelspringyoucanuseanelectricdriventuningfork,seeC,inwhichanelectromagnetisfixedontheinsideoftheprongsandwhenthisisenergizedbyabatterycurrentthevibrationsoftheprongsoftheforkarekeptgoing,oraresustained,asshowninthediagramatD.

DampedandSustainedElectricOscillations.--Thevibratingsteelspringdescribedaboveisaverygoodanalogueofthewaythatdampedelectricoscillationswhichsurgeinacircuitsetupandsendoutperiodicelectricwavesintheetherwhiletheelectricdriventuningforkjustdescribedislikewiseagoodanalogueofhowsustainedoscillationssurgeinacircuitandsetupandsendoutcontinuouselectricwavesintheetherasthefollowingshows.

NowtheinductanceandresistanceofacircuitsuchasisshownatAinFig.35,slowsdown,andfinallydampsoutentirely,theelectricoscillationsofthehighfrequencycurrents,seeB,wherethesearesetupbytheperiodicdischargeofacondenser,preciselyasthevibrationsofthespringaredampedoutbythefrictionoftheairandotherresistancesthatactuponit.Astheelectricoscillationssurgetoandfrointhecircuititisopposedbytheactionoftheetherwhichsurroundsitandelectricwavesaresetupinandsentoutthroughitandthistransformationsoonusesuptheenergyofthecurrentthatflowsinthecircuit.

Tosendoutcontinuouswavesintheethersuchasareneededforwirelesstelephonyinsteadofdampedwaveswhichare,atthepresentwriting,generallyusedforwirelesstelegraphy,anelectricoscillationarcoravacuumtubeoscillatormustbeused,seeC,insteadofasparkgap.Whereasparkgapisusedthecondenserinthecircuitischargedperiodicallyandwithconsiderablelapsesoftimebetweeneachofthechargingprocesses,when,ofcourse,thecondenserdischargesperiodicallyandwiththesametimeelementbetweenthem.WhereanoscillationarcoravacuumtubeisusedthecondenserischargedasrapidlyasitisdischargedandtheresultistheoscillationsaresustainedasshownatD.

AboutMechanicalTuning.--Atuningforkisbetterthanaspringorastraightsteelbarforsettingupmechanicalvibrations.Asamatteroffactatuningforkissimplyasteelbarbentinthemiddlesothatthetwoendsareparallel.Ahandleisattachedtomiddlepointoftheforksothatitcanbeheldeasilyandwhichalsoallowsittovibratefreely,whentheendsoftheprongsalternatelyapproachandrecedefromoneanother.Whentheprongsvibratethehandlevibratesupanddowninunisonwithit,andimpartsitsmotiontothesoundingbox,orresonancecaseasitissometimescalled,whereoneisused.

If,now,youwillmounttheforkonasoundingboxwhichistunedsothatitwillbeinresonancewiththevibrationsoftheforktherewillbeadirectreinforcementofthevibrationswhenthenoteemittedbyitwillbeaugmentedinstrengthandquality.Thisiscalledsimpleresonance.Further,ifyoumountapairofforks,eachonaseparatesoundingbox,andhavetheforksofthesamesize,toneandpitch,andtheboxessynchronized,thatis,tunedtothesamefrequencyofvibration,thensetthetwoboxesafootorsoapart,asshownatAinFig.36,whenyoustrikeoneoftheforkswitharubberhammeritwillvibratewithadefinitefrequencyand,hence,sendoutsoundwavesofagivenlength.Whenthelatterstrikethesecondforktheimpactofthemoleculesofairofwhichthesoundwavesareformedwillsetitsprongstovibratinganditwill,inturn,emitsoundwavesofthesamelengthandthisiscalledsympatheticresonance,oraswewouldsayinwirelesstheforksareintune.

Tuningforksaremadewithadjustableweightsontheirprongsandbyfixingthesetodifferentpartsofthemthefrequencywithwhichtheforksvibratecanbechangedsincethefrequencyvariesinverselywiththesquareofthelengthanddirectlywiththethickness[Footnote:Thislawisforforkshavingarectangularcross-section.Thosehavingaroundcross-sectionvaryastheradius.]oftheprongs.Nowbyadjustingoneoftheforkssothatitvibratesatafrequencyof,say,16persecondandadjustingtheotherforksothatitvibratesatafrequencyof,say,18or20persecond,thentheforkswillnotbeintunewitheachotherand,hence,ifyoustrikeoneofthemtheotherwillnotrespond.Butifyoumaketheforksvibrateatthesamefrequency,say16,20or24persecond,whenyoustrikeoneofthemtheotherwillvibrateinunisonwithit.

AboutElectricTuning.--ElectricresonanceandelectrictuningareverylikethoseofacousticresonanceandacoustictuningwhichIhavejustdescribed.Justasacousticresonancemaybesimple

orsympatheticsoelectricresonancemaybesimpleorsympathetic.Simpleacousticresonanceisthedirectreinforcementofasimplevibrationandthisconditionishadwhenatuningforkismountedonasoundingbox.Insimpleelectricresonanceanoscillatingcurrentofagivenfrequencyflowinginacircuithavingtheproperinductanceandcapacitancemayincreasethevoltageuntilitisseveraltimesgreaterthanitsnormalvalue.Tuningthereceptorcircuitstothetransmittercircuitsareexamplesofsympatheticelectricresonance.AsademonstrationifyouhavetwoLeydenjars(capacitance)connectedincircuitwithtwoloopsofwire(inductance)whoseinductancecanbevariedasshownatBinFig.36,whenyoumakeasparkpassbetweentheknobsofoneofthembymeansofasparkcoilthenasparkwillpassinthegapoftheotheroneprovidedtheinductanceofthetwoloopsofwireisthesame.Butifyouvarytheinductanceoftheoneloopsothatitislargerorsmallerthanthatoftheotherloopnosparkwilltakeplaceinthesecondcircuit.

Whenatuningforkismadetovibrateitsendsoutwavesintheair,orsoundwaves,inalldirectionsandjustsowhenhighfrequencycurrentssurgeinanoscillationcircuittheysendoutwavesintheether,orelectricwaves,thattravelinalldirections.Forthisreasonelectricwavesfromatransmittingstationcannotbesenttooneparticularstation,thoughtheydogofurtherinonedirectionthaninanother,accordingtothewayyouraerialwirepoints.

Sincetheelectricwavestraveloutinalldirectionsanyreceivingsetproperlytunedtothewavelengthofthesendingstationwillreceivethewavesandtheonlylimitonyourabilitytoreceivefromhigh-powerstationsthroughouttheworlddependsentirelyonthewavelengthandsensitivityofyourreceivingset.Asfortuning,justaschangingthelengthandthethicknessoftheprongsofatuningforkvariesthefrequencywithwhichitvibratesand,hence,thelengthofthewavesitsendsout,so,too,byvaryingthecapacitanceofthecondenserandtheinductanceofthetuningcoilofthetransmitterthefrequencyoftheelectricoscillationssetupinthecircuitmaybechangedand,consequently,thelengthoftheelectricwavestheysendout.Likewise,byvaryingthecapacitanceandtheinductanceofthereceptorthecircuitscanbetunedtoreceiveincomingelectricwavesofwhateverlengthwithinthelimitationoftheapparatus.

CHAPTERVIII

ASIMPLEVACUUMTUBEDETECTORRECEIVINGSET

WhileyoucanreceivedotsanddashesfromsparkwirelesstelegraphstationsandhearspokenwordsandmusicfromwirelesstelephonestationswithacrystaldetectorreceivingsetsuchasdescribedinChapterIII,youcangetstationsthataremuchfartherawayandhearthembetterwithavacuumtubedetectorreceivingset.

Thoughthevacuumtubedetectorrequirestwobatteriestooperateitandthereceivingcircuitsaresomewhatmorecomplicatedthanwhereacrystaldetectorisusedstilltheformerdoesnothavetobeconstantlyadjustedasdoesthelatterandthisisanotherverygreatadvantage.Takenallinallthevacuumtubedetectoristhemostsensitiveandthemostsatisfactoryofthedetectorsthatareinuseatthepresenttime.

Notonlyisthevacuumtubeadetectorofelectricwavesignalsandspeechandmusicbutitcanalsobeusedtoamplifythem,thatis,tomakethemstrongerand,hence,louderinthetelephonereceiverandfurtheritspowersofamplificationaresogreatthatitwillreproducethembymeansofaloudspeaker,justasahornamplifiesthesoundsofaphonographreproducer,untiltheycanbeheardbyaroomoranauditoriumfullofpeople.Therearetwogeneraltypesofloudspeakers,thoughbothusetheprincipleofthetelephonereceiver.Theconstructionoftheseloudspeakerswillbefullydescribedinalaterchapter.

AssembledVacuumTubeReceivingSets.--Youcanbuyareceivingsetwithavacuumtubedetectorfromtheverysimplesttype,whichisdescribedinthischapter,tothosethatareprovidedwithregenerativecircuitsandamplifyingtubesorboth,whichweshalldescribeinlaterchapters,fromdealersinelectricalapparatusgenerally.Whileoneofthesesetscostsmorethanyoucanassembleasetforyourself,still,especiallyinthebeginning,itisagoodplantobuyanassembledoneforitisfittedwithapanelonwhichtheadjustingknobsoftherheostat,tuningcoilandcondenseraremountedandthismakesitpossibletooperateitassoonasyougetithomeandwithouttheslightesttroubleonyourpart.

Youcan,however,buyallthevariouspartsseparatelyandmountthemyourself.Ifyouwantthereceptorsimplyforreceivingthenitisagoodschemetohaveallofthepartsmountedinaboxorenclosedcase,butifyouwantitforexperimentalpurposesthenthepartsshouldbemountedonabaseorapanelsothatalloftheconnectionsareinsightandaccessible.

ASimpleVacuumTubeReceivingSet.--Forthissetyoushoulduse:(1)aloosecoupledtuningcoil,(2)avariablecondenser,(3)avacuumtubedetector,(4)anAorstoragebatterygiving6volts,(5)aBordrycellbatterygiving22-1/2volts,(6)arheostatforvaryingthestoragebatterycurrent,and(7)apairof2,000-ohmheadtelephonereceivers.Theloosecoupledtuningcoil,thevariablecondenserandthetelephonereceiversarethesameasthosedescribedinChapterIII.

TheVacuumTubeDetector.WithTwoElectrodes.--AvacuumtubeinitssimplestformconsistsofaglassbulblikeanincandescentlampinwhichawirefilamentandametalplatearesealedasshowninFig.37,Theairisthenpumpedoutofthetubeandavacuumleftorafteritisexhausteditisfilled

withnitrogen,whichcannotburn.

Whenthevacuumtubeisusedasadetector,thewirefilamentisheatedred-hotandthemetalplateischargedwithpositiveelectricitythoughitremainscold.Thewirefilamentisformedintoalooplikethatofanincandescentlampanditsoutsideendsareconnectedwitha6-voltstoragebattery,whichiscalledtheAbattery;thenthe+orpositiveterminalofa22-1/2voltdrycellbattery,calledtheBbattery,isconnectedtothemetalplatewhilethe-ornegativeterminalofthebatteryisconnectedtooneoftheterminalsofthewirefilament.Thediagram,Fig.37,simplyshowshowthetwoelectrodevacuumtube,theAordrybattery,andtheBorstoragebatteryareconnectedup.

ThreeElectrodeVacuumTubeDetector.--ThethreeelectrodevacuumtubedetectorshownatAinFig.38,ismuchmoresensitivethanthetwoelectrodetubeandhas,inconsequence,allbutsupplantedit.Inthismorerecenttypeofvacuumtubethethirdelectrode,orgrid,asitiscalled,isplacedbetweenthewirefilamentandthemetalplateandthisallowsthecurrenttobeincreasedordecreasedatwilltoaveryconsiderableextent.

ThewaythethreeelectrodevacuumtubedetectorisconnectedwiththebatteriesisshownatB.Theplate,theAordrycellbatteryandoneterminalofthefilamentareconnectedinseries--thatis,oneaftertheother,andtheendsofthefilamentareconnectedtotheBorstoragebattery.Inassemblingareceivingsetyoumust,ofcourse,haveasocketforthevacuumtube.Avacuumtubedetectorcostsfrom$5.00to$6.00.

TheDryCellandStorageBatteries.--Thereasonthatastoragebatteryisusedforheatingthefilamentofthevacuumtubedetectorisbecausethecurrentdeliveredisconstant,whereaswhenadrycellbatteryisusedthecurrentsoonfallsoffand,hence,theheatofthefilamentgraduallygrowsless.ThesmallestAor6voltstoragebatteryonthemarkethasacapacityof20to40amperehours,weighs13poundsandcostsabout$10.00.ItisshownatAinFig.39.TheBordrycellbatteryforthevacuumtubeplatecircuitthatgives22-1/2voltscanbeboughtalreadyassembledinsealedboxes.Thesmallsizeisfittedwithapairofterminalswhilethelargersizeisprovidedwithtapssothatthevoltagerequiredbytheplatecanbeadjustedastheproperoperationofthetuberequirescarefulregulationoftheplatevoltage.AdrycellbatteryforaplatecircuitisshownatB.

TheFilamentRheostat.--Anadjustableresistance,calledarheostat,mustbeusedinthefilamentandstoragebatterycircuitsothatthecurrentflowingthroughthefilamentcanbecontrolledtoanicety.Therheostatconsistsofaninsulatingandaheatresistingformonwhichiswoundanumberofturnsofresistancewire.Amovablecontactarmthatslidesoverandpressesontheturnsofwireisfixedtotheknobontopoftherheostat.Arheostatthathasaresistanceof6ohmsandacurrentcarryingcapacityof1.5ampereswhichcanbemountedonapanelboardistherightkindtouse.ItisshownatAandBinFig.40andcosts$1.25.

AssemblingtheParts.--Beginbyplacingalloftheseparatepartsofthereceivingsetonaboardorabaseofothermaterialandsetthetuningcoilonthelefthandsidewiththeadjustableswitchendtowardtherighthandsidesothatyoucanreachiteasily.Thensetthevariablecondenserinfrontofit,setthevacuumtubedetectorattherighthandendofthetuningcoilandtherheostatinfrontofthedetector.Placethetwosetsofbatteriesbackoftheinstrumentsandscrewacoupleofbindingpostsa

andbtotherighthandloweredgeofthebaseforconnectingintheheadphonesallofwhichisshownatAinFig.41.

ConnectingUptheParts.--Towireupthedifferentpartsbeginbyconnectingtheslidingcontactof

theprimarycoiloftheloosecoupledtuningcoil(thisyouwillrememberistheoutsideonethatiswoundwithfinewire)totheupperpostofthelightningswitchandconnectoneterminalofthiscoilwiththewaterpipe.Nowconnectthefreeendofthesecondarycoilofthetuningcoil(thisistheinsidecoilthatiswoundwithheavywire)tooneofthebindingpostsofthevariablecondenserandconnectthemovablecontactarmoftheadjustableswitchoftheprimaryofthetuningcoilwiththeotherpostofthevariablecondenser.

NextconnectthegridofthevacuumtubetooneofthepostsofthecondenserandthenconnecttheplateofthetubetothecarbonterminaloftheBordrycellbatterywhichisthe+orpositivepoleandconnectthezincterminalofthe-ornegativepoletothebindingposta,connectthepostbtotheothersideofthevariablecondenserandthenconnecttheterminalsoftheheadphonestothebindingpostsaandb.Whateveryoudobecarefulnottogettheplateconnectionsofthebatteryreversed.

Nowconnectoneofthepostsoftherheostattooneterminalofthefilamentandtheotherterminalofthefilamenttothe-ornegativeterminaloftheAorstoragebatteryandthe+orpositiveterminaloftheAorstoragebatterytotheotherpostoftherheostat.Finallyconnectthe+orpositiveterminaloftheAorstoragebatterywiththewirethatrunsfromtheheadphonestothevariablecondenser,allofwhichisshowninthewiringdiagramatBinFig.41.

AdjustingtheVacuumTubeDetectorReceivingSet.--AvacuumtubedetectoristunedexactlyinthesamewayastheCrystalDetectorSetNo.2describedinChapterIII,in-so-farasthetuningcoilandvariablecondenserareconcerned.Thesensitivityofthevacuumtubedetectorreceivingsetand,hence,thedistanceoverwhichsignalsandothersoundscanbehearddependsverylargelyonthesensitivityofthevacuumtubeitselfandthisinturndependson:(1)therightamountofheatdevelopedbythefilament,orfilamentbrilliancyasitiscalled,(2)therightamountofvoltageappliedtotheplate,and(3)theextenttowhichthetubeisexhaustedwherethiskindofatubeisused.

TovarythecurrentflowingfromtheAorstoragebatterythroughthefilamentsothatitwillbeheatedtotherightdegreeyouadjusttherheostatwhileyouarelisteningintothesignalsorothersounds.Bycarefullyadjustingtherheostatyoucaneasilyfindthepointatwhichitmakesthetubethemostsensitive.Arheostatisalsousefulinthatitkeepsthefilamentfromburningoutwhenthecurrentfromthebatteryfirstflowsthroughit.YoucanveryoftenincreasethesensitivenessofavacuumtubeafteryouhaveuseditforawhilebyrechargingtheAorstoragebattery.

Thedegreetowhichavacuumtubehasbeenexhaustedhasaverypronouncedeffectonitssensitivity.Thelongerthetubeisusedtheloweritsvacuumgetsandgenerallythelesssensitiveitbecomes.Whenthistakesplace(andyoucanonlyguessatit)youcanveryoftenmakeitmoresensitivebywarmingitovertheflameofacandle.Vacuumtubeshavingagascontent(inwhichcasetheyare,ofcourse,nolongervacuumtubesinthestrictsense)makebetterdetectorsthantubesfromwhichtheairhasbeenexhaustedandwhicharesealedoffinthisevacuatedconditionbecausetheirsensitivenessisnotdependentonthedegreeofvacuumasinthelattertubes.Moreover,atubethatiscompletelyexhaustedcostsmorethanonethatisfilledwithgas.

CHAPTERIX

VACUUMTUBEAMPLIFIERRECEIVINGSETS

Thereasonavacuumtubedetectorismoresensitivethanacrystaldetectorisbecausewhilethelattermerelyrectifiestheoscillatingcurrentthatsurgesinthereceivingcircuits,theformeractsasanamplifieratthesametime.Thevacuumtubecanbeusedasaseparateamplifierinconnectionwitheither:(1)acrystaldetectoror(2)avacuumtubedetector,and(a)itwillamplifyeithertheradiofrequencycurrents,thatisthehighfrequencyoscillatingcurrentswhicharesetupintheoscillationcircuitsor(b)itwillamplifytheaudiofrequencycurrents,thatis,thelowfrequencyalternatingcurrentsthatflowthroughtheheadphonecircuit.

Tousetheamplifiedradiofrequencyoscillatingcurrentsoramplifiedaudiofrequencyalternatingcurrentsthataresetupbyanamplifiertubeeitherahighresistance,calledagridleak,oranamplifyingtransformer,withorwithoutanironcore,mustbeconnectedwiththeplatecircuitofthefirstamplifiertubeandthegridcircuitofthenextamplifiertubeordetectortube,orwiththewirepointofacrystaldetector.Wheretwoormoreamplifiertubesarecoupledtogetherinthiswaytheschemeisknownascascadeamplification.

Whereeitheraradiofrequencytransformer,thatisonewithouttheironcore,oranaudiofrequencytransformer,thatisonewiththeironcore,isusedtocoupletheamplifiertubecircuitstogetherbetterresultsareobtainedthanwhereahighresistancegridleakisused,buttheamplifyingtubeshavetobemorecarefullyshieldedfromeachotherortheywillreactandsetupahowlingnoiseintheheadphones.Ontheotherhandgridleakscostlessbuttheyaremoretroublesometouseasyouhavetofindoutforyourselftheexactresistancevaluetheymusthaveandthisyoucandoonlybytestingthemout.

AGridLeakAmplifierReceivingSet.WithCrystalDetector.--Theapparatusyouneedforthissetincludes:(1)aloosecoupledtuningcoil,(2)avariablecondenser,(3)twofixedcondensers,(4)acrystaldetector,orbetteravacuumtubedetector,(5)anAor6voltstoragebattery,(6)arheostat,(7)aBor22-1/2voltdrycellbattery,(8)afixedresistanceunit,orleakgridasitiscalled,and(9)apairofhead-phones.Thetuningcoil,variablecondenser,fixedcondensers,crystaldetectorsandhead-phonesareexactlythesameasthosedescribedinSetNo.2inChapterIII.TheAandBbatteriesareexactlythesameasthosedescribedinChapterVIII.Thevacuumtubeamplifierandthegridleakaretheonlynewpiecesofapparatusyouneedandnotdescribedbefore.

TheVacuumTubeAmplifier.--ThisconsistsofathreeelectrodevacuumtubeexactlylikethevacuumtubedetectordescribedinChapterVIIIandpicturedinFig.38,exceptthatinsteadofbeingfilledwithanon-combustiblegasitisevacuated,thatis,theairhasbeencompletelypumpedoutofit.Thegasfilledtube,however,canbeusedasanamplifierandeitherkindoftubecanbeusedforeitherradiofrequencyoraudiofrequencyamplification,thoughwiththeexhaustedtubeitiseasiertoobtaintherightplateandfilamentvoltagesforgoodworking.

TheFixedResistanceUnit,orGridLeak.--Gridleaksaremadeindifferentwaysbutallofthemhaveanenormouslyhighresistance.Onewayofmakingthemconsistsofdepositingathinfilmofgoldonasheetofmicaandplacinganothersheetofmicaontoptoprotectitthewholebeingenclosedina

glasstubeasshownatAinFig.42.Thesegridleaksaremadeinunitsoffrom50,000ohms(.05megohm)to5,000,000ohms(5megohms)andcostfrom$1to$2.

Asthevalueofthegridleakyouwillneeddependsverylargelyupontheconstructionofthedifferentpartsofyourreceivingsetandonthekindofaerialwiresystemyouusewithityouwillhavetotryoutvariousresistancesuntilyouhittherightone.Theresistancethatwillgivethebestresults,however,liessomewherebetween500,000ohms(1/2amegohm)and3,000,000ohms(3megohms)andtheonlywayforyoutofindthisoutistobuy1/2,1and2megohmgridleakresistancesandconnectthemupindifferentways,asshownatB,untilyoufindtherightvalue.

AssemblingthePartsforaCrystalDetectorSet.--Beginbylayingthevariouspartsoutonabaseorapanelwiththeloosecoupledtuningcoilonthelefthandside,butwiththeadjustableswitchofthesecondarycoilontherighthandendorinfrontaccordingtothewayitismade.Thenplacethevariablecondenser,therheostat,thecrystaldetectorandthebindingpostsfortheheadphonesinfrontofandinalinewitheachother.SetthevacuumtubeamplifierbackoftherheostatandtheAandBbatteriesbackofthepartsorinanyotherplacethatmaybeconvenient.Thefixedcondensersandthegridleakcanbeplacedanywheresothatitwillbeeasytoconnecttheminandyouarereadytowireuptheset.

ConnectingUpthePartsforaCrystalDetector.--Firstconnecttheslidingcontactoftheprimaryofthetuningcoiltotheleading-inwireandoneoftheendwiresoftheprimarytothewaterpipe,asshowninFig.43.Nowconnecttheadjustablearmthatmakescontactwithoneendofthesecondaryofthetuningcoiltooneofthepostsofthevariablecondenser;thenconnecttheotherpostofthelatter

withapostofthefixedcondenserandtheotherpostofthiswiththegridoftheamplifyingtube.

Connectthefirstpostofthevariablecondensertothe+orpositiveelectrodeoftheAbatteryandits-ornegativeelectrodewiththerotatingcontactarmoftherheostat.Nextconnectoneendoftheresistancecoiloftherheostattooneofthepostsoftheamplifiertubethatleadstothefilamentandtheotherfilamentposttothe+orpositiveelectrodeoftheAbattery.Thisdoneconnectthenegative,thatis,thezincpoleoftheBbatterytothepositiveelectrodeoftheAbatteryandconnectthepositive,orcarbonpoleoftheformerwithoneendofthegridleakandconnecttheotherendofthistotheplateoftheamplifiertube.

Totheendofthegridleakconnectedwiththeplateoftheamplifiertubeconnectthemetalpointofyourcrystaldetector,thecrystalofthelatterwithonepostoftheheadphonesandtheotherpostofthemwiththeotherendofthegridleakand,finally,connectafixedcondenserinparallelwith--thatisacrosstheendsofthegridleak,allofwhichisshowninthewiringdiagraminFig.43.

AGridLeakAmplifyingReceivingSetWithVacuumTubeDetector.--Abetteramplifyingreceivingsetcanbemadethantheonejustdescribedbyusingavacuumtubedetectorinsteadofthecrystaldetector.ThissetisbuiltupexactlylikethecrystaldetectordescribedaboveandshowninFig.43uptoandincludingthegridleakresistance,butshuntedacrossthelatterisavacuumtubedetector,whichismadeandwireduppreciselyliketheoneshownatAinFig.41inthechapteraheadofthisone.Thewayagridleakandvacuumtubedetectorwithaone-stepamplifierareconnectedupisshownatAinFig.44.Whereyouhaveavacuumtubedetectorandoneormoreamplifyingtubesconnectedup,orincascadeasitiscalled,youcanuseanA,orstoragebatteryof6voltsforallofthemasshownatBinFig.44,butforeveryvacuumtubeyouuseyoumusthaveaBor22-1/2voltdrybatterytochargetheplatewith.

ARadioFrequencyTransformerAmplifyingReceivingSet.--Insteadofusingagridleakresistancetocoupleuptheamplifieranddetectortubecircuitsyoucanusearadiofrequencytransformer,thatis,atransformermadelikealoosecoupledtuningcoil,andwithoutanironcore,asshowninthewiringdiagramatAinFig.45.Inthisset,whichgivesbetterresultsthanwhereagridleakisused,theamplifiertubeisplacedinthefirstoscillationcircuitandthedetectortubeinthesecondcircuit.

Sincetheradiofrequencytransformerhasnoironcorethehighfrequency,orradiofrequencyoscillatingcurrents,astheyarecalled,surgethroughitandarenotchangedintolowfrequency,oraudiofrequencypulsatingcurrents,untiltheyflowthroughthedetector.Sincethediagramshowsonlyoneamplifierandoneradiofrequencytransformer,itisconsequentlyaonestepamplifier;however,two,threeormore,amplifyingtubescanbeconnectedupbymeansofanequalnumberofradiofrequencytransformerswhenyouwillgetwonderfulresults.Whereasixstepamplifier,thatis,wheresixamplifyingtubesareconnectedtogether,orincascade,thefirstthreeareusuallycoupledupwithradiofrequencytransformersandthelastthreewithaudiofrequencytransformers.AradiofrequencytransformerisshownatBandcosts$6to$7.

AnAudioFrequencyTransformerAmplifyingReceivingSet.--Whereaudiofrequencytransformersareusedforsteppingupthevoltageofthecurrentofthedetectorandamplifiertubes,theradiofrequencycurrentdoesnotgetintotheplatecircuitofthedetectoratallforthereasonthattheironcoreofthetransformerchokesthemoff,hence,thesucceedingamplifiersoperateataudiofrequencies.AnaudiofrequencytransformerisshownatAinFig.46andawiringdiagramshowinghowthetubesare

connectedincascadewiththetransformersisshownatB;itisthereforeatwo-stepaudiofrequencyreceivingset.

ASixStepAmplifierReceivingSetWithaLoopAerial.--Byusingareceivingsethavingathreestepradiofrequencyandathreestepaudiofrequency,thatis,asetinwhichtherearecoupledthreeamplifyingtubeswithradiofrequencytransformersandthreeamplifyingtubeswithaudiofrequencytransformersasdescribedunderthecaptionARadioFrequencyTransformerReceivingSet,youcanusealoopaerialinyourroomthusgettingaroundthedifficulties--ifsuchtherebe--inerectinganout-dooraerial.Youcaneasilymakealoopaerialbywinding10turnsofNo.14or16copperwireabout1/16inchapartonawoodenframetwofeetonthesideasshowninFig.47.Withthissixstepamplifiersetandloopaerialyoucanreceivewavelengthsof150to600metersfromvarioushighpowerstationswhichareatconsiderabledistancesaway.

HowtoPreventHowling.--Whereradiofrequencyoraudiofrequencyamplifiersareusedtocoupleyouramplifiertubesincascadeyoumusttakeparticularpainstoshieldthemfromoneanotherinordertopreventthefeedbackofthecurrentsthroughthem,whichmakestheheadphonesorloudspeakerhowl.Toshieldthemfromeachotherthetubesshouldbeenclosedinmetalboxesandplacedatleast6inchesapartwhilethetransformersshouldbesetsothattheircoresareatrightanglestoeachotherandthesealsoshouldbenotlessthansixinchesapart.

CHAPTERX

REGENERATIVEAMPLIFICATIONRECEIVINGSETS

Whileavacuumtubedetectorhasanamplifyingactionofitsown,andthisaccountsforitsgreatsensitiveness,itsamplifyingactioncanbefurtherincreasedtoanenormousextentbymakingtheradiofrequencycurrentsthataresetupintheoscillationcircuitsreactonthedetector.

Suchcurrentsarecalledfeed-backorregenerativecurrentsandwhencircuitsaresoarrangedastocausethecurrentstoflowbackthroughthedetectortubetheamplificationkeepsonincreasinguntilthecapacityofthetubeitselfisreached.Itislikeusingsteamoverandoveragaininasteamturbineuntilthereisnomoreenergyleftinit.AsystemofcircuitswhichwillcausethisregenerativeactiontotakeplaceisknownastheArmstrongcircuitsandissocalledaftertheyoungmanwhodiscoveredit.

Sincetheregenerativeactionoftheradiofrequencycurrentsisproducedbythedetectortubeitselfandwhichsetsupanamplifyingeffectwithouttheadditionofanamplifyingtube,thistypeofreceivingsethasfoundgreatfavorwithamateurs,whileincombinationwithamplifyingtubesitmultipliestheirpowerproportionatelyanditisinconsequenceusedinoneformoranotherinallthebettersets.

Therearemanydifferentkindsofcircuitswhichcanbeusedtoproducetheregenerativeamplificationeffectwhilethevariouskindsoftuningcoilswillserveforcouplingthem;forinstanceatwoorthreeslidesingletuningcoilwillanswerthepurposebutasitdoesnotgivegoodresultsitisnotadvisabletospendeithertimeormoneyonit.Abetterschemeistousealoosecouplerformedoftwoorthreehoneycomborothercompactcoils,whileavariocoupleroravariometerortwowillproducethemaximumregenerativeaction.

TheSimplestTypeofRegenerativeReceivingSet.WithLooseCoupledTuningCoil.--Whilethisregenerativesetisthesimplestthatwillgiveanythinglikefairresultsitisheredescribednotonaccountofitsdesirability,butbecauseitwillservetogiveyouthefundamentalideaofhowthefeed-backcircuitisformed.

Forthissetyouneed:(1)aloose-coupledtuningcoilsuchasdescribedinChapterIII,(2)avariablecondenserof.001mfd.(microfarad)capacitance;(3)onefixedcondenserof.001mfd.;(4)onefixedcondenserforthegridleakcircuitof.00025mfd.;(5)agridleakof1/2to2megohmsresistance;(6)avacuumtubedetector;(7)anA6voltbattery;(8)arheostat;(9)aB221/2voltbattery;and(10)apairof2000ohmheadphones.

ConnectingUptheParts.--Beginbyconnectingtheleading-inwireoftheaerialwiththebindingpostendoftheprimarycoiloftheloosecouplerasshowninthewiringdiagramFig.48andthenconnecttheslidingcontactwiththewaterpipeorotherground.Connectthebindingpostendoftheprimarycoilwithonepostofthevariablecondenser,connecttheotherpostofthiswithoneofthepostsofthe.00025mfd.condenserandtheotherendofthiswiththegridofthedetectortube;thenaroundthiscondensershuntthegridleakresistance.

Nextconnecttheslidingcontactoftheprimarycoilwiththeotherpostofthevariablecondenserandfromthisleadawireonovertooneoftheterminalsofthefilamentofthevacuumtube;totheotherterminalofthefilamentconnectoneofthepostsoftherheostatandconnecttheotherposttothe-ornegativeelectrodeoftheAbatteryandthenconnectthe+orpositiveelectrodeofittotheotherterminalofthefilament.

Connectthe+orpositiveelectrodeoftheAbatterywithonepostofthe.001mfd.fixedcondenserandconnecttheotherpostofthistooneoftheendsofthesecondarycoilofthetuningcoilandwhichisnowknownastheticklercoil;thenconnecttheotherendofthesecondary,orticklercoiltotheplateofthevacuumtube.Inthewiringdiagramthesecondary,orticklercoilisshownaboveandinalinewiththeprimarycoilbutthisisonlyforthesakeofmakingtheconnectionsclear;inrealitythesecondary,orticklercoilslidestoandfrointheprimarycoilasshownanddescribedinChapterIII.Finallyconnectthenegative,orzincpoleoftheBbatterytoonesideofthefixedcondenser,thepositive,orcarbon,poletooneoftheterminalsoftheheadphonesandtheotherterminalofthistotheotherpostofthefixedcondenserwhenyourregenerativesetiscomplete.

AnEfficientRegenerativeReceivingSet.WithThreeCoilLooseCoupler.--Toconstructareallygoodregenerativesetyoumustusealoosecoupledtunerthathasthreecoils,namelyaprimary,asecondaryandaticklercoil.AtunerofthiskindismadelikeanordinaryloosecoupledtuningcoilbutithasathirdcoilasshownatAandBinFig.49.Themiddlecoil,whichisthesecondary,isfixedtothebase,andthelargeoutsidecoil,whichistheprimary,ismovable,thatisitslidestoandfrooverthemiddlecoil,whilethesmallinsidecoil,whichisthetickler,isalsomovableandcanslideinoroutofthemiddlecoil.Noneofthesecoilsisvariable;allarewoundtoreceivewavesupto360metersinlengthwhenusedwithavariablecondenserof.001mfd.capacitance.Inotherwordsyou

slidethecoilsinandouttogettherightamountofcouplingandyoutunebyadjustingthevariablecondensertogettheexactwavelengthyouwant.

WithCompactCoils.--Compactcoiltunersareformedofthreefixedinductanceswoundinflatcoils,andthesearepivotedinamountingsothatthedistancebetweenthemand,therefore,thecoupling,canbevaried,asshownatAinFig.50.Thesecoilsarewoundupbythemakersforvariouswavelengthsrangingfromasmallonethatwillreceivewavesofanylengthupto360meterstoalargeonethathasamaximumof24,000meters.Foranamateursetgetthreeofthesmallestcoilswhenyoucannotonlyhearamateurstationsthatsendona200meterwavebutbroadcastingstationsthatsendona360meterwave.

Thesethreecoilsaremountedwithpanelplugswhichlatterfitintoastand,ormounting,sothatthemiddlecoilisfixed,thatis,stationary,whilethetwooutsidecoilscanbeswungtoandfrolikeadoor;thisschemepermitssmallvariationsofcouplingtobehadbetweenthecoilsandthiscanbedoneeitherbyhandlesorbymeansofknobsonapanelboard.WhileIhavesuggestedtheuseofthesmallestsizecoils,youcangetandusethosewoundforanywavelengthyouwanttoreceiveandwhenthoseareconnectedwithvariometersandvariablecondensers,andwithaproperaerial,youwillhaveahighlyefficientreceptorthatwillworkoverallrangesofwavelengths.Thesmallestsizecoilscostabout$1.50apieceandthemountingcostsabout$6or$7each.

TheABatteryPotentiometer.--Thisdeviceissimplyaresistanceliketherheostatdescribedinconnectionwiththeprecedingvacuumtubereceivingsetsbutitiswoundto200or300ohmsresistanceasagainst1-1/2to6ohmsoftherheostat.Itis,however,usedaswellastherheostat.Withavacuumtubedetector,andespeciallywithonehavingagas-content,apotentiometerisverynecessaryasitisonlybymeansofitthatthepotentialoftheplateofthedetectorcanbeaccuratelyregulated.Theresultofproperregulationisthatwhenthecriticalpotentialvalueisreachedthereisamarkedincreaseintheloudnessofthesoundsthatareemittedbytheheadphones.

AsyouwillseefromAinFig.51ithasthreetaps.ThetwotapswhichareconnectedwiththeendsoftheresistancecoilareshuntedaroundtheAbatteryandthethirdtap,whichisattachedtothemovablecontactarm,isconnectedwiththeBbatterytap,seeB,atwhichthisbatterygives18volts.SincetheAbatterygives6voltsyoucanvarythepotentialoftheplatefrom18to24volts.ThepotentiometermustneverbeshuntedaroundtheBbatteryorthelatterwillsoonrundown.Apotentiometercostsacoupleofdollars.

ThePartsandHowtoConnectThemUp.--Forthisregenerativesetyouwillneed:(1)ahoneycomborothercompactthree-coiltuner,(2)twovariable(.001and.0005mfd.)condensers;(3)a.00025mfd.fixedcondenser;(4)a1/2to2megohmgridleak;(5)atubedetector;(6)a6voltAbattery;(7)arheostat;(8)apotentiometer;(9)an18or20voltBbattery;(10)afixedcondenserof.001mfd.fixedcondenser;and(11)apairof2000ohmheadphones.

Towireupthepartsconnecttheleading-inwireoftheaerialwiththeprimarycoil,whichisthemiddleoneofthetuner,andconnecttheotherterminalwiththeground.Connecttheendsofthesecondarycoil,whichisthemiddleone,withthepostsofthevariablecondenserandconnectoneofthepostsofthelatterwithonepostofthefixed.00025mfd.condenserandtheotherpostofthiswiththegrid;thenshuntthegridleakaroundit.Nextconnecttheotherpostofthevariablecondensertothe-ornegativeelectrodeoftheAbattery;the+orpositiveelectrodeofthistooneterminalofthedetectorfilamentandtheotherendofthelattertotheelectrodeoftheAbattery.

Nowconnectoneendoftheticklercoilwiththedetectorplateandtheotherposttothefixed.001mfd.condenser,thentheotherendofthistothepositiveorcarbonpoleoftheBbattery.

ThisdoneshuntthepotentiometeraroundtheAbatteryandrunawirefromthemovablecontactofit(thepotentiometer)overtothe18volttap,(seeB,Fig.51),oftheBbattery.Finally,shunttheheadphonesandthe.001mfd.fixedcondenserandyouarereadytotryoutconclusions.

ARegenerativeAudioFrequencyAmplifierReceivingSet.--Theuseofamateurregenerativecascadeaudiofrequencyreceivingsetsisgettingtobequitecommon.Togetthegreatestamplificationpossiblewithamplifyingtubesyouhavetokeepanegativepotentialonthegrids.Youcan,however,getverygoodresultswithoutanyspecialchargingarrangementbysimplyconnectingonepostoftherheostatwiththenegativeterminalofthefilamentandconnectingthelowpotentialendofthesecondaryofthetuningcoilwiththe-ornegativeelectrodeoftheAbattery.Thisschemewillgivethegridsanegativebiasofabout1volt.Youdonotneedtobotherabouttheseaddedfactorsthatmakeforhighefficiencyuntilafteryouhavegotyourreceivingsetinworkingorderandunderstand

allaboutit.

ThePartsandHowtoConnectThemUp.--Exactlythesamepartsareneededforthissetastheonedescribedabove,butinadditionyouwillwant:(1)twomorerheostats;(2)twomoresetsofB22-1/2voltbatteries;(3)twoamplifiertubes,and(4)twoaudiofrequencytransformersasdescribedinChapterIXandpicturedatAinFig.46.

Towireupthepartsbeginbyconnectingtheleading-inwiretooneendoftheprimaryofthetuningcoilandthenconnecttheotherendofthecoilwiththeground.Avariablecondenserof.001mfd.capacitancecanbeconnectedinthegroundwire,asshowninFig.52,togoodadvantagealthoughitisnotabsolutelyneeded.Nowconnectoneendofthesecondarycoiltoonepostofa.001mfd.variablecondenserandtheotherendofthesecondarytotheotherpostofthecondenser.

Nextbringalead(wire)fromthefirstpostofthevariablecondenserovertothepostofthefirstfixedcondenserandconnecttheotherpostofthelatterwiththegridofthedetectortube.Shunt1/2to2megohmgridleakresistancearoundthefixedcondenserandthenconnectthesecondpostofthevariablecondensertooneterminalofthedetectortubefilament.Runthiswireonoverandconnectitwiththefirstpostofthesecondrheostat,thesecondpostofwhichisconnectedwithoneterminalofthefilamentofthefirstamplifyingtube;thenconnectthefirstpostoftherheostatwithoneendofthesecondarycoilofthefirstaudiofrequencytransformer,andtheotherendofthiscoilwiththegridofthefirstamplifiertube.

Connecttheleadthatrunsfromthesecondpostofvariablecondensertothefirstpostofthethirdrheostat,thesecondpostofwhichisconnectedwithoneterminalofthesecondamplifyingtube;thenconnectthefirstpostoftherheostatwithoneendofthesecondarycoilofthesecondaudiofrequencytransformerandtheotherendofthiscoilwiththegridofthesecondamplifiertube.

Thisdoneconnectthe-ornegativeelectrodeoftheAbatterywiththesecondpostofthevariablecondenserandconnectthe+orpositiveelectrodewiththefreepostofthefirstrheostat,theotherpostofwhichconnectswiththefreeterminalofthefilamentofthedetector.Fromthisleadtapoffawireandconnectittothefreeterminalofthefilamentofthefirstamplifiertube,andfinallyconnecttheendoftheleadwiththefreeterminalofthefilamentofthesecondamplifiertube.

NextshuntapotentiometeraroundtheAbatteryandconnectthethirdpost,whichconnectswiththeslidingcontact,tothenegativeorzincpoleofaBbattery,thenconnectthepositiveorcarbonpoleofittothenegativeorzincpoleofasecondBbatteryandthepositiveorcarbonpoleofthelatterwithoneendoftheprimarycoilofthesecondaudiofrequencytransformerandtheotherendofittotheplateofthefirstamplifyingtube.Runtheleadonoverandconnectittooneoftheterminalsofthesecondfixedcondenserandtheotherterminalofthiswiththeplateofthesecondamplifyingtube.Thenshunttheheadphonesaroundthecondenser.

FinallyconnectoneendoftheticklercoilofthetunerwiththeplateofthedetectortubeandconnecttheotherendoftheticklertooneendoftheprimarycoilofthefirstaudiofrequencytransformerandtheotherendofittothewirethatconnectsthetwoBbatteriestogether.

CHAPTERXI

SHORTWAVEREGENERATIVERECEIVINGSETS

Ashortwavereceivingsetisonethatwillreceivearangeofwavelengthsoffrom150to600meterswhilethedistanceoverwhichthewavescanbereceivedaswellastheintensityofthesoundsreproducedbytheheadphonesdependson:(1)whetheritisaregenerativesetand(2)whetheritisprovidedwithamplifyingtubes.

High-graderegenerativesetsdesignedespeciallyforreceivingamateursendingstationsthatmustuseashortwavelengtharebuiltontheregenerativeprinciplejustlikethosedescribedinthelastchapterandfurtheramplificationcanbehadbytheuseofamplifiertubesasexplainedinChapterIX,butthenewfeatureofthesesetsistheuseofthevariocouplerandoneormorevariometers.Thesetuningdevicescanbeconnectedupindifferentwaysandareverypopularwithamateursatthepresenttime.

Differingfromtheordinaryloosecouplerthevariometerhasnomovablecontactswhilethevariometerisprovidedwithtapssothatyoucanconnectitupforthewavelengthyouwanttoreceive.Allyouhavetodoistotunetheoscillationcircuitstoeachotheristoturntherotor,whichisthesecondarycoil,aroundinthestator,astheprimarycoiliscalledinordertogetaveryfinevariationofthewavelength.Itisthisconstructionthatmakessharptuningwiththesesetspossible,bywhichismeantthatallwavelengthsaretunedoutexcepttheonewhichthereceivingsetistunedfor.

AShortWaveRegenerativeReceiver--WithOneVariometerandThreeVariableCondensers.--Thissetalsoincludesavariocouplerandagridcoil.Thewaythatthepartsareconnectedtogethermakesitasimpleandatthesametimeaveryefficientregenerativereceiverforshortwaves.Whilethissetcanbeusedwithoutshieldingthepartsfromeachotherthebestresultsarehadwhenshieldsareused.

Thepartsyouneedforthissetinclude:(1)onevariocoupler;(2)one.001microfaradvariablecondenser;(3)one.0005microfaradvariablecondenser;(4)one.0007microfaradvariablecondenser;(5)one2megohmgridleak;(6)onevacuumtubedetector;(7)one6voltAbattery;(8)one6ohm,1-1/2ampererheostat;(9)one200ohmpotentiometer;(10)one22-1/2voltBbattery;(11)one.001microfaradfixedcondenser,(12)onepairof2,000ohmheadphones,and(13)avariometer.

TheVariocoupler.--Avariocouplerconsistsofaprimarycoilwoundontheoutsideofatubeofinsulatingmaterialandtocertainturnsofthistapsareconnectedsothatyoucanfixthewavelengthwhichyouraerialsystemistoreceivefromtheshortestwave;i.e.,150metersonupbystepstothelongestwave,i.e.,600meters,whichistherangeofmostamateurvariocouplersthataresoldintheopenmarket.Thisisthepartofthevariocouplerthatiscalledthestator.

Thesecondarycoiliswoundonthesectionofaballmountedonashaftandthisisswunginbearingsonthestatorsothatitcanturninit.Thispartofthevariocoupleriscalledtherotorandisarrangedsothatitcanbemountedonapanelandadjustedbymeansofaknoboradial.AdiagramofavariocouplerisshownatAinFig.53,andthecoupleritselfatB.Therearevariousmakesandmodificationsofvariocouplersonthemarketbutallofthemareaboutthesamepricewhichis$6.00or$8.00.

TheVariometer.--Thisdeviceisquitelikethevariocoupler,butwiththesedifferences:(1)therotorturnsinthestator,whichisalsothesectionofaball,and(2)oneendoftheprimaryisconnectedwithoneendofthesecondarycoil.Tobereallyefficientavariometermusthaveasmallresistanceandalargeinductanceaswellasasmalldielectricloss.Tosecurethefirsttwoofthesefactorsthewireshouldbeformedofanumberoffine,purecopperwireseachofwhichisinsulatedandthewholestrandthencoveredwithsilk.Thiskindofwireisthebestthathasyetbeendevisedforthepurposeandissoldunderthetradenameoflitzendraht.

Anewtypeofvariometerhaswhatisknownasabasketweave,orwavywoundstatorandrotor.Thereisnowood,insulatingcompoundorotherdielectricmaterialsinlargeenoughquantitiestoabsorbtheweakcurrentsthatflowbetweenthem,henceweakersoundscanbeheardwhenthiskindofavariometerisused.Withityoucantunesharplytowavesunder200metersinlengthanduptoandincludingwavelengthsof360meters.Whenamateurstationsofsmallpoweraresendingontheseshortwavesthisstyleofvariometerkeepstheelectricoscillationsattheirgreateststrengthand,hence,thereproducedsoundswillbeofmaximumintensity.AwiringdiagramofavariometerisshownatAinFig.54andabasketballvariometerisshowncompleteatB.

ConnectingUptheParts.--Tohook-upthesetconnecttheleading-inwiretooneendoftheprimarycoil,orstator,ofthevariocouplerandsolderawiretooneofthetapsthatgivesthelongestwavelengthyouwanttoreceive.Connecttheotherendofthiswirewithonepostofa.001microfaradvariablecondenserandconnecttheotherpostwiththegroundasshowninFig.55.Nowconnectoneendofthesecondarycoil,orrotor,toonepostofa.0007mfd.variablecondenser,theotherpostofthistooneendofthegridcoilandtheotherendofthiswiththeremainingendoftherotorofthevariocoupler.

Nextconnectonepostofthe.0007mfd.condenserwithoneoftheterminalsofthedetectorfilament;thenconnecttheotherpostofthiscondenserwithonepostofthe.0005mfd.variablecondenserandtheotherpostofthiswiththegridofthedetector,thenshuntthemegohmgridleakaroundthelattercondenser.Thisdoneconnecttheotherterminalofthefilamenttoonepostoftherheostat,theotherpostofthistothe-ornegativeelectrodeofthe6voltAbatteryandthe+orpositiveelectrodeofthelattertotheotherterminalofthefilament.

ShuntthepotentiometeraroundtheAbatteryandconnecttheslidingcontactwiththe-orzincpoleoftheBbatteryandthe+orcarbonpolewithoneterminaloftheheadphone;connecttheotherterminaltooneofthepostsofthevariometerandtheotherpostofthevariometertotheplateofthedetector.Finallyshunta.001mfd.fixedcondenseraroundtheheadphones.IfyouwanttoamplifythecurrentwithavacuumtubeamplifierconnectintheterminalsoftheamplifiercircuitshownatAinFigs.44or45atthepointwheretheyareconnectedwiththesecondarycoiloftheloosecoupledtuningcoil,inthosediagramswiththebindingpostsofFig.55wherethephonesareusuallyconnectedin.

ShortWaveRegenerativeReceiver.WithTwoVariometersandTwoVariableCondensers.--Thistypeofregenerativereceptorisverypopularwithamateurswhoareusinghigh-gradeshort-wavesets.Whenyouconnectupthisreceptoryoumustkeepthevariouspartswellseparated.Screwthevariocouplertothemiddleofthebaseboardorpanel,andsecurethevariometersoneithersideofitsothatthedistancebetweenthemwillbe9or10inches.Bysoplacingthemthecouplingwillbethesameonbothsidesandbesidesyoucanshieldthemfromeachothereasier.

Fortheshielduseasheetofcopperonthebackofthepanelandplaceasheetofcopperbetweentheparts,orbetter,enclosethevariometersanddetectorandamplifyingtubesifyouusethelatterinsheetcopperboxes.Whenyousetupthevariometersplacethemsothattheirstatorsareatrightanglestoeachotherforotherwisethemagneticlinesofforcesetupbythecoilsofeachonewillbemutuallyinductiveandthiswillmaketheheadphonesorloudspeakerhowl.Whatevertendencythereceptorhastohowlwiththisarrangementcanbeovercomebyputtinginagridleakoftherightresistanceandadjustingthecondenser.

ThePartsandHowtoConnectThemUp.--Forthissetyourequire:(1)onevariocoupler;(2)twovariometers;(3)one.001microfaradvariablecondenser;(4)one.0005microfaradvariablecondenser;(5)one2megohmgridleakresistance;(6)onevacuumtubedetector;(7)one6voltAbattery;(8)one200ohmpotentiometer;(9)one22-1/2voltBbattery;(10)one.001microfaradfixedcondenser,and(11)onepairof2,000ohmheadphones.

Towireupthesetbeginbyconnectingtheleading-inwiretothefixedendoftheprimarycoil,orstator,ofthevariocoupler,asshowninFig.56,andconnectonepostofthe.001mfd.variablecondensertothestatorbysolderingashortlengthofwiretothetapofthelatterthatgivesthelongestwaveyouwanttoreceive.Nowconnectoneendofthesecondarycoil,orrotor,ofthevariocouplerwithonepostofthe.0005mfd.variablecondenserandtheotherparttothegridofthedetectortube.Connecttheotherendoftherotorofthevariocouplertooneofthepostsofthefirstvariometerandtheotherpostofthistooneoftheterminalsofthedetectorfilament.

Connectthisfilamentterminalwiththe-ornegativeelectrodeoftheAbatteryandthe+orpositiveelectrodeofthiswithonepostoftherheostatandleadawirefromtheotherposttothefreeterminalofthefilament.ThisdoneshuntthepotentialaroundtheAbatteryandconnecttheslidingcontacttothe-orzincpoleoftheBbatteryandthe+orcarbonpoleofthistooneterminaloftheheadphones,whiletheotherterminalofthisleadstooneofthepostsofthesecondvariometer,theotherpostofwhichisconnectedtotheplateofthedetectortube.Ifyouwanttoaddanamplifiertubethenconnectittothepostsinsteadoftheheadphonesasdescribedintheforegoingset.

CHAPTERXII

INTERMEDIATEANDLONGWAVEREGENERATIVERECEIVINGSETS

Allreceivingsetsthatreceiveoverarangeofwavelengthsoffrom150metersto3,000metersarecalledintermediatewavesetsandallsetsthatreceivewavelengthsoverarangeofanythingmorethan3,000metersarecalledlongwavesets.Therangeofintermediatewavereceptorsissuchthattheywillreceiveamateur,broadcasting,shipandshoreNavy,commercial,Arlington'stimeandallotherstationsusingsparktelegraphdampedwavesorarcorvacuumtubetelephonecontinuouswavesbutnotcontinuouswavetelegraphsignals,unlessthesehavebeenbrokenupintogroupsatthetransmittingstation.Toreceivecontinuouswavetelegraphsignalsrequiresreceivingsetsofspecialkindandthesewillbedescribedinthenextchapter.

IntermediateWaveReceivingSets.--Therearetwochiefschemesemployedtoincreasetherangeofwavelengthsthatasetcanreceiveandthesearebyusing:(1)loadingcoilsandshuntcondensers,and(2)bank-woundcoilsandvariablecondensers.Ifyouhaveashort-wavesetandplantoreceiveintermediatewaveswithitthenloadingcoilsandfixedcondensersshuntedaroundthemaffordsyouthewaytodoit,butifyouprefertobuyanewreceptorthenthebetterwayistogetonewithbank-woundcoilsandvariablecondensers;thislatterwaypreservestheelectricalbalanceoftheoscillationcircuitsbetter,theelectricallossesarelessandthetuningeasierandsharper.

IntermediateWaveSetWithLoadingCoils.--Forthisintermediatewavesetyoucanuseeitheroftheshort-wavesetsdescribedintheforegoingchapter.Fortheloadingcoilsusehoneycombcoils,orothergoodcompactinductancecoils,asshowninChapterXandhavingarangeofwhateverwavelengthyouwishtoreceive.Thefollowingtableshowstherangeofwavelengthofthevarioussizedcoilswhenusedwithavariablecondenserhavinga.001microfaradcapacitance,theapproximateinductanceofeachcoilinmillihenriesandpricesatthepresentwriting:

TABLEOFCHARACTERISTICSOFHONEYCOMBCOILS

ApproximateWave

LengthinMetersin

Millihenries

Inductance.001mfd.VariableMounted

Appx.AirCondenser.onPlug

.040130--375$1.40

.075180--5151.40

.15240--7301.50

.3330--10301.50

.6450--14601.55

1.3660--22001.60

2.3930--28501.65

4.51300--40001.70

6.51550--48001.75

11.2050--63001.80

20.3000--85002.00

40.4000--120002.15

65.5000--150002.35

100.6200--190002.60

125.7000--210003.00

175.8200--240003.50

Theseandotherkindsofcompactcoilscanbeboughtatelectricalsupplyhousesthatsellwirelessgoods.Ifyouraerialisnotveryhighorlongyoucanuseloadingcoils,buttogetanythinglikeefficientresultswiththemyoumusthaveanaerialoflargecapacitanceandtheonlywaytogetthisistoputupahighandlongonewithtwoormoreparallelwiresspacedagoodlydistanceapart.

ThePartsandHowtoConnectThemUp.--Get(1)twohoneycomborothercoilsofthegreatestwavelengthyouwanttoreceive,forinordertoproperlybalancetheaerial,orprimaryoscillationcircuit,andtheclosed,orsecondaryoscillationcircuit,youhavetotunethemtothesamewavelength;(2)two.001mfd.variablecondensers,thoughfixedcondenserswilldo,and(3)twosmallsingle-throwdouble-poleknifeswitchesmountedonporcelainbases.

Tousetheloadingcoilsallyouhavetodoistoconnectoneofthemintheaerialabovetheprimarycoiloftheloosecoupler,orvariocouplerasshowninthewiringdiagraminFig.57,thenshuntoneofthecondensersarounditandconnectoneoftheswitchesaroundthis;thisswitchenablesyoutocutinorouttheloadingcoilatwill.Likewiseconnecttheotherloadingcoilinonesideoftheclosed,orsecondarycircuitbetweenthevariable.0007mfd.condenserandthesecondarycoiloftheloosecouplerorvariocouplerasshowninFig.53.TheotherconnectionsareexactlythesameasshowninFigs.44and45.

AnIntermediateWaveSetWithVariocouplerInductanceCoils.--Byusingthecoilwoundontherotorofthevariocouplerastheticklerthecouplingbetweenthedetectortubecircuitsandtheaerialwiresystemincreasesasthesetistunedforgreaterwavelengths.Thisschememakesthecontroloftheregenerativecircuitfarmorestablethanitiswhereanordinaryloosecoupledtuningcoilisused.

Whenthevariocouplerisadjustedforreceivingverylongwavestherotorsetsatrightanglestothestatorand,sincewhenitisinthispositionthereisnomutualinductionbetweenthem,theticklercoilservesasaloadingcoilforthedetectorplateoscillationcircuit.Inductancecoilsforshortwavelengthsareusuallywoundinsinglelayersbutbank-woundcoils,astheyarecalledarenecessarytogetcompactnesswherelongwavelengthsaretobereceived.Bywindinginductancecoilswithtwoormorelayersthehighestinductancevaluescanbeobtainedwiththeleastresistance.AwiringdiagramofamultipointinductancecoilisshowninFig.58.Youcanbuythisintermediatewavesetassembledandreadytouseorgetthepartsandconnectthemupyourself.

ThePartsandHowtoConnectThemUp.--Forthisregenerativeintermediatewavesetget:(1)one12sectiontriplebank-woundinductancecoil,(2)onevariometer,and(3)alltheotherpartsshowninthediagramFig.58exceptthevariocoupler.Firstconnectthefreeendofthecondenserintheaerialtooneoftheterminalsofthestatorofthevariocoupler;thenconnecttheotherterminalofthestatorwithoneoftheendsofthebank-woundinductancecoilandconnectthemovablecontactofthiswiththeground.

Nextconnectawiretotheaerialbetweenthevariablecondenserandthestatorandconnectthistoonepostofa.0005microfaradfixedcondenser,thenconnecttheotherpostofthiswiththegridofthedetectorandshunta2megohmgridleakaroundit.Connectawiretothegroundwirebetweenthebank-woundinductancecoilandthegroundproper,i.e.,theradiatororwaterpipe,connecttheotherendofthistothe+electrodeoftheAbatteryandconnectthisendalsotooneoftheterminalsofthe

filament.Thisdoneconnecttheotherterminalofthefilamenttoonepostoftherheostatandtheotherpostofthistothe-ornegativesideoftheAbattery.

Tothe+electrodeoftheAbatteryconnectthe-orzincpoleoftheBbatteryandconnectthe+orcarbonpoleofthelatterwithonepostofthefixed.001microfaradcondenser.Thisdoneconnectoneterminaloftheticklercoilwhichisontherotorofthevariometertotheplateofthedetectorandtheotherterminaloftheticklertotheotherpostofthe.001condenserandaroundthisshuntyourheadphones.Orifyouwanttouseoneormoreamplifyingtubesconnectthecircuitofthefirstone,seeFig.45,tothepostsoneithersideofthefixedcondenserinsteadoftheheadphones.

ALongWaveReceivingSet.--ThevividimaginationofJulesVerneneverconceivedanythingsofascinatingasthereceptionofmessageswithoutwiressentoutbystationshalfwayroundtheworld;andinthesedaysofhighpowercablelessstationsonthefivecontinentsyoucanlisten-intothemessagesandhearwhatisbeingsentoutbytheLyons,ParisandotherFrenchstations,byGreatBritain,Italy,GermanyandevenfaroffRussiaandJapan.

Alongwavesetforreceivingthesestationsmustbeabletotunetowavelengthsupto20,000meters.Differingfromthewayinwhichtheregenerativeactionoftheshortwavesetsdescribedintheprecedingchapterissecuredandwhichdependsonaticklercoilandthecouplingactionofthedetectorinthislongwaveset,[Footnote:Alloftheshortwaveandintermediatewavereceiversdescribed,areconnectedupaccordingtothewiringdiagramusedbytheA.H.GrebeCompany,RichmondHill,LongIsland,N.Y.]thisactionisobtainedbytheuseofaticklercoilintheplatecircuitwhichisinductivelycoupledtothegridcircuitandthisfeedsbackthenecessaryamountofcurrent.Thisisaverygoodwaytoconnectupthecircuitsforthereasonthat:(1)thewiringissimplified,and(2)itgivesasinglevariableadjustmentfortheentirerangeofwavelengthsthereceptorisintendedtocover.

ThePartsandHowtoConnectThemUp.--Thetwochieffeaturesasfarasthepartsareconcernedofthislongwavelengthreceivingsetare(1)thevariablecondensers,and(2)thetuninginductancecoils.Thevariablecondenserusedinserieswiththeaerialwiresystemhas26platesandisequaltoacapacitanceof.0008mfd.whichisthenormalaerialcapacitance.Thecondenserusedinthesecondarycoilcircuithas14platesandthisisequaltoacapacitanceof.0004mfd.

Thereareanumberofinductancecoilsandthesearearrangedsothattheycanbeconnectedinorcutoutandcombinationsarethusformedwhichgiveahighefficiencyandyetallowthemtobecompactlymounted.Theinductancecoilsoftheaerialwiresystemandthoseofthesecondarycoilcircuitarepracticallyalike.Forwavelengthsupto2,200metersbanklitz-woundcoilsareusedandthesearewoundupin2,4and6banksinordertogivetheproperdegreeofcouplingandinductancevalues.

Wherewavelengthsofmorethan2,200metersaretobereceivedcoto-coilsareusedasthesearethe"lastword"ininductancecoildesign,andareespeciallyadaptedformediumaswellaslongwavelengths.[Footnote:CanbehadoftheCotoCoilCo.,Providence,R.I.]Thesevariouscoilsarecutinandoutbymeansoftwofive-pointswitcheswhichareprovidedwithauxiliaryleversandcontactorsfordead-endingtherightamountofthecoils.Incuttingincoilsforincreasedwavelengths,thatisfrom10,000to20,000meters,allofthecoilsoftheaerialareconnectedinseriesaswellasallofthecoilsofthesecondarycircuit.TheconnectionsforalongwavereceptorareshowninthewiringdiagraminFig.59.

CHAPTERXIII

HETERODYNEORBEATLONGWAVETELEGRAPHRECEIVINGSET

Anyofthereceivingsetsdescribedintheforegoingchapterswillrespondtoeither:(1)awirelesstelegraphtransmitterthatusesasparkgapandwhichsendsoutperiodicelectricwaves,orto(2)awirelesstelephonetransmitterthatusesanarcoravacuumtubeoscillatorandwhichsendsoutcontinuouselectricwaves.Toreceivewirelesstelegraphsignals,however,fromatransmitterthatusesanarcoravacuumtubeoscillatorandwhichsendsoutcontinuouswaves,eitherthetransmitterorthereceptormustbesoconstructedthatthecontinuouswaveswillbebrokenupintogroupsofaudiofrequencyandthisisdoneinseveraldifferentways.

Therearefourdifferentwaysemployedatthepresenttimetobreakupthecontinuouswavesofawirelesstelegraphtransmitterintogroupsandtheseare:(a)theheterodyne,orbeat,method,inwhichwavesofdifferentlengthsareimpressedonthereceivedwavesandsoproducesbeats;(b)thetikker,orchoppermethod,inwhichthehighfrequencycurrentsarerapidlybrokenup;(c)thevariablecondensermethod,inwhichthemovableplatesaremadetorapidlyrotate;(d)thetonewheel,orfrequencytransformer,asitisoftencalled,andwhichisreallyamodifiedformofandanimprovementonthetikker.Theheterodynemethodwillbedescribedinthischapter.

WhattheHeterodyneorBeatMethodIs.--ThewordheterodynewascoinedfromtheGreekwordsheteroswhichmeansother,ordifferent,anddynewhichmeanspower;inotherwordsitmeanswhenusedinconnectionwithawirelessreceptorthatanotheranddifferenthighfrequencycurrentisusedbesidestheonethatisreceivedfromthesendingstation.Inmusicabeatmeansaregularlyrecurrentswellingcausedbythereinforcementofasoundandthisissetupbytheinterferenceofsoundwaveswhichhaveslightlydifferentperiodsofvibrationas,forinstance,whentwotonestakeplacethatarenotquiteintunewitheachother.This,then,istheprincipleoftheheterodyne,orbeat,receptor.

Intheheterodyne,orbeatmethod,separatesustainedoscillations,thatarejustaboutasstrongasthoseoftheincomingwaves,aresetupinthereceivingcircuitsandtheirfrequencyisjustalittlehigheroralittlelowerthanthosethataresetupbythewavesreceivedfromthedistanttransmitter.Theresultisthattheseoscillationsofdifferentfrequenciesinterfereandreinforceeachotherwhenbeatsareproduced,theperiodofwhichisslowenoughtobeheardintheheadphones,hencetheincomingsignalscanbeheardonlywhenwavesfromthesendingstationarebeingreceived.AfullerexplanationofhowthisisdonewillbefoundinChapterXV.

TheAutodyneorSelf-HeterodyneLong-WaveReceivingSet.--Thisisthesimplesttypeofheterodynereceptoranditwillreceiveperiodicwavesfromsparktelegraphtransmittersorcontinuouswavesfromanarcorvacuumtubetelegraphtransmitter.Inthistypeofreceptorthedetectortubeitselfismadetosetuptheheterodyneoscillationswhichinterferewiththosethatareproducedbytheincomingwavesthatarealittleoutoftunewithit.

Withalongwaveautodyne,orself-heterodynereceptor,asthistypeiscalled,andatwo-stepaudio-frequencyamplifieryoucanclearlyhearmanyofthecablelessstationsofEuropeandothersthatsendoutlongwaves.Forreceivinglongwavestations,however,youmusthavealongaerial--asinglewire200ormorefeetinlengthwilldo--andthehigheritisthelouderwillbethesignals.

Whereitisnotpossibletoputtheaerialupahundredfeetormoreabovetheground,youcanusealoweroneandstillgetmessagesinInternationalMorsefairlystrong.

ThePartsandConnectionsofanAutodyne,orSelf-Heterodyne,ReceivingSet.--Forthislongwavereceivingsetyouwillneed:(1)onevariocouplerwiththeprimarycoilwoundonthestatorandthesecondarycoilandticklercoilwoundontherotor,oryoucanusethreehoneycomborothergoodcompactcoilsofthelongestwaveyouwanttoreceive,atableofwhichisgiveninChapterXII;(2)two.001mfd.variablecondensers;(3)one.0005mfd.variablecondenser;(4)one.5to2megohmgridleakresistance;(5)onevacuumtubedetector;(6)oneAbattery;(7)onerheostat;(8)oneBbattery;(9)onepotentiometer;(10)one.001mfd.fixedcondenserand(11)onepairofheadphones.Forthetwo-stepamplifieryoumust,ofcourse,havebesidestheabovepartstheamplifiertubes,variablecondensers,batteriesrheostats,potentiometersandfixedcondensersasexplainedinChapterIX.Theconnectionsfortheautodyne,orself-heterodyne,receivingsetareshowninFig.60.

TheSeparateHeterodyneLongWaveReceivingSet.--Thisisabetterlongwavereceptorthantheselfheterodynesetdescribedaboveforreceivingwirelesstelegraphsignalssentoutbyacontinuouslongwavetransmitter.Thegreatadvantageofusingaseparatevacuumtubetogeneratetheheterodyneoscillationsisthatyoucanmakethefrequencyoftheoscillationsjustwhatyouwantittobeandhenceyoucanmakeitalittlehigheroralittlelowerthantheoscillationssetupbythereceivedwaves.

ThePartsandConnectionsofaSeparateHeterodyneLongWaveReceivingSet.--Thepartsrequiredforthislongwavereceivingsetare:(1)fourhoneycomborothergoodcompactinductancecoilsofthelongestwavelengththatyouwanttoreceive;(2)three.001mfd.variablecondensers;(3)one.0005mfd.variablecondenser;(4)one1megohmgridleakresistance;(5)onevacuumtubedetector;(6)oneAbattery;(7)tworheostats;(8)twoBbatteries,oneofwhichissuppliedwithtaps;(9)onepotentiometer;(10)onevacuumtubeamplifier,forsettinguptheheterodyneoscillations;(11)apair

ofheadphonesand(12)allofthepartsforatwo-stepamplifierasdetailedinChapterIX,thatisifyouaregoingtouseamplifiers.TheconnectionsareshowninFig.61.

InusingeitheroftheseheterodynereceiversbesuretocarefullyadjusttheBbatterybymeansofthepotentiometer.

[Footnote:Theamplifiertubeinthiscaseisusedasageneratorofoscillations.]

CHAPTERXIV

HEADPHONESANDLOUDSPEAKERS

WirelessHeadphones.--AtelephonereceiverforawirelessreceivingsetismadeexactlyonthesameprincipleasanordinaryBelltelephonereceiver.Theonlydifferencebetweenthemisthattheformerismadeflatandcompactsothatapairofthemcanbefastenedtogetherwithabandandwornonthehead(whenitiscalledaheadset),whilethelatterislongandcylindricalsothatitcanbeheldtotheear.Afurtherdifferencebetweenthemisthatthewirelessheadphoneismadeassensitiveaspossiblesothatitwillrespondtoveryfeeblecurrents,whiletheordinarytelephonereceiverisfarfrombeingsensitiveandwillrespondonlytocomparativelylargecurrents.

HowaBellTelephoneReceiverIsMade.--Anordinarytelephonereceiverconsistsofthreechiefpartsandtheseare:(1)ahard-rubber,orcomposition,shellandcap,(2)apermanentsteelbarmagnetononeendofwhichiswoundacoiloffineinsulatedcopperwire,and(3)asoftirondisk,ordiaphragm,allofwhichareshowninthecross-sectioninFig.62.Thebarmagnetissecurelyfixedinsideofthehandlesothattheoutsideendcomestowithinabout1/32ofaninchofthediaphragmwhenthisislaidontopoftheshellandthecapisscrewedon.

Photographunavailableoriginal©UnderwoodandUnderwood.

AlexanderGrahamBell,InventoroftheTelephone,nowanardentRadioEnthusiast.

Theendsofthecoilofwireareconnectedwithtwobindingpostswhichareintheendoftheshell,butareshowninthepictureatthesidesforthesakeofclearness.Thiscoilusuallyhasaresistanceofabout75ohmsandthemeaningoftheohmicresistanceofareceiveranditsbearingonthesensitivenessofitwillbeexplainedalittlefartheralong.Afterthedisk,ordiaphragm,whichis

generallymadeofthin,softsheetironthathasbeentinnedorjapanned,[Footnote:Adiskofphotographictin-typeplateisgenerallyused.]isplacedovertheendofthemagnet,thecap,whichhasasmallopeninginit,isscrewedonandthereceiverisreadytouse.

HowaWirelessHeadphoneIsMade.--Forwirelessworkareceiverofthewatch-casetypeisusedandnearlyalwaystwosuchreceiversareconnectedwithaheadband.ItconsistsofapermanentbarmagnetbentsothatitwillfitintotheshellofthereceiverasshownatAinFig.63.

Theendsofthismagnet,whicharecalledpoles,arebentup,andhencethistypeiscalledabipolarreceiver.Themagnetsarewoundwithfineinsulatedwireasbeforeandthediaphragmisheldsecurelyinplaceoverthembyscrewingonthecap.

AboutResistance,TurnsofWireandSensitivityofHeadphones.--Ifyouareabeginnerinwirelessyouwillhearthosewhoareexperiencedspeakofatelephonereceiverashavingaresistanceof75ohms,1,000ohms,2,000or3,000ohms,asthecasemaybe;fromthisyouwillgatherthatthehighertheresistanceofthewireonthemagnetsthemoresensitivethereceiveris.Inasensethisistrue,butitisnottheresistanceofthemagnetcoilsthatmakesitsensitive,infact,itcutsdownthecurrent,butitisthenumberofturnsofwireonthemthatdeterminesitssensitiveness;itiseasytoseethatthisisso,forthelargerthenumberofturnsthemoreoftenwillthesamecurrentflowroundthecoresofthemagnetandsomagnetizethemtoagreaterextent.

Buttowindalargenumberofturnsofwirecloseenoughtothecorestobeeffectivethewiremustbeverysmallandso,ofcourse,thehighertheresistancewillbe.NowthewireusedforwindinggoodreceiversisusuallyNo.40,andthishasadiameterof.0031inch;consequently,whenyouknowtheohmicresistanceyougetanideaofthenumberofturnsofwireandfromthisyougatherinageneralwaywhatthesensitivityofthereceiveris.

Areceiverthatissensitiveenoughforwirelessworkshouldbewoundtonotlessthan1,000ohms(thismeanseachearphone),whilethoseofabettergradearewoundtoashighas3,000ohmsfor

eachone.Ahigh-gradeheadsetisshowninFig.64.Eachphoneofaheadsetshouldbewoundtothesameresistance,andtheseareconnectedinseriesasshown.Wheretwoormoreheadsetsareusedwithonewirelessreceivingsettheymustallbeofthesameresistanceandconnectedinseries,thatis,thecoilsofoneheadsetareconnectedwiththecoilsofthenextheadsetandsoontoformacontinuouscircuit.

TheImpedanceofHeadphones.--Whenacurrentisflowingthroughacircuitthematerialofwhichthewireismadenotonlyopposesitspassage--thisiscalleditsohmicresistance--butacounter-electromotiveforcetothecurrentissetupduetotheinductiveeffectsofthecurrentonitselfandthisiscalledimpedance.Whereawireiswoundinacoiltheimpedanceofthecircuitisincreasedandwhereanalternatingcurrentisusedtheimpedancegrowsgreaterasthefrequencygetshigher.Theimpedanceofthemagnetcoilsofareceiverissogreatforhighfrequencyoscillationsthatthelattercannotpassthroughthem;inotherwords,theyarechokedoff.

HowtheHeadphonesWork.--Asyouwillseefromthecross-sectionsinFigs.62and63thereisnoconnection,electricalormechanical,betweenthediaphragmandtheotherpartsofthereceiver.Nowwheneitherfeebleoscillations,whichhavebeenrectifiedbyadetector,orsmallcurrentsfromaBbattery,flowthroughthemagnetcoilsthepermanentsteelmagnetisenergizedtoagreaterextentthanwhennocurrentisflowingthroughit.Thisaddedmagneticenergymakesthemagnetattractthediaphragmmorethanitwoulddobyitsownforce.If,ontheotherhand,thecurrentiscutoffthepullofthemagnetislessenedandasitsattractionforthediaphragmisdecreasedthelatterspringsbacktoitsoriginalposition.Whenvaryingcurrentsflowthroughthecoilsthediaphragmvibratesaccordinglyandsendsoutsoundwaves.

AboutLoudSpeakers.--Thesimplestacousticinstrumenteverinventedisthemegaphone,whichlatterisaGreekwordmeaninggreatsound.ItisaveryprimitivedeviceandourIndiansmadeitoutofbirch-barkbeforeColumbusdiscoveredAmerica.Initssimplestformitconsistsofacone-shapedhornandasthespeakertalksintothesmallendtheconcentratedsoundwavespassoutofthelargeendinwhateverdirectionitisheld.

Nowaloudspeakerofwhateverkindconsistsoftwochiefpartsandtheseare:(1)atelephone

receiver,and(2)amegaphone,orhornasitiscalled.Aloudspeakerwhenconnectedwithawirelessreceivingsetmakesitpossibleforaroom,oranauditorium,fullofpeople,oranoutdoorcrowd,tohearwhatisbeingsentoutbyadistantstationinsteadofbeinglimitedtoafewpersonslistening-inwithheadphones.Tousealoudspeakeryoushouldhaveavacuumtubedetectorreceivingsetandthismustbeprovidedwithaone-stepamplifieratleast.

Togetreallygoodresultsyouneedatwo-stepamplifierandthenenergizetheplateofthesecondvacuumtubeamplifierwitha100voltBbattery;orifyouhaveathree-stepamplifierthenusethehighvoltageontheplateofthethirdamplifiertube.Amplifyingtubesaremadetostandaplatepotentialof100voltsandthisisthekindyoumustuse.Nowitmayseemcurious,butwhenthecurrentflowsthroughthecoilsofthetelephonereceiverinonedirectionitgivesbetterresultsthanwhenitflowsthroughintheotherdirection;tofindoutthewaythecurrentgivesthebestresultstryitoutbothwaysandthisyoucandobysimplyreversingtheconnections.

TheSimplestTypeofLoudSpeaker.--Thisloudspeaker,whichiscalled,theArkay,[Footnote:MadebytheRiley-KlotzMfg.Co.,Newark,N.J.]willworkonaone-ortwo-stepamplifier.Itconsistsofabrasshornwithacurveinitandinthebottomthereisanadapter,orframe,withasetscrewinitsothatyoucanfitinoneofyourheadphonesandthisisallthereistoit.Theconstructionisrigidenoughtopreventovertones,ordistortionofspeechormusic.ItisshowninFig.65.

AnotherSimpleKindofLoudSpeaker.--Anotherloudspeaker,seeFig.66,isknownastheAmplitone[Footnote:MadebytheAmericanPattern,FoundryandMachineCo.,82ChurchStreet,N.Y.C.]anditlikewisemakesuseoftheheadphonesasthesoundproducer.Thisdevicehasacastmetalhornwhichimprovesthequalityofthesound,andallyouhavetodoistosliptheheadphonesontheinlettubesofthehornanditisreadyforuse.Thetwoheadphonesnotonlygivealongervolumeofsoundthanwhereasingleoneisusedbutthereisacertainblendedqualitywhichresultsfromonephonesmoothingouttheimperfectionsoftheother.

AThirdKindofSimpleLoudSpeaker.--TheoperationoftheAmplitron,[Footnote:MadebytheRadioServiceCo.,110W.40thStreet,N.Y.]asthisloudspeakeriscalled,isslightlydifferentfromothersusedforthesamepurpose.Thesoundssetupbytheheadphoneareconveyedtotheapexofaninvertedcopperconewhichis7incheslongand10inchesindiameter.Hereitisreflectedbyaparabolicmirrorwhichgreatlyamplifiesthesounds.Theamplificationtakesplacewithoutdistortion,thesoundsremainingasclearandcrispaswhenprojectedbythetransmittingstation.Byremovingthecapfromthereceivertheshellisscrewedintoareceptacleontheendoftheloudspeakerandtheinstrumentisreadyforuse.ItispicturedinFig.67.

ASuperLoudSpeaker.--Thisloudspeaker,whichisknownastheMagnavoxTelemegafone,wastheinstrumentusedbyLt.HerbertE.Metcalf,3,000feetintheair,andwhichstartledtheCityofWashingtononApril2,1919,byrepeatingPresidentWilson'sVictoryLoanMessagefromanairplaneinflightsothatitwasdistinctlyheardby20,000peoplebelow.

ThiswonderfulachievementwasaccomplishedthroughtheinstallationoftheMagnavoxand

amplifiersinfrontoftheTreasuryBuilding.EverywordLt.MetcalfspokeintohiswirelesstelephonetransmitterwascaughtandswelledinvolumebytheTelemegafonesbelowandpersonsblocksawaycouldhearthemessageplainly.Twokindsoftheseloudspeakersaremadeandtheseare:(1)asmallloudspeakerfortheuseofoperatorssothatheadphonesneednotbeworn,and(2)alargeloudspeakerforauditoriumandout-dooraudiences.

Photographunavailableoriginal©UnderwoodandUnderwood.

World'sLargestLoudSpeakerevermade.InstalledinLytlePark,Cincinnati,Ohio,topermitPresidentHarding'sAddressatPointPleasant,Ohio,duringtheGrantCentenaryCelebrationtobe

heardwithinaradiusofonesquare.

Eitherkindmaybeusedwithaone-ortwo-stepamplifierorwithacascadeofhalfadozenamplifiers,accordingtothedegreeofloudnessdesired.TheTelemegafoneitselfisnotanamplifierinthetruesenseinasmuchasitcontainsnoelementswhichwilllocallyincreasetheincomingcurrent.Itdoes,however,transformthevariableelectriccurrentsofthewirelessreceivingsetintosoundvibrationsinamostwonderfulmanner.

Atelemegafoneofeitherkindisformedof:(1)atelephonereceiveroflargeproportions,(2)astep-downinductioncoil,and(3)a6voltstoragebatterythatenergizesapowerfulelectromagnetwhichworksthediaphragm.Anelectromagnetisusedinsteadofapermanentmagnetandthisisenergizedbya6-voltstoragebatteryasshowninthewiringdiagramatAinFig.68.Oneendofthecoreofthismagnetisfixedtotheironcaseofthespeakerandtogethertheseformtheequivalentofahorseshoemagnet.Amovablecoilofwireissupportedfromthecenterofthediaphragmtheedgeofwhichisrigidlyheldbetweenthecaseandthesmallendofthehorn.Thiscoilisplacedovertheupperendofthemagnetanditsterminalsareconnectedtothesecondaryoftheinductioncoil.Nowwhenthecoilisenergizedbythecurrentfromtheamplifiersitandthecoreactlikeasolenoidinthatthecoiltendstosuckthecoreintoit;butsincethecoreisfixedandthecoilismovablethecoredrawsthecoildowninstead.Theresultisthatwitheveryvariationofthecurrentthatflowsthroughthecoilitmovesupanddownandpullsandpushesthediaphragmdownandupwithit.Thelargeamplitudeofthevibrationsofthelattersetuppowerfulsoundwaveswhichcanbeheardseveralblocksawayfromthehorn.Inthiswaythenarethefaintincomingsignals,speechandmusicwhicharereceivedbytheamplifyingreceivingsetreproducedandmagnifiedenormously.TheTelemegafoneisshowncompleteatB.

CHAPTERXV

OPERATIONOFVACUUMTUBERECEPTORS

Fromtheforegoingchaptersyouhaveseenthatthevacuumtubecanbeusedeitherasadetectororanamplifierorasageneratorofelectricoscillations,asinthecaseoftheheterodynereceivingset.Tounderstandhowavacuumtubeactsasadetectorandasanamplifieryoumustfirstknowwhatelectronsare.ThewayinwhichthevacuumtubesetsupsustainedoscillationswillbeexplainedinChapterXVIIIinconnectionwiththeOperationofVacuumTubeTransmitters.

WhatElectronsAre.--Scienceteachesusthatmassesofmatteraremadeupofmolecules,thateachoftheseismadeupofatoms,andeachofthese,inturn,ismadeupofacentralcoreofpositiveparticlesofelectricitysurroundedbynegativeparticlesofelectricityasshownintheschematicdiagram,Fig.69.Thelittleblackcirclesinsidethelargecirclerepresentpositiveparticlesofelectricityandthelittlewhitecirclesoutsideofthelargecirclerepresentnegativeparticlesofelectricity,orelectronsastheyarecalled.

Itisthenumberofpositiveparticlesofelectricityanatomhasthatdeterminesthekindofanelementthatisformedwhenenoughatomsofthesamekindarejoinedtogethertobuilditup.Thushydrogen,whichisthelightestknownelement,hasonepositiveparticleforitsnucleus,whileuranium,theheaviestelementnowknown,has92positiveparticles.Nowbeforeleavingtheatompleasenotethatitisasmuchsmallerthanthediagramasthelatterissmallerthanoursolarsystem.

WhatIsMeantbyIonization.--Ahydrogenatomisnotonlylighterbutitissmallerthantheatomofanyotherelementwhileanelectronismorethanathousandtimessmallerthantheatomofwhichitisapart.Nowaslongasalloftheelectronsremainattachedtothesurfaceofanatomitspositiveandnegativechargesareequalizedanditwill,therefore,beneitherpositivenornegative,thatis,itwillbe

perfectlyneutral.When,however,oneormoreofitselectronsareseparatedfromit,andthereareseveralwaysbywhichthiscanbedone,theatomwillshowapositivechargeanditisthencalledapositiveion.

Inotherwordsapositiveionisanatomthathaslostsomeofitsnegativeelectronswhileanegativeionisonethathasacquiredsomeadditionalnegativeelectrons.Whenanumberofelectronsarebeingconstantlygivenbytheatomsofanelement,whichletussupposeisametal,andarebeingattractedtoatomsofanotherelement,whichwewillsayisalsoametal,aflowofelectronstakesplacebetweenthetwooppositelychargedelementsandformacurrentofnegativeelectricityasrepresentedbythearrowsatAinFig.70.

Whenastreamofelectronsisflowingbetweentwometalelements,asafilamentandaplateinavacuumtubedetector,oranamplifier,theyactascarriersformorenegativeelectronsandthesearesuppliedbyabatteryasweshallpresentlyexplain.Ithasalwaysbeencustomaryforustothinkofacurrentofelectricityasflowingfromthepositivepoleofabatterytothenegativepoleofitandhencewehavecalledthisthedirectionofthecurrent.Sincetheelectronictheoryhasbeenevolvedithasbeenshownthattheelectrons,ornegativechargesofelectricity,flowfromthenegativetothepositivepoleandthattheionizedatoms,whicharemorepositivethannegative,flowintheoppositedirectionasshownatB.

HowElectronsareSeparatedfromAtoms.--Thenextquestionthatarisesishowtomakeametalthrowoffsomeoftheelectronsoftheatomsofwhichitisformed.Thereareseveralwaysthatthiscanbedonebutinanyeventeachatommustbegivenagood,hardblow.Asimplewaytodothisistoheatametaltoincandescencewhentheatomswillbombardeachotherwithterrificforceandmanyoftheelectronswillbeknockedoffandthrownoutintothesurroundingspace.

Butall,ornearlyall,ofthemwillreturntotheatomsfromwhencetheycameunlessameansofsomekindisemployedtoattractthemtotheatomsofsomeotherelement.Thiscanbedonebygivingthelatterpieceofmetalapositivecharge.Ifnowthesetwopiecesofmetalareplacedinabulbfromwhichtheairhasbeenexhaustedandthefirstpieceofmetalisheatedtobrilliancywhilethesecondpieceofmetaliskeptpositivelyelectrifiedthenastreamofelectronswillflowbetweenthem.

ActionoftheTwoElectrodeVacuumTube.--Nowinavacuumtubedetectorawirefilament,likethatofanincandescentlamp,isconnectedwithabatteryandthisformsthehotelementfromwhichtheelectronsarethrownoff,andametalplatewithaterminalwiresecuredtoitisconnectedtothe

positiveorcarbontapofadrybattery;nowconnectthenegativeorzinctapofthiswithoneendofatelephonereceiverandtheotherendofthiswiththeterminalsofthefilamentasshownatAinFig.71.IfnowyouheatthefilamentandholdthephonetoyourearyoucanhearthecurrentfromtheBbatteryflowingthroughthecircuit.

Sincetheelectronsarenegativechargesofelectricitytheyarenotonlythrownoffbythehotwirebuttheyareattractedbythepositivechargedmetalplateandwhenenoughelectronspass,orflow,fromthehotwiretotheplatetheyformaconductingpathandsocompletethecircuitwhichincludesthefilament,theplateandtheBorplatebattery,whenthecurrentcanthenflowthroughit.Asthenumberofelectronsthatarethrownoffbythefilamentisnotgreatandthevoltageoftheplateisnothighthecurrentthatflowsbetweenthefilamentandtheplateisalwaysquitesmall.

HowtheTwoElectrodeTubeActsasaDetector.--Astheactionofatwoelectrodetubeasadetector[Footnote:Thethreeelectrodevacuumtubehasentirelytakentheplaceofthetwoelectrodetype.]issimplerthanthatofthethreeelectrodevacuumtubeweshalldescribeitfirst.Thetwoelectrode

vacuumtubewasfirstmadebyMr.EdisonwhenhewasworkingontheincandescentlampbutthatitwouldserveasadetectorofelectricwaveswasdiscoveredbyProf.Fleming,ofOxfordUniversity,London.Asamatteroffact,itisnotreallyadetectorofelectricwaves,butitactsas:(1)arectifieroftheoscillationsthataresetupinthereceivingcircuits,thatis,itchangesthemintopulsatingdirectcurrentssothattheywillflowthroughandaffectatelephonereceiver,and(2)itactsasarelayandthefeeblereceivedoscillatingcurrentcontrolsthelargerdirectcurrentfromtheBbatteryinverymuchthesamewaythatatelegraphrelaydoes.Thislatterrelayactionwillbeexplainedwhenwecometoitsoperationasanamplifier.

Wehavejustlearnedthatwhenthestreamofelectronsflowfromthehotwiretothecoldpositiveplateinthetubetheyformaconductingpaththroughwhichthebatterycurrentcanflow.Nowwhentheelectricoscillationssurgethroughtheclosedoscillationcircuit,whichincludesthesecondaryofthetuningcoil,thevariablecondenser,thefilamentandtheplateasshownatBinFig.71thepositivepartofthempassesthroughthetubeeasilywhilethenegativepartcannotgetthrough,thatis,thetop,orpositive,partofthewave-formremainsintactwhilethelower,ornegative,partiscutoffasshowninthediagramatC.AsthereceivedoscillationsareeitherbrokenupintowavetrainsofaudiofrequencybythetelegraphtransmitteroraremodulatedbyatelephonetransmittertheycarrythelargerimpulsesofthedirectcurrentfromtheBbatteryalongwiththemandtheseflowthroughtheheadphones.Thisisthereasonthevacuumtubeamplifiesaswellasdetects.

HowtheThreeElectrodeTubeActsasaDetector.--ThevacuumtubeasadetectorhasbeenmadeverymuchmoresensitivebytheuseofathirdelectrodeshowninFig.72.Inthistypeofvacuumtubethethirdelectrode,orgrid,isplacedbetweenthefilamentandtheplateandthiscontrolsthenumberofelectronsflowingfromthefilamenttotheplate;inpassingbetweenthesetwoelectrodestheyhavetogothroughtheholesformedbythegridwires.

Ifnowthegridischargedtoahighernegativevoltagethanthefilamenttheelectronswillbestoppedbythelatter,seeA,thoughsomeofthemwillgothroughtotheplatebecausetheytravelatahighrateofspeed.Thehigherthenegativechargeonthegridthesmallerwillbethenumberofelectronsthatwillreachtheplateand,ofcourse,thesmallerwillbetheamountofcurrentthatwillflowthroughthetubeandtheheadphonesfromtheBbattery.

Ontheotherhandifthegridischargedpositively,seeB,thenmoreelectronswillstriketheplatethanwhenthegridisnotusedorwhenitisnegativelycharged.ButwhenthethreeelectrodetubeisusedasadetectortheoscillationssetupinthecircuitschangethegridalternatelyfromnegativetopositiveasshownatCandhencethevoltageoftheBbatterycurrentthatisallowedtoflowthroughthedetectorfromtheplatetothefilamentrisesandfallsinunisonwiththevoltageoftheoscillatingcurrents.Thewaythepositiveandnegativevoltagesoftheoscillationswhicharesetupbytheincomingwaves,

energizethegrid;howtheoscillatortubeclipsoffthenegativepartsofthem,and,finally,howthesecarrythebatterycurrentthroughthetubeareshowngraphicallybythecurvesatD.

HowtheVacuumTubeActsasanAmplifier.--Ifyouconnectupthefilamentandtheplateofathreeelectrodetubewiththebatteriesanddonotconnectinthegrid,youwillfindthattheelectronswhicharethrownoffbythefilamentwillnotgetfartherthanthegridregardlessofhowhighthevoltageisthatyouapplytotheplate.Thisisduetothefactthatalargenumberofelectronswhicharethrownoffbythefilamentstrikethegridandgiveitanegativecharge,andconsequently,theycannotgetanyfarther.SincetheelectronsdonotreachtheplatethecurrentfromtheBbatterycannotflowbetweenitandthefilament.

Nowwithaproperlydesignedamplifiertubeaverysmallnegativevoltageonthegridwillkeepaverylargepositivevoltageontheplatefromsendingacurrentthroughthetube,andoppositely,averysmallpositivevoltageonthegridwillletaverylargeplatecurrentflowthroughthetube;thisbeingtrueitfollowsthatanysmallvariationofthevoltagefrompositivetonegativeonthegridandtheotherwayaboutwillvaryalargecurrentflowingfromtheplatetothefilament.

IntheMorsetelegraphtherelaypermitsthesmallcurrentthatisreceivedfromthedistantsendingstationtoenergizeapairofmagnets,andthesedrawanarmaturetowardthemandcloseasecondcircuitwhenalargecurrentfromalocalbatteryisavailableforworkingthesounder.Theamplifiertubeisavariablerelayinthatthefeeblecurrentssetupbytheincomingwavesconstantlyandproportionatelyvaryalargecurrentthatflowsthroughtheheadphones.Thisthenistheprincipleonwhichtheamplifyingtubeworks.

TheOperationofaSimpleVacuumTubeReceivingSet.--Thewayasimplevacuumtubedetectorreceivingsetworksislikethis:whenthefilamentisheatedtobrilliancyitgivesoffelectronsaspreviouslydescribed.Nowwhentheelectricwavesimpingeontheaerialwiretheysetuposcillationsinitandthesesurgethroughtheprimarycoiloftheloosecoupledtuningcoil,adiagramofwhichisshownatBinFig.41.

Theenergyoftheseoscillationssetsuposcillationsofthesamefrequencyinthesecondarycoilandthesehighfrequencycurrentswhosevoltageisfirstpositiveandthennegative,surgeintheclosedcircuitwhichincludesthesecondarycoilandthevariablecondenser.Atthesametimethealternatingpositiveandnegativevoltageoftheoscillatingcurrentsisimpressedonthegrid;ateachchangefrom+to-andbackagainitallowstheelectronstostriketheplateandthenshutsthemoff;astheelectronsformtheconductingpathbetweenthefilamentandtheplatethelargerdirectcurrentfromtheBbatteryispermittedtoflowthroughthedetectortubeandtheheadphones.

OperationofaRegenerativeVacuumTubeReceivingSet.--ByfeedingbackthepulsatingdirectcurrentfromtheBbatterythroughtheticklercoilitsetsupotherandstrongeroscillationsinthesecondaryofthetuningcoilwhentheseactonthedetectortubeandincreaseitssensitivenesstoaremarkableextent.Theregenerative,orfeedback,actionofthereceivingcircuitsusedwillbeeasilyunderstoodbyreferringbacktoBinFig.47.

Whenthewavessetuposcillationsintheprimaryofthetuningcoiltheenergyofthemproduceslikeoscillationsintheclosedcircuitwhichincludesthesecondarycoilandthecondenser;thealternatingpositiveandnegativevoltagesoftheseareimpressedonthegridandthese,aswehaveseenbefore,causesimilarvariationsofthedirectcurrentfromtheBbatterywhichactsontheplateandwhich

flowsbetweenthelatterandthefilament.

Thisvaryingdirectcurrent,however,ismadetoflowbackthroughthethird,orticklercoilofthetuningcoilandsetsupinthesecondarycoilandcircuitsotherandlargeroscillatingcurrentsandtheseaugmenttheactionoftheoscillationsproducedbytheincomingwaves.TheseextraandlargercurrentswhicharetheresultofthefeedbackthenactonthegridandcausestilllargervariationsofthecurrentintheplatevoltageandhenceofthecurrentoftheBbatterythatflowsthroughthedetectorandtheheadphones.Atthesametimethetubekeepsonrespondingtothefeebleelectricoscillationssetupinthecircuitsbytheincomingwaves.Thisregenerativeactionofthebatterycurrentaugmentstheoriginaloscillationsmanytimesandhenceproducesoundsintheheadphonesthataremanytimesgreaterthanwherethevacuumtubedetectoraloneisused.

OperationofAutodyneandHeterodyneReceivingSets.--Onpage109[ChapterVII]wediscussedandatAinFig.36isshownapictureoftwotuningforksmountedonsoundingboxestoillustratetheprincipleofelectricaltuning.Whenapairoftheseforksaremadetovibrateexactlythesamenumberoftimespersecondtherewillbeacondensationoftheairbetweenthemandthesoundwavesthataresentoutwillbeaugmented.Butifyouadjustoneoftheforkssothatitwillvibrate256timesasecondandtheotherforksothatitwillvibrate260timesasecondthentherewillbeaphasedifferencebetweenthetwosetsofwavesandthelatterwillaugmenteachother4timeseverysecondandyouwillheartheserisingandfallingsoundsasbeats.

Nowelectricoscillationssetupintwocircuitsthatarecoupledtogetheractinexactlythesamewayassoundwavesproducedbytwotuningforksthatareclosetoeachother.Sincethisistrueifyoutuneoneoftheclosedcircuitssothattheoscillationsinitwillhaveafrequencyofa1,000,000andtunetheothercircuitsothattheoscillationsinithaveafrequencyof1,001,000asecondthentheoscillationswillaugmenteachother1,000timeseverysecond.

AstheserisingandfallingcurrentsactonthepulsatingcurrentsfromtheBbatterywhichflowthroughthedetectortubeandtheheadphonesyouwillhearthemasbeats.Agraphicrepresentationoftheoscillatingcurrentssetupbytheincomingwaves,thoseproducedbytheheterodyneoscillatorandthebeatstheyformisshowninFig.73.Toproducethesebeatsareceptorcanuse:(1)asinglevacuumtubeforsettinguposcillationsofbothfrequencieswhenitiscalledanautodyne,orself-heterodynereceptor,or(2)aseparatevacuumtubeforsettinguptheoscillationsforthesecondcircuitwhenitiscalledaheterodynereceptor.

TheAutodyne,orSelf-HeterodyneReceivingSet.--Whereonlyonevacuumtubeisusedforproducingbothfrequenciesyouneedonlyaregenerative,orfeed-backreceptor;thenyoucantunetheaerialwiresystemtotheincomingwavesandtunetheclosedcircuitofthesecondarycoilsothatitwillbeoutofstepwiththeformerby1,000oscillationspersecond,moreorless,theexactnumberdoesnotmatterintheleast.Fromthisyouwillseethatanyregenerativesetcanbeusedforautodyne,orself-heterodyne,reception.

TheSeparateHeterodyneReceivingSet.--Thebetterway,however,istouseaseparatevacuumtubeforsettinguptheheterodyneoscillations.Thelatterthenactontheoscillationsthatareproducedbytheincomingwavesandwhichenergizethegridofthedetectortube.Notethatthevacuumtubeusedforproducingtheheterodyneoscillationsisageneratorofelectricoscillations;thelatterareimpressedonthedetectorcircuitsthroughthevariablecoupling,thesecondaryofwhichisinserieswiththeaerialwireasshowninFig.74.ThewayinwhichthetubeactsasageneratorofoscillationswillbetoldinChapterXVIII.

CHAPTERXVI

CONTINUOUSWAVETELEGRAPHTRANSMITTINGSETSWITHDIRECTCURRENT

Inthefirstpartofthisbookwelearnedaboutspark-gaptelegraphsetsandhowtheoscillationstheysetuparedampedandthewavestheysendoutareperiodic.Inthisandthenextchapterweshallfindouthowvacuumtubetelegraphtransmittersaremadeandhowtheysetuposcillationsthataresustainedandradiatewavesthatarecontinuous.

Sendingwirelesstelegraphmessagesbycontinuouswaveshasmanyfeaturestorecommenditasagainstsendingthembyperiodicwavesandamongthemostimportantofthesearethatthetransmittercanbe:(1)moresharplytuned,(2)itwillsendsignalsfartherwiththesameamountofpower,and(3)itisnoiselessinoperation.Thedisadvantageousfeaturesarethat:(1)abatterycurrentisnotsatisfactory,(2)itscircuitsaresomewhatmorecomplicated,and(3)theoscillatortubesburnoutoccasionally.Thereis,however,agrowingtendencyamongamateurstousecontinuouswavetransmittersandtheyarecertainlymoreup-to-dateandinterestingthansparkgapsets.

Nowtherearetwopracticalwaysbywhichcontinuouswavescanbesetupforsendingeithertelegraphicsignalsortelephonicspeechandmusicandthesearewith:(a)anoscillationarclamp,and(b)avacuumtubeoscillator.Theoscillationarcwastheearliestknownwayofsettingupsustainedoscillations,anditisnowlargelyusedforcommercialhighpower,longdistancework.Butsincethevacuumtubehasbeendevelopedtoahighdegreeofefficiencyandistheschemethatisnowinvogueforamateurstationsweshallconfineoureffortsheretoexplainingtheapparatusnecessaryandhowtowirethevariouspartstogethertoproduceseveralsizesofvacuumtubetelegraphtransmitters.

SourcesofCurrentforTelegraphTransmittingSets.--Differingfromaspark-gaptransmitteryoucannotgetanyappreciableresultswithalowvoltagebatterycurrenttostartwith.ForapurelyexperimentalvacuumtubetelegraphtransmitteryoucanuseenoughBbatteriestooperateitbutthecurrentstrengthofthesedropssofactwhentheyareinuse,thattheyarenotatallsatisfactoryforthework.

Youcan,however,use110voltdirectcurrentfromalightingcircuitasyourinitialsourceofpowertoenergizetheplateofthevacuumtubeoscillatorofyourexperimentaltransmitter.Whereyouhavea110voltdirectcurrentlightingserviceinyourhomeandyouwantahighervoltageforyourplate,youwillthenhavetouseamotor-generatorsetandthiscostsmoney.Ifyouhave110voltalternatingcurrentlightingserviceathandyourtroublesareoversofarascostisconcernedforyoucanstepituptoanyvoltageyouwantwithapowertransformer.Inthischapterwillbeshownhowtouseadirectcurrentforyoursourceofinitialpowerandinthenextchapterhowtouseanalternatingcurrentfortheinitialpower.

AnExperimentalContinuousWaveTelegraphTransmitter.--YouwillrememberthatinChapterXVwelearnedhowtheheterodynereceiverworksandthatintheseparateheterodynereceivingsetthesecondvacuumtubeisusedsolelytosetuposcillations.Nowwhilethisextratubeisusedasageneratorofoscillationstheseare,ofcourse,veryweakandhenceadetectortubecannotbeusedto

generateoscillationsthatareusefulforotherpurposesthanheterodynereceptorsandmeasurements.

Thereisavacuumtubeamplifier[Footnote:ThisistheradiationUV-201,madebytheRadioCorporationofAmerica,WoolworthBldg.,NewYorkCity.]madethatwillstandaplatepotentialof100volts,andthiscanbeusedasageneratorofoscillationsbyenergizingitwitha110voltdirectcurrentfromyourlightingservice.OrinapinchyoucanusefivestandardBbatteriestodeveloptheplatevoltage,butthesewillsoonrundown.Butwhateveryoudo,neveruseacurrentfromalightingcircuitonatubeofanykindthathasaratedplatepotentialoflessthan100volts.

TheApparatusYouNeed.--Forthisexperimentalcontinuouswavetelegraphtransmittergetthefollowingpiecesofapparatus:(1)onesinglecoiltunerwiththreeclips;(2)one.002mfd.fixedcondenser;(3)three.001mfd.condensers;(4)oneadjustablegridleak;(5)onehot-wireammeter;(6)onebuzzer;(7)onedrycell;(8)onetelegraphkey;(9)one100voltplatevacuumtubeamplifier;(10)one6voltstoragebattery;(11)onerheostat;(12)oneoscillationchokecoil;(13)onepanelcut-outwithasingle-throw,double-poleswitch,andapairoffusesocketsonit.

TheTuningCoil.--Youcaneithermakethistuningcoilorbuyone.Tomakeitgettwodisksofwood3/4-inchthickand5inchesindiameterandfourstripsofhardwood,orbetter,hardrubberorcompositionstrips,suchasbakelite,1/2-inchthick,1inchwideand5-3/4incheslong,andscrewthemtothedisksasshownatAinFig.75.Nowwraponthisformabout25turnsofNo.8or10,BrownandSharpegauge,barecopperwirewithaspaceof1/8-inchbetweeneachturn.Getthreeofthesmallestsizeterminalclips,seeB,andclipthemontothedifferentturns,whenyourtuningcoilisreadyforuse.Youcanbuyacoilofthiskindfor$4.00or$5.00.

TheCondensers.--Fortheaerialseriescondensergetonethathasacapacitanceof.002mfd.andthatwillstandapotentialof3,000volts.[Footnote:TheUC-1014FaradoncondensermadebytheRadioCorporationofAmericawillservethepurpose.]ItisshownatC.Theotherthreecondensers,seeD,arealsoofthefixedtypeandmayhaveacapacitanceof.001mfd.;[Footnote:ListNo.266;fixedreceivingcondenser,soldbytheManhattanElectricalSupplyCo.]theblockingcondensershouldpreferablyhaveacapacitanceof1/2amfd.Inthesecondenserstheleavesofthesheetmetalareembeddedincomposition.Theaerialcondenserwillcostyou$2.00andtheothers75centseach.

TheAerialAmmeter.--Thisinstrumentisalsocalledahot-wireammeterbecausetheoscillatingcurrentsflowingthroughapieceofwireheatitaccordingtotheircurrentstrengthandasthewirecontractsandexpandsitmovesaneedleoverascale.Theammeterisconnectedintheaerialwiresystem,eitherintheaerialsideorthegroundside--thelatterplaceisusuallythemostconvenient.Whenyoutunethetransmittersothattheammetershowsthelargestamountofcurrentsurgingintheaerialwiresystemyoucanconsiderthattheoscillationcircuitsareintune.Ahot-wireammeterreadingto2.5ampereswillserveyourneeds,itcosts$6.00andisshownatEinFig.75.

PhotographunavailableUnitedStatesNavalHighPowerStation,ArlingtonVa.GeneralviewofPowerRoom.AttheleftcanbeseentheControlSwitchboards,andoverhead,thegreat30K.W.ArcTransmitterwithAccessories.

TheBuzzerandDryCell.--Whileaheterodyne,orbeat,receptorcanreceivecontinuouswavetelegraphsignalsanordinarycrystalorvacuumtubedetectorreceivingsetcannotreceivethemunlesstheyarebrokenupintotrainseitheratthesendingstationoratthereceivingstation,anditisconsideredthebetterpracticetodothisattheformerratherthanatthelatterstation.ForthissmalltransmitteryoucanuseanordinarybuzzerasshownatF.Adrycellortwomustbeusedtoenergizethebuzzer.Youcangetoneforabout75cents.

TheTelegraphKey.--Anykindofatelegraphkeywillservetobreakupthetrainsofsustainedoscillationsintodotsanddashes.ThekeyshownatGismountedonacompositionbaseandisthecheapestkeymade,costing$1.50.

TheVacuumTubeOscillator.--Asexplainedbeforeyoucanuseanyamplifyingtubethatismadeforaplatepotentialof100volts.Thecurrentrequiredforheatingthefilamentisabout1ampereat6volts.Aporcelainsocketshouldbeusedforthistubeasitisthebestinsulatingmaterialforthepurpose.AnamplifiertubeofthistypeisshownatHandcosts$6.50.

TheStorageBattery.--Astoragebatteryisusedtoheatthefilamentofthetube,justasitiswithadetectortube,anditcanbeofanymakeorcapacityaslongasitwilldevelop6volts.Thecheapest6voltstoragebatteryonthemarkethasa20to40ampere-hourcapacityandsellsfor$13.00.

TheBatteryRheostat.--Aswiththereceptorsarheostatisneededtoregulatethecurrentthatheatsthefilament.ArheostatofthiskindisshownatIandislistedat$1.25.

TheOscillationChokeCoil.--Thiscoilisconnectedinbetweentheoscillationcircuitsandthesourceofcurrentwhichfeedstheoscillatortubetokeeptheoscillationssetupbythelatterfromsurgingbackintotheservicewireswheretheywouldbreakdowntheinsulation.Youcanmakeanoscillationchokecoilbywindingsay100turnsofNo.28BrownandSharpegaugedoublecottoncoveredmagnetwireonacardboardcylinder2inchesindiameterand2-1/2incheslong.

TransmitterConnectors.--Forconnectingupthedifferentpiecesofapparatusofthetransmitteritisagoodschemetousecopperbraid;thisismadeofbraidedcopperwireinthreesizesandsellsfor7,15and20centsafootrespectively.ApieceofitispicturedatJ.

ThePanelCut-Out.--Thisisusedtoconnectthecordofthe110-voltlampsocketwiththetransmitter.Itconsistsofapairofplugcutoutsandasingle-throw,double-poleswitchmountedonaporcelainbaseasshownatK.Insomelocalitiesitisnecessarytoplacetheseinanironboxtoconformtotherequirementsofthefireunderwriters.

ConnectingUptheTransmittingApparatus.--Thewaythevariouspiecesofapparatusareconnectedtogetherisshowninthewiringdiagram.Fig.76.Beginbyconnectingonepostoftheammeterwiththewirethatleadstotheaerialandtheotherpostofittooneendofthetuningcoil;connectclip1tooneterminalofthe.002mfd.3,000voltaerialcondenserandtheotherpostofthiswiththeground.

Nowconnecttheendofthetuningcoilthatleadstotheammeterwithoneendofthe.001mfd.gridcondenserandtheotherendofthiswiththegridofthevacuumtube.Connectthetelegraphkey,thebuzzerandthedrycellinseriesandthenshuntthemaroundthegridcondenser.Nextconnecttheplateofthetubewithoneendofthe.001mfd.blockingcondenserandtheotherendofthiswiththeclip2onthetuningcoil.

Connectoneendofthefilamentwiththe+orpositiveelectrodeofthestoragebattery,the-ornegativeelectrodeofthiswithonepostoftherheostatandtheotherpostofthelatterwiththeotherendofthefilament;thenconnectclip3withthe+orpositivesideofthestoragebattery.Thisdoneconnectoneendofthechokecoiltotheconductorthatleadstotheplateandconnecttheotherendofthechokecoiltooneofthetapsoftheswitchonthepanelcut-out.Connectthe+orpositiveelectrodeofthestoragebatterytotheotherswitchtapandbetweentheswitchandthechokecoilconnecttheprotectivecondenseracrossthe110voltfeedwires.Finallyconnectthelampcordfromthesockettotheplugfusetapswhenyourexperimentalcontinuouswavetelegraphtransmitterisreadytouse.

A100MileC.W.TelegraphTransmitter.--Hereisacontinuouswavetelegraphtransmitterthatwillcoverdistancesupto100milesthatyoucanrelyon.Itisbuiltonexactlythesamelinesastheexperimentaltransmitterjustdescribed,butinsteadofusinga100voltplateamplifierasamakeshiftgeneratorofoscillationsitemploysavacuumtubemadeespeciallyforsettinguposcillationsandinsteadofhavingalowplatevoltageitisenergizedwith350volts.

TheApparatusYouNeed.--Forthistransmitteryourequire:(1)oneoscillationtransformer;(2)onehot-wireammeter;(3)oneaerialseriescondenser;(4)onegridleakresistance;(5)onechopper;(6)

onekeycircuitchokecoil;(7)one5wattvacuumtubeoscillator;(8)one6voltstoragebattery;(9)onebatteryrheostat;(10)onebatteryvoltmeter;(11)oneblockingcondenser;(12)onepowercircuitchokecoil,and(13)onemotor-generator.

TheOscillationTransformer.--Thetuningcoil,oroscillationtransformerasthisoneiscalled,isaconductivelycoupledtuner--thatis,theprimaryandsecondarycoilsformonecontinuouscoilinsteadoftwoseparatecoils.Thistunerismadeupof25turnsofthincopperstrip,3/8inchwideandwithitsedgesrounded,andthisissecuredtoawoodbaseasshownatAinFig.77.Itisfittedwithonefixedtapandthreeclipstoeachofwhichalengthofcopperbraidisattached.Ithasadiameterof6-1/4inches,aheightof7-7/8inchesandalengthof9-3/8inches,anditcosts$11.00.

TheAerialCondenser.--Thiscondenserismadeupofthreefixedcondensersofdifferentcapacitances,namely.0003,.0004and.0005mfd.,andthesearemadetostandapotentialof7500volts.Thecondenseristhereforeadjustableand,asyouwillseefromthepictureB,ithasoneterminalwireatoneendandthreeterminalwiresattheotherendsothatone,twoorthreecondenserscanbeusedinserieswiththeaerial.Acondenserofthiskindcosts$5.40.

TheAerialAmmeter.--Thisisthesamekindofahot-wireammeteralreadydescribedinconnectionwiththeexperimentalset,butitreadsto5amperes.

TheGridandBlockingCondensers.--Eachoftheseisafixedcondenserof.002mfd.capacitanceandisratedtostand3,000volts.Itismadeliketheaerialcondenserbuthasonlytwoterminals.Itcosts$2.00.

TheKeyCircuitApparatus.--Thisconsistsof:(1)thegridleak;(2)thechopper;(3)thechokecoil,and(4)thekey.Thegridleakisconnectedintheleadfromthegridtotheaerialtokeepthevoltageonthegridattherightpotential.Ithasaresistanceof5000ohmswithamid-tapat2500ohmsasshownatC.Itcosts$2.00.

Thechopperissimplyarotaryinterrupterdrivenbyasmallmotor.Itcomprisesawheelofinsulatingmaterialinwhich30ormoremetalsegmentsaresetinaninsulatingdiskasshownatD.Ametalcontactcalledabrushisfixedoneithersideofthewheel.Itcostsabout$7.00andthemotortodriveitisextra.Thechokecoiliswoundupofabout250turnsofNo.30BrownandSharpegaugecottoncoveredmagnetwireonaspoolwhichhasadiameterof2inchesandalengthof3-1/4inches.

The5WattOscillatorVacuumTube.--Thistubeismadeliketheamplifiertubedescribedforusewiththeprecedingexperimentaltransmitter,butitislarger,hasamoreperfectvacuum,andwillstandaplatepotentialof350voltswhiletheplatecurrentis.045ampere.Thefilamenttakesacurrentofalittlemorethan2amperesat7.5volts.Astandard4-tapbaseisusedwithit.Thetubecosts$8.00andtheporcelainbaseis$1.00extra.ItisshownatE.

TheStorageBatteryandRheostat.--Thismustbea5-cellbatterysothatitwilldevelop10volts.Astoragebatteryofanycapacitycanbeusedbutthelowestpricedonecostsabout$22.00.Therheostatforregulatingthebatterycurrentisthesameasthatusedintheprecedingexperimentaltransmitter.

TheFilamentVoltmeter.--Togetthebestresultsitisnecessarythatthevoltageofthecurrentwhichheatsthefilamentbekeptatthesamevalueallofthetime.Forthistransmitteradirectcurrentvoltmeterreadingfrom0to15voltsisused.ItisshownatFandcosts$7.50.

TheOscillationChokeCoil.--Thisismadeexactlyliketheonedescribedinconnectionwiththeexperimentaltransmitter.

TheMotor-GeneratorSet.--Whereyouhaveonlya110ora220voltdirectcurrentavailableasasourceofpoweryouneedamotor-generatortochangeitto350volts,andthisisanexpensivepieceofapparatus.Itconsistsofasinglearmaturecorewithamotorwindingandageneratorwindingonitandeachofthesehasitsowncommutator.Wherethelowvoltagecurrentflowsintooneofthewindingsitdrivesitsasamotorandthisinturngeneratesthehighervoltagecurrentintheotherwinding.Geta100watt350voltmotor-generator;itisshownatFandcostsabout$75.00.

ThePanelCut-Out.--Thisswitchandfuseblockisthesameasthatusedintheexperimentalset.

TheProtectiveCondenser.--Thisisafixedcondenserhavingacapacitanceof1mfd.andwillstand750volts.Itcosts$2.00.

ConnectingUptheTransmittingApparatus.--Fromallthathasgonebeforeyouhaveseenthateachpieceofapparatusisfittedwithterminal,wires,tapsorbindingposts.ToconnectupthepartsofthistransmitteritisonlynecessarytomaketheconnectionsasshowninthewiringdiagramFig.78.

A200MileC.W.TelegraphTransmitter.--Tomakeacontinuouswavetelegraphtransmitterthatwillcoverdistancesupto200milesallyouhavetodoistousetwo5wattvacuumtubesinparallel,alloftherestoftheapparatusbeingexactlythesame.Connectingtheoscillatortubesupinparallelmeansthatthetwofilamentsareconnectedacrosstheleadsofthestoragebattery,thetwogridsonthesameleadthatgoestotheaerialandthetwoplatesonthesameleadthatgoestothepositivepoleofthegenerator.Wheretwoormoreoscillatortubesareusedonlyonestoragebatteryisneeded,buteachfilamentmusthaveitsownrheostat.ThewiringdiagramFig.79showshowthetwotubesareconnectedupinparallel.

A500MileC.W.TelegraphTransmitter.--Forsendingtodistancesofover200milesandupto500milesyoucanuseeither:(1)threeorfour5wattoscillatortubesinparallelasdescribedabove,or(2)one50wattoscillatortube.Muchoftheapparatusfora50watttubesetisexactlythesameasthatusedforthe5wattsets.Someoftheparts,however,mustbeproportionatelylargerthoughthedesignallthewaythroughremainsthesame.

TheApparatusandConnections.--Theaerialseriescondenser,theblockingcondenser,thegridcondenser,thetelegraphkey,thechopper,thechokecoilinthekeycircuit,thefilamentvoltmeterandtheprotectivecondenserinthepowercircuitareidenticalwiththosedescribedforthe5watttransmittingset.

The50WattVacuumTubeOscillator.--Thisisthesizeoftubegenerallyusedbyamateursforlongdistancecontinuouswavetelegraphy.Asingletubewilldevelop2to3amperesinyouraerial.Thefilamenttakesa10voltcurrentandaplatepotentialof1,000voltsisneeded.OneofthesetubesisshowninFig.80andthecostis$30.00.Atubesockettofititcosts$2.50extra.

TheAerialAmmeter.--Thisshouldreadto5amperesandthecostis$6.25.

TheGridLeakResistance.--Ithasthesameresistance,namely5,000ohmsastheoneusedwiththe5

watttubetransmitter,butitisalittlelarger.Itislistedat$1.65.

TheOscillationChokeCoil.--Thechokecoilinthepowercircuitismadeofabout260turnsofNo.30B.&S.cottoncoveredmagnetwirewoundonaspool2-1/4inchesindiameterand3-1/4incheslong.

TheFilamentRheostat.--Thisismadetotakecareofa10voltcurrentanditcosts$10.00.

TheFilamentStorageBattery.--Thismustdevelop12voltsandonehavinganoutputof40ampere-hourscostsabout$25.00.

TheProtectiveCondenser.--Thiscondenserhasacapacitanceof1mfd.andcosts$2.00.

TheMotor-Generator.--Whereyouuseone50wattoscillatortubeyouwillneedamotor-generatorthatdevelopsaplatepotentialof1000voltsandhasanoutputof200watts.Thismachinewillstandyouabout$100.00.

ThedifferentpiecesofapparatusforthissetareconnectedupexactlythesameasshowninthewiringdiagraminFig.78.

A1000MileC.W.TelegraphTransmitter.--Allofthepartsofthistransmittingsetarethesameasforthe500miletransmitterjustdescribedexceptthemotorgeneratorandwhilethisdevelopsthesameplatepotential,i.e.,1,000volts,itmusthaveanoutputof500watts;itwillcostyouintheneighborhoodof$175.00.Forthislongdistancetransmitteryouusetwo50wattoscillatortubesinparallelandallofthepartsareconnectedtogetherexactlythesameasforthe200miletransmittershowninthewiringdiagraminFig.79.

CHAPTERXVII

CONTINUOUSWAVETELEGRAPHTRANSMITTINGSETSWITHALTERNATINGCURRENT

Withinthelastfewyearsalternatingcurrenthaslargelytakentheplaceofdirectcurrentforlight,heatandpowerpurposesinandaroundtownsandcitiesandifyouhavealternatingcurrentserviceinyourhomeyoucaninstallalongdistancecontinuouswavetelegraphtransmitterwithverylittletroubleandatacomparativelysmallexpense.

A100MileC.W.TelegraphTransmittingSet.--Theprincipalpiecesofapparatusforthistransmitterarethesameasthoseusedforthe100MileContinuousWaveTelegraphTransmittingSetdescribedandpicturedintheprecedingchapterwhichuseddirectcurrent,exceptthatanalternatingcurrentpowertransformerisemployedinsteadofthemorecostlymotor-generator.

TheApparatusRequired.--Thevariouspiecesofapparatusyouwillneedforthistransmittingsetare:(1)onehot-wireammeterfortheaerialasshownatEinFig.75,butwhichreadsto5amperesinsteadofto2.5amperes;(2)onetuningcoilasshownatAinFig.77;(3)oneaerialcondenserasshownatBinFig.77;(4)onegridleakasshownatCinFig.77;(5)onetelegraphkeyasshownatGinFig.75;(6)onegridcondenser,madeliketheaerialcondenserbuthavingonlytwoterminals;(7)one5wattoscillatortubeasshownatEinFig.77;(8)one.002mfd.3,000voltby-passcondenser,madeliketheaerialandgridcondensers;(9)onepairofchokecoilsforthehighvoltagesecondarycircuit;(10)onemilli-ammeter;(11)oneA.C.powertransformer;(12)onerheostatasshownatIinFig.75,and(13)onepanelcut-outasshownatKinFig.75.

TheChokeCoils.--Eachoftheseismadebywindingabout100turnsofNo.28,BrownandSharpegauge,cottoncoveredmagnetwireonaspool2inchesindiameterand2-1/2incheslong,whenitwillhaveaninductanceofabout0.5millihenry[Footnote:Amillihenryis1/1000thpartofahenry.]at1,000cycles.

TheMilli-ammeter.--Thisisanalternatingcurrentammeterandreadsfrom0to250milliamperes;[Footnote:Amilliampereisthe1/1000thpartofanampere.]andisusedformeasuringthesecondarycurrentthatenergizestheplateoftheoscillatortube.Itlooksliketheaerialammeterandcostsabout$7.50.

TheA.C.PowerTransformer.--Differingfromthemotorgeneratorsetthepowertransformerhasnomovingparts.Forthistransmittingsetyouneedatransformerthathasaninputof325volts.Itismadetoworkona50to60cyclecurrentat102.5to115volts,whichistherangeofvoltageoftheordinaryalternatinglightingcurrent.Thisadjustmentforvoltageismadebymeansoftapsbroughtoutfromtheprimarycoiltoarotaryswitch.

Thehighvoltagesecondarycoilwhichenergizestheplatehasanoutputof175wattsanddevelopsapotentialoffrom350to1,100volts.Thelowvoltagesecondarycoilwhichheatsthefilamenthasanoutputof175wattsanddevelops7.5volts.Thistransformer,whichisshowninFig.81,islargeenoughtotakecareoffromonetofour5wattoscillatortubes.Itweighsabout15poundsandsellsfor$25.00.

PhotographunavailableTheTransformerandTuneroftheWorld'sLargestRadioStation.OwnedbytheRadioCorporation

ofAmericaatRockyPointnearPortJeffersonL.I.

ConnectingUptheApparatus.--ThewiringdiagramFig.82showsclearlyhowalloftheconnectionsaremade.Itwillbeobservedthatastoragebatteryisnotneededasthesecondarycoilofthetransformersuppliesthecurrenttoheatthefilamentoftheoscillator.Thefilamentvoltmeterisconnectedacrossthefilamentsecondarycoilterminals,whiletheplatemilli-ammeterisconnectedtothemid-tapsoftheplatesecondarycoilandthefilamentsecondarycoil.

A200to500MileC.W.TelegraphTransmittingSet.--Distancesoffrom200to500milescanbesuccessfullycoveredwithatelegraphtransmitterusingtwo,threeorfour5wattoscillatortubesinparallel.Theapparatusneededisidenticalwiththatusedforthe100miletransmitterjustdescribed.ThetubesareconnectedinparallelasshowninthewiringdiagraminFig.83.

A500to1,000MileC.W.TelegraphTransmittingSet.--Withtheapparatusdescribedfortheabovesetandasingle50wattoscillatortubeadistanceofupwardsof500milescanbecovered,whilewithtwo50wattoscillatortubesinparallelyoucancoveradistanceof1,000mileswithoutdifficulty,andnearly2,000mileshavebeencoveredwiththisset.

TheApparatusRequired.--AlloftheapparatusforthisC.W.telegraphtransmittingsetisthesameasthatdescribedforthe100and200milesetsbutyouwillneed:(1)oneortwo50wattoscillatortubeswithsockets;(2)onekeycondenserthathasacapacitanceof1mfd.,andaratedpotentialof1,750volts;(3)one0to500milli-ammeter;(4)oneaerialammeterreadingto5amperes,and(5)anA.C.powertransformerforoneortwo50watttubes.

Photographunavailable

BroadcastingGovernmentReportsbyWirelessfromWashington.ThisshowsMr.GaleatworkwithhissetinthePostOfficeDepartment.

TheAlternatingCurrentPowerTransformer.--Thispowertransformerismadeexactlyliketheonedescribedinconnectionwiththepreceding100miletransmitterandpicturedinFig.81,butitisconsiderablylarger.Likethesmallerone,however,itismadetoworkwitha50to60cyclecurrentat102.5to115voltsand,hence,canbeusedwithanyA.C.lightingcurrent.

Ithasaninputof750voltsandthehighvoltagesecondarycoilwhichenergizestheplatehasanoutputof450wattsanddevelops1,500to3,000volts.Thelowvoltagesecondarycoilwhichheatsthefilamentdevelops10.5volts.Thistransformerwillsupplycurrentforoneortwo50-wattoscillatortubesanditcostsabout$40.00.

ConnectingUptheApparatus.--WhereasingleoscillatortubeisusedthepartsareconnectedasshowninFig.82,andwheretwotubesareconnectedinparallelthevariouspiecesofapparatusarewiredtogetherasshowninFig.83.Theonlydifferencebetweenthe5watttubetransmitterandthe50watttubetransmitterisinthesizeoftheapparatuswithoneexception;whereoneortwo50watttubesareusedasecondcondenseroflargecapacitance(1mfd.)isplacedinthegridcircuitandthetelegraphkeyisshuntedarounditasshowninthediagramFig.83.

CHAPTERXVIII

WIRELESSTELEPHONETRANSMITTINGSETSWITHDIRECTANDALTERNATINGCURRENTS

Intimepastthemostdifficultofallelectricalapparatusfortheamateurtomake,installandworkwasthewirelesstelephone.Thiswasbecauseitrequiredadirectcurrentofnotlessthan500voltstosetupthesustainedoscillationsandallordinarydirectcurrentforlightingpurposesisusuallygeneratedatapotentialof110volts.

Nowasyouknowitiseasytostep-upa110voltalternatingcurrenttoanyvoltageyouwishwithapowertransformerbutuntilwithincomparativelyrecentyearsanalternatingcurrentcouldnotbeusedfortheproductionofsustainedoscillationsfortheverygoodreasonthatthestateofthearthadnotadvancedthatfar.Intheneworderofthingsthesedifficultieshaveallbutvanishedandwhileawirelesstelephonetransmitterstillrequiresahighvoltagedirectcurrenttooperateitthisiseasilyobtainedfrom110voltsourceofalternatingcurrentbymeansofvacuumtuberectifiers.

Thepulsatingdirectcurrentsarethenpassedthroughafilteringreactancecoil,calledareactor,andoneormorecondensers,andthesesmooththemoutuntiltheyapproximateacontinuousdirectcurrent.Thelatteristhenmadetoflowthroughavacuumtubeoscillatorwhenitisconvertedintohighfrequencyoscillationsandthesearevaried,ormodulated,asitiscalled,byamicrophonetransmittersuchasisusedforordinarywiretelephony.Theenergyofthesesustainedmodulatedoscillationsisthenradiatedintospacefromtheaerialintheformofelectricwaves.

Thedistancethatcanbecoveredwithawirelesstelephonetransmitterisaboutone-fourthasgreatasthatofawirelesstelegraphtransmitterhavingthesameinputofinitialcurrent,butitislongenoughtosatisfythemostenthusiasticamateur.Forinstancewithawirelesstelephonetransmitterwhereanamplifiertubeisusedtosetuptheoscillationsandwhichismadeforaplatepotentialof100volts,distancesupto10or15milescanbecovered.

Withasingle5wattoscillatortubeenergizedbyadirectcurrentof350voltsfromeitheramotor-generatororfromapowertransformer(afterithasbeenrectifiedandsmoothedout)speechandmusiccanbetransmittedtoupwardsof25miles.Wheretwo5watttubesconnectedinparallelareusedwirelesstelephonemessagescanbetransmittedtodistancesof40or50miles.Further,asingle50wattoscillatortubewillsendtodistancesof50to100mileswhiletwoofthesetubesinparallelwillsendfrom100to200miles.Finally,wherefourorfiveoscillatortubesareconnectedinparallelproportionatelygreaterdistancescanbecovered.

AShortDistanceWirelessTelephoneTransmittingSet-With110VoltDirectLightingCurrent.--Forthisverysimple,shortdistancewirelesstelephonetransmittingsetyouneedthesameapparatusasthatdescribedandpicturedinthebeginningofChapterXVIforaShortDistanceC.W.TelegraphTransmitter,exceptthatyouuseamicrophonetransmitterinsteadofatelegraphkey.Ifyouhavea110voltdirectlightingcurrentinyourhomeyoucanputupthisshortdistancesetforverylittlemoneyanditwillbewellworthyourwhiletodoso.

TheApparatusYouNeed.--Forthissetyourequire:(1)onetuningcoilasshownatAandBinFig.75;

(2)oneaerialammeterasshownatCinFig.75;(3)oneaerialcondenserasshownatCinFig.75;(4)onegrid,blockingandprotectivecondenserasshownatDinFig.75;(5)onegridleakasshownatCinFig.77;(6)onevacuumtubeamplifierwhichisusedasanoscillator;(7)one6voltstoragebattery;(8)onerheostatasshownatIinFig.75;(9)oneoscillationchokecoil;(10)onepanelcut-outasshownatKinFig.75andanordinarymicrophonetransmitter.

TheMicrophoneTransmitter.--ThebestkindofamicrophonetousewiththisandothertelephonetransmittingsetsisaWesternElectricNo.284-W.[Footnote:MadebytheWesternElectricCompany,Chicago,Ill.]ThisisknownasasolidbacktransmitterandisthestandardcommercialtypeusedonalllongdistanceBelltelephonelines.Itarticulatessharplyanddistinctlyandtherearenocurrentvariationstodistortthewaveformofthevoiceanditwillnotbuzzorsizzle.ItisshowninFig.84andcosts$2.00.Anyothergoodmicrophonetransmittercanbeusedifdesired.

ConnectingUptheApparatus.--Beginbyconnectingtheleading-inwirewithoneoftheterminalsofthemicrophonetransmitter,asshowninthewiringdiagramFig.85,andtheotherterminalofthistooneendofthetuningcoil.Nowconnectclip1ofthetuningcoiltooneofthepostsofthehot-wireammeter,theotherpostofthistooneendofaerialcondenserand,finally,theotherendofthelatterwiththewaterpipeorotherground.Themicrophonecanbeconnectedinthegroundwireandtheammeterintheaerialwireandtheresultswillbepracticallythesame.

Nextconnectoneendofthegridcondensertothepostofthetuningcoilthatmakesconnectionwiththemicrophoneandtheotherendtothegridofthetube,andthenshuntthegridleakaroundthecondenser.Connectthe+orpositiveelectrodeofthestoragebatterywithoneterminalofthefilamentofthevacuumtube,theotherterminalofthefilamentwithonepostoftherheostatandtheotherpostofthiswiththe-ornegativeelectrodeofthebattery.Thisdone,connectclip2ofthetuningcoiltothe+orpositiveelectrodeofthebatteryandbringaleadfromittooneoftheswitchtapsofthepanelcut-out.

Nowconnectclip3ofthetuningcoilwithoneendoftheblockingcondenser,theotherendofthiswithoneterminalofthechokecoilandtheotherterminalofthelatterwiththeotherswitchtapofthecut-out.Connecttheprotectivecondenseracrossthedirectcurrentfeedwiresbetweenthepanelcut-outandthechokecoil.Finallyconnecttheendsofalampcordtothefusesockettapsofthecut-out,andconnecttheotherendstoalampplugandscrewitintothelampsocketofthefeedwires.Screwinapairof5amperefuseplugs,closetheswitchandyouarereadytotunethetransmitterandtalktoyourfriends.

A25to50MileWirelessTelephoneTransmitter--WithDirectCurrentMotorGenerator.--Whereyouhavetostartwith110or220voltdirectcurrentandyouwanttotransmittoadistanceof25milesormoreyouwillhavetoinstallamotor-generator.Tomakethistransmitteryouwillneedexactlythesameapparatusasthatdescribedandpicturedforthe100MileC.W.TelegraphTransmittingSetinChapterXVI,exceptthatyoumustsubstituteamicrophonetransmitterandatelephoneinductioncoil,oramicrophonetransformer,orstillbetter,amagneticmodulator,forthetelegraphkeyandchopper.

TheApparatusYouNeed.--Toreiterate;thepiecesofapparatusyouneedare:(1)oneaerialammeterasshownatEinFig.75;(2)onetuningcoilasshownatAinFig.77;(3)oneaerialcondenserasshownatBinFig.77;(4)onegridleakasshownatCinFig.77;(5)onegrid,blockingandprotectivecondenser;(6)one5wattoscillatortubeasshownatEinFig.77;(7)onerheostatasshownatIinFig.75;(8)one10volt(5cell)storagebattery;(9)onechokecoil;(10)onepanelcut-outasshownatKinFig.75,and(11)amotor-generatorhavinganinputof110or220voltsandanoutputof350volts.

Inadditiontotheaboveapparatusyouwillneed:(12)amicrophonetransmitterasshowninFig.84;(13)abatteryoffourdrycellsora6voltstoragebattery,andeither(14)atelephoneinductioncoilasshowninFig.86;(15)amicrophonetransformerasshowninFig.87;oramagneticmodulatorasshowninFig.88.Allofthesepartshavebeendescribed,assaidabove,inChapterXVI,exceptthemicrophonemodulators.

TheTelephoneInductionCoil.--Thisisalittleinductioncoilthattransformsthe6-voltbatterycurrentafterithasflowedthroughandbeenmodulatedbythemicrophonetransmitterintoalternatingcurrentsthathaveapotentialof1,000voltsofmore.ItconsistsofaprimarycoilofNo.20B.andS.gaugecottoncoveredmagnetwirewoundonacoreofsoftironwireswhilearoundtheprimarycoiliswoundasecondarycoilofNo.30magnetwire.Getastandardtelephoneinductioncoilthathasaresistanceof500or750ohmsandthiswillcostyouacoupleofdollars.

TheMicrophoneTransformer.--Thisdeviceisbuiltonexactlythesameprincipleasthetelephoneinductioncoiljustdescribedbutitismoreeffectivebecauseitisdesignedespeciallyformodulatingtheoscillationssetupbyvacuumtubetransmitters.Aswiththetelephoneinductioncoil,themicrophonetransmitterisconnectedinserieswiththeprimarycoilanda6voltdryorstoragebattery.

Inthebettermakesofmicrophonetransformer,thereisathirdwinding,calledasidetonecoil,towhichaheadphonecanbeconnectedsothattheoperatorwhoisspeakingintothemicrophonecanlisten-inandsolearnifhistransmitterisworkinguptostandard.

TheMagneticModulator.--Thisisasmallclosedironcoretransformerofpeculiardesignandhavingaprimaryandasecondarycoilwoundonit.Thisdeviceisusedtocontrolthevariationsoftheoscillatingcurrentsthataresetupbytheoscillatortube.Itismadeinthreesizesandforthetransmitterheredescribedyouwantthesmallestsize,whichhasanoutputof1/2to1-1/2amperes.Itcostsabout$10.00.

HowtheApparatusIsConnectedUp.--Thedifferentpiecesofapparatusareconnectedtogetherinexactlythesamewayasthe100MileC.W.TelegraphSetinChapterXVIexceptthatthemicrophonetransmitterandmicrophonemodulator(whicheverkindyouuse)issubstitutedforthetelegraphkeyandchopper.

Nowtherearethreedifferentwaysthatthemicrophoneanditsmodulatorcanbeconnectedincircuit.TwoofthebestwaysareshownatAandBinFig.89.InthefirstwaythesecondaryterminalsofthemodulatorareshuntedaroundthegridleakinthegridcircuitasatA,andinthesecondthesecondaryterminalsareconnectedintheaerialasatB.Whereaninductioncoiloramicrophonetransformerisusedtheyareshuntedaroundacondenser,butthisisnotnecessarywiththemagneticmodulator.WhereasecondtubeisusedasinFig.90thenthemicrophoneanditsmodulatorareconnectedwiththegridcircuitandclip3ofthetuningcoil.

A50to100MileWirelessTelephoneTransmitter--WithDirectCurrentMotorGenerator.--Astheinitialsourceofcurrentavailableistakentobea110or220voltdirectcurrentamotor-generatorhavinganoutputof350voltsmustbeusedasbefore.Theonlydifferencebetweenthistransmitterandtheprecedingoneisthat:(1)two5watttubesareused,thefirstservingasanoscillatorandthesecondasamodulator;(2)anoscillationchokecoilisusedintheplatecircuit;(3)areactancecoilorreactor,isusedintheplatecircuit;and(4)areactorisusedinthegridcircuit.

TheOscillationChokeCoil.--Youcanmakethischokecoilbywindingabout275turnsofNo.28B.andS.gaugecottoncoveredmagnetwireonaspool2inchesindiameterand4incheslong.Giveitagoodcoatofshellacvarnishandletitdrythoroughly.

ThePlateandGridCircuitReactanceCoils.--Whereasingletubeisusedasanoscillatorandasecondtubeisemployedasamodulator,areactor,whichisacoilofwirewoundonanironcore,isusedintheplatecircuittokeepthehighvoltagedirectcurrentofthemotor-generatorthesameatalltimes.Likewisethegridcircuitreactorisusedtokeepthevoltageofthegridataconstantvalue.ThesereactorsaremadealikeandapictureofoneofthemisshowninFig.91andeachonewillcostyou$5.75.

ConnectinguptheApparatus.--AllofthedifferentpiecesofapparatusareconnectedupasshowninFig.89.Oneoftheendsofthesecondaryoftheinductioncoil,orthemicrophonetransformer,orthemagneticmodulatorisconnectedtothegridcircuitandtheotherendtoclip3ofthetuningcoil.

A100to200MileWirelessTelephoneTransmitter--WithDirectCurrentMotorGenerator.--ByusingthesameconnectionsshowninthewiringdiagramsinFig.89andasingle50wattoscillatortubeyourtransmitterwillthenhavearangeof100milesorso,whileifyouconnectuptheapparatusasshowninFig.90andusetwo50watttubesyoucanworkupto200miles.Muchoftheapparatusfora50wattoscillatorsetwhereeitheroneortwotubesareusedisofthesamesizeanddesignasthatjustdescribedforthe5wattoscillatorsets,but,asintheC.W.telegraphsets,someofthepartsmustbeproportionatelylarger.Therequiredpartsare(1)the50watttube;(2)thegridleakresistance;(3)thefilamentrheostat;(4)thefilamentstoragebattery;and(5)themagneticmodulator.Alloftheseparts,exceptthelatter,aredescribedindetailundertheheadingofa500MileC.W.TelegraphTransmittingSetinChapterXVI,andarealsopicturedinthatchapter.

Itisnotadvisabletouseaninductioncoilforthemodulatorforthisset,butuse,instead,eitheratelephonetransformer,orbetter,amagneticmodulatorofthesecondsizewhichhasanoutputof

from1-1/2to3-1/2amperes.Themagneticmodulatorisdescribedandpicturedinthischapter.

A50to100MileWirelessTelephoneTransmittingSet--With110VoltAlternatingCurrent.--Ifyouhavea110volt[Footnote:Alternatingcurrentforlightingpurposesrangesfrom102.5voltsto115volts,sowetakethemedianandcallit110volts.]alternatingcurrentavailableyoucanuseitfortheinitialsourceofenergyforyourwirelesstelephonetransmitter.Thechiefdifferencebetweenawirelesstelephonetransmittingsetthatusesanalternatingcurrentandonethatusesadirectcurrentisthat:(1)apowertransformerisusedforsteppingupthevoltageinsteadofamotor-generator,and(2)avacuumtuberectifiermustbeusedtoconvertthealternatingcurrentintodirectcurrent.

TheApparatusYouNeed.--Forthistelephonetransmittingsetyouneed:(1)oneaerialammeter;(2)onetuningcoil;(3)onetelephonemodulator;(4)oneaerialseriescondenser;(5)one4celldrybatteryora6voltstoragebattery;(6)onemicrophonetransmitter;(7)onebatteryswitch;(8)onegridcondenser;(9)onegridleak;(10)two5wattoscillatortubeswithsockets;(11)oneblockingcondenser;(12)oneoscillationchokecoil;(13)twofiltercondensers;(14)onefilterreactancecoil;(15)analternatingcurrentpowertransformer,and(16)two20wattrectifiervacuumtubes.

Alloftheabovepiecesofapparatusarethesameasthosedescribedforthe100MileC.W.TelegraphTransmitterinChapterXVII,except:(a)themicrophonemodulator;(b)themicrophonetransmitterand(c)thedryorstoragebattery,allofwhicharedescribedinthischapter;andthenewpartswhichare:(d)therectifiervacuumtubes;(e)thefiltercondensers;and(f)thefilterreactancecoil;furtherandfinally,thepowertransformerhasathirdsecondarycoilonitanditisthisthatfeedsthealternatingcurrenttotherectifiertubes,whichinturnconvertsitintoapulsatingdirectcurrent.

TheVacuumTubeRectifier.--Thisrectifierhastwoelectrodes,thatis,ithasafilamentandaplateliketheoriginalvacuumtubedetector,Thesmallestsizerectifiertuberequiresaplatepotentialof550voltswhichisdevelopedbyoneofthesecondarycoilsofthepowertransformer.Thefilamentterminaltakesacurrentof7.5voltsandthisissuppliedbyanothersecondarycoilofthetransformer.Thisrectifiertubedeliversadirectcurrentof20wattsat350volts.Itlooksexactlylikethe5wattoscillatortubewhichispicturedatEinFig.77.Thepriceis$7.50.

TheFilterCondensers.--Thesecondensersareusedinconnectionwiththereactancecoiltosmoothoutthepulsatingdirectcurrentafterithaspassedthroughtherectifiertube.Theyhaveacapacitanceof1mfd.andwillstand750volts.Thesecondenserscostabout$2.00each.

TheFilterReactanceCoil.--ThisreactorwhichisshowninFig.92,hasaboutthesameappearanceasthepowertransformerbutitissomewhatsmaller.Itconsistsofacoilofwirewoundonasoftironcoreandhasalargeinductance,hencethecapacitanceofthefiltercondensersareproportionatelysmallerthanwhereasmallinductanceisusedwhichhasbeenthegeneralpractice.Thesizeyourequireforthissethasanoutputof160milliamperesanditwillsupplycurrentforonetofour5wattoscillatortubes.Thissizeofreactorcosts$11.50.

ConnectingUptheApparatus.--ThewiringdiagraminFig.93showshowthevariouspiecesofapparatusforthistelephonetransmitterareconnectedup.Youwillobserve:(1)thattheterminalsofthepowertransformersecondarycoilwhichdevelops10voltsareconnectedtothefilamentsoftheoscillatortubes;(2)thattheterminalsoftheothersecondarycoilwhichdevelops10voltsareconnectedwiththefilamentsoftherectifiertubes;(3)thattheterminalsofthethirdsecondarycoilwhichdevelops550voltsareconnectedwiththeplatesoftherectifiertubes;(4)thatthepairoffiltercondensersareconnectedinparallelandtheseareconnectedtothemid-tapsofthetwofilamentsecondarycoils;(5)thatthereactancecoilandthethirdfiltercondenserareconnectedtogetherinseriesandtheseareshuntedacrossthefiltercondensers,whichareinparallel;and,finally,(6)aleadconnectsthemid-tapofthe550-voltsecondarycoilofthepowertransformerwiththeconnectionbetweenthereactorandthethirdfiltercondenser.

A100to200MileWirelessTelephoneTransmittingSet--With110VoltAlternatingCurrent.--ThistelephonetransmitterisbuiltupofexactlythesamepiecesofapparatusandconnectedupinpreciselythesamewayastheonejustdescribedandshowninFig.93.

ApparatusRequired.--Theonlydifferencesbetweenthisandtheprecedingtransmitterare:(1)themagneticmodulator,ifyouuseone,shouldhaveanoutputof3-1/2to5amperes;(2)youwillneedtwo50wattoscillatortubeswithsockets;(3)two150wattrectifiertubeswithsockets;(4)anaerialammeterthatreadsto5amperes;(5)three1mfd.filtercondensersinparallel;(6)twofiltercondensersof1mfd.capacitancethatwillstand1750volts;and(6)a300milliamperefilterreactor.

TheapparatusiswiredupasshowninFig.93.

CHAPTERXIX

THEOPERATIONOFVACUUMTUBETRANSMITTERS

Thethreeforegoingchaptersexplainedindetailthedesignandconstructionof(1)twokindsofC.W.telegraphtransmitters,and(2)twokindsofwirelesstelephonetransmitters,thedifferencebetweenthembeingwhethertheyused(A)adirectcurrent,or(B)analternatingcurrentastheinitialsourceofenergy.Ofcoursethereareotherdifferencesbetweenthoseofliketypesas,forinstance,theapparatusandconnectionsused(a)inthekeycircuits,and(b)inthemicrophonecircuits.Butinallofthetransmittersdescribedofwhatevertypeorkindthesamefundamentaldeviceisusedforsettingupsustainedoscillationsandthisisthevacuumtube.

TheOperationoftheVacuumTubeOscillator.--Theoperationofthevacuumtubeinproducingsustainedoscillationsdependson(1)theactionofthetubeasavalveinsettinguptheoscillationsinthefirstplaceand(2)theactionofthegridinamplifyingtheoscillationsthussetup,bothofwhichweexplainedinChapterXIV.Inthatchapteritwasalsopointedoutthataverysmallchangeinthegridpotentialcausesacorrespondingandlargerchangeintheamountofcurrentflowingfromtheplatetothefilament;andthatifavacuumtubeisusedfortheproductionofoscillationstheinitialsourceofcurrentmusthaveahighvoltage,infactthehighertheplatevoltagethemorepowerfulwillbetheoscillations.

Tounderstandhowoscillationsaresetupbyavacuumtubewhenadirectcurrentisappliedtoit,takealookatthesimplecircuitsshowninFig.94.Nowwhenyouclosetheswitchthevoltagefromthebatterychargesthecondenserandkeepsitchargeduntilyouopenitagain;theinstantyoudothisthecondenserdischargesthroughthecircuitwhichincludesitandtheinductancecoil,andthedischargeofacondenserisalwaysoscillatory.

WhereanoscillatortubeisincludedinthecircuitsasshownatAandBinFig.94,thegridtakestheplaceoftheswitchandanyslightchangeinthevoltageofeitherthegridortheplateissufficienttostartatrainofoscillationsgoing.Astheseoscillationssurgethroughthetubethepositivepartsofthemflowfromtheplatetothefilamentandthesecarrymoreofthedirectcurrentwiththem.

Tomakeatubesetuppowerfuloscillationsthen,itisonlynecessarythatanoscillationcircuitshallbeprovidedwhichwillfeedpartoftheoscillationssetupbythetubebacktothegridcircuitandwhenthisisdonetheoscillationswillkeeponbeingamplifieduntilthetubereachesthelimitofitsoutput.

TheOperationofC.W.TelegraphTransmittersWithDirectCurrent--ShortDistanceC.W.Transmitter.--InthetransmittershowninthewiringdiagraminFig.76thepositivepartofthe110voltdirectcurrentiscarrieddownfromthelampsocketthroughonesideofthepanelcut-out,thencethroughthechokecoilandtotheplateoftheoscillatortube,whenthelatterischargedtothepositivesign.Thenegativepartofthe110voltdirectcurrentthenflowsdowntheotherwiretothefilamentsothatthereisadifferenceofpotentialbetweentheplateandthefilamentof110volts.Nowwhenthe6-voltbatterycurrentisswitchedonthefilamentisheatedtobrilliancy,andtheelectronsthrownoffbyitformaconductingpathbetweenitandtheplate;the110voltcurrentthenflowsfromthelattertotheformer.

Nowfollowthewiringfromtheplateovertotheblockingcondenser,thencetoclip3ofthetuningcoil,throughtheturnsofthelattertoclip2andovertothefilamentand,whenthelatterisheated,youhaveaclosedoscillationcircuit.Theoscillationssurginginthelattersetupotherandlikeoscillationsinthetuningcoilbetweentheendofwhichisconnectedwiththegrid,theaerialandtheclip2,andthesesurgethroughthecircuitformedbythisportionofthecoil,thegridcondenserandthefilament;thisistheamplifyingcircuitanditcorrespondstotheregenerativecircuitofareceivingset.

Whenoscillationsaresetupinitthegridisalternatelychargedtothepositiveandnegativesigns.Thesereversalsofvoltagesetupstrongerandeverstrongeroscillationsintheplatecircuitasbeforeexplained.Notonlydotheoscillationssurgeintheclosedcircuitsbuttheyruntoandfroontheaerialwirewhentheirenergyisradiatedintheformofelectricwaves.TheoscillationsarevariedbymeansofthetelegraphkeywhichisplacedinthegridcircuitasshowninFig.76.

TheOperationoftheKeyCircuit.--TheeffectinaC.W.transmitterwhenatelegraphkeyisconnectedinserieswithabuzzerandabatteryandtheseareshuntedaroundthecondenserinthegridcircuit,istorapidlychangethewaveformofthesustainedoscillations,andhence,thelengthofthewavesthataresentout.Whilenosoundcanbeheardintheheadphonesatthereceivingstationsolongasthe

pointsofthekeyarenotincontact,whentheyareincontacttheoscillationsaremodulatedandsoundsareheardintheheadphonesthatcorrespondtothefrequencyofthebuzzerinthekeycircuit.

TheOperationofC.W.TelegraphTransmitterswithDirectCurrent.--Thechiefdifferencesbetweenthelongdistancesetswhichuseadirectcurrent,i.e.,thosedescribedinChapterXVI,andtheshortdistancetransmittingsetsarethattheformeruse:(1)amotor-generatorsetforchangingthelowvoltagedirectcurrentintohighvoltagedirectcurrent,and(2)achopperinthekeycircuit.Thewaythemotor-generatorchangesthelow-intohigh-voltagecurrenthasbeenexplainedinChapterXVI.

Thechopperinterruptstheoscillationssurgingthroughthegridcircuitatafrequencythattheearcanhear,thatistosay,about800to1,000timespersecond.Whenthekeyisopen,ofcourse,thesustainedoscillationssetupinthecircuitswillsendoutcontinuouswavesbutwhenthekeyisclosedtheseoscillationsarebrokenupandthentheysendoutdiscontinuouswaves.Ifaheterodynereceivingset,seeChapterXV,isbeingusedattheotherendyoucandispensewiththechopperandthekeycircuitneededisverymuchsimplified.Theoperationofkeycircuitsofthelatterkindwillbedescribedpresently.

TheOperationofC.W.TelegraphTransmitterswithAlternatingCurrent--WithaSingleOscillatorTube.--Whereanoscillatortubetelegraphtransmitterisoperatedbya110voltalternatingcurrentastheinitialsourceofenergy,abuzzer,chopperorotherinterruptorisnotneededinthekeycircuit.Thisisbecauseoscillationsaresetuponlywhentheplateisenergizedwiththepositivepartofthealternatingcurrentandthisproducesanintermittentmusicaltoneintheheadphones.Hencethiskindofasendingsetiscalledatonetransmitter.

Sinceoscillationsaresetuponlybythepositivepartorvoltageofanalternatingcurrentitisclearthat,asamatteroffact,thiskindofatransmitterdoesnotsendoutcontinuouswavesandthereforeitisnotaC.W.transmitter.ThisisgraphicallyshownbythecurveofthewaveformofthealternatingcurrentandtheoscillationsthataresetupbythepositivepartofitinFig.95.Wheneverthepositivehalfofthealternatingcurrentenergizestheplatethenoscillationsaresetupbythetubeand,conversely,whenthenegativehalfofthecurrentchargestheplatenooscillationsareproduced.

Youwillalsoobservethattheoscillationssetupbythepositivepartofthecurrentarenotofconstantamplitudebutstartatzerotheinstantthepositivepartbeginstoenergizetheplateandtheykeeponincreasinginamplitudeasthecurrentrisesinvoltageuntilthelatterreachesitsmaximum;thenasitgraduallydropsagaintozerotheoscillationsdecreaseproportionatelyinamplitudewithit.

HeatingtheFilamentwithAlternatingCurrent.--Whereanalternatingcurrentpowertransformerisusedtodevelopthenecessaryplatevoltageasecondsecondarycoilisgenerallyprovidedforheatingthefilamentoftheoscillationtube.Thisisbetterthanadirectcurrentforitaddstothelifeofthefilament.Whenyouuseanalternatingcurrenttoheatthefilamentkeepitatthesamevoltageratherthanatthesameamperage(currentstrength).Todothisyouneedonlytouseavoltmeteracrossthefilamentterminalsinsteadofanammeterinserieswithit;thenregulatethevoltageofthefilamentwitharheostat.

TheOperationofC.W.TelegraphTransmitterswithAlternatingCurrent--WithTwoOscillatorTubes.--ByusingtwooscillatortubesandconnectingthemupwiththepowertransformerandoscillatingcircuitsasshowninthewiringdiagraminFig.83theplatesarepositivelyenergizedalternatelywitheveryreversalofthecurrentand,consequently,thereisnotimeperiodbetweentheendingoftheoscillationssetupbyonetubeandthebeginningoftheoscillationssetupbytheothertube.Inotherwordstheseoscillationsaresustainedbutasinthecaseofthoseofasingletube,theiramplituderisesandfalls.Thiskindofasetiscalledafullwaverectificationtransmitter.

Thewavesradiatedbythistransmittercanbereceivedbyeitheracrystaldetectororaplainvacuum-tubedetectorbuttheheterodynereceptorwillgiveyoubetterresultsthaneitheroftheforegoingtypes.

TheOperationofWirelessTelephoneTransmitterswithDirectCurrent--ShortDistanceTransmitter.--Theoperationofthisshortdistancewirelesstelephonetransmitter,awiringdiagramofwhichisshowninFig.85isexactlythesameasthatoftheDirectCurrentShortDistanceC.W.TelegraphTransmitteralreadyexplainedinthischapter.Theonlydifferenceintheoperationofthesesetsisthesubstitutionofthemicrophonetransmitterforthetelegraphkey.

TheMicrophoneTransmitter.--Themicrophonetransmitterthatisusedtovary,ormodulate,thesustainedoscillationssetupbytheoscillatortubeandcircuitsisshowninFig.84.ByreferringtothediagramatAinthisfigureyouwillreadilyunderstandhowitoperates.Whenyouspeakintothemouthpiecethesoundwaves,whicharewavesintheair,impingeuponthediaphragmandthesesetitintovibration--thatis,theymakeitmovetoandfro.

Whenthediaphragmmovestowardthebackofthetransmitteritforcesthecarbongranulesthatareinthecupclosertogether;thislowerstheirresistanceandallowsmorecurrentfromthebatterytoflowthroughthem;whenthepressureoftheairwavesisremovedfromthediaphragmitspringsbacktowardthemouth-pieceandthecarbongranulesloosenupwhentheresistanceofferedbythemisincreasedandlesscurrentcanflowthroughthem.Wheretheoscillationcurrentintheaerialwireissmallthetransmittercanbeconnecteddirectlyinserieswiththelatterwhentheformerwillsurgethroughit.Asyouspeakintothemicrophonetransmitteritsresistanceisvariedandthecurrentstrengthoftheoscillationsisvariedaccordingly.

TheOperationofWirelessTelephoneTransmitterswithDirectCurrent--LongDistanceTransmitters.--Inthewirelesstelephonetransmittersforlongdistanceworkwhichwereshownanddescribedintheprecedingchapterabatteryisusedtoenergizethemicrophonetransmitter,andthesetwoelementsareconnectedinserieswithamicrophonemodulator.Thislatterdevicemaybeeither(1)atelephoneinductioncoil,(2)amicrophonetransformer,or(3)amagneticmodulator;thefirsttwoofthesedevicesstep-upthevoltageofthebatterycurrentandtheamplifiedvoltagethusdevelopedisimpressedontheoscillationsthatsurgethroughtheclosedoscillationcircuitortheaerialwire

systemaccordingtotheplacewhereyouconnectit.Thethirddeviceworksonadifferentprincipleandthiswillbedescribedalittlefartheralong.

TheOperationofMicrophoneModulators--TheInductionCoil.--Thisdeviceisreallyaminiaturetransformer,seeAinFig.86,anditspurposeistochangethe6voltdirectcurrentthatflowsthroughthemicrophoneinto100voltsalternatingcurrent;inturn,thisisimpressedontheoscillationsthataresurgingineither(1)thegridcircuitasshownatAinFig.89,andinFig.90,(2)theaerialwiresystem,asshownatBinFig.89andFig.93.Whenthecurrentfromthebatteryflowsthroughtheprimarycoilitmagnetizesthesoftironcoreandasthemicrophonevariesthestrengthofthecurrentthehighvoltagealternatingcurrentssetupinthesecondarycoiloftheinductioncoilarelikewisevaried,whentheyareimpresseduponandmodulatetheoscillatingcurrents.

TheMicrophoneTransformer.--Thisisaninductioncoilthatisdesignedespeciallyforwirelesstelephonemodulation.Theironcoreofthistransformerisalsooftheopenmagneticcircuittype,seeAinFig.87,andtheratiooftheturns[Footnote:SeeChapterVI]oftheprimaryandthesecondarycoilissuchthatwhenthesecondarycurrentisimpresseduponeitherthegridcircuitortheaerialwiresystemitcontrolstheoscillationsflowingthroughitwiththegreatestefficiency.

TheMagneticModulator.--Thispieceofapparatusisalsocalledamagneticamplifier.Theironcoreisformedofverythinplates,orlaminationsastheyarecalled,andthispermitshigh-frequencyoscillationstosurgeinacoilwoundonit.Inthistransformer,seeAinFig.88,thecurrentflowingthroughthemicrophonevariesthemagneticpermeabilityofthesoftironcorebythemagneticsaturationofthelatter.Sincethemicrophonecurrentisabsolutelydistinctfromtheoscillatingcurrentssurgingthroughthecoilofthetransformeraverysmalldirectcurrentflowingthroughacoilonthelatterwillvaryormodulateverylargeoscillatingcurrentssurgingthroughtheformer.ItisshownconnectedintheaerialwiresystematAinFig.88,andinFig.93.

OperationoftheVacuumTubeasaModulator.--Whereamicrophonemodulatoroftheinductioncoilormicrophonetransformertypeisconnectedinthegridcircuitoraerialwiresystemthemodulationisnotveryeffective,butbyusingasecondtubeasamodulator,asshowninFig.90,anefficientdegreeofmodulationcanbehad.Nowtherearetwomethodsbywhichavacuumtubecanbeusedasamodulatorandtheseare:(1)bytheabsorptionoftheenergyofthecurrentsetupbytheoscillatortube,and(2)byvaryingthedirectcurrentthatenergizestheplateoftheoscillatortube.

Thefirstofthesetwomethodsisnotusedbecauseitabsorbstheenergyoftheoscillatingcurrentproducedbythetubeanditisthereforewasteful.Thesecondmethodisanefficientone,asthedirectcurrentisvariedbeforeitpassesintotheoscillatortube.Thisissufficientreasonfordescribingonlythesecondmethod.Thevoltageofthegridofthemodulatortubeisvariedbythesecondarycoiloftheinductioncoilormicrophonetransformer,abovedescribed.Inthiswaythemodulatortubeactslikeavariableresistancebutitamplifiesthevariationsimpressedontheoscillationssetupbytheoscillatortube.Asthemagneticmodulatordoesthesamethingavacuumtubeusedasamodulatorisnotneededwheretheformerisemployed.Forthisreasonamagneticmodulatoristhecheapestinthelongrun.

TheOperationofWirelessTelephoneTransmitterswithAlternatingCurrent.--Whereaninitialalternatingcurrentisusedforwirelesstelephony,thecurrentmustberectifiedfirstandthensmoothedoutbeforepassingintotheoscillatortubetobeconvertedintooscillations.Furthersothattheoscillationswillbesustained,twooscillatortubesmustbeused,and,finally,inorderthatthe

oscillationsmaynotvaryinamplitudethealternatingcurrentmustbefirstchangedintodirectcurrentbyapairofrectifiervacuumtubes,asshowninFig.93.Whenthisisdonetheplateswillbepositivelychargedalternatelywitheveryreversalofthecurrentinwhichcasetherewillbenobreakinthecontinuityoftheoscillationssetupandthereforeinthewavesthataresentout.

TheOperationofRectifierVacuumTubes.--Thevacuumtuberectifierissimplyatwoelectrodevacuumtube.ThewayinwhichitchangesacommercialalternatingcurrentintopulsatingdirectcurrentisthesameasthatinwhichatwoelectrodevacuumtubedetectorchangesanoscillatingcurrentintopulsatingdirectcurrentsandthishasbeenexplainedindetailundertheheadingofTheOperationofaTwoElectrodeVacuumTubeDetectorinChapterXII.IntheC.W.TelegraphTransmittingSetsdescribedinChapterXVII,theoscillatortubesactasrectifiersaswellasoscillatorsbutforwirelesstelephonythealternatingcurrentmustberectifiedfirstsothatacontinuousdirectcurrentwillresult.

TheOperationofReactorsandCondensers.--Areactorisasinglecoilofwirewoundonanironcore,seeFig.90andAinFig.91,anditshouldpreferablyhavealargeinductance.ThereactorfortheplateandgridcircuitofawirelesstelephonetransmitterwhereoneormoretubesareusedasmodulatorsasshowninthewiringdiagraminFig.90,andthefilterreactorshowninFig.92,operateinthesameway.

Whenanalternatingcurrentflowsthroughacoilofwirethereversalsofthecurrentsetupacounterelectromotiveforceinitwhichopposes,thatisreacts,onthecurrent,andthehigherthefrequencyofthecurrentthegreaterwillbethereactance.Whenthepositivehalfofanalternatingcurrentismadetoflowthroughalargeresistancethecurrentissmoothedoutbutatthesametimealargeamountofitsenergyisusedupinproducingheat.

Butwhenthepositivehalfofanalternatingcurrentismadetoflowthroughalargeinductanceitactslikealargeresistanceasbeforeandlikewisesmoothsoutthecurrent,butnoneofitsenergyiswastedinheatandsoacoilhavingalargeinductance,whichiscalledaninductivereactance,orjustreactorforshort,isusedtosmoothout,orfilter,thealternatingcurrentafterithasbeenchangedintoapulsatingdirectcurrentbytherectifiertubes.

Acondenseralsohasareactanceeffectonanalternatingcurrentbutdifferentfromaninductioncoilthelowerthefrequencythegreaterwillbethereactance.Forthisreasonbothafilterreactorandfiltercondensersareusedtosmoothoutthepulsatingdirectcurrents.

CHAPTERXX

HOWTOMAKEARECEIVINGSETFOR$5.00ORLESS

InthechaptersonReceptorsyouhavebeentoldhowtobuilduphigh-gradesets.Buttherearethousandsofboys,and,probably,notafewmen,whocannotaffordtoinvest$25.00,moreorless,inareceivingsetandwouldliketoexperimentinasmallway.

Thefollowingsetisinexpensive,andwiththischeap,littleportablereceptoryoucangettheMorsecodefromstationsahundredmilesdistantandmessagesandmusicfrombroadcastingstationsifyoudonotlivetoofarawayfromthem.Allyouneedforthissetare:(1)acrystaldetector,(2)atuningcoiland(3)anearphone.Youcanmakeacrystaldetectoroutofacoupleofbindingposts,abitofgalenaandapieceofbrasswire,or,better,youcanbuyoneallreadytousefor50cents.

PhotographunavailableWirelessReceptor,thesizeofaSafetyMatchBox.AYouthfulGeniusinthepersonofKennethR.Hinman,Whoisonlytwelveyearsold,hasmadeaWirelessReceivingSetthatfitsneatlyintoa

SafetyMatchBox.WiththisInstrumentandaPairofOrdinaryReceivers,HeisabletocatchnotonlyCodeMessagesbuttheregularBroadcastingProgramsfromStationsTwentyandThirtyMiles

Distant.

TheCrystalDetector.--ThisisknownastheRascobabydetectoranditismadeandsoldbytheRadioSpecialtyCompany,96ParkPlace,NewYorkCity.ItisshowninFig.96.Thebaseismadeofblackcompositionandonitismountedastandardinwhicharodslidesandononeendofthisthereisfixedahardrubberadjustingknobwhiletheotherendcarriesathinpieceofphosphor-bronzewire,calledacat-whiskerTosecurethegalenacrystalinthecupyousimplyunscrewtheknurledcap,placeitinthecavityofthepostandscrewthecapbackonagain.Thefreeendofthecat-whiskerwireisthenadjustedsothatitwillrestlightlyontheexposedpartofthegalena.

TheTuningCoil.--Youwillhavetomakethistuningcoil,whichyoucandoatacostoflessthan$1.00,asthecheapesttuningcoilyoucanbuycostsatleast$3.00,andweneedtherestofour$5.00toinvestintheearphone.Getacardboardtube,suchasisusedformailingpurposes,2inchesindiameterand3incheslong,seeAinFig.97.Nowwindon250turnsofNo.40BrownandSharpegaugeplainenameledmagnetwire.YoucanuseNo.40doublecottoncoveredmagnetwire,inwhichcaseyouwillhavetoshellacthetubeandthewireafteryougetiton.

Asyouwindonthewiretakeoffatapatevery15thturn,thatis,scrapethewireandsolderonapieceabout7incheslong,asshowninFig.99;anddothisuntilyouhave6tapstakenoff.Insteadofleavingthewiresoutsideofthetubebringthemtotheinsideofitandthenoutthroughoneoftheopenends.Nowbuyaroundwood-baseswitchwith7contactpointsonitasshownatBinFig.97.Thiswillcostyou25or50cents.

TheHeadphone.--AnordinaryBelltelephonereceiverisofsmalluseforwirelessworkasitiswoundtotoolowaresistanceandthediaphragmismuchtoothick.IfyouhappentohaveaBellphoneyoucanrewinditwithNo.40singlecoveredsilkmagnetwire,orenameledwireofthesamesize,whenitssensitivitywillbeverygreatlyimproved.Thenyoumustgetathindiaphragmandthisshouldnotbeenameled,asthistendstodampenthevibrationsofit.Youcangetadiaphragmoftherightkindfor5cents.

Thebetterway,though,istobuyanearphonemadeespeciallyforwirelesswork.Youcangetonewoundto1000ohmsresistancefor$1.75andthispriceincludesacord.[Footnote:ThisisMesco,No.470wirelessphone.SoldbytheManhattanElectricalSupplyCo.,ParkPlace,N.Y.C.]For$1.00extrayoucangetahead-bandforit,andthenyourphonewilllookliketheonepicturedinFig.98.

HowtoMounttheParts.--Nowmountthecoilonawoodbase,1/2or1inchthick,3-1/2incheswideand5-1/2incheslong,andthenconnectoneendofthecoiltooneoftheendpointsontheswitch,andconnecteachsucceedingtaptooneoftheswitchpoints,asshownschematicallyinFig.99anddiagrammaticallyinFig.100.Thisdone,screwtheswitchdowntothebase.Finallyscrewthedetectortothebaseandscrewtwobindingpostsinfrontofthecoil.Thesearefortheearphone.

TheCondenser.--Youdonothavetoconnectacondenseracrosstheearphonebutifyoudoyouwillimprovethereceivingqualitiesofthereceptor.

HowtoConnectUptheReceptor.--NowconnectupallthepartsasshowninFigs.99and100,thenconnecttheleading-inwireoftheaerialwiththeleveroftheswitch;andconnectthefreeendofthetuningcoilwiththeground.Ifyouhavenoaerialwiretryhookingituptoarainpipethatisnotgroundedorthesteelframeofanumbrella.Foragroundyoucanuseawaterpipe,anironpipedrivenintotheground,orahydrant.Putonyourheadphone,adjustthedetectorandmovetheleverovertheswitchcontactsuntilitisinadjustmentandthen,ifallyourconnectionsareproperlymade,youshouldbeabletopickupmessages.

PhotographunavailableWirelessSetmadeintoaRing,designedbyAlfredG.Rinehart,ofElizabeth,NewJersey.ThislittleReceptorisaPracticalSet;itwillreceiveMessages,Concerts,etc.,Measures1"by5/8"by7/8".An

ordinaryUmbrellaisusedasanAerial.

APPENDIX

USEFULINFORMATION

ABBREVIATIONSOFUNITS

UnitAbbreviation

ampereamp.

ampere-hoursamp.-hr.

centimetercm.

centimeter-gram-secondc.g.s.

cubiccentimeterscm.^3

cubicinchescu.in.

cyclespersecond~

degreesCentigrade°C.

degreesFahrenheit°F.

feetft.

foot-poundsft.-lb.

gramsg.

henriesh.

inchesin.

kilogramskg.

kilometerskm.

kilowattskw.

kilowatt-hourskw.-hr.

kilovolt-ampereskv.-a.

metersm.

microfarads[Greek:mu]f.

micromicrofarads[Greek:mumu]f.

millihenriesmh.

millimetersmm.

poundslb.

secondssec.

squarecentimeterscm.^2

squareinchessq.in.

voltsv.

wattsw.

PREFIXESUSEDWITHMETRICSYSTEMUNITS

PrefixAbbreviationMeaning

micro[Greek:mu].1millionth

millim.1thousandth

centic.1hundredth

decid.1tenth

dekadk.10

hektoh.1hundred

kilok.1thousand

megam.1million

SYMBOLSUSEDFORVARIOUSQUANTITIES

QuantitySymbol

capacitanceC

conductanceg

couplingco-efficientk

current,instantaneousi

current,effectivevalueI

decrement[Greek:delta]

dielectricconstant[Greek:alpha]

electricfieldintensity[Greek:epsilon]

electromotiveforce,

instantaneousvalueE

electromotiveforce,

effectivevalueF

energyW

forceF

frequencyf

frequencyx2[Greek:pi][Greek:omega]

impedanceZ

inductance,selfL

inductance,mutualM

magneticfieldintensityA

magneticflux[Greek:Phi]

magneticinductionB

periodofacomplete

oscillationT

potentialdifferenceV

quantityofelectricityQ

ratioofthe

circumferenceofa

circletoitsdiameter

=3.1416[Greek:pi]

reactanceX

resistanceR

timet

velocityv

velocityoflightc

wavelength[Greek:lambda]

wavelengthinmeters[Greek:lambda]m

workW

permeability[Greek:mu]

Squareroot[Math:squareroot]

TABLEOFENAMELEDWIRE

No.ofTurnsTurnsOhmsper

Wire,perperCubicInch

B.&S.LinearSquareof

GaugeInchInchWinding

2030885.748

223714001.88

244621604.61

2658346011.80

2873540029.20

3091826070.90

3211621,0007547.00

3414513,4302968.00

3617831,8201098.00

3823254,080456.00

4029486,500183.00

TABLEOFFREQUENCYANDWAVELENGTHS

W.L.--WaveLengthsinMeters.

F.--NumberofOscillationsperSecond.

O.orsquarerootL.C.iscalledOscillationConstant.

C.--CapacityinMicrofarads.

L.--InductanceinCentimeters.

1000Centimeters=1Microhenry.

W.L.FOL.C.

506,000,000.839.7039

1003,000,0001.682.82

1502,000,0002.526.35

2001,500,0003.3611.29

2501,200,0004.1917.55

3001,000,0005.0525.30

350857,1005.8734.46

400750,0006.7145.03

450666,7007.5557.00

500600,0008.3970.39

550545,4009.2385.19

600500,00010.07101.41

700428,60011.74137.83

800375,00013.42180.10

900333,30015.10228.01

1,000300,00016.78281.57

1,100272,73018.45340.40

1,200250,00020.13405.20

1,300230,76021.81475.70

1,400214,38023.49551.80

1,500200,00025.17633.50

1,600187,50026.84720.40

1,700176,46028.52813.40

1,800166,67030.20912.00

1,900157,80031.881,016.40

2,000150,00033.551,125.60

2,100142,85035.231,241.20

2,200136,36036.911,362.40

2,300130,43038.591,489.30

2,400125,00040.271,621.80

2,500120,00041.951,759.70

2,600115,38043.621,902.60

2,700111,11045.302,052.00

2,800107,14046.892,207.00

2,900103,45048.662,366.30

3,000100,00050.332,533.20

4,00075,00067.114,504.00

5,00060,00083.897,038.00

6,00050,000100.710,130.00

7,00041,800117.313,630.00

8,00037,500134.118,000.00

9,00033,300151.022,820.00

10,00030,000167.928,150.00

11,00027,300184.834,150.00

12,00025,000201.540,600.00

13,00023,100218.347,600.00

14,00021,400235.055,200.00

15,00020,000252.063,500.00

16,00018,750269.072,300.00

PRONUNCIATIONOFGREEKLETTERS

ManyofthephysicalquantitiesuseGreeklettersforsymbols.ThefollowingistheGreekalphabetwiththewaythelettersarepronounced:

aalpha

bbeta

ggamma

ddelta

eepsilon

zzeta

aeeta

ththeta

iiota

kkappa

llambda

mmu

nnu

xXi(Zi)

oomicron

ppi

rrho

ssigma

ttau

uupsilon

phphi

chchi

pspsi

oomega

TABLEOFSPARKINGDISTANCES

InAirforVariousVoltagesbetweenNeedlePoints

VoltsDistance

InchesCentimeter

5,000.225.57

10,000.4701.19

15,000.7251.84

20,0001.0002.54

25,0001.3003.30

30,0001.6254.10

35,0002.0005.10

40,0002.4506.20

45,0002.957.50

50,0003.559.90

60,0004.6511.8

70,0005.8514.9

80,0007.1018.0

90,0008.3521.2

100,0009.6024.4

110,00010.7527.3

120,00011.8530.1

130,00012.9532.9

140,00013.9535.4

150,00015.0038.1

FEETPERPOUNDOFINSULATEDMAGNETWIRE

No.ofSingleDoubleSingleDouble

B.&S.Cotton,Cotton,Silk,Silk,Enamel

Gauge4-Mils8-Mils1-3/4-Mils4-Mils

20311298319312320

21389370408389404

22488461503498509

23612584636631642

24762745800779810

259579031,0059661,019

261,1921,1181,2651,2021,286

271,4881,4221,5901,5431,620

281,8521,7591,9721,9172,042

292,3752,2072,5702,4352,570

302,8602,5343,1452,9003,240

313,8002,7683,9433,6834,082

324,3753,7374,9504,6545,132

335,5904,6976,1805,6896,445

346,5006,1687,7407,1118,093

358,0506,7379,6008,58410,197

369,8207,87712,00010,03912,813

3711,8609,30915,00010,66616,110

3814,30010,63618,66014,22220,274

3917,13011,90723,15016,51625,519

4021,59014,22228,70021,33332,107

INTERNATIONALMORSECODEANDCONVENTIONALSIGNALS

TOBEUSEDFORALLGENERALPUBLICSERVICERADIOCOMMUNICATION

1. Adashisequaltothreedots.2. Thespacebetweenpartsofthesameletterisequaltoonedot.3. Thespacebetweentwolettersisequaltothreedots.4. Thespacebetweentwowordsisequaltofivedots.

[Note:perioddenotesMorsedot,hyphendenotesMorsedash]

A.-

B-...

C-.-.

D-..

E.

F..-.

G--.

H....

I..

J.---

K-.-

L.-..

M--

N-.

O---

P.--.

Q--.-

R.-.

S...

T-

U..-

V...-

W.--

X-..-

Y-.--

Z--..

Ä(German).-.-

ÁorÅ(Spanish-Scandinavian).--.-

CH(German-Spanish)----

É(French)..-..

Ñ(Spanish)--.--

Ö(German)---.

Ü(German)..--

1.----

2..---

3...--

4....-

5.....

6-....

7--...

8---..

9----.

0-----

Period......

Semicolon-.-.-.

Comma-.-.-.

Colon---...

Interrogation..--..

Exclamationpoint--..--

Apostrophe.----.

Hyphen-....-

Barindicatingfraction-..-.

Parenthesis-.--.-

Invertedcommas.-..-.

Underline..--.-

Doubledash-...-

DistressCall...---...

Attentioncalltoprecedeeverytransmission-.-.-

Generalinquirycall-.-.--.-

From(de)-...

Invitationtotransmit(goahead)-.-

Warning--highpower--..--

Question(pleaserepeatafter...)--interruptinglongmessages..--..

Wait.-...

Break(Bk.)(doubledash)-...-

Understand...-.

Error........

Received(O.K.).-.

Positionreport(toprecedeallpositionmessages)-.-.

Endofeachmessage(cross).-.-.

Transmissionfinished(endofwork)(conclusionofcorrespondence)...-.-

INTERNATIONALRADIOTELEGRAPHICCONVENTION

LISTOFABBREVIATIONSTOBEUSEDINRADIOCOMMUNICATION

ABBREVIATIONQUESTIONANSWERORREPLY

PRBDoyouwishtocommunicateIwishtocommunicatebymeans

bymeansoftheInternationaloftheInternationalSignalCode.

SignalCode?

QRAWhatshiporcoaststationisThisis....

that?

QRBWhatisyourdistance?Mydistanceis....

QRCWhatisyourtruebearing?Mytruebearingis....

QRDWhereareyouboundfor?Iamboundfor....

QRFWhereareyouboundfrom?Iamboundfrom....

QRGWhatlinedoyoubelongto?Ibelongtothe...Line.

QRHWhatisyourwavelengthinMywavelengthis...meters.

meters?

QRJHowmanywordshaveyoutosend?Ihave...wordstosend.

QRKHowdoyoureceiveme?Iamreceivingwell.

QRLAreyoureceivingbadly?Iamreceivingbadly.Please

ShallIsend20?send20.

...-....-.

foradjustment?foradjustment.

QRMAreyoubeinginterferedwith?Iambeinginterferedwith.

QRNAretheatmosphericsstrong?Atmosphericsareverystrong.

QROShallIincreasepower?Increasepower.

QRPShallIdecreasepower?Decreasepower.

QRQShallIsendfaster?Sendfaster.

QRSShallIsendslower?Sendslower.

QRTShallIstopsending?Stopsending.

QRUHaveyouanythingforme?Ihavenothingforyou.

QRVAreyouready?Iamready.Allrightnow.

QRWAreyoubusy?Iambusy(or:Iambusywith...).

Pleasedonotinterfere.

QRXShallIstandby?Standby.Iwillcallyouwhen

required.

QRYWhenwillbemyturn?YourturnwillbeNo....

QRZAremysignalsweak?Yousignalsareweak.

QSAAremysignalsstrong?Yousignalsarestrong.

QSBIsmytonebad?Thetoneisbad.

Ismysparkbad?Thesparkisbad.

QSCIsmyspacingbad?Yourspacingisbad.

QSDWhatisyourtime?Mytimeis....

QSFIstransmissiontobeinTransmissionwillbein

alternateorderorinseries?alternateorder.

QSGTransmissionwillbeina

seriesof5messages.

QSHTransmissionwillbeina

seriesof10messages.

QSJWhatrateshallIcollectfor...?Collect....

QSKIsthelastradiogramcanceled?Thelastradiogramiscanceled.

QSLDidyougetmyreceipt?Pleaseacknowledge.

QSMWhatisyourtruecourse?Mytruecourseis...degrees.

QSNAreyouincommunicationwithland?Iamnotincommunicationwithland.

QSOAreyouincommunicationwithIamincommunicationwith...

anyshiporstation(through...).

(or:with...)?

QSPShallIinform...thatyouareInform...thatIamcallinghim.

callinghim?

QSQIs...callingme?Youarebeingcalledby....

QSRWillyouforwardtheradiogram?Iwillforwardtheradiogram.

QSTHaveyoureceivedthegeneralGeneralcalltoallstations.

call?

QSUPleasecallmewhenyouhaveWillcallwhenIhavefinished.

finished(or:at...o'clock)?

QSVIspubliccorrespondencebeingPubliccorrespondenceisbeing

handled?handled.Pleasedonotinterfere.

[Footnote:Publiccorrespondenceisanyradiowork,officialorprivate,handledoncommercialwavelengths.]

QSWShallIincreasemysparkIncreaseyoursparkfrequency.

frequency?

QSXShallIdecreasemysparkDecreaseyoursparkfrequency.

frequency?

QSYShallIsendonawavelengthLetuschangetothewavelength

of...meters?of...meters.

QSZSendeachwordtwice.Ihave

difficultyinreceivingyou.

QTARepeatthelastradiogram.

Whenanabbreviationisfollowedbyamarkofinterrogation,itreferstothequestionindicatedforthatabbreviation.

UsefulInformation

SymbolsUsedForApparatus

alternatorammeteraerialarcbatterybuzzercondenservariablecondenserconnectionofwiresnoconnectioncoupledcoils

variablecouplingdetectorgap,plaingap,quenchedgroundhotwireammeterinductorvariableinductorkeyresistorvariableresistorswitchs.p.s.t."s.p.d.t."d.p.s.t."d.p.d.t."reversingphonereceiver"transmitterthermoelementtransformervacuumtubevoltmeterchokecoil

DEFINITIONSOFELECTRICANDMAGNETICUNITS

Theohmistheresistanceofathreadofmercuryatthetemperatureofmeltingice,14.4521gramsinmass,ofuniformcross-sectionandalengthof106.300centimeters.

Theampereisthecurrentwhichwhenpassedthroughasolutionofnitrateofsilverinwateraccordingtocertainspecifications,depositssilverattherateof0.00111800ofagrampersecond.

Thevoltistheelectromotiveforcewhichproducesacurrentof1amperewhensteadilyappliedtoaconductortheresistanceofwhichis1ohm.

Thecoulombisthequantityofelectricitytransferredbyacurrentof1amperein1second.

Theampere-houristhequantityofelectricitytransferredbyacurrentof1amperein1hourandis,therefore,equalto3600coulombs.

Thefaradisthecapacitanceofacondenserinwhichapotentialdifferenceof1voltcausesittohaveachargeof1coulombofelectricity.

Thehenryistheinductanceinacircuitinwhichtheelectromotiveforceinducedis1voltwhentheinducingcurrentvariesattherateof1amperepersecond.

Thewattisthepowerspentbyacurrentof1ampereinaresistanceof1ohm.

ThejouleistheenergyspentinIsecondbyaflowof1amperein1ohm.

Thehorse-powerisusedinratingsteammachinery.Itisequalto746watts.

Thekilowattis1,000watts.

Theunitsofcapacitanceactuallyusedinwirelessworkarethemicrofarad,whichisthemillionthpartofafarad,becausethefaradistoolargeaunit;andtheC.G.S.electrostaticunitofcapacitance,whichisoftencalledthecentimeterofcapacitance,whichisaboutequalto1.11microfarads.

Theunitsofinductancecommonlyusedinradioworkarethemillihenry,whichisthethousandthpartofahenry;andthecentimeterofinductance,whichisoneone-thousandthpartofamicrohenry.

Note.--ForfurtherinformationaboutelectricandmagneticunitsgettheBureauofStandardsCircularNo.60,calledElectricUnitsandStandards,thepriceofwhichis15cents;alsogetScientificPaperNo.292,calledInternationalSystemofElectricandMagneticUnits,price10cents.TheseandotherinformativepaperscanbehadfromtheSuperintendentofDocuments,GovernmentPrintingOffice,Washington,D.C.

WIRELESSBOOKS

TheAdmiraltyManualofWirelessTelegraphy.1920.PublishedbyHisMajesty'sStationeryOffice,London.

RalphE.Batcher.--PreparedRadioMeasurements.1921.WirelessPress,Inc.,NewYorkCity.

ElmerE.Bucher.--PracticalWirelessTelegraphy.1918.WirelessPress,Inc.,NewYorkCity.

ElmerE.Bucher.--VacuumTubesinWirelessCommunication.1919.WirelessPress,Inc.,NewYorkCity.

ElmerE.Bucher.--TheWirelessExperimenter'sManual.1920.WirelessPress,Inc.,NewYorkCity.

1. FrederickCollins.--WirelessTelegraphy,ItsHistory,Theory,andPractice.1905.McGrawPub.Co.,NewYorkCity.

2. H.Dellinger.--PrinciplesUnderlyingRadioCommunication.3. SignalCorps,U.S.Army,Washington,D.C.4. M.Dorsett.--WirelessTelegraphyandTelephony.1920.WirelessPress,Ltd.,London.5. A.Fleming.--PrinciplesofElectricWaveTelegraphy.1919.Longmans,GreenandCo.,London.

CharlesB.Hayward.--HowtoBecomeaWirelessOperator.1918.AmericanTechnicalSociety,Chicago,Ill.

G.D.Robinson.--ManualofRadioTelegraphyandTelephony.1920.UnitedStatesNavalInstitute,Annapolis,Md.

RupertStanley.--TextbookofWirelessTelegraphy.1919.Longmans,GreenandCo.,London.

E.W.Stone.--ElementsofRadioTelegraphy.1919.D,VanNostrandCo.,NewYorkCity.

L.B.Turner.--WirelessTelegraphyandTelephony.1921.CambridgeUniversityPress.Cambridge,England.

SendtotheSuperintendentofDocuments,GovernmentPrintingOffice,Washington,D.C.,foracopyofPriceListNo.64whichliststheGovernment'sbooksandpamphletsonwireless.Itwillbesenttoyoufreeofcharge.

TheGovernmentpublishes;(1)AListofCommercialGovernmentandSpecialWirelessStations,everyyear,price15cents;(2)AListofAmateurWirelessStations,yearly,price15cents;(3)AWirelessServiceBulletinispublishedmonthly,price5centsacopy,or25centsyearly;and(4)WirelessCommunicationLawsoftheUnitedStates,theInternationalWirelessTelegraphicConventionandRegulationsGoverningWirelessOperatorsandtheUseofWirelessonShipsandLandStations,price15centsacopy.OrdersfortheabovepublicationsshouldbeaddressedtotheSuperintendentofDocuments,GovernmentPrintingOffice,Washington,D.C.

ManufacturersandDealersinWirelessApparatusandSupplies:

Adams-MorganCo.,UpperMontclair,N.J.

AmericanHardRubberCo.,11MercerStreet,NewYorkCity.

AmericanRadioandResearchCorporation,MedfordHillside,Mass.

Brach(L.S.)Mfg.Co.,127SussexAve.,Newark,N.J.

Brandes(C.)Inc.,237LafayetteSt.,NewYorkCity.

Bunnell(J.H.)Company,ParkPlace,NewYorkCity.

BurgessBatteryCompany,HarrisTrustCo.Bldg.,Chicago,Ill.

Clapp-EastmanCo.,120MainSt.,Cambridge,Mass.

ConnecticutTelephoneandTelegraphCo.,Meriden,Conn.

ContinentalFiberCo.,Newark,Del.

Coto-CoilCo.,Providence,R.I.

CrosleyMfg.Co.,Cincinnati,Ohio.

Doolittle(F.M.),817ChapelSt.,NewHaven,Conn.

Edelman(PhilipE.),9CortlandtSt.,NewYorkCity.

EdisonStorageBatteryCo.,Orange,N.J.

ElectricSpecialtyCo.,Stamford,Conn.

ElectroseMfg.Co.,60WashingtonSt.,Brooklyn,N.Y.

GeneralElectricCo.,Schenectady,N.Y.

Grebe(A.H.)andCo.,Inc.,RichmondHill,N.Y.C.

InternationalBrassandElectricCo.,176BeekmanSt.,NewYorkCity.

InternationalInsulatingCo.,25West45thSt.,NewYorkCity.

KingAmplitoneCo.,82ChurchSt.,NewYorkCity.

Kennedy(ColinB.)Co.,RialtoBldg.,SanFrancisco,Cal.

MagnavoxCo.,Oakland,Cal.

ManhattanElectricalSupplyCo.,ParkPlace,N.Y.

Marshall-GerkenCo.,Toledo,Ohio.

MichiganPaperTubeandCanCo.,2536GrandRiverAve.,Detroit,Mich.

Murdock(Wm.J.)Co.,Chelsea,Mass.

NationalCarbonCo.,Inc.,LongIslandCity,N.Y.

PittsburghRadioandApplianceCo.,112DiamondSt.,Pittsburgh,Pa,

RadioCorporationofAmerica,233Broadway,NewYorkCity.

Riley-KlotzMfg.Co.,17-19MulberrySt.,Newark,N.J.

RadioSpecialtyCo.,96ParkPlace,NewYorkCity.

Roller-SmithCo.,15BarclaySt.,NewYorkCity.

Tuska(C.D.)Co.,Hartford,Conn.

WesternElectricCo.,Chicago,Ill.

WestinghouseElectricCo.,Pittsburgh,Pa.

WestonElectricalInstrumentCo.,173WestonAve.,Newark,N.J.

WestfieldMachineCo.,Westfield,Mass.

ABBREVIATIONSOFCOMMONTERMS

A...............Aerial

A.C.............AlternatingCurrent

A.F.............AudioFrequency

B.andS........Brown&SharpeWireGauge

C...............CapacityorCapacitance

C.G.S...........Centimeter-Grain-Second

Cond............Condenser

Coup............Coupler

C.W.............ContinuousWaves

D.C.............DirectCurrent

D.P.D.T.........DoublePointDoubleThrow

D.P.S.T.........DoublePointSingleThrow

D.X.............Distance

E...............ShortforElectromotiveForce(Volt)

E.M.F...........ElectromotiveForce

F...............FilamentorFrequency

G...............Grid

Gnd.............Ground

I...............CurrentStrength(Ampere)

I.C.W...........InterruptedContinuousWaves

KW..............Kilowatt

L...............Inductance

L.C.............LooseCoupler

Litz............Litzendraht

Mfd.............Microfarad

Neg.............Negative

O.T.............OscillationTransformer

P...............Plate

Prim............Primary

Pos.............Positive

R...............Resistance

R.F.............RadioFrequency

Sec.............Secondary

S.P.D.T.........SinglePointDoubleThrow

S.P.S.T.........SinglePointSingleThrow

S.R.............SelfRectifying

T...............TelephoneorPeriod(time)ofComplete

Oscillation

Tick............Tickler

V...............PotentialDifference

Var.............Variometer

Var.Cond.......VariableCondenser

V.T.............VacuumTube

W.L.............WaveLength

X...............Reactance

GLOSSARY

ABATTERY.--SeeBatteryA.

ABBREVIATIONS,CODE.--Abbreviationsofquestionsandanswersusedinwirelesscommunication.TheabbreviationofaquestionisusuallyinthreelettersofwhichthefirstisQ.ThusQRBisthecodeabbreviationof"whatisyourdistance?"andtheanswer"Mydistanceis..."SeePage306[Appendix:ListofAbbreviations].

ABBREVIATIONS,UNITS.--Abbreviationsofvariousunitsusedinwirelesselectricity.TheseabbreviationsareusuallylowercaselettersoftheRomanalphabet,butoccasionallyGreeklettersareusedandothersigns.Thusamperesisabbreviatedamp.,micro,whichmeansonemillionth,[Greek:mu],etc.SeePage301[Appendix:UsefulAbbreviations].

ABBREVIATIONSOFWORDSANDTERMS.--Lettersusedinsteadofwordsandtermsforshorteningthemupwherethereisaconstantrepetitionofthem,asA.C.foralternatingcurrent;C.W.forcontinuouswaves;V.T.forvacuumtube,etc.SeePage312[Appendix:AbbreviationsofCommonTerms].

AERIAL.--Alsocalledantenna.Anaerialwire.Oneormorewiressuspendedintheairandinsulatedfromitssupports.Itistheaerialthatsendsoutthewavesandreceivesthem.

AERIAL,AMATEUR.--Anaerialsuitableforsendingout200meterwavelengths.Suchanaerialwiresystemmustnotexceed120feetinlengthfromthegrounduptotheaerialswitchandfromthisthroughtheleading-inwiretotheendoftheaerial.

AERIALAMMETER.--SeeAmmeter,HotWire.

AERIAL,BED-SPRINGS.--Whereanoutdooraerialisnotpracticablebed-springsareoftenmadetoservethepurpose.

AERIALCAPACITY.--SeeCapacity,Aerial.

AERIALCOUNTERPOISE.--Whereitisnotpossibletogetagoodgroundanaerialcounterpoiseorearthcapacitycanbeusedtoadvantage.Thecounterpoiseismadeliketheaerialandissupporteddirectlyunderitclosetothegroundbutinsulatedfromit.

AERIAL,DIRECTIONAL.--Aflat-toporotheraerialthatwilltransmitandreceiveovergreaterdistancestoandfromonedirectionthantoandfromanother.

AERIAL,GROUND.--Signalscanbereceivedonasinglelongwirewhenitisplacedonorburiedintheearthorimmersedinwater.Itisalsocalledagroundantennaandanundergroundaerial.

AERIAL,LOOP.--Alsocalledacoilaerial,coilantenna,loopaerial,loopantennaandwhenusedforthepurposeadirectionfinder.Acoilofwirewoundonaverticalframe.

AERIALRESISTANCE.--SeeResistance,Aerial.

AERIALSWITCH.--SeeSwitchAerial.

AERIALWIRE.--(1)Awireorwiresthatformtheaerial.(2)Wirethatisusedforaerials;thisisusuallycopperorcopperalloy.

AERIALWIRESYSTEM.--Anaerialandgroundwireandthatpartoftheinductancecoilwhichconnectsthem.Theopenoscillationcircuitofasendingorareceivingstation.

AIRCORETRANSFORMER.--SeeTransformer,AirCore.

AMATEURAERIALORANTENNA.--SeeAerial,Amateur.

ALTERNATOR.--Anelectricmachinethatgeneratesalternatingcurrent.

ALPHABET,INTERNATIONALCODE.--AmodifiedMorsealphabetofdotsanddashesoriginallyusedinContinentalEuropeand,hence,calledtheContinentalCode.Itisnowusedforallgeneralpublicservicewirelesscommunicationallovertheworldand,hence,itiscalledtheInternationalCode.Seepage305[Appendix:InternationalMorseCode].

ALTERNATINGCURRENT(A.C.)--SeeCurrent.

ALTERNATINGCURRENTTRANSFORMER.--SeeTransformer.

AMATEURGROUND.--SeeGround,Amateur.

AMMETER.--Aninstrumentusedformeasuringthecurrentstrength,intermsofamperes,thatflowsinacircuit.Ammetersusedformeasuringdirectandalternatingcurrentsmakeuseofthemagneticeffectsofthecurrents.Highfrequencycurrentsmakeuseoftheheatingeffectsofthecurrents.

AMMETER,HOT-WIRE.--Highfrequencycurrentsareusuallymeasuredbymeansofaninstrumentwhichdependsonheatingawireormetalstripbytheoscillations.Suchaninstrumentisoftencalledathermalammeter,radioammeterandaerialammeter.

AMMETER,AERIAL.--SeeAmmeter,HotWire.

AMMETER,RADIO.--SeeAmmeter,HotWire.

AMPERE.--Thecurrentwhichwhenpassedthroughasolutionofnitrateofsilverinwateraccordingtocertainspecifications,depositssilverattherateof0.00111800ofagrampersecond.

AMPERE-HOUR.--Thequantityofelectricitytransferredbyacurrentof1amperein1hourandis,therefore,equalto3600coulombs.

AMPERE-TURNS.--Whenacoiliswoundupwithanumberofturnsofwireandacurrentismadetoflowthroughit,itbehaveslikeamagnet.BThestrengthofthemagneticfieldinsideofthecoildependson(1)thestrengthofthecurrentand(2)thenumberofturnsofwireonthecoil.Thusafeeblecurrentflowingthroughalargenumberofturnswillproduceasstrongamagneticfieldasastrongcurrentflowingthroughafewturnsofwire.Thisproductofthecurrentinamperestimesthenumberofturnsofwireonthecoiliscalledtheampere-turns.

AMPLIFICATION,AUDIOFREQUENCY.--Acurrentofaudiofrequencythatisamplifiedbyanamplifiertubeorothermeans.

AMPLIFICATION,CASCADE.--SeeCascadeAmplification.

AMPLIFICATION,RADIOFREQUENCY.--Acurrentofradiofrequencythatisamplifiedbyanamplifiertubeorothermeansbeforeitreachesthedetector.

AMPLIFICATION,REGENERATIVE.--Aschemethatusesathirdcircuittofeedbackpartoftheoscillationsthroughavacuumtubeandwhichincreasesitssensitivenesswhenusedasadetectorandmultipliesitsactionasanamplifierandanoscillator.

AMPLIFIER,AUDIOFREQUENCY.--Avacuumtubeorotherdevicethatamplifiesthesignalsafterpassingthroughthedetector.

AMPLIFIER,MAGNETIC.--Adeviceusedforcontrollingradiofrequencycurrentseitherbymeansofatelegraphkeyoramicrophonetransmitter.Thecontrollingcurrentflowsthroughaseparatecircuitfromthatoftheradiocurrentandafractionofanamperewillcontrolseveralamperesintheaerialwire.

AMPLIFIERS,MULTI-STAGE.--Areceivingsetusingtwoormoreamplifiers.Alsocalledcascadeamplification.

AMPLIFIER,VACUUMTUBE.--Avacuumtubethatisusedeithertoamplifytheradiofrequencycurrentsortheaudiofrequencycurrents.

AMPLITUDEOFWAVE.--Thegreatestdistancethatapointmovesfromitspositionofrest.

AMPLIFYINGTRANSFORMER,AUDIO.--SeeTransformer,AudioAmplifying.

AMPLIFYINGMODULATORVACUUMTUBE.--SeeVacuumTube,AmplifyingModulator.

AMPLIFYINGTRANSFORMERRADIO.--SeeTransformer,RadioAmplifying.

ANTENNA,AMATEUR.--SeeAerial,Amateur.

ANTENNASWITCH.--SeeSwitch,Aerial.

APPARATUSSYMBOLS.--SeeSymbols,Apparatus.

ARMSTRONGCIRCUIT.--SeeCircuit,Armstrong.

ATMOSPHERICS.--SameasStatic,whichsee.

ATTENUATION.--InSendingwirelesstelegraphandtelephonemessagestheamplitudeoftheelectricwavesisdampedoutasthedistanceincreases.Thisiscalledattenuationanditincreasesasthefrequencyisincreased.Thisisthereasonwhyshortwavelengthswillnotcarryasfaraslongwavelengths.

AUDIOFREQUENCYAMPLIFIER.--SeeAmplifier,AudioFrequency.

AUDIOFREQUENCYAMPLIFICATION.--SeeAmplification,AudioFrequency.

AUDIBILITYMETER.--SeeMeter,Audibility.

AUDIOFREQUENCY.--SeeFrequency,Audio.

AUDIOFREQUENCYCURRENT.--SeeCurrent,AudioFrequency.

AUDION.--Anearlytradenamegiventothevacuumtubedetector.

AUTODYNERECEPTOR.--SeeReceptor,Autodyne.

AUTOTRANSFORMER.--SeeTransformer,Auto.

BAKELITE.--Amanufacturedinsulatingcompound.

BBATTERY.--SeeBatteryB.

BAND,WAVELENGTH.--SeeWaveLengthBand.

BASKETWOUNDCOILS.--SeeCoils,Inductance.

BATTERY,A.--The6-voltstoragebatteryusedtoheatthefilamentofavacuumtube,detectororamplifier.

BATTERY,B.--The22-1/2-voltdrycellbatteryusedtoenergizetheplateofavacuumtubedetectororamplifier.

BATTERY,BOOSTER.--Thisisthebatterythatisconnectedinserieswiththecrystaldetector.

BATTERY,C.--Asmalldrycellbatterysometimesusedtogivethegridofavacuumtubedetectorabiaspotential.

BATTERY,EDISONSTORAGE.--Astoragebatteryinwhichtheelementsaremadeofnickelandironandimmersedinanalkalineelectrolyte.

BATTERY,LEADSTORAGE.--Astoragebatteryinwhichtheelementsaremadeofleadandimmersedinanacidelectrolyte.

BATTERYPOLES.--SeePoles,Battery.

BATTERY,PRIMARY.--Abatterythatgeneratescurrentbychemicalaction.

BATTERY,STORAGE.--Abatterythatdevelopsacurrentafterithasbeencharged.

BEATRECEPTION.--SeeHeterodyneReception.

BEDSPRINGSAERIAL.--SeeAerial,BedSprings.

BLUBBLUB.--Overmodulationinwirelesstelephony.

BROADWAVE.--SeeWave,Broad.

BRUSHDISCHARGE.--SeeDischarge.

BUZZERMODULATION.--SeeModulation,Buzzer.

BLUEGLOWDISCHARGE.--SeeDischarge.

BOOSTERBATTERY.--SeeBattery,Booster.

BROADCASTING.--Sendingoutintelligenceandmusicfromacentralstationforthebenefitofallwholivewithinrangeofitandwhohavereceivingsets.

CAPACITANCE.--Alsocalledbytheoldernameofcapacity.Thecapacityofacondenser,inductancecoilorotherdevicecapableofretainingachargeofelectricity.Capacitanceismeasuredintermsofthemicrofarad.

CAPACITIVECOUPLING.--SeeCoupling,Capacitive.

CAPACITY.--Anyobjectthatwillretainachargeofelectricity;henceanaerialwire,acondenserorametalplateissometimescalledacapacity.

CAPACITY,AERIAL.--Theamounttowhichanaerialwiresystemcanbecharged.Thecapacitanceofasmallamateuraerialisfrom0.0002to0.0005microfarad.

CAPACITY,DISTRIBUTED.--Acoilofwirenotonlyhasinductance,butalsoacertainsmallcapacitance.Coilswoundwiththeirturnsparallelandhavinganumberoflayershaveabunchedcapacitancewhichproducesuntowardeffectsinoscillationcircuits.Inhoneycombandotherstaggerwoundcoilsthecapacitanceismoreevenlydistributed.

CAPACITYREACTANCE.--SeeReactance,Capacity.

CAPACITYUNIT.--SeeFarad.

CARBONRHEOSTATS.--SeeRheostat,Carbon.

CARBORUNDUMDETECTOR.--SeeDetector.

CARRIERCURRENTTELEPHONY.--SeeWired-Wireless.

CARRIERFREQUENCY.--SeeFrequency,Carrier.

CARRIERFREQUENCYTELEPHONY.--SeeWired-Wireless.

CASCADEAMPLIFICATION.--Twoormoreamplifyingtubeshookedupinareceivingset.

CATWHISKERCONTACT.--Along,thinwirewhichmakescontactwiththecrystalofadetector.

CENTIMETEROFCAPACITANCE.--Equalto1.11microfarads.

CENTIMETEROFINDUCTANCE.--Equaltooneone-thousandthpartofamicrohenry.

CELLULARCOILS.--SeeCoils,Inductance.

C.G.S.ELECTROSTATICUNITOFCAPACITANCE.--SeeCentimeterofCapacitance.

CHARACTERISTICS.--Thespecialbehaviorofadevice,suchasanaerial,adetectortube,etc.

CHARACTERISTICS,GRID.--SeeGridCharacteristics.

CHOKECOILS.--Coilsthatpreventthehighvoltageoscillationsfromsurgingbackintothetransformerandbreakingdowntheinsulation.

CHOPPERMODULATION.--SeeModulation,Chopper.

CIRCUIT.--Anyelectricalconductorthroughwhichacurrentcanflow.Alowvoltagecurrentrequiresaloopofwireorotherconductorbothendsofwhichareconnectedtothesourceofcurrentbeforeitcanflow.Ahighfrequencycurrentwillsurgeinawirewhichisopenatbothendsliketheaerial.

ClosedCircuit.--Acircuitthatiscontinuous.OpenCircuit.--Aconductorthatisnotcontinuous.CoupledCircuits.--Openandclosedcircuitsconnectedtogetherbyinductancecoils,condensersorresistances.Seecoupling.CloseCoupledCircuits.--Openandclosedcircuitsconnecteddirectlytogetherwithasingleinductancecoil.LooseCoupledCircuits.--Openedandclosedcurrentsconnectedtogetherinductivelybymeansofatransformer.Stand-byCircuits.--Alsocalledpick-upcircuits.Whenlistening-inforpossiblecallsfromanumberofstations,areceiverisusedwhichwillrespondtoawidebandofwavelengths.ArmstrongCircuits.--TheregenerativecircuitinventedbyMajorE.H.Armstrong.

CLOSECOUPLEDCIRCUITS.--SeeCurrents,CloseCoupled.

CLOSEDCIRCUIT.--SeeCircuit,Closed.

CLOSEDCORETRANSFORMER.--SeeTransformer,ClosedCore.

CODE.--

Continental.--SameasInternational.International.--OnthecontinentofEuropelandlinesusetheContinentalMorsealphabeticcode.ThiscodehascometobeusedthroughouttheworldforwirelesstelegraphyandhenceitisnowcalledtheInternationalcode.ItisgivenonPage305.[Appendix:InternationalMorseCode].Morse.--ThecodedevisedbySamuelF.B.MorseandwhichisusedonthelandlinesintheU.S.NationalElectric.--AsetofrulesandrequirementsdevisedbytheNationalBoardofFireUnderwritersfortheelectricalinstallationsinbuildingsonwhichinsurancecompaniescarryrisks.Thiscodealsocoverstherequirementsforwirelessinstallations.Acopymaybehadfrom

theNationalBoardofFireUnderwriters,NewYorkCity,orfromyourinsuranceagent.NationalElectricSafety.--TheBureauofStandards,Washington,D.C.,haveinvestigatedtheprecautionswhichshouldbetakenforthesafeoperationofallelectricequipment.AcopyoftheBureauofStandardsHandbookNo.3canbehadfor40centsfromtheSuperintendentofDocuments.

COEFFICIENTOFCOUPLING.--SeeCoupling,Coefficientof.

COILAERIAL.--SeeAerial,Loop.

COILANTENNA.--SeeAerial,Loop.

COIL,INDUCTION.--Anapparatusforchanginglowvoltagedirectcurrentsintohighvoltage,lowfrequencyalternatingcurrents.Whenfittedwithasparkgapthehighvoltage,lowfrequencycurrentsareconvertedintohighvoltage,highfrequencycurrents.ItisthenalsocalledasparkcoilandaRuhmkorffcoil.

COIL,LOADING.--Acoilconnectedintheaerialorclosedoscillationcircuitsothatlongerwavelengthscanbereceived.

COIL,REPEATING.--SeeRepeatingCoil.

COIL,ROTATING.--Onewhichrotatesonashaftinsteadofslidingasinaloosecoupler.Therotorofavariometerorvariocouplerisarotatingcoil.

COILS,INDUCTANCE.--Thesearethetuningcoilsusedforsendingandreceivingsets.Forsendingsetstheyareformedofoneandtwocoils,asinglesendingcoilisgenerallycalledatuninginductancecoil,whileatwo-coiltuneriscalledanoscillationtransformer.Receivingtuningcoilsaremadewithasinglelayer,singlecoil,orapairofcoils,whenitiscalledanoscillationtransformer.Sometuninginductancecoilshavemorethanonelayer,theyarethencalledlatticewound,cellular,basketwound,honeycomb,duo-lateral,staggerwound,spider-webandslabcoils.

COMMERCIALFREQUENCY.--SeeFrequency,Commercial.

CONDENSER,AERIALSERIES.--Acondenserplacedintheaerialwiresystemtocutdownthewavelength.

CONDENSER,VERNIER.--Asmallvariablecondenserusedforreceivingcontinuouswaveswhereverysharptuningisdesired.

CONDENSER.--Allconductingobjectswiththeirinsulationformcapacities,butacondenserisunderstoodtomeantwosheetsorplatesofmetalplacedcloselytogetherbutseparatedbysomeinsulatingmaterial.

AdjustableCondenser.--Wheretwoormorecondenserscanbecoupledtogetherbymeansofplugs,switchesorotherdevices.AerialCondenser.--Acondenserconnectedintheaerial.AirCondenser.--Whereaironlyseparatesthesheetsofmetal.By-PassCondenser.--Acondenserconnectedinthetransmittingcurrentssothatthehigh

frequencycurrentscannotflowbackthroughthepowercircuit.FilterCondenser.--Acondenseroflargecapacitanceusedincombinationwithafilterreactorforsmoothingoutthepulsatingdirectcurrentsastheycomefromtherectifier.FixedCondenser.--Wheretheplatesarefixedrelativelytooneanother.GridCondenser.--Acondenserconnectedinserieswiththegridlead.LeydenJarCondenser.--Whereglassjarsareused.MicaCondenser.--Wheremicaisused.OilCondenser.--Wheretheplatesareimmersedinoil.PaperCondenser.--Wherepaperisusedastheinsulatingmaterial.Protective.--Acondenseroflargecapacityconnectedacrossthelowvoltagesupplycircuitofatransmittertoformaby-pathofkick-backoscillations.VariableCondenser.--Wherealternateplatescanbemovedandsomadetointerleavemoreorlesswithasetoffixedplates.Vernier.--Asmallcondenserwithavernieronitsothatitcanbeveryaccuratelyvaried.Itisconnectedinparallelwiththevariablecondenserusedintheprimarycircuitandisusedforthereceptionofcontinuouswaveswheresharptuningisessential.

CONDENSITE.--Amanufacturedinsulatingcompound.

CONDUCTIVITY.--Theconductanceofagivenlengthofwireofuniformcrosssection.Thereciprocalofresistivity.

CONTACTDETECTORS.--SeeDetectors,Contact.

CONTINENTALCODE.--SeeCode,Continental.

COULOMB.--Thequantityofelectricitytransferredbyacurrentof1amperein1second.

CONVECTIVEDISCHARGE.--SeeDischarge.

CONVENTIONALSIGNALS.--SeeSignals,Conventional.

COUNTERELECTROMOTIVEFORCE.--SeeElectromotiveForce,Counter.

COUNTERPOISE.Aduplicateoftheaerialwirethatisraisedafewfeetabovetheearthandinsulatedfromit.Usuallynoconnectionismadewiththeearthitself.

COUPLEDCIRCUITS.--SeeCircuit,Coupled.

COUPLING.--Whentwooscillationcircuitsareconnectedtogethereitherbythemagneticfieldofaninductancecoil,orbytheelectrostaticfieldofacondenser.

COUPLING,CAPACITIVE.--Oscillationcircuitswhenconnectedtogetherbycondensersinsteadofinductancecoils.

COUPLING,COEFFICIENTOF.--Themeasureoftheclosenessofthecouplingbetweentwocoils.

COUPLING,INDUCTIVE.--Oscillationcircuitswhenconnectedtogetherbyinductancecoils.

COUPLING,RESISTANCE.--Oscillationcircuitsconnectedtogetherbyaresistance.

CRYSTALRECTIFIER.--Acrystaldetector.

CURRENT,ALTERNATING(A.C.).--Alowfrequencycurrentthatsurgestoandfroinacircuit.

CURRENT,AUDIOFREQUENCY.--Acurrentwhosefrequencyislowenoughtobeheardinatelephonereceiver.Suchacurrentusuallyhasafrequencyofbetween200and2,000cyclespersecond.

CURRENT,PLATE.--Thecurrentwhichflowsbetweenthefilamentandtheplateofavacuumtube.

CURRENT,PULSATING.--Adirectcurrentwhosevoltagevariesfrommomenttomoment.

CURRENT,RADIOFREQUENCY.--Acurrentwhosefrequencyissohighitcannotbeheardinatelephonereceiver.Suchacurrentmayhaveafrequencyoffrom20,000to10,000,000persecond.

CURRENTS,HIGHFREQUENCY.--(1)Currentsthatoscillatefrom10,000to300,000,000timespersecond.(2)Electricoscillations.

CURRENTS,HIGHPOTENTIAL.--(1)Currentsthathaveapotentialofmorethan10,000volts.(2)Highvoltagecurrents.

CYCLE.--(1)Aseriesofchangeswhichwhencompletedareagainatthestartingpoint.(2)Aperiodoftimeattheendofwhichanalternatingoroscillatingcurrentrepeatsitsoriginaldirectionofflow.

DAMPING.--Thedegreetowhichtheenergyofanelectricoscillationisreduced.Inanopencircuittheenergyofanoscillationsetupbyasparkgapisdampedoutinafewswings,whileinaclosedcircuititisgreatlyprolonged,thecurrentoscillating20timesormorebeforetheenergyisdissipatedbythesumoftheresistancesofthecircuit.

DECREMENT.--Theactorprocessofgraduallybecomingless.

DETECTOR.--Anydevicethatwill(1)changetheoscillationssetupbytheincomingwavesintodirectcurrent,thatiswhichwillrectifythem,or(2)thatwillactasarelay.

Carborundum.--Onethatusesacarborundumcrystalforthesensitiveelement.Carborundumisacrystallinesiliconcarbideformedintheelectricfurnace.CatWhiskerContact.--SeeCatWhiskerContact.Chalcopyrite.--Copperpyrites.Abrasscoloredmineralusedasacrystalfordetectors.SeeZincite.Contact.--Acrystaldetector.Anykindofadetectorinwhichtwodissimilarbutsuitablesolidsmakecontact.Ferron.--Adetectorinwhichironpyritesareusedasthesensitiveelement.Galena.--Adetectorthatusesagalenacrystalfortherectifyingelement.IronPyrites.--Adetectorthatusesacrystalofironpyritesforitssensitiveelement.Molybdenite.--Adetectorthatusesacrystalofsulphideofmolybdenumforthesensitiveelement.Perikon.--Adetectorinwhichabornitecrystalmakescontactwithazincitecrystal.Silicon.--Adetectorthatusesacrystalofsiliconforitssensitiveelement.

VacuumTube.--Avacuumtube(whichsee)usedasadetector.Zincite.--Adetectorinwhichacrystalofzinciteisusedasthesensitiveelement.

DETUNING.--Amethodofsignalingbysustainedoscillationsinwhichthekeywhenpresseddowncutsouteithersomeoftheinductanceorsomeofthecapacityandhencegreatlychangesthewavelength.

DIELECTRIC.--Aninsulatingmaterialbetweentwoelectricallychargedplatesinwhichthereissetupanelectricstrain,ordisplacement.

DIELECTRICSTRAIN.--Theelectricdisplacementinadielectric.

DIRECTIONALAERIAL.--SeeAerial,Directional.

DIRECTIONFINDER.--SeeAerial,Loop.

DISCHARGE.--(1)Afaintlyluminousdischargethattakesplacefromthepositivepointedterminalofaninductioncoil,orotherhighpotentialapparatus;istermedabrushdischarge.(2)Acontinuousdischargebetweentheterminalsofahighpotentialapparatusistermedaconvectivedischarge.(3)Thesuddenbreaking-downoftheairbetweentheballsformingthesparkgapistermedadisruptivedischarge;alsocalledanelectricspark,orjustsparkforshort.(4)Whenatubehasapoorvacuum,ortoolargeabatteryvoltage,itglowswithabluelightandthisiscalledablueglowdischarge.

DISRUPTIVEDISCHARGE.--SeeDischarge.

DISTRESSCALL.[Morsecode:]...---...(SOS).

DISTRIBUTEDCAPACITY.--SeeCapacity,Distributed.

DOUBLEHUMPRESONANCECURVE.--Aresonancecurvethathastwopeaksorhumpswhichshowthattheoscillatingcurrentswhicharesetupwhentheprimaryandsecondaryofatuningcoilarecloselycoupledhavetwofrequencies.

DUO-LATERALCOILS.--SeeCoils,Inductance.

DUPLEXCOMMUNICATION.--Awirelesstelephonesystemwithwhichitispossibletotalkbetweenbothstationsineitherdirectionwithouttheuseofswitches.Thisisknownastheduplexsystem.

EARTHCAPACITY.--Anaerialcounterpoise.

EARTHCONNECTION.--Metalplatesorwiresburiedinthegroundorimmersedinwater.Anykindofmeansbywhichthesendingandreceivingapparatuscanbeconnectedwiththeearth.

EDISONSTORAGEBATTERY.--SeeStorageBattery,Edison.

ELECTRICENERGY.--Thepowerofanelectriccurrent.

ELECTRICOSCILLATIONS.--SeeOscillations,Electric.

ELECTRICSPARK.--SeeDischarge,Spark.

ELECTRICITY,NEGATIVE.--Theoppositeofpositiveelectricity.Negativeelectricityisformedofnegativeelectronswhichmakeuptheoutsideparticlesofanatom.

ELECTRICITY,POSITIVE.--Theoppositeofnegativeelectricity.Positiveelectricityisformedofpositiveelectronswhichmakeuptheinsideparticlesofanatom.

ELECTRODES.--Usuallythepartsofanapparatuswhichdipintoaliquidandcarryacurrent.Theelectrodesofadrybatteryarethezincandcarbonelements.TheelectrodesofanEdisonstoragebatteryaretheironandnickelelements,andtheelectrodesofaleadstoragebatteryaretheleadelements.

ELECTROLYTES.--Theacidoralkalinesolutionsusedinbatteries.

ELECTROMAGNETICWAVES.--SeeWaves,Electric.

ELECTROMOTIVEFORCE.--Abbreviatedemf.Theforcethatdrivesanelectriccurrentalongaconductor.Alsolooselycalledvoltage.

ELECTROMOTIVEFORCE,COUNTER.--Theemf.thatissetupinadirectionoppositetothatinwhichthecurrentisflowinginaconductor.

ELECTRON.--(1)Anegativeparticleofelectricitythatisdetachedfromanatom.(2)Anegativeparticleofelectricitythrownofffromtheincandescentfilamentofavacuumtube.

ELECTRONFLOW.--Thepassageofelectronsbetweentheincandescentfilamentandthecoldpositivelychargedplateofavacuumtube.

ELECTRONRELAY.--SeeRelay,Electron.

ELECTRONTUBE.--Avacuumtubeoragas-contenttubeusedforanypurposeinwirelesswork.SeeVacuumTube.

ELECTROSEINSULATORS.--InsulatorsmadeofacompositionmaterialthetradenameofwhichisElectrose.

ENERGY,ELECTRIC.--SeeElectricEnergy.

ENERGYUNIT.--Thejoule,whichsee,Page308[Appendix:DefinitionsofElectricandMagneticUnits].

FADING.--Thesuddenvariationinstrengthofsignalsreceivedfromatransmittingstationwhenalltheadjustmentsofbothsendingandreceivingapparatusremainthesame.Alsocalledswinging.

FARAD.--Thecapacitanceofacondenserinwhichapotentialdifferenceof1voltcausesittohaveachargeof1coulombofelectricity.

FEED-BACKACTION.--Feedingbacktheoscillatingcurrentsinavacuumtubetoamplifyitspower.

Alsocalledregenerativeaction.

FERROMAGNETICCONTROL.--SeeMagneticAmplifier.

FILAMENT.--Thewireinavacuumtubethatisheatedtoincandescenceandwhichthrowsoffelectrons.

FILAMENTRHEOSTAT.--SeeRheostat,Filament.

FILTER.--Inductancecoilsorcondensersorbothwhich(1)preventtroublesomevoltagesfromactingonthedifferentcircuits,and(2)smoothoutalternatingcurrentsaftertheyhavebeenrectified.

FILTERREACTOR.--SeeReactor,Filter.

FIREUNDERWRITERS.--SeeCode,NationalElectric.

FIXEDGAP.--SeeGap.

FLEMINGVALVE.--Atwo-electrodevacuumtube.

FORCEDOSCILLATIONS.--SeeOscillations,Forced.

FREEOSCILLATIONS.--SeeOscillations,Free.

FREQUENCY,AUDIO.--(1)Analternatingcurrentwhosefrequencyislowenoughtooperateatelephonereceiverand,hence,whichcanbeheardbytheear.(2)Audiofrequenciesareusuallyaround500or1,000cyclespersecond,butmaybeaslowas200andashighas10,000cyclespersecond.

Carrier.--Aradiofrequencywavemodulatedbyanaudiofrequencywavewhichresultsinsettingofthreeradiofrequencywaves.Theprincipalradiofrequencyiscalledthecarrierfrequency,sinceitcarriesortransmitstheaudiofrequencywave.Commercial.--(1)Alternatingcurrentthatisusedforcommercialpurposes,namely,light,heatandpower.(2)Commercialfrequenciesnowingeneralusearefrom25to50cyclespersecond.Natural.--Thependulumandvibratingspringhaveanaturalfrequencywhichdependsonthesize,materialofwhichitismade,andthefrictionwhichithastoovercome.Likewiseanoscillationcircuithasanaturalfrequencywhichdependsuponitsinductance,capacitanceandresistance.Radio.--(1)Anoscillatingcurrentwhosefrequencyistoohightoaffectatelephonereceiverand,hence,cannotbeheardbytheear.(2)Radiofrequenciesareusuallybetween20,000and2,000,000cyclespersecondbutmaybeaslowas10,000andashighas300,000,000cyclespersecond.Spark.--Thenumberofsparkspersecondproducedbythedischargeofacondenser.

GAP,FIXED.--Onewithfixedelectrodes.

GAP,NON-SYNCHRONOUS.--Arotarysparkgaprunbyaseparatemotorwhichmaybewidelydifferentfromthatofthespeedofthealternator.

GAP,QUENCHED.--(1)Asparkgapfortheimpulseproductionofoscillatingcurrents.(2)Thismethodcanbelikenedtoonewhereaspringisstruckasinglesharpblowandthencontinuestosetupvibrations.

GAP,ROTARY.--Onehavingfixedandrotatingelectrodes.

GAP,SYNCHRONOUS.--Arotarysparkgaprunatthesamespeedasthealternatorwhichsuppliesthepowertransformer.Suchagapusuallyhasasmanyteethastherearepolesonthegenerator.Henceonesparkoccursperhalfcycle.

GAS-CONTENTTUBE.--SeeVacuumTube.

GENERATORTUBE.--Avacuumtubeusedtosetuposcillations.Asamatteroffactitdoesnotgenerateoscillations,butchangestheinitiallowvoltagecurrentthatflowsthroughitintooscillations.Alsocalledanoscillatortubeandapowertube.

GRIDBATTERY.--SeeBatteryC.

GRIDCHARACTERISTICS.--Thevariousrelationsthatcouldexistbetweenthevoltagesandcurrentsofthegridofavacuumtube,andthevalueswhichdoexistbetweenthemwhenthetubeisinoperation.Thesecharacteristicsaregenerallyshownbycurves.

GRIDCONDENSER.--SeeCondenser,Grid.

GRIDLEAK.--Ahighresistanceunitconnectedinthegridleadofbothsendingandreceivingsets.Inasendingsetitkeepsthevoltageofthegridataconstantvalueandsocontrolstheoutputoftheaerial.Inareceivingsetitcontrolsthecurrentflowingbetweentheplateandfilament.

GRIDMODULATION.--SeeModulation,Grid.

GRIDPOTENTIAL.--Thenegativeorpositivevoltageofthegridofavacuumtube.

GRIDVOLTAGE.--SeeGridPotential.

GRINDERS.--ThemostcommonformofStatic,whichsee.Theymakeagrindingnoiseintheheadphones.

GROUND.--SeeEarthConnection.

GROUND,AMATEUR.--Awater-pipeground.

GROUND,WATERPIPE.--Acommonmethodofgroundingbyamateursistousethewaterpipe,gaspipeorradiator.

GUIDEDWAVETELEPHONY.--SeeWiredWireless.

HARDTUBE.--Avacuumtubeinwhichthevacuumishigh,thatis,exhaustedtoahighdegree.

HELIX.--(1)Anycoilofwire.(2)Specificallyatransmittertuninginductancecoil.

HENRY.--Theinductanceinacircuitinwhichtheelectromotiveforceinducedis1voltwhentheinducingcurrentvariesattherateof1amperepersecond.

HETERODYNERECEPTION.--(1)Receivingbythebeatmethod.(2)Receivingbymeansofsuperposingoscillationsgeneratedatthereceivingstationontheoscillationssetupintheaerialbytheincomingwaves.

HETERODYNERECEPTOR.--SeeReceptor,Heterodyne.

HIGHFREQUENCYCURRENTS.--SeeCurrents,HighFrequency.

HIGHFREQUENCYRESISTANCE.--SeeResistance,HighFrequency.

HIGHPOTENTIALCURRENTS.--SeeCurrents,HighPotential.

HIGHVOLTAGECURRENTS.--SeeCurrents,HighPotential.

HONEYCOMBCOILS.--SeeCoils,Inductance.

HORSE-POWER.--Usedinratingsteammachinery.Itisequalto746watts.

HOTWIREAMMETER.--SeeAmmeter,HotWire.

HOWLING.--Wheremorethanthreestagesofradioamplification,ormorethantwostagesofaudioamplification,areusedhowlingnoisesareapttooccurinthetelephonereceivers.

IMPEDANCE.--Anoscillationcircuithasreactanceandalsoresistance,andwhenthesearecombinedthetotaloppositiontothecurrentiscalledimpedance.

INDUCTANCECOILS.--SeeCoils,Inductance.

INDUCTANCECOIL,LOADING.--SeeCoil,LoadingInductance.

INDUCTIVECOUPLING.--SeeCoupling,Inductive.

INDUCTIVEREACTANCE.--SeeReactance,Inductive.

INDUCTIONCOIL.--SeeCoil,Induction.

INDUCTION,MUTUAL.--Inductionproducedbetweentwocircuitsorcoilsclosetoeachotherbythemutualinteractionoftheirmagneticfields.

INSULATION.--Materialsusedonandaroundwiresandotherconductorstokeepthecurrentfromleakingaway.

INSPECTOR,RADIO.--AU.S.inspectorwhosebusinessitistoissuebothstationandoperators'licensesinthedistrictofwhichheisincharge.

INTERFERENCE.--Thecrossingorsuperposingoftwosetsofelectricwavesofthesameorslightly

differentlengthswhichtendtoopposeeachother.Itistheuntowardinterferencebetweenelectricwavesfromdifferentstationsthatmakesselectivesignalingsodifficultaproblem.

INTERMEDIATEWAVES.--SeeWaves.

IONICTUBES.--SeeVacuumTubes.

INTERNATIONALCODE.--SeeCode,International.

JAMMING.--Wavesthatareofsuchlengthandstrengththatwhentheyinterferewithincomingwavestheydrownthemout.

JOULE.--Theenergyspentin1secondbyaflowof1amperein1ohm.

JOULE'SLAW.--Therelationbetweentheheatproducedinsecondstotheresistanceofthecircuit,tothecurrentflowinginit.

KENOTRON.--ThetradenameofavacuumtuberectifiermadebytheRadioCorporationofAmerica.

KICK-BACK.--Oscillatingcurrentsthatriseinvoltageandtendtoflowbackthroughthecircuitthatissupplyingthetransmitterwithlowvoltagecurrent.

KICK-BACKPREVENTION.--SeePrevention,Kick-Back.

KILOWATT.--1,000watts.

LAMBDA.--SeePages301,302.[Appendix:UsefulAbbreviations].

LATTICEWOUNDCOILS.--SeeCoils,Inductance.

LIGHTNINGSWITCH.--SeeSwitch,Lightning.

LINERADIOCOMMUNICATION.--SeeWiredWireless.

LINERADIOTELEPHONY.--SeeTelephony,LineRadio.

LITZENDRAHT.--Aconductorformedofanumberoffinecopperwireseithertwistedorbraidedtogether.Itisusedtoreducetheskineffect.SeeResistance,HighFrequency.

LOADFLICKER.--Theflickeringofelectriclightsonlinesthatsupplywirelesstransmittingsetsduetovariationsofthevoltageonopeningandclosingthekey.

LOADINGCOIL.--SeeCoil,Loading.

LONGWAVES.--SeeWaves.

LOOPAERIAL.--SeeAerial,Loop.

LOOSECOUPLEDCIRCUITS.--SeeCircuits,LooseCoupled.

LOUDSPEAKER.--Atelephonereceiverconnectedtoahorn,oraspeciallymadeone,thatreproducestheincomingsignals,wordsormusicloudenoughtobeheardbyaroomoranauditoriumfullofpeople,orbylargecrowdsout-doors.

MAGNETICPOLES.--SeePoles,Magnetic.

MEGOHM.--Onemillionohms.

METER,AUDIBILITY.--Aninstrumentformeasuringtheloudnessofasignalbycomparisonwithanothersignal.Itconsistsofapairofheadphonesandavariableresistancewhichhavebeencalibrated.

MHO.--Theunitofconductance.Asconductanceisthereciprocalofresistanceitismeasuredbythereciprocalohmormho.

MICA.--Atransparentmineralhavingahighinsulatingvalueandwhichcanbesplitintoverythinsheets.Itislargelyusedinmakingcondensersbothfortransmittingandreceivingsets.

MICROFARAD.--Themillionthpartofafarad.

MICROHENRY.--Themillionthpartofafarad.

MICROMICROFARAD.--Themillionthpartofamicrofarad.

MICROHM.--Themillionthpartofanohm.

MICROPHONETRANSFORMER.--SeeTransformer,Microphone.

MICROPHONETRANSMITTER.--SeeTransmitter,Microphone.

MILLI-AMMETER.--Anammeterthatmeasuresacurrentbytheone-thousandthofanampere.

MODULATION.--(1)Inflectionorvaryingthevoice.(2)Varyingtheamplitudeofoscillationsbymeansofthevoice.

MODULATION,BUZZER.--Themodulationofradiofrequencyoscillationsbyabuzzerwhichbreaksupthesustainedoscillationsofatransmitterintoaudiofrequencyimpulses.

MILLIHENRY.--Thethousandthpartofahenry.

MODULATION,CHOPPER.--Themodulationofradiofrequencyoscillationsbyachopperwhichbreaksupthesustainedoscillationsofatransmitterintoaudiofrequencyimpulses.

MODULATION,GRID.--Theschemeofmodulatinganoscillatortubebyconnectingthesecondaryofatransformer,theprimaryofwhichisconnectedwithabatteryandamicrophonetransmitter,inthegridlead.

MODULATION,OVER.--SeeBlubBlub.

MODULATION,PLATE.--Modulatingtheoscillationssetupbyavacuumtubebyvaryingthecurrentimpressedontheplate.

MODULATORTUBE.--Avacuumtubeusedasamodulator.

MOTION,WAVE.--(1)Thetoandfromotionofwateratsea.(2)Wavestransmittedby,inandthroughtheair,orsoundwaves.(3)Wavestransmittedby,inandthroughtheether,orelectromagneticwaves,orelectricwavesforshort.

MOTOR-GENERATOR.--Amotorandadynamobuilttorunatthesamespeedandmountedonacommonbase,theshaftsbeingcoupledtogether.Inwirelessitisusedforchangingcommercialdirectcurrentintodirectcurrentofhighervoltagesforenergizingtheplateofavacuumtubeoscillator.

MULTI-STAGEAMPLIFIERS.--SeeAmplifiers,Multi-Stage.

MUTUALINDUCTION.--SeeInduction,Mutual.

MUSH.--Irregularintermediatefrequenciessetupbyarctransmitterswhichinterferewiththefundamentalwavelengths.

MUSHYNOTE.--Anotethatisnotclearcut,andhencehardtoread,whichisreceivedbytheheterodynemethodwhendampedwavesormodulatedcontinuouswavesarebeingreceived.

NATIONALELECTRICCODE.--SeeCode,NationalElectric.

NATIONALELECTRICSAFETYCODE.--SeeCode,NationalElectricSafety.

NEGATIVEELECTRICITY.--SeeElectricity,Negative.

NON-SYNCHRONOUSGAP.--SeeGap,Non-Synchronous.

OHM.--Theresistanceofathreadofmercuryatthetemperatureofmeltingice,14.4521gramsinmass,ofuniformcross-sectionandalengthof106.300centimeters.

OHM'SLAW.--Theimportantfixedrelationbetweentheelectriccurrent,itselectromotiveforceandtheresistanceoftheconductorinwhichitflows.

OPENCIRCUIT.--SeeCircuit,Open.

OPENCORETRANSFORMER.--SeeTransformer,OpenCore.

OSCILLATIONTRANSFORMER.--SeeTransformer,Oscillation.

OSCILLATIONS,ELECTRIC.--Acurrentofhighfrequencythatsurgesthroughanopenoraclosedcircuit.(1)Electricoscillationsmaybesetupbyasparkgap,electricarcoravacuumtube,whentheyhavenotonlyahighfrequencybutahighpotential,orvoltage.(2)Whenelectricwavesimpingeonanaerialwiretheyaretransformedintoelectricoscillationsofafrequencyequaltothosewhichemittedthewaves,butsinceaverysmallamountofenergyisreceivedtheirpotentialorvoltageislikewiseverysmall.

Sustained.--Oscillationsinwhichthedampingfactorissmall.Damped.--Oscillationsinwhichthedampingfactorislarge.Free.--Whenacondenserdischargesthroughanoscillationcircuit,wherethereisnooutsideelectromotiveforceactingonit,theoscillationsaresaidtobefree.Forced.--Oscillationsthataremadetosurgeinacircuitwhosenaturalperiodisdifferentfromthatoftheoscillationssetupinit.

OSCILLATIONTRANSFORMER.--SeeTransformer.

OSCILLATIONVALVE.--SeeVacuumTube.

OSCILLATORTUBE.--Avacuumtubewhichisusedtoproduceelectricoscillations.

OVERMODULATION.--SeeBlubBlub.

PANCAKEOSCILLATIONTRANSFORMER.--Disk-shapedcoilsthatareusedforreceivingtuninginductances.

PERMEABILITY,MAGNETIC.--Thedegreetowhichasubstancecanbemagnetized.Ironhasagreatermagneticpermeabilitythanair.

PHASE.--Acharacteristicaspectorappearancethattakesplaceatthesamepointorpartofacycle.

PICK-UPCIRCUITS.--SeeCircuits,Stand-by.

PLATECIRCUITREACTOR.--SeeReactor,PlateCircuit.

PLATECURRENT.--SeeCurrent,Plate.

PLATEMODULATION.--SeeModulation,Plate.

PLATEVOLTAGE.--SeeFoliage,Plate.

POLES,BATTERY.--Thepositiveandnegativeterminalsoftheelementsofabattery.Onastoragebatterythesepolesaremarked+and-respectively.

POLES,MAGNETIC.--Theendsofamagnet.

POSITIVEELECTRICITY.--SeeElectricity,Positive.

POTENTIALDIFFERENCE.--Theelectricpressurebetweentwochargedconductorsorsurfaces.

POTENTIOMETER.--Avariableresistanceusedforsubdividingthevoltageofacurrent.Avoltagedivider.

POWERTRANSFORMER.--SeeTransformer,Power.

POWERTUBE.--SeeGeneratorTube.

PRIMARYBATTERY.--SeeBattery,Primary.

PREVENTION,KICK-BACK.--Achokecoilplacedinthepowercircuittopreventthehighfrequencycurrentsfromgettingintothetransformerandbreakingdowntheinsulation.

QST.--Anabbreviationusedinwirelesscommunicationfor(1)thequestion"Haveyoureceivedthegeneralcall?"and(2)thenotice,"Generalcalltoallstations."

QUENCHEDGAP.--SeeGap,Quenched.

RADIATION.--Theemission,orthrowingoff,ofelectricwavesbyanaerialwiresystem.

RADIOAMMETER.--SeeAmmeter,HotWire.

RADIOFREQUENCY.--SeeFrequency,Radio.

RADIOFREQUENCYAMPLIFICATION.--SeeAmplification,RadioFrequency.

RADIOFREQUENCYCURRENT.--SeeCurrent,RadioFrequency.

RADIOINSPECTOR.--SeeInspector,Radio.

RADIOTRON.--Thetradenameofvacuumtubedetectors,amplifiers,oscillatorsandmodulatorsmadebytheRadioCorporationofAmerica.

RADIOWAVES.--SeeWaves,Radio.

REACTANCE.--Whenacircuithasinductanceandthecurrentchangesinvalue,itisopposedbythevoltageinducedbythevariationofthecurrent.

REACTANCE,CAPACITY.--Thecapacityreactanceistheoppositionofferedtoacurrentbyacapacity.Itismeasuredasaresistance,thatis,inohms.

RECEIVINGTUNINGCOILS.--SeeCoils,Inductance.

RECEIVER,LOUDSPEAKING.--SeeLoudSpeakers.

RECEIVER,WATCHCASE.--Acompacttelephonereceiverusedforwirelessreception.

REACTANCE,INDUCTIVE.--Theinductivereactanceistheoppositionofferedtothecurrentbyaninductancecoil.Itismeasuredasaresistance,thatis,inohms.

REACTOR,FILTER.--Areactancecoilforsmoothingoutthepulsatingdirectcurrentsastheycomefromtherectifier.

REACTOR,PLATECIRCUIT.--Areactancecoilusedintheplatecircuitofawirelesstelephonetokeepthedirectcurrentsupplyataconstantvoltage.

RECEIVER.--(1)Atelephonereceiver.(2)Anapparatusforreceivingsignals,speechormusic.(3)

Bettercalledareceptortodistinguishitfromatelephonereceiver.

RECTIFIER.--(1)Anapparatusforchangingalternatingcurrentintopulsatingdirectcurrent.(2)Specificallyinwireless(a)acrystalorvacuumtubedetector,and(b)atwo-electrodevacuumtubeusedforchangingcommercialalternatingcurrentintodirectcurrentforwirelesstelephony.

REGENERATIVEAMPLIFICATION.--SeeAmplification,Regenerative.

RECEPTOR.--Areceivingset.

RECEPTOR,AUTODYNE.--Areceptorthathasaregenerativecircuitandthesametubeisusedasadetectorandasageneratoroflocaloscillations.

RECEPTOR,BEAT.--Aheterodynereceptor.

RECEPTOR,HETERODYNE.--Areceivingsetthatusesaseparatevacuumtubetosetupthesecondseriesofwavesforbeatreception.

REGENERATIVEACTION.--SeeFeed-BackAction.

REGENERATIVEAMPLIFICATION.--SeeAmplification,Regenerative.

RELAY,ELECTRON.--Avacuumtubewhenusedasadetectororanamplifier.

REPEATINGCOIL.--Atransformerusedinconnectingupawirelessreceiverwithawiretransmitter.

RESISTANCE.--Theoppositionofferedbyawireorotherconductortothepassageofacurrent.

RESISTANCE,AERIAL.--Theresistanceoftheaerialwiretooscillatingcurrents.Thisisgreaterthanitsordinaryohmicresistanceduetotheskineffect.SeeResistance,HighFrequency.

RESISTANCEBOX.--SeeResistor.

RESISTANCECOUPLING.--SeeCoupling,Resistance.

RESISTANCE,HIGHFREQUENCY.--Whenahighfrequencycurrentoscillatesonawiretwothingstakeplacethataredifferentthanwhenadirectoralternatingcurrentflowsthroughit,andtheseare(1)thecurrentinsideofthewirelagsbehindthatofthecurrentonthesurface,and(2)theamplitudeofthecurrentislargestonthesurfaceandgrowssmallerasthecenterofthewireisreached.Thisunevendistributionofthecurrentisknownastheskineffectanditamountstothesamethingasreducingthesizeofthewire,hencetheresistanceisincreased.

RESISTIVITY.--Theresistanceofagivenlengthofwireofuniformcrosssection.Thereciprocalofconductivity.

RESISTOR.--Afixedorvariableresistanceunitoragroupofsuchunits.Variableresistorsarealsocalledresistanceboxesandmoreoftenrheostats.

RESONANCE.--(1)Simpleresonanceofsoundisitsincreasesetupbyonebodybythesympathetic

vibrationofasecondbody.(2)Byextensiontheincreaseintheamplitudeofelectricoscillationswhenthecircuitinwhichtheysurgehasanaturalperiodthatisthesame,ornearlythesame,astheperiodofthefirstoscillationcircuit.

RHEOSTAT.--Avariableresistanceunit.SeeResistor.

RHEOSTAT,CARBON.--Acarbonrod,orcarbonplatesorblocks,whenusedasvariableresistances.

RHEOSTAT,FILAMENT.--Avariableresistanceusedforkeepingthecurrentofthestoragebatterywhichheatsthefilamentofavacuumtubeataconstantvoltage.

ROTATINGCOIL.--SeeCoil.

ROTARYGAP.--SeeGap.

ROTOR.--Therotatingcoilofavariometeroravariocoupler.

RUHMKORFFCOIL.--SeeCoil,Induction.

SATURATION.--Themaximumplatecurrentthatavacuumtubewilltake.

SENSITIVESPOTS.--Spotsondetectorcrystalsthataresensitivetotheactionofelectricoscillations.

SHORTWAVES.--SeeWaves.

SIDEWAVES.--SeeWaveLengthBand.

SIGNALS,CONVENTIONAL.--(1)TheInternationalMorsealphabetandnumeralcode,punctuationmarks,andafewimportantabbreviationsusedinwirelesstelegraphy.(2)Dotanddashsignalsfordistresscall,invitationtotransmit,etc.Nowusedforallgeneralpublicservicewirelesscommunication.

SKINEFFECT.--SeeResistance,HighFrequency.

SOFTTUBE.--Avacuumtubeinwhichthevacuumislow,thatis,itisnothighlyexhausted.

SPACECHARGEEFFECT.--Theelectricfieldintensityduetothepressureofthenegativeelectronsinthespacebetweenthefilamentandplatewhichatlastequalsandneutralizesthatduetothepositivepotentialoftheplatesothatthereisnoforceactingontheelectronsnearthefilament.

SPARK.--SeeDischarge.

SPARKCOIL.--SeeCoil,Induction.

SPARKDISCHARGE.--SeeSpark,Electric.

SPARKFREQUENCY.--SeeFrequency,Spark.

SPARKGAP.--(1)Asparkgap,withoutthehyphen,meanstheapparatusinwhichsparkstakeplace;it

isalsocalledasparkdischarger.(2)Spark-gap,withthehyphen,meanstheair-gapbetweentheopposedfacesoftheelectrodesinwhichsparksareproduced.

Plain.--Asparkgapwithfixedelectrodes.Rotary.--Asparkgapwithapairoffixedelectrodesandanumberofelectrodesmountedonarotatingelement.Quenched.--Asparkgapformedofanumberofmetalplatesplacedcloselytogetherandinsulatedfromeachother.

SPIDERWEBINDUCTANCECOIL.--SeeCoil,SpiderWebInductance.

SPREADER.--Astickofwood,orspar,thatholdsthewiresoftheaerialapart.

STAGGERWOUNDCOILS.--SeeCoils,Inductance.

STAND-BYCIRCUITS.--SeeCircuits,Stand-By.

STATIC.--Alsocalledatmospherics,grinders,strays,X's,and,whenbadenough,byothernames.Itisanelectricaldisturbanceintheatmospherewhichmakesnoisesinthetelephonereceiver.

STATOR.--Thefixedorstationarycoilofavariometeroravariocoupler.

STORAGEBATTERY.--SeeBattery,Storage.

STRAYELIMINATION.--Amethodforincreasingthestrengthofthesignalsasagainstthestrengthofthestrays.SeeStatic.

STRAYS.--SeeStatic.

STRANDEDWIRE.--SeeWire,Stranded.

SUPER-HETERODYNERECEPTOR.--SeeHeterodyne,Super.

SWINGING.--SeeFading.

SWITCH,AERIAL.--Aswitchusedtochangeoverfromthesendingtothereceivingset,andtheotherwayabout,andconnectthemwiththeaerial.

SWITCH,LIGHTNING.--Theswitchthatconnectstheaerialwiththeoutsidegroundwhentheapparatusisnotinuse.

SYMBOLS,APPARATUS.--Alsocalledconventionalsymbols.Thesearediagrammaticlinesrepresentingvariouspartsofapparatussothatwhenawiringdiagramofatransmitterorareceptoristobemadeitisonlynecessarytoconnectthemtogether.Theyareeasytomakeandeasytoread.SeePage307[Appendix:SymbolsUsedforApparatus].

SYNCHRONOUSGAP.--SeeGap,Synchronous.

TELEPHONY,LINERADIO.--SeeWiredWireless.

THERMALAMMETER.--SeeAmmeter,HotWire.

THREEELECTRODEVACUUMTUBE.--SeeVacuumTube,ThreeElectrode.

TIKKER.--Aslippingcontactdevicethatbreaksupthesustainedoscillationsatthereceivingendintogroupssothatthesignalscanbeheardintheheadphones.Thedeviceusuallyconsistsofafinesteelorgoldwireslippinginthesmoothgrooveofarotatingbrasswheel.

TRANSFORMER.--Aprimaryandasecondarycoilforsteppingupordownaprimaryalternatingoroscillatingcurrent.

A.C.--SeePowerTransformer.AirCooled.--Atransformerinwhichthecoilsareexposedtotheair.AirCore.--Withhighfrequencycurrentsitisthegeneralpracticenottouseironcoresasthesetendtochokeofftheoscillations.Hencethecoreconsistsoftheairinsideofthecoils.Auto.--Asinglecoilofwireinwhichonepartformstheprimaryandtheotherpartthesecondarybybringingoutanintermediatetap.AudioAmplifying.--Thisisatransformerwithanironcoreandisusedforfrequenciesuptosay3,000.ClosedCore.--Atransformerinwhichthepathofthemagneticfluxisentirelythroughiron.Powertransformershaveclosedcores.Microphone.--Asmalltransformerformodulatingtheoscillationssetupbyanarcoravacuumtubeoscillator.OilCooled.--Atransformerinwhichthecoilsareimmersedinoil.OpenCore.--Atransformerinwhichthepathofthemagneticfluxispartlythroughironandpartlythroughair.Inductioncoilshaveopencores.Oscillation.--Acoilorcoilsfortransformingorsteppingdownoruposcillatingcurrents.Oscillationtransformersusuallyhavenoironcoreswhentheyarealsocalledaircoretransformers.Power.--Atransformerforsteppingdownacommercialalternatingcurrentforlightingandheatingthefilamentandforsteppingupthecommerciala.c.,forchargingtheplateofavacuumtubeoscillator.RadioAmplifying.--Thisisatransformerwithanaircore.Itdoesnotinitselfamplifybutissocalledbecauseitisusedinconnectionwithanamplifyingtube.

TRANSMITTER,MICROPHONE.--AtelephonetransmitterofthekindthatisusedintheBelltelephonesystem.

TRANSMITTINGTUNINGCOILS.--SeeCoils,Inductance.

TUNING.--Whentheopenandclosedoscillationcircuitsofatransmitterorareceptorareadjustedsothatbothoftheformerwillpermitelectricoscillationstosurgethroughthemwiththesamefrequency,theyaresaidtobetuned.Likewise,whenthesendingandreceivingstationsareadjustedtothesamewavelengththeyaresaidtobetuned.

CoarseTuning.--Thefirstadjustmentinthetuningoscillationcircuitsofareceptorismadewiththeinductancecoilandthistunesthemcoarse,orroughly.FineTuning.--Aftertheoscillationcircuitshavebeenroughlytunedwiththeinductancecoilthe

exactadjustmentisobtainedwiththevariablecondenserandthisisfinetuning.Sharp.--Whenasendingsetwilltransmitorareceivingsetwillreceiveawaveofgivenlengthonlyitissaidtobesharplytuned.Thesmallerthedecrementthesharperthetuning.

TUNINGCOILS.--SeeCoils,Inductance.

TWOELECTRODEVACUUMTUBE.--SeeVacuumTube,TwoElectrode.

VACUUMTUBE.--Atubewithtwoorthreeelectrodesfromwhichtheairhasbeenexhausted,orwhichisfilledwithaninertgas,andusedasadetector,anamplifier,anoscillatororamodulatorinwirelesstelegraphyandtelephony.

Amplifier.--SeeAmplifier,VacuumTube.AmplifyingModulator.--Avacuumtubeusedformodulatingandamplifyingtheoscillationssetupbythesendingset.GasContent.--Atubemadelikeavacuumtubeandusedasadetectorbutwhichcontainsaninertgasinsteadofbeingexhausted.Hard.--SeeHardTube.Rectifier.--(1)Avacuumtubedetector.(2)atwo-electrodevacuumtubeusedforchangingcommercialalternatingcurrentintodirectcurrentforwirelesstelephony.Soft.--SeeSoftTube.ThreeElectrode.--Avacuumtubewiththreeelectrodes,namelyafilament,agridandaplate.TwoElectrode.--Avacuumtubewithtwoelectrodes,namelythefilamentandtheplate.

VALVE.--SeeVacuumTube.

VALVE,FLEMING.--SeeFlemingValve.

VARIABLECONDENSER.--SeeCondenser,Variable.

VARIABLEINDUCTANCE.--SeeInductance,Variable.

VARIABLERESISTANCE.--SeeResistance,Variable.

VARIOCOUPLER.--Atuningdeviceforvaryingtheinductanceofthereceivingoscillationcircuits.Itconsistsofafixedandarotatablecoilwhosewindingsarenotconnectedwitheachother.

VARIOMETER.--Atuningdeviceforvaryingtheinductanceofthereceivingoscillationcurrents.Itconsistsofafixedandarotatablecoilwiththecoilsconnectedinseries.

VERNIERCONDENSER.--SeeCondenser,Vernier.

VOLT.--Theelectromotiveforcewhichproducesacurrentof1amperewhensteadilyappliedtoaconductortheresistanceofwhichisoneohm.

VOLTAGEDIVIDER.--SeePotentiometer.

VOLTAGE,PLATE.--Thevoltageofthecurrentthatisusedtoenergizetheplateofavacuumtube.

VOLTMETER.--Aninstrumentformeasuringthevoltageofanelectriccurrent.

WATCHCASERECEIVER.--SeeReceiver,WatchCase.

WATER-PIPEGROUND.--SeeGround,Water-Pipe.

WATT.--Thepowerspentbyacurrentof1ampereinaresistanceof1ohm.

WAVE,BROAD.--Awavehavingahighdecrement,whenthestrengthofthesignalsisnearlythesameoverawiderangeofwavelengths.

WAVELENGTH.--Everywaveofwhateverkindhasalength.Thewavelengthisusuallytakentomeanthedistancebetweenthecrestsoftwosuccessivewaves.

WAVELENGTHBAND.--Inwirelessreceptionwhencontinuouswavesarebeingsentoutandthesearemodulatedbyamicrophonetransmitterthedifferentaudiofrequenciessetupcorrespondingradiofrequenciesandtheenergyoftheseareemittedbytheaerial;thisresultsinwavesofdifferentlengths,orabandofwavesasitiscalled.

WAVEMETER.--Anapparatusformeasuringthelengthsofelectricwavessetupintheoscillationcircuitsofsendingandreceivingsets.

WAVEMOTION.--Disturbancessetupinthesurroundingmediumaswaterwavesinandonthewater,soundwavesintheairandelectricwavesintheether.

WAVES.--SeeWaveMotion.

WAVES,ELECTRIC.--Electromagneticwavessetupinandtransmittedbyandthroughtheether.

Continuous.AbbreviatedC.W.--Wavesthatareemittedwithoutabreakfromtheaerial.Alsocalledundampedwaves.Discontinuous.--Wavesthatareemittedperiodicallyfromtheaerial.Alsocalleddampedwaves.Damped.--SeeDiscontinuousWaves.Intermediate.--Wavesfrom600to2,000metersinlength.Long.--Wavesover2,000metersinlength.Radio.--Electricwavesusedinwirelesstelegraphyandtelephony.Short.--Wavesupto600metersinlength.Wireless.--Electricwavesusedinwirelesstelegraphyandtelephony.Undamped.--SeeContinuousWaves.

WIRELESSTELEGRAPHCODE.--SeeCode,International.

WIRE,ENAMELLED.--Wirethatisgivenathincoatofenamelwhichinsulatesit.

WIRE,PHOSPHORBRONZE.--Averystrongwiremadeofanalloyofcopperandcontainingatraceofphosphorus.

WIREDWIRELESS.--Continuouswavesofhighfrequencythataresentovertelephonewiresinsteadofthroughspace.Alsocalledlineradiocommunication;carrierfrequencytelephony,carriercurrent

telephony;guidedwavetelephonyandwiredwireless.

X'S.--SeeStatic.

ZINCITE.--SeeDetector.

WIRELESSDON'TS

AERIALWIREDON'TS

Don'tuseironwireforyouraerial.

Don'tfailtoinsulateitwellatbothends.

Don'thaveitlongerthan75feetforsendingouta200-meterwave.

Don'tfailtousealightningarrester,orbetter,alightningswitch,foryourreceivingset.

Don'tfailtousealightningswitchwithyourtransmittingset.

Don'tforgetyoumusthaveanoutsideground.

Don'tfailtohavetheresistanceofyouraerialassmallaspossible.Usestrandedwire.

Don'tfailtosoldertheleading-inwiretotheaerial.

Don'tfailtoproperlyinsulatetheleading-inwirewhereitgoesthroughthewindoworwall.

Don'tletyouraerialorleading-inwiretouchtreesorotherobjects.

Don'tletyouraerialcometooclosetooverheadwiresofanykind.

Don'trunyouraerialdirectlyunder,orover,orparallelwithelectriclightorotherwires.

Don'tfailtomakeagoodgroundconnectionwiththewaterpipeinside.

TRANSMITTINGDON'TS

Don'tattempttosenduntilyougetyourlicense.

Don'tfailtoliveuptoeveryruleandregulation.

Don'tuseaninputofmorethan1/2akilowattifyoulivewithin5nauticalmilesofanavalstation.

Don'tsendonmorethana200-meterwaveifyouhavearestrictedorgeneralamateurlicense.

Don'tusesparkgapelectrodesthataretoosmallortheywillgethot.

Don'tusetoolongortooshortasparkgap.Therightlengthcanbefoundbytryingitout.

Don'tfailtouseasafetysparkgapbetweenthegridandthefilamentterminalswheretheplatepotentialisabove2,000volts.

Don'tbuyamotor-generatorsetifyouhavecommercialalternatingcurrentinyourhome.

Don'toverloadanoscillationvacuumtubeasitwillgreatlyshortenitslife.Usetwoinparallel.

Don'toperateatransmittingsetwithoutahot-wireammeterintheaerial.

Don'tusesolidwireforconnectingupthepartsoftransmitters.Usestrandedorbraidedwire.

Don'tfailtosoldereachconnection.

Don'tusesolderingfluid,userosin.

Don'tthinkthatalloftheenergyofanoscillationtubecannotbeusedforwavelengthsof200metersandunder.Itcanbeifthetransmittingsetandaerialareproperlydesigned.

Don'trunthewiresofoscillationcircuitstooclosetogether.

Don'tcrossthewiresofoscillationcircuitsexceptatrightangles.

Don'tsetthetransformerofatransmittingsetnearerthan3feettothecondenserandtuningcoil.

Don'tusearotarygapinwhichthewheelrunsoutoftrue.

RECEIVINGDON'TS

Don'texpecttogetasgoodresultswithacrystaldetectoraswithavacuumtubedetector.

Don'tbediscouragedifyoufailtohitthesensitivespotofacrystaldetectorthefirsttime--orseveraltimesthereafter.

Don'tuseawirelargerthanNo.80forthewireelectrodeofacrystaldetector.

Don'ttrytousealoudspeakerwithacrystaldetectorreceivingset.

Don'texpectaloopaerialtogiveworthwhileresultswithacrystaldetector.

Don'thandlecrystalswithyourfingersasthisdestroystheirsensitivity.Usetweezersoracloth.

Don'timbedthecrystalinsolderastheheatdestroysitssensitivity.UseWood'smetal,orsomeotheralloywhichmeltsatornearthetemperatureofboilingwater.

Don'tforgetthatstrongstaticandstrongsignalssometimesdestroythesensitivityofcrystals.

Don'theatthefilamentofavacuumtubetogreaterbrilliancythanisnecessarytosecurethesensitivenessrequired.

Don'tuseaplatevoltagethatislessormorethanitisratedfor.

Don'tconnectthefilamenttoalightingcircuit.

Don'tusedrycellsforheatingthefilamentexceptinapinch.

Don'tuseaconstantcurrenttoheatthefilament,useaconstantvoltage.

Don'tuseavacuumtubeinahorizontalpositionunlessitismadetobesoused.

Don'tfailtoproperlyinsulatethegridandplateleads.

Don'tusemorethan1/3oftheratedvoltageonthefilamentandontheplatewhentryingitoutforthefirsttime.

Don'tfailtousealternatingcurrentforheatingthefilamentwherethisispossible.

Don'tfailtouseavoltmetertofindthepropertemperatureofthefilament.

Don'texpecttogetresultswithaloudspeakerwhenusingasinglevacuumtube.

Don'tfailtoprotectyourvacuumtubesfrommechanicalshocksandvibration.

Don'tfailtocutofftheAbatteryentirelyfromthefilamentwhenyouarethroughreceiving.

Don'tswitchontheAbatterycurrentallatoncethroughthefilamentwhenyoustarttoreceive.

Don'texpecttogetthebestresultswithagas-contentdetectortubewithoutusingapotentiometer.

Don'tconnectapotentiometeracrosstheBbatteryoritwillspeedilyrundown.

Don'texpecttogetasgoodresultswithasinglecoiltunerasyouwouldwithaloosecoupler.

Don'texpecttogetasgoodresultswithatwo-coiltuneraswithonehavingathird,ortickler,coil.

Don'tthinkyouhavetousearegenerativecircuit,thatis,onewithaticklercoil,toreceivewithavacuumtubedetector.

Don'tthinkyouaretheonlyamateurwhoistroubledwithstatic.

Don'texpecttoeliminateinterferenceiftheamateursaroundyouaresendingwithsparksets.

Don'tlayoutorassembleyoursetonapanelfirst.Connectituponaboardandfindoutifeverythingisright.

Don'ttrytoconnectupyoursetwithoutawiringdiagraminfrontofyou.

Don'tfailtoshieldradiofrequencyamplifiers.

Don'tsettheaxesofthecoresofradiofrequencytransformersinaline.Setthematrightanglestoeachother.

Don'tusewiresmallerthanNo.14forconnectingupthevariousparts.

Don'tfailtoadjusttheBbatteryafterputtinginafreshvacuumtube,asitssensitivitydependslargelyonthevoltage.

Don'tfailtoproperlyspacethepartswhereyouusevariometers.

Don'tfailtoputacoppershieldbetweenthevariometerandthevariocoupler.

Don'tfailtokeeptheleadstothevacuumtubeasshortaspossible.

Don'tthrowyourreceivingsetoutofthewindowifithowls.Tryplacingtheaudio-frequencytransformersfartherapartandthecoresofthematrightanglestoeachother.

Don'tusecondenserswithpaperdielectricsforanamplifierreceivingsetoritwillbenoisy.

Don'texpectasgoodresultswithaloopaerial,orwhen?usingthebedsprings,asanout-dooraerialwillgiveyou.

Don'tuseanamplifierhavingaplatepotentialoflessthan100voltsforthelaststepwherealoudspeakeristobeused.

Don'ttrytoassembleasetifyoudon'tknowthedifferencebetweenabindingpostandablueprint.Buyasetreadytouse.

Don'texpecttogetArlingtontimesignalsandthebigcablelessstationsifyourreceiverismadeforshortwavelengths.

Don'ttakeyourheadphonesapart.Youarejustasapttospoilthemasyouwouldawatch.

Don'texpecttogetresultswithaBelltelephonereceiver.

Don'tforgetthatthereareotheroperatorsusingtheetherbesidesyourself.

Don'tletyourBbatterygetdampanddon'tletitfreeze.

Don'ttrytorechargeyourBbatteryunlessitisconstructedforthepurpose.

STORAGEBATTERYDON'TS

Don'tconnectasourceofalternatingcurrentdirecttoyourstoragebattery.Youhavetousearectifier.

Don'tconnectthepositiveleadofthechargingcircuitwiththenegativeterminalofyourstoragebattery.

Don'tlettheelectrolytegetlowerthanthetopsoftheplatesofyourstoragebattery.

Don'tfailtolookaftertheconditionofyourstoragebatteryonceinawhile.

Don'tbuyastoragebatterythatgiveslessthan6voltsforheatingthefilament.

Don'tfailtokeepthespecificgravityoftheelectrolyteofyourstoragebatterybetween1.225and1.300Baume.Thisyoucandowithahydrometer.

Don'tfailtorechargeyourstoragebatterywhenthehydrometershowsthatthespecificgravityoftheelectrolyteiscloseto1.225.

Don'tkeepchargingthebatteryafterthehydrometershowsthatthespecificgravityis1.285.

Don'tletthestoragebatteryfreeze.

Don'tletitstandforlongerthanamonthwithoutusingunlessyouchargeit.

Don'tmonkeywiththestoragebatteryexcepttoaddalittlesulphuricacidtotheelectrolytefromtimetotime.Ifanythinggoeswrongwithitbettertakeittoaservicestationandlettheexpertdoit.

EXTRADON'TS

Don'tthinkyouhaveanup-to-datetransmittingstationunlessyouareusingC.W.

Don'tuseawirefromyourlightningswitchdowntotheoutsidegroundthatissmallerthanNo.4.

Don'ttrytooperateyoursparkcoilwith110-voltdirectlightingcurrentwithoutconnectinginarheostat.

Don'ttrytooperateyoursparkcoilwith110-voltalternatinglightingcurrentwithoutconnectinginanelectrolyticinterrupter.

Don'ttrytooperateanalternatingcurrentpowertransformerwith110-voltdirectcurrentwithoutconnectinginanelectrolyticinterruptor.

Don't--nonever--connectonesideofthesparkgaptotheaerialwireandtheothersideofthesparkgaptotheground.TheGovernmentwon'thaveit--that'sall.

Don'ttrytotuneyourtransmittertosendoutwavesofgivenlengthbyguesswork.Useawavemeter.

Don'tusehardfiberforpanels.Itisaverypoorinsulatorwherehighfrequencycurrentsareused.

Don'tthinkyouaretheonlyonewhodoesn'tknowallaboutwireless.Wirelessisaverycomplexartandtherearemanythingsthatthoseexperiencedhavestilltolearn.

THEEND.

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