S-Pixie QRP Kit

Student Manual

Revision V 1-0

IntroductionThePixie2isasmall,versatileradiotransceiverthatisverypopularwithQRP(lowpower)amateurradiooperatorstheworldover.Itreflectsahistoryofcontributionsfromamateurradiooperatorslookingtobuildthesimplesttransceiverpossible.Atit’scoreitisacrystalcontrolled(singlefrequency)sub1-WattQRPCWtransceiver.OneofthemostimpressivefeaturesofthePixie2besidesitssimplicity,arethemodificationpossibilitiessuchasoperatingatawiderangeofRFfrequencies.Inthisguide,theversionwewillbebuildingistheS-PixieasdesignedbyJasonBG2XNNofLXQQFY.cominChina.JasonhastakentheoriginalPixiedesignandproducedakitthatisavailableonlineviahiswebsitehttp://www.lxqqfy.comaswellasanumberofresellersoneBay.

WhatyouwillneedKitbuildingismeanttobetimeenjoyedandnotaracetothefinish.Whileitispossibletoputthiskittogetherintwohours,takethetimetoenjoytheexperience.Patiencecomesinbecauseyouareworkingwithsmallcomponents.Hereisalistoftoolsrequired:

Tools CommentsSolderingStation HakkoFX888orWellerWES51equivalentSolder Standard60/40RosinCoreSolderwick FlatcopperbraidusedfordesolderingDesolderingpump/SolderSuckit Alternatemethodfordesolderinga

componentDigitalMultimeter Verifythevaluesforvariouscomponents

beforeinstallingSmallPhillipsScrewdriver Donotuseonewithdull/chippedtipBoardVise Holdsthecircuitboardatvariousangles

whilesolderingcomponentsMagnifierHeadset Helpstoseewhatyouaresoldering.Many

smallcomponentswithsmallmarkingsSmallFlushDiagonalcutters Fornippingleadsoffofcomponentsonce

solder.Useaqualitytool.

TheoryandDesignTheS-Pixiedesignconsistsoffoursections;oscillator,poweramplifier/mixer,lowpassfilter,andaudioamplifier.

OscillatorA9-12VDCpowersourceisconnectedtoJ1,anAntennatoJ2,aMorseCWkeytoJ3,andaspeakertoJ4.WhenpowerisappliedtoJ1,Q1andX1plussurroundingpassivecomponentsarepartofacontinuallyrunningColpittsoscillatorwitha7030KHzsignalattheemitterofQ1.Runningtheoscillatorcontinuouslyassuresfrequencystability.

ReceiveModeandMixerWhenJ3isopen(MorseCWkeynotkeyed),theradioisinreceivemodewithQ2andsurroundingpassivecomponentsservingasaMixer.ThemixertakesthesignalfromtheColpittsoscillatorcapacitivelycoupled(C4)intothebaseofQ2andmixesitwiththesignalsreceivedonit’scollector.TheQ2collectoriscapacitivelycoupled(C2)toalowpassfilter(C5,L2,andC6)andthentoanAntennaconnectedatJ2.ThefrequencydifferenceemergesfromtheQ2emitterataudiofrequenciesandissenttotheAudioamplifier(U1)andinturntoaspeakerconnectedtoJ4.

TransmitModeandPowerAmplifierWhenJ3isclosed(MorseCWkeyed),theradioisintransmitmode.Q2andsurroundingpassivecomponentsserveasaClassCPowerAmplifiertakingthesignalfromtheColpittsoscillatorcapacitivelycoupledviaC4intothebaseofQ2andamplifyingit.TheamplifiedsignalatQ2collectoriscapacitivelycoupled(C2)tothelowpassfilterandouttheAntenna(J2.)

Preparation

InventoryStartwithininventoryingallparts.Itisnotuncommonforkitstoincludeextraresistorsorcapacitors.Besuretoverifyvaluesofallresistorsandcapacitorswithchartsand/ormultimetergiventhemarkingscanbequitesmall.

Resistors(1/4Watt)

Capacitors(Ceramic)

Capacitors(Electrolytic)

R1 47K C1,C10 0.1uF(104) CP1 100uF/16VR2 33K C2,C4,C8,

C1110nF(103) CP2,CP3,

CP410uF/(16V

R3 1K C3,C7 100pF(101) R4 470ohm C5,C6 470pF(471) InductorsR5,R8 10K C9 47nF(473) L1 22uH(Red,Red,Black,Silver)R6 100K L2 1uH

(Brown,Black,Gold,Silver)R7 10ohm L3 100uH

(Brown,Black,Brown,Silver)

Transistors Assorted DiodesQ1 9018

Triode U1 LM386Audio

Amp D1 2W10BridgeRectifier

Q2 8050Triode

Y1 7.030MhzCrystal

D2 1N4001

W1 47KVarResistor

D3 1N4148

PCB D4 LED AcrylicCase Buzzer Connectors 51OhmRes(DummyLoad) J1 DCJack J2 Antenna(BNC) J3 Key(3.5mm) J4 Speaker(3.5mm) J5 Pin&JumperCap

ApproachWhichcomponentsshouldIsolderfirst?Thetablebelowistherecommendedorderofinstallation.

1. Resistors 11. PhoneJack

2. Inductors 12. KeyJack

3. Diodes(SignalandRectifier) 13. PowerJack

4. CeramicCapacitors 14. AntennaJack

5. Crystaloscillator 15. Buzzer

6. ICSocket 16. VariableResistor

7. Electrolyticcapacitors 17. Jumper

8. Transistors 18. ICintosocket

9. BridgeRectifier 19. Case

10. LED

BeforeyousolderitTrustbutverify.Beforesolderingeachcomponentconfirmthecomponentsvalueandthecorrectlocationitshouldbesolderedontotheboard.Especiallyimportantwhenitcomestoyourfirstcomponentverifyingyouaresolderingitonthecorrectsideoftheprintedcircuitboard.Componentssitonthesilkscreenedsidewiththeirleadsinsertedintothethroughholesandsolderedontheotherside.Evenexperiencedkitbuildersmakethemistakeofputtingthefirstcomponentonthewrongsideoftheboard.

SolderingMainthingtorememberwhensolderingisnottousetoomuchsolder,touseenoughheat,andtotrytogetitrightthefirsttime.Thesekitsarefairlyrobust,soitisnottooseriousifyouneedtorepeatedlysolderthesamepad.Thatbeingsaid,itispreferabletoonlydoitonce.Ifyoumustresolderacomponentsjustusesolderwicktokeeptheboardtidyandtoreducetheriskofunintentionalshorts.Whatalsohelpsreduceunintentionalshortsisuseaqualityflushdiagonalcutterwhennippingleadsoffofcomponentsoncetheyaresoldered.Youwillgetcleanclosecutstotheboardwithoutleaving“tails.”Alsobesuretoaccountforallleadsnippedtoinsurenopiecesareeitherontheboardoronyourbenchandriskapossibleshortcircuit.

Construction

Resistors,Inductors,Diodes,CeramicCapacitorsWestartwithsolderingthelowestprofilecomponentsontheboardfirstinthefollowingorder;resistors,inductors,signalandrectifierdiodes,thenceramiccapacitors.

Crystal,ICSocket,ElectrolyticCapacitorsNextwesolderthecrystal.Goingforwardweneedtobeconscientiousofcomponentsthatrequireinstallationinaparticularorientation.NotetheICsockethasanotchononeend.Insurethenotchisalignedwiththesilkscreensilhouetteontheboard.Forelectrolyticcapacitorstakenotethepolarityorientationiscorrectwhensoldering.Thenegativelead(whichistheshortest)goesthroughtheshadedsideofthesilkscreensilhouette.

Transistors,BridgeRectifier,LEDAswiththeprevioussection,beconscientiousoftheorientationofeachofthesecomponents.Fortransistors,insuretheflatslideisalignedwiththeflatsideofthesilhouette.Forthebridgerectifiertakenoteofthearealabeled+and–onboththerectifierandthesilhouette.FortheLED,insuretheflatslideisalignedwiththeflatsideofthesilhouette.

Connectors,Buzzer,VariableResistor,Jumper

Yourcanbemoreliberalwithsolderusedoncomponentsinthissection(lessthebuzzer)sincetheyhavetodealwiththestrainofphysicalinteraction.StartwithsolderingthePhoneconnectorandKeyconnector–theyuseidenticalparts.Theninordersolderthepowerandantennaconnectors,buzzer,variableresistor,andjumper.BesuretoinsertthejumpercapandfinallyinserttheICintoitssocketnotingcorrectorientation.

AcrylicCaseRemovetheprotectivepaperfromtheacrylicpieces.Thebottomportionofthecaseisassembledfirstusingthelongplasticscrewsfirstthroughthefeet,thenthebottomofthecase.Nextscrewthelongplasticscrewsintotheplasticstandoffsthecircuitboardwillsitontopof.Placethecircuitboardonthestandoffsandthenplacetheacrylicslidesthathaveconnectorholesinplace.Thenscrewtheplasticextensionstothestandoffs.Nextplacetheacrylicslidewithnoholesinplaceandthenacrylictop.Usetheremainingshortscrewstosecurethetop.

Testing

SetupPriortoapplyingpowerconnecteitheranantennaordummyloadtotheantennajack(J2.)A50Ohmresistorisincludedtobeusedasadummyload.SimplysoldertheresistoracrossthecenterandshieldofaBNCconnector.

Key&Headphone

Stereoconnectorsareusedforboththekey(J3)andphone(J4)connections.Sincethestraightkeyusesamonojack,themiddleandoutersleevesofthekeyconnector(J3)areground.Use8ohmheadphoneswhenconnectingtothephone(J4)connection.

OperationWithantenna,headphone,andkeyconnected,goaheadandapplypower.Don’texpecttheaudiotobeloudortoreadilyhearsignals.UsingthepotentiometeryouwillbeabletotuneafewKHzaroundyouroperatingfrequencyof7030KHz.TaptheCWkeyandyouwillhearthebuzzeremitasidetoneasyoutransmitasignal.

Appendices

Schematic

ResistorChart

AdvancedTopic

DDSVFOTheS-Pixiecanbemodifiedtocoverthewhole40MeterbandbyreplacingtheoscillatorwithaVFO.ApopularapproachhasbeentouseaDirectDigitalSynthesizer(DDS)controlledbyanArduino.ThehumaninterfaceincludesanLCDdisplayandrotaryencoder.PopularDDSchoicesincludetheAD9850andtheSI5351. Remove/Omit C3, C7, Y1, W1, D2, R6, and C8.

Place a 47K resistor between Q1 base and GND. Connect the DDS across that resistor.