SDRSOFTWAREDEFINEDRADIO
NARCPRESENTATION– JANUARY2016
STEPHENOLESEN – VE6SLP
WHATISSDR?
• SDR– SoftwareDefinedRadio
• InsteadofusingdiscretecomponentsordedicatedICsfortuning, receptionanddemodulation,softwaremaytakeonmanyoftheseroles.
• Hardwarecomponent tendstoonlyprovideRFtoIFconversion (including azero-IF).
• Usessoftwaretodemodulatereceivedsignals.
• Usessoftwaretomodulatetransmittedsignals.
WHYUSESDR?
• SDRprovides flexibilitybyremoving restrictionsimposedbyhardwareinthesignalchain.
• AsingleRFfrontendcanbeusedbymultiple signalprocessorsastheincomingRFisdigitizedearlyon intheprocess.
• Generalpurposecomputerscanbeusedwithhighperformance toanalyzeandworkwithcomplexsignalsormultiple (independent ordependent) signalsatonce.
• DigitizationoftheRFsignalinbothdirectionsallowsforveryaccuratereproduction andanalysisofsignalswithout introducing further noiseinanalogcomponents.
BASICCONCEPTSHARDWARECOMPONENTS
• Thehardwareinvolves:
• AnRFfrontend,generallycanbequitewidebandandoftenfoundasamonolithicIC.
• Analogtodigitalconversion,eitherfromanIForfrombaseband.
• Inatransmitter,adigitaltoanalogconverterisalsoused.
• Maysendbaseband toanIFmixerordirecttoRF.
• ComponentsaresimpleraslessamplificationneedstotakeplacebeforetheADC,filtering andprocessingaredonedigitallyinsoftware.
BASICCONCEPTSSOFTWARECOMPONENTS
• ThesoftwareonlyneedstoworkwithadigitalstreamofdatawhichistheRFdataconvertedfromtheRFfrontend.
• Softwarecanreceiverealsamplesorcomplexsamples(I/Q– in-phase/quadrature).
• Canrunasaservice,asauserapplication, indedicatedhardware(suchasFPGAs,DSPsorevenArduinos/microcontrollers).
• Datacanbetransmitteddigitallyovernetworkswithout lossof signalfidelity.
BASICCONCEPTSSOFTWARE
• Examplesofsoftwareinclude:
• SDR#(SDRSharp,Windows)
• SDR-Console(Windows)
• HDSDR(Windows)
• GNURadio(Linux)
• Linrad (Linux)
• SDR-Shell(Linux)
• Gqrx (Linux,Mac)
• WebSDR (Linux,provideswebinterfacetomultipleusers)
BASICCONCEPTSRFDIGITIZATION
• TheRFisreceivedonanantenna.
• RFfrontendusuallyprovidesnormal frontend filtering (bandpass, lowpass,etc.)
• RFiseitherdirectlymixedtobasebandortoanIF
• IFiseitherdirectlysampledormixedtobaseband
• Samplesaresenttothecomputeraseitherrealorcomplexsamples
• Realcanbeconvertedtocomplex,andviceversa
• Basebandcaneasilybesampledwithacomputersoundcard
• IFgenerallyrequiresdedicatedhardwarefortheconversionofthehigh frequency IF
• Receivebandwidth limitedbytheanalogtodigitalconverter(orsound card)
BASICCONCEPTSDEALINGWITHTHEDIGITALSIGNAL
• TherealsamplesgenerallyareconvertedtoI/Qsamples,providing a90degreeoutofphasesampleoftheRFdata
• Thecomplexsampleisabletoproduceamplitudeandphaseacrosstheentirereceivedspectrumwhileeliminating imagesduetomixing
• Realsampleswhenconvertedhavenodirectphaseinformation andwillhaveanimagesignalpresentafterconversion• Thiscanberemovedusingdigitalfilters
• Digitalsignalcanbesentthrough extremelycomplexormany-poledfiltersprovidingsharp,narrowfiltersontherawRFdata
• Originalsignaldatacanbeusedinmultiple filters/demodulators simultaneouslyacrosstheentirereceivedbandwidth.
BASICCONCEPTSSAMPLINGRATE,NUMBEROFBITS,BANDWIDTH
• SincetheRFsignalisdigitized, theanalogtodigitalconversionwillhaveafixedsamplerate.
• Depending onthehardware(ADCandDAC),thissampling ratemaybeatsoundcardspeeds(48or96kHz,or96kSPS/192kSPS) orhigher (suchastheBladeRF at40MSPS)
• Usablebandwidth ishalfthesampling rate(192kSPSprovides96kHzbandwidth,40MSPSprovides20MHzbandwidth)
• Bitlengthprovides thetotalsignalamplitude rangeandrelatesstronglytotheachievableSNR,dynamicrange,accuracyandoverloadcharacteristics.8bitsiscommon,providing 256levelsofsignalstrength.
COMMONHARDWARERTL-SDR
• SimpleUSBdevicesknownasRTL-SDR(RTL2832)areeasytofindandalowcostwaytoexperiment withreceptiononlySDR.
• AvailableinCanadaforaslowas$15,butgenerally intherangeof$25-$30.
• Availablewithavarietyoftunerchipsets,mostcommonthesedaysistheR820T.
• ConnectsviaUSBtoacomputer.
• Abletotunefromaround50MHzto1.5GHzandabove.
• Provides8bitsamplesatupto3.2MSPS(usuallyonlyusableupto2.4MSPSorso)
COMMONHARDWARESOFTROCK
• TheSoftrock seriesbyFiveDash(KB9YIG)areakitversionofHFSDRswhichuseacomputersoundcardforthedigitizationportion.
• LowcostandasimpledesignallowagoodunderstandingofthehardwaresideofSDR.
• Rangeinpricefrom$21USDtoaround$100USD.
• UseUSBforpowerandfrequencycontrol,regular3.5mmaudiocablesforthebasebandaudiotobedigitized.
• Compatiblewithawidevarietyofsoftwareastheonlyrequirementisthesoundcarddriver.
• Capableofbothtransmission(lowpower,around1watt)andreception,96kHzbandwidth(192kSPS)
COMMONHARDWAREFLEXSDR
• FlexRadioprovidesall-in-onesolutions forhighendperformance.
• Acombinationofhardwarebaseddigitalprocessingandcomputerbasedsignalprocessing.
• Higherpoweroutputs thantheSoftRock.
• Rangeinpricefrom$1000to$11,000.
• Familiarriglayoutanddesignwithmanyinputandoutputoptions.
• NARCownsaFlexRadioSDRattheshack.
• Somesupport dualRFfrontends,widebandwidth (not limitedbyacomputersoundcard)
ADVANCEDHARDWAREBLADERF ANDHACKRF• BoththeBladeRF andHackRF aresmallUSBcontrolledSDRhardwarefrontends.
• ProvideonboardADCandDAC.• BladeRF capableoffullduplexcommunication.
• Verylowoutputpowers(10mWorless).
• BladeRF iscapableof40MSPSand300MHzto3.8GHztransmit/receive,12bits.
• HackRF iscapableof20MSPSand1Mhzto6GHz,8bits.
• BladeRF runsaround$600-$1000USD,HackRF isaround$350-450USD.
• BladeRF hasanonboardFPGA,HackRF usesaCPLD.
• Designedforexperimentation,protocoldesign,advanceddecoding.
• TheyhavebeenusedtoprovideGSM/LTEcellularnetworkservices,digitalTV(ATSC)transmission,andmore.
USINGWHATYOUHAVEANYRIGUSINGASOUNDCARD
• SincetherealideaofSDRisthatsoftwarehandlesallthesignalprocessing,anyRFfrontend cantheoreticallybeusedtogetthesignalintothesoftware.
• Usinganormalradio(HF,VHF,UHF,etc.)withanaudioconnection toacomputercanprovide low-bandwidthSDRservices.
• Bandwidth limitedbythein-radiofilters(USB,LSB,FM,etc.)
• Thissortof setupiscommonly foundwithPSK,JT65,WSPR.
• TheRFfrontend isafullradiocapableofdemodulation ofaudio,butisunawareofwhatthataudio is.Thecomputer thenprocessestheinput likeanSDRtoprovide thesedigitalmodes.
• Fldigi andHamRadioDeluxeprovideconvenient interfacestoclassicradiosviathesoundcard(andoftenaconnecting interfacetoprovidePTTandlevelcontrol).
INTERFACINGUSBANDSOUNDCARDINPUTS
• ThesimplestSDRRFfrontendoutputs thebasebandsignalviaregularanalogaudiosignalstoacomputer’s soundcard.
• Limitedbandwidth (audiobandwidthranges).
• I/Qimbalanceismorecommonandhardertofix.
• USBinputsvary,withdevicesliketheRTL-SDR,Flex,BladeRF andHackRF havingintegratedADCs/DACs.
• SomeUSBSDRdevicesusebuilt-insoundcardswhichconnectoverUSB,butarestilllimitedtoaudioranges.TheRigBlaster seriesisanexampleofanSDR-likeinterfacewithintegratedsoundcard.
COSTOVERVIEW
• Startingwithequipmentyoualreadyhave,experiencing thebasicsofSDRandtheintegrationofcomputerswithradios,cancostnearlynothing.
• UsinganRTL-SDRbasedUSBadaptercangetyouupandrunning forunder$25.
• Adding ontransmitcapabilitiescanstartaslowas$70fortheSoftRock,uptotheFlexRadioseriesatmanythousand ofdollars.
• BecausetheRFportion isrelativelystraightforward,designing yourownSDRfrontend canbedone(thisgenerallyinvolvesoversamplingyourdesired frequency togetI/QsamplesandmixingwithanIFtoconverttobaseband,andnotmuchelse).
RFCHARACTERISTICS
• Ingeneral,SDRprovides foracleanoutput signal.
• Sharpandcomplexfilterscanbeusedinsoftwaretoremoveasmuchextrasideband/noise aspossible.
• ExtremelycomplexsignalscanbesentdigitallytoahighperformanceDACwhichproduces thevoltageoutput totheRFtransmitterwithoutneeding complexanalogfiltersorintegrationtojoinmultiplesignalstogether.
• Signalnoise isinfluencedbythebitsizeandsamplerateusedtogeneratethesignal.
• SincetheRFfrontend isstraightforward(ADC/DAC,mixerandamplifier), thesignalpathisshort,preventingextraoscillatorsandparasitics fromcompromising thesignal.
SOMEEXAMPLEUSES
• ADS-B(1090MHz)planetransponder tracking
• Multi-channel trunking scanners
• Widebandbandlistening/waterfall(includingmulti-userdemodulation), ie.WebSDR
• Remotelistening/transmitting
• PSK, JT65,WSPR(allatthesametime,withoneantennaandSDRfrontend)
• Experimentaldigitaloranalogmodedesign
• Satellitetrackingandtelemetry
• Discovering theRFworldaroundyouwithout spinning thedial(awidebandwidth receivershowing20MHzofRFspectrumatoncegivesaniceoverviewofnearlyalltheHFspectrumatonce)
QUESTIONS?