5HFHSWLRQRQORQJZDYHDQGPHGLXPZDYHIURPFHQWUDO(XURSHXVLQJWKH+)LVFRYHUSURWRWSHRXUWHV)HQX5DGLR 7605HYLHZV $LU6S+)LVFRYHU ,WVD:KROH1HZ:RUOGRI5DGLR /DUU9DQ+RUQ1)3:DQGDOH9DQ+RUQ:9+ ymottohasalwaysbeen:“Givemeashortwave gainsatyourlocalhamfesteamarketorjunkinthetrunk. radioandIcanmonitortheworld.”Buttheworld Itwaseventhehumbletransistorthatlaunchedthepub- 0ofshortwaveradiosisnotthesameonethatIstart- licsafetyscannermarket.Theystartedoutastunableanalog edwithinthehobbymanyyearsago. dialradios,thenmigratedtocrystal-controlledradios.With 7RUORUDRUFUVDWVDVVRFDWOFWUR- theinventionofintegratedcircuit(IC)chips,therevolution- icshasundergonequiteanevolutionoverthelast130years aryphaselockedloop(PLL)circuitwasbornthatpropelled orsothattheyhavebeenaround.Astechnologyhasad- thescannerindustrytoproducethehightechnologypro- vanced,sohasthecapability,spectrumcoverage,andutility grammablescannersweusetoday. ofthereceiversthatweuseinourradiomonitoringhobby. Itistheintegratedcircuitthathascreatedthepersonal 7DUWDORRWXEUDRVUVWDUWD computer/smartdevicesboom,amarketplacethatcontinues inthelate1950sandearly1960swiththeintroductionofra- evolveevenasthispieceisbeingwritten. diocircuitsthatusedtinychipsofgermaniumknownastran- sistors.Duetotemperatureconcerns,germaniumwassoon 6KKK,WV$OO$ERXWWKH65V replacedbysilicon-basedtransistors.Consequently,most majorradiomanufacturersstartedproducingtransistor-based OWWUWDOUDRDVEDURXVFW receiverdesignsthatdidn’tneedatubecheckeranymore. V8RUWFUFOVWDVWXWOWDWW Mostradioold-timers(includingtheauthors)stillhave termsoftwareradiorstsurfaced.Atrst,manyold-timers foundmemoriesofthoseboatanchordays,youcanusually intheradiohobbyscoffedattheideathatanyradiothat seeacollectionofthosewonderfuloldtube-basedradiobar- didn’thaveatuningknobandallthecircuitryassociated 6HSWHPEHU HSHFWUP0RLWRU :HLJKLQJVOLJKWOPRUHWKDQRQHRXQFHWKLVVPDOOSDFNDJHGHOLY :HLJKLQJSRXQGVWKH5$855ZDVDJRWRUHFHLYHUIRU HUVKXJH+)SHUIRUPDQFH$LU6S+)LVFRYHUFRYHUV PDQVKRUWZDYHOLVWHQHUVIRUGHFDGHV$ERYHLVWKH6WHZDUW:DU WR0+]SOXV0+]RXUWHV$LUVS QHU(OHFWURQLFVYHUVLRQRXUWHV8QLYHUVDO5DGLR withitwasn’tarealradio.Peoplepushingacomputer-based personalcomputerorembeddedsystem. technologywereontheoutsidelookinginasfarasmajor AbasicSDRsystemmayconsistofapersonalcom- manufacturerswereconcerned.Itdidnottakelongforthose puterequippedwithasoundcard,orotheranalog-to-digital whisperedwords,software-denedradio,orSDR,tocome converter,precededbysomeformofradiofrequency(RF) outoftheshadowsandbeembracedbytheradiohobby frontend.Signicantamountsofsignalprocessingarehand- industry. edovertothegeneral-purposeprocessor,ratherthanbeing In1991alittle-knownAustraliancompanyknownas doneinspecial-purposehardware(electroniccircuits). WiNRADiOleveragedcomputertechnologytolaunchtheir TheSDRsoftwareperformsallthedemodulation,lter- rstsoftware-denedradios.Theyweresoonfollowedby ing(bothradiofrequencyandaudiofrequency),andsignal anotherindustrygiant,Icom,andtheirPCRseriesSDRs. enhancement(equalizationandbinauralpresentation). Foundedin2003,FlexRadioSystemsinAustin,Texas, SDRusagesincludeeverycommonamateurmodula- wasapioneerinthedesignanddevelopmentofSDRsforthe tion:Morsecode,singlesideband,frequencymodulation, amateurradiomarket.Manyintheindustrywilladmitthat amplitudemodulation,andawidevarietyofdigitalmodes FlexRadio’sinnovativeapproachtoSDRsanditssupporting suchasRTTY,SSTV,packetradio,andmanyothers.SDRs VRWDUDVFDWDFRDDWXUUDRDVR DUDOVREXVWRRXODWWDODR0RDO ittoday. (DRM)broadcaststreamswithouttheneedtopurchasea Eveninitsheydayourbelovedold0RQLWRULQJ7LPHV hardware-basedreceiver.Listenersusingthismethodcan magazinehadaComputerandRadiocolumnwrittenbyJohn usetheDREAMopen-sourceprojectthatdecodesthecoded Catalanothatcoveredmanyoftheearlybattlesbetween orthogonalfrequencydivisionmultiplexing(COFDM)tech- hardware-basedradiosandtheearlySDRsastheywere. niquetolistentoDRMtransmissions. Allthesenewtechnologieshaveledthewaytoawhole 7ERWWRORFRDURXVWDORVD UDWRRUDRVWDWRXOWDE modulationschemesisthis.Thedaysofthehardwarede- thoughtofjustthreedecadesago. coderareover.NowwithanSDR,inordertoreceiveanew 2RWRVUDRVRDDODEOVW modulationordigitalmode,youonlyneedtoupgradeasoft- focusofthisreview—theAirSpyHF+Discovery. warepackageorrmwareintheradioinsteadofreplacing thewholehardware-basedunitaswehavedoneinthepast. :KDWLV657HFKQRORJ 7KH$LUVS65V Inordertoappreciatethemarvelthatisthesoftware denedradioliketheAirspy,abriefprimerisinorder. AirspyisalineofpopularSDRreceiversdeveloped Thesoftware-denedradioisatechnologythatoffers anddesignedtoachievehighperformanceatanaffordable asimplealternativetobulkieranalogradios,addingmore price.Theyaccomplishthisusingsomeinnovativecombina- exibilityandperformanceinamuchsmallercase.Youmay tionsofdigitalsignalprocessing(DSP)andRFtechniques. notrealizeitbutSDRsareeverywhere,fromyourcellphone YoussefTouil,theownerofAirspyandthedeveloperofthe toyourwirelessheadsetandevenyourcablemodem. companySDRsandtheirsoftwaresupport,wasthehardware Inanutshell,anSDRisaradiowherethecomponents engineerfortheHF+Discoveryproject,theSDRweare thathavebeentraditionallyimplementedinhardware(e.g. reviewing. mixers,lters,ampliers,modulators/demodulators,detec- InouronlineinterviewwithYoussef,hestated,“My tors,etc.)areinsteadimplementedbymeansofsoftwareona goalwiththisnewSDRwastoincorporateabuilt-inpre- HSHFWUP0RLWRU 6HSWHPEHU LQJWKH$0DQG)0EDQGVRQWKH$LUVS+)LVFRYHUVKRZVJUHDWGHWDLORIWKHDFWXDOVLJQDORQWKHVFRSH7KLVLV:-5)0 IURPQHDUEKDWWDQRRJD7HQQHVVHH1RWH56GDWDLQXSSHUOHIWXQGHUWKHIUHTXHQF1)3:SKRWR selectorandbuildasmallerandcheaperSDRcomparedto regularlyheardatourlocation.Sixoutofsevenfrequencies theHF+atacheaperprice.”Basedonourinitialtestingwe werereceivedwithsignalstrengthsInormallyseeonmy agreethathehasaccomplishedthosegoalswiththeHF+ otherradiosintheshackthatcoverthesefrequencies. Discovery. ThenextbigtestwasintheFMbroadcastband.While IspecializedinHFutilityandallbandmilitarymonitoring,I ,QLWLDO7HVWLQJ stillDXmyradiorootsandprowltheAM/FMbandslook- ingfornewstationssoIamveryfamiliarwiththeAM/FM Intheinterestoffulldisclosure,Airspyisanadvertiser bandsasreceivedhereinBrasstown. 7KH6SHFWUXP0RQLWRU.Inkeepingwith760WRUDO AsIstartedtuningupofthebottomoftheFMbroad- guidelines,ourtestunitwaspurchasedbytheauthorsfrom castband,ImanagedtosnagtwonewFMstations–KRLE- AirspyUS.Theresultsofourtestswerenotreviewedbythe FM89.7CarbonHill,AL(182miles)andWMAB-FM89.9 manufacturerpriortopublication. MississippiStateinStarkville,MS(277miles).Thesetwo Wereceivedpromptandcourteousservicefromthe wereheardusingmyroofmountedGroveScantenna.While company.TheunitwasshippedfromtheirNewJersey Ididn’thavedeadbandconditionsduringthispartofthetest locationviaUSPSPriorityMail.,Itwaswellpackagedand (probablysomelocallyenhancedtroposphericbending),both arrivedingoodshape. stationswereverystrong,andthesoftwareevendecodedthe Normally,priorthissectioninmyreviews,isthepart twostationsradiobroadcastdatasystem(RBDS)streams. whereIwouldtellyouwhatisinthebox.Thatisquitesim- TheHF+Discovery’sexcellentFMperformanceis pleinthiscase–theHF+Discoveryunititselfandashield- achievedbythereceiverusingsignalpathscomposedof edmicro-USB-to-standard-USBconnector.Acompletesetof bandlters;highlinearitylownoiseampliers(LNA)witha specicationsforthisunitcanbefoundinTableOne. steppedautomaticgaincontrol(AGC)andaharmonicrejec- Letmemakethisclearfromtheonset,thereareno tionmixerandintermediatefrequency(IF)ltersthathave instructionsormanualsincludedinthebox.Youwillneedto beenoptimizedfortheFMbroadcastband.Theamplier interfacewiththeAirSpywebsiteforinstallationandaddi- gainisswitchablein3dB-stepsandfullycontrolledbythe tionaloperationalinformation(seethelinkslistedinTable AGCfunctionrunningintheDSPmodule.ExtendedVHF/ Two). UHF(118-260MHz)coverageusesasecondtuner,butit ThersttestIranwasintheVHF/UHFspectrum.A doeshavereducedperformance. quickcheckofthesevenNOAAnationwideweatherfre- Radiotoursthroughthe2-meterhamband,VHF-pub- quenciesshowedactivitythatwasconsistentwithstations licsafetyband,thecivilianaircraftbandsproducedsimilar 6HSWHPEHU HSHFWUP0RLWRU /HIW$QDXGLRVLJQDOZLWKRXWSURFHVVLQJ5LJKW6DPHDXGLRVLJQDOQRWHGDVQRLVEXWQRZZLWKXVLQJWKH$LUVSGLJLWDOQRLVHUHGXF WLRQSURFHVVLQJFRXUWHV$LUVS andacceptableresults.IwasverypleasednottoseeanyFM costreasons,andwillsufferstrongsignaloverloadespecial- bandinterferenceinanyoftheotherVHFbandsIchecked. lyinhighRFareas(urban/metroareas). Withoutexception,thesedevicesusuallyhavemajor +)DQGVDQGHORZ&LUFXLWU problemswiththeantennasthatradiohobbyistuse.They overloadveryquickly,whichmakesseriousreceptionon AirspyHF+DiscoveryachievesexcellentHFper- long,mediumandshortwavesratherdifcult. formancebymeansofalow-losspreselectionlter,high TheHF+Discoveryisthebigexception.Despiteits linearityLNA,highlinearitytunableRFlter,apolyphase smallsize,ithasabuilt-inpreselector,thatconsistsofsev- harmonicrejection(HR)mixerthatrejectsuptothe21st erallowandhighpasslters.Thedifferenceisnoticeable harmonicandmulti-stageanaloganddigitalIFltering. whenIcomparedittoseveralotherSDRsweown.Again, Harmonicrejectioncanbeakeyissueinsomewide-band regardlessoftheantennaweusedtherewaszerooverload- HFSDRreceiversbecauseofthelargesignalbandwidthof ingissuesnotedduringourtest. theinputsignal. Duringthetestweusedan80-meterG5RV,a100-foot The6-dBsteppedAGCgainisfullycontrolledbythe longwire,andaKiwimediumwaveampliedloop,Idid softwarerunningintheembeddedDSPmodulewhichopti- notnoticeanyoverloadingissuesfromthelongormedium mizesthegaindistributioninrealtimeforoptimalsensitivity waveintheVLForlongwavespectrum.Likewise,Isawno andlinearity. indicationofoverloadinganywhereintheshortwaveradio OncethereceivedsignalleavestheIF-lteritisdigi-