Com-Power CGO Series User manual

CombGeneratorsmodelCGO‐520 Page1of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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INSTRUCTIONMANUAL
Forthe
CombGenerators
CGOSeries
ModelsCGO‐520
20MHzstep
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CombGeneratorsmodelCGO‐520 Page2of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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Table of Contents
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Productspecifications…………………………………………………………3
Importantprecautionsandmaintenance...………………………………….4
Warrantyinformation…………………………………………………………5
ProductDescription……………………………………………………………6
Controls&Indicators…………………………………………………………..7
Theory………………….………………………………………………………..8
Application…………….………………………………………………………...9
Typicalradiatedoutput......................................................................................11
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CombGeneratorsmodelCGO‐520 Page3of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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Introduction
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ThismanualprovidesonhowmaintainandusetheCombGenerator.
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InformationcontainedinthismanualisthepropertyofCom‐PowerCorporation.Itisissuedwiththe
understandingthatnoneofthematerialmaybereproducedofcopiedwithoutpermissionfromCom‐Power.
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ProductSpecifications
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Frequencystepsize: 20MHz
Numberofantennasincluded:   Two
Antenna1Freq.range/height: 20–580MHz/(12inches/30.4cm)
Antenna2Freq.range/height: 580to4500MHz/(2inches/5cm)
OutputVariation: <±1dB(attheantennainput)*
UsableFrequencyradiated:   20MHz‐4.5GHz
InternalBatteryType: 6VRechargeableNimH
Batterychargeradapterspecifications: 
‐Input:  115/230VAC,60/50Hz
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 ‐Output:  6VDC@500mA(unregulated)
  ‐Plugtype:  2.5IDx5.5ODmm(centerpinpositive)
Outputconnectortype: SMA(f)
OperatingtemperatureRange: 5°Cto40°C
Weight: 2lb.(max.) 
Circularbasedimensions(WxH):  7x0.75inches/17.7x1.9cm
Weight(lb/kg):2lb/0.9kg
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*ThisisconductedoutputvariationwithCombGeneratorconnecteddirectlytoEMIreceiverorspectrumanalyzer.
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OtherCombGeneratormodelsavailablefromCom‐Power
• CGO‐501CombGenerator,1MHzstep
• CGO‐505CombGenerator,5MHzstep
• CGO‐5100BCombGenerator,100MHzstep
• CGO‐51000CombGenerator,1GHzstep
• CGC‐510EConductedCombGenerator,100/500KHzstep
• CGC‐255EConductedCombGenerator,50/250kHzstep

CombGeneratorsmodelCGO‐520 Page4of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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Important precautions and Maintenance
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Precautions:
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ACombGeneratorisanintentionalradiatordesignedtoproducessignalsoverwidefrequencyrange.Itwas
designedforuseinEMItestlaboratorytoverifyoperationofEMIemissionstestequipment.Theseradiated
signalsmaycauseunwantedradiofrequencyinterferencetootherequipmentoperatinginthevicinity.Ifyou
detectanyinterferenceincreasetheseparationbetweenCombGeneratorandtheotherequipment.
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Maintenance:
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Therearenouserserviceablepartsinsidetheunit.UsermodificationstotheCombGeneratorwillvoidwarranty.
TheCombGeneratorusesre‐chargeableNimHbatteries.Callthefactoryifthebatteryneedsreplacement.Send
CombGeneratortoauthorizedCom‐Powerservicecenterifneedsrepair.Pleasevisitourwebsiteatwww.com‐
power.comtorequestareturnmerchandiseauthorizationnumber(RMA)beforeyousendtheunitinforservice.
Batterycareandinstructions
Toavoidanyriskofexplosion
• Replacebatterieswiththesizeandtypespecifiedinthismanual.
• Donotdisposeofbatteriesinafireortrashincinerator,orleavebatteriesunderdirectsunlight.
• Donotimmersebatteriesinwaterorotherwisegetthemwet.
• Donotchargebatteries,thatappeartobeleaking,discolored,rusty,deformed;emitanodor
• UseonlybatterychargeradaptersuppliedwiththeCombGeneratortochargethebatteries.
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EnvironmentalConditions
ThisequipmentisdesignedforindoorandoutdooruseandissafeunderthefollowingenvironmentalConditions:
• Temperature:5°Cto40°C
• Maximumrelativehumidity:80%
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CombGeneratorsmodelCGO‐520 Page5of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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Warranty
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Com‐PowerwarrantstoitsCustomersthattheproductsitmanufactureswillbefreefromdefectsinmaterialsand
workmanshipforaperiodof3years.Thiswarrantyshallnotapplyto:
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a)Transportdamagesduringshipmentfromyourplant.
b)Damagesduetopoorpackaging.
c)Productoperatedoutsidetheirspecification.
d)Improperlymaintainedormodified.
e)Consumableitems,fuses,powercords,cables,etc.
f)Normalwear
g)Calibration
h)ProductisshippedoutsidetheUnitedStateswithoutthepriorknowlegeofCom‐Power.
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Inaddition,Com‐Powershallnotbeobligedtoprovideserviceunderthiswarrantytorepairdamageresultingfrom
attemptstoinstall,repair,serviceormodifytheinstrumentbypersonnelotherthanCom‐Powerservice
representative.
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UndernocircumstancesdoesCom‐Powerrecognizeorassumeliabilityforanyloss,damageorexpensearising,
eitherdirectlyorindirectlyfromtheuseorhandlingofthisproduct,oranyinabilitytousethisproductseperately
orincombinationwithotherequipment.
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Whenrequestingwarrantyservices,itisrecommendedthattheoriginalpackagingmaterialbeusedforshipping.
Damageduetoimproperpackagingwillvoidwarranty.
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Inthecaseofacomplaint,alabelshouldbeattachedtothehousingoftheinstrumentwhichdescribesbrieflythe
faultsobserved.Ifatthesametimethenameandtelephonenumber(dialingcodeandtelephoneordirectnumber
ordepartmentdesignation)isstatedforpossiblequeries,thishelpstowardsspeedinguptheprocessingof
warantyclaims.Inordertoobtainserviceunderthiswarranty,CustomersmustcontacttheCom‐Power.

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CombGeneratorsmodelCGO‐520 Page6of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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Product Description
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Overview
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TheCGOseriesCombGeneratorsarereferencesignalsources.TheyweredesignedforEMClaboratoriesuse.Itis
idealforquicklydetectingmalfunctioningequipmentintheradiatedemissionstestsetupinbetweenfull
calibrationintervals.Thesemalfunctionsmaygoundetected,unlessittheyarecheckedoften.Fullsitecalibration
althoughmoreaccurateistimeconsumingisnotpracticalforaquicktest.BycomparingCombGeneratordata
takenatregularly,theEMIlabcanensurethatallthetestequipmentandaccessoriesareoperatingwithinthe
expectedrange.Ifanyabnormalityisdetected,itcanbequicklyinvestigatedandrectifiedbeforeitcauses
measurementerrors.
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TheCombGeneratorscanalsousedforcomparingtwoormoresiteswithsimilarsetup.Theycanalsobeutilized
asconductedsignalsourcefortestingLineImpedanceStabilizationNetwork(LISN),filtersandcables.
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ItemsincludedwithCombGenerators
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Equipment,accessories,anddocumentssuppliedwithCGO‐520CombGeneratorsareasfollows:
o User'sguide
o Customwoodenstoragebox
o BatteryChargeradapter
o Twoantennas
o Testdata(optionalreferencedataatextracost)
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CombGeneratorsmodelCGO‐520 Page7of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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Controls and indicators
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PoweronSwitch
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ThisislocatedonthesideoftheCombGenerator.Itnotonlypowersunitonoroff,italsoenablesordisablesthe
signaloutput.
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Outputconnector
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ThecombgeneratoroutputisavailableattheSMA(f)connectorlocatedonthetopoftheunit.Thisoutputcanbe
usedforradiatedorconductedemissionstesting.Forradiatedmeasurements,themonopoleantennaisattached
tothisconnector.TherearetwoantennaswithSMAmaleconnectorsprovidedtocovertheCombGenerator
radiatedfrequencyrange.Pleaserefertopage3todeterminetheapproximatefrequencyrangeofeachantenna.
Theantennacanbedisconnectedforconductedemissionsmeasurements.DonotconnecttheCombGenerator
conductedoutputtoaLineImpedanceStabilizationNetwork(LISN)thatisconnectedtoACpower.Wealsodo
notrecommendconnectingtheCombGeneratorconductedoutputdirectlytoapreamplifierinput.
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PowerOnindicator
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ThegreenpoweronLEDislit,theCombGeneratorispoweredonandoutputisavailableformeasurement.
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BatteryLowindicator
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WhenredbatteryLowLEDislit,theinternalbatteryneedsrecharging.Theoutputmaynotbereliable.Turnoff
CombGeneratorandchargethebatterywiththesuppliedadapter.Theapproximatetimetofullychargethe
batteryis8hours.TheCombGeneratorcanoperateapproximately18hourswhenfullycharged.Pleasenote
however,thattheoperatingtimegiveninthismanualisapproximateanddependsontheconditionofbattery,
storageperiodandthenumbertimesithasbeenchargedanddischarged.Iftheoperatingtimekeepsdecreasing,
youmayneedtoreplacethebattery.
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CombGeneratorsmodelCGO‐520 Page8of11 
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(949)459‐9600 www.com‐power.com Rev.0216
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Theory
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TheCombGeneratorusesanimpulsetogenerateitsstepfrequencyoutput.Itusesastablepowersupplyand
signalshapingcircuittoobtainrelativelystablesignaloutputwithfrequencycomponentsextendingbeyond1GHz.
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TheCombGeneratoroperatesonbatterypower.Thebatteryoutputiscontrolledbyavoltagetheregulatorcircuit
toprovidestablepoweroutputtothesignalgeneratingcircuit.Thesignalgeneratingcircuitconsistsofaclock
generator,impulsegenerator,waveshapingcircuitandoutputmatching.Thesignalfrequencyisgeneratedbya
crystaloscillator.
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Animpulseintimedomaincorrespondstoaflatoutputacrosstheentirefrequencyspectruminfrequency
domain.Anidealimpulse,bydefinitionisaninfinitemagnitudepulsewithzeroriseandfalltimewithzero
duration.Suchapulseisnotpractical;however,theModelCGO‐520CombGeneratorsusethisprincipletogetan
outputacrossawideband.Thehighlystablefrequencyoutputfromtheoscillatorisusedtogenerateanimpulse
withveryshortdurationandsharpriseandfalltimes.Theshapingcircuitwasdesignedforimprovedstability,
extendedfrequencyresponse,andoutputimpedancematchingto50ohms.
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Theradiatedreferencesignalistransmittedbytheantennasaffixedontopoftheunit.Anelectricallyshort
monopoleantennaisanantennathatisshortcomparedtothewavelengthofthefrequencyitradiates.Suchan
antennageneratesaradiatedfieldproportionaltoitslength.Theradiatedfield,therefore,compensatesfor
decreasingsignaluptoafrequency,wheretheantennacannotbecalledelectricallyshort.Thistheorydescribes
thegeneralbehaviorofthefield,buteachCombGeneratormaybehaveslightlydifferentthantheotherdueto
circuitvariation.SincetheCombGeneratorsweredesignedtoprovideareferencereadingatagivenfrequency,
thislimitationisnotaproblem.
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Application
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RadiatedEmissions
EMItestsitessuchasOpenAreaTestSite(OATS)orAnechoicchambersareconstructedwithspecific
requirementsandarecalibratedinaprecisemannertooptimizethereliabilityoftheemissionsmeasurements.
Thetimeandexpenseincurredisconsideredessentialtoincreasetherepeatabilityofthedata.
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Thedatatakenontheabovesitesaregenerallyreliable.However,insomeinstances,discrepanciesdooccur,and
thereliabilityofdataisquestionable.Suchdiscrepanciescouldbediscoveredwheneither(a)datafromtwosites
forthesameequipmentdonotmatch,or(b)thedatafromtwodifferentoccasionsforthesameequipmentatthe
sameOATSarenotconsistent.Itisimportanttofindthecauseforsuchinconsistency.Thisisgenerallyaverytime
consuminganddifficultprocessbecausethereasoncouldbeoneoffourcomplexfactors.
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(1)Equipmentundertest(EUT),
(2)TheTestSite
(3)Instrumentation
(4)Testpersonnel.
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Eachofthesefactorsmayhavemanypossiblecauses.TheEUT,forexample,mayhavechangeddueto
componentvariation,temperature,operatingmode,wearandtear,designetc.Thetestsitemaybeacausedueto
areflectiveobjectnearthesite,variationofgroundsaturationorambientsignalpresence.Italsocouldbedueto
malfunctioningtestinstrumentation.
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Byestablishingsimplemeasurementproceduresimilartotheonedescribedbelowthetestlabcanreduce
occurrenceoftheseproblems.Therebyincreasingthereliabilityofmeasurementstakenonthesite.The
proceduredescribedisjustaguideandcanvariedaccordingtoyourneeds.
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MeasurementProcedure
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Asmentionedbefore,takingmeasurementmorefrequentlyisimportant.Createalogwithfrequencyandlevels
thatyouwouldliketorecord.Thiscanbedaily,weeklyormonthlylog.WerecommendtakingCombGenerator
measurementbeforetostartingaradiatedemissionstest.SetuptheCombGeneratorwiththeappropriate
antenna(seefrequencyrangeonpage3).PuttheCombGeneratorwheretheequipmentundertest(EUT)is
normallyplacedduringthetest.
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MakeameasurementlikeyouwouldonaEUT.Werecommendusingdiscretefrequencypointsratherthanawide
frequencysweep.Suchas30MHz,40MHz,100Hz,900MHz,etc.Recordthelevelforeachfrequency.
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Comparetheselevelswithallsubsequentmeasurementstomakesurethatthepatterndoesnothaveabrupt
changefromtheestablisheddailylogatanyfrequency.Themorehigherthenumberoffrequencypointsthe
highertheaccuracyofthereferencemeasurements.
Thislogisusedtodetectanytestequipmentortestsiterelatedproblemasdescribedbelow.
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ProblemsRelatedtoTestEquipment
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VariationonthelogoftheCombGeneratoroutputdataisdependentonthetestequipmentaswellassite.The
CombGeneratorreplacestheEUT.TheCombGeneratornotonlygeneratestheoutputsimultaneouslyatallthe
harmonics,butitminimizesanyvariationofitsoutput.Thisisachievedbyutilizingastabilizedsignalcircuitaswell
asgeometryoftheradiator.Thecircuitstabilityismaximizedbydesign,whereasthegeometryoftheradiated
sourceisoptimizedbyeliminatingallcablesduringtheRadiatedEmissionMode.ThetypicalvariationofComb
Generatoroutputatanyfrequencyislessthan±1dB.
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WiththevariationsduetotheEUTpracticallyeliminated,onlyvariationsremainingareduetootherfactors,
mainlythetestinstrumentationandthesite.Thevariationduetotestinstrumentationislimitedtothesumtotal
ofthetoleranceonalltestequipmentused(spectrumanalyzer,antenna,preamplifier,cables).Afewdaysofdata
willestablishtherangeofvariationtobeexpectedatasite.Thisisgenerallylessthan±3dB.Anyvariationinthe
readingsabovenormalvariationindicatesapotentialproblem.
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Afterthedailylogisestablishedforafewdays,anyproblemiseasilydetectedasalargervariation.Thisprocedure
allowsimmediatedetectionofamajorproblemwiththetestequipment.
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ProblemsRelatedtosite
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Theaboveprocedurecannotdistinguishtheproblemsrelatedtothetestsite.TheCombGeneratorcanbeusedin
twowaystodetectanyproblemwithatestsite.Onemethodistostartthedailylogimmediatelyafterthetestsite
iscalibrated.Thisway,oneiscertainaboutthevalidityofthedatatakenonthetestsite.Thesecondmethodisto
calibratetheCombGeneratorradiatedoutputasabsoluteemissionlevel.Suchcalibrationisprovidedasanoption
withtheCombGenerators.
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Inaddition,whendifficultyariseswithanyEUTdatatakenattwodifferentsites,theCombGeneratorcanbeused
todetermineifbothsitesgivereliableresults,justbycomparingthedataatthetwositeswiththeComb
Generator.Inthiscase,ifthetwositesdonotproducecomparableresults,aCombGeneratorwithcalibrateddata
iscertainlyrequiredtodeterminethefaultysite.
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ProblemsRelatedtoTestPersonnel
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TheCombGeneratorcannotdirectlyhelptoeliminatethetestpersonnelrelatedproblems.However,by
increasingtheconfidencelevelandestablishingdefiniteproceduresforeliminatingsiteandequipmentrelated
problemsithelpstremendouslytoreducetheproblemsrelatedtoEMImeasurements.

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Typical radiated output
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TheseareCombGeneratorradiatedoutputat3meterdistancewiththereceivingantennaheightvariedfrom1to
4meterstakeninanopenareatestsite.
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Figure1:20MHzstepsize
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