Eight Markers in Perseus That Will Change DXing

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1 EightMarkersinPerseusThatWillChangeDXing withappendix:markers ResolutioninaNutshell ByNilsSchiffhauer,DK8OK Englishtranslation/editingassistance:GuyAtkins Perseussoftwareversion2.1hprovidesuptoeight"markers"whosevaluescanbesavedtoalogfile.Nils Schiffhauer,DK8OK,describeswhatthemarkersaremeasuringandwhatyoucandowiththedata. Incidentally,notonlyPerseus,butalsosomeotherreceiverscanrecordthesignallevelforuselaterina spreadsheet.eversincethefirstversionofperseussoftware,therehavebeenmarkersavailable.theycanbe placedwithamouseclickonanyfrequencywithinthelargedisplay.thevalueshownistherespectivelevel. Withsoftwareversion2.1h,therearenoweightmarkers,whosevaluesareoptionallystoredinthefilenamed "markers.log".theconceptofthismarkerisintroducedinthefollowingarticle,andtheirresultsovertimeare investigatedfurther. First,whatisactuallybeingmeasuredaccurately? TheunitsinPerseus'"SoftwareSettings"permityoutochoosebetweentheinputpower(dBm)andtheinput voltage(dbuv)seefigure1. Figure1:Under"SoftwareSettings"isfoundtheunitsforthesignalmeterandthemarkers:dBmordBmV. Forpower,thereferenceofallcalculationsis1milliwatt(mW)attheantennajack.Thewaytodescribevalues otherthan1mwisthedecibel/milliwatt(dbm):10dbmare10milliwatts,100milliwattsofpowerare20dbm, and10dbmare0.1milliwatts,thus20dbmcorrespondingto0.01milliwatts.

2 ThevalueofS9ontheSmeterindicates73dBminputpower. 1 Astronglocalstationattheantennacan measure20dbm(s9+50dbonthesmeter).dxsignalsareoftenfarbelows9. Forvoltage,thereferenceofallcalculationsis1microvolt(uV)attheantennajack.Thewaytodescribevalues otherthan1uvisthedecibel/microvolt(db/uv):10db/uvare3.16uvmilliwatts,20db/uvare10uvofinput voltage,and10db/uvcorrespondingto0.316microvoltsattheantennajack. ThevalueofS9displaysontheSmeterwhen50microvoltsinputlevelisreached.Stronglocalstationsonthe antennaoftenreach84dbuv(s9+50dbonthesmeter)seefigure2. Figure2:Localstationcanachievealevelof23dBm.Relatedtothefilterbandwidthof10kHz,thiscorresponds to63db/hz,whenthepowerisevenlydistributedwithintheband. Theuseofmicrovoltsisarelicfromthepast;aprofessionalwillworkwiththeinputpower. Note:whenreferringtothevoltageinmicrovolts,thisreferstothevoltageattheantennajack.Don tmixitup withthefieldstrength,whichisgiveninmicrovolts/meter(uv/m)withinseveralpropagationprograms,voacap amongthem.thefieldstrengthjustdescribestheelectromagneticfield.simplyput,agoodantennagetsahigh voltageoutofthisfield,whereabadantennarecoversanonlysmallvoltageoutofthisfield.therelationship betweenthefieldstrengthandthevoltageactuallymeasuredattheantennajackofthereceiveriscalled "antennafactor".formostantennas,thisantennafactorvariesoverfrequency.butthereareprofessionalactive antennasformeasurementpurposeswhichshowaconstantantennafactoroveraverywidefrequencyrange. (ForSWLs,theDXoneprofessionalisagoodexample.) WewillthereforeprimarilyrefertothepowerindBmattheantennaconnector. Note:OnlywithprofessionalsoftwaredefinedradiossuchasPerseuscanthemeasuredvaluesbeaccurate withinafrequencyrange!almostallotherreceiversindicateweaksignalslowerthantheyreallyare,andstrong signalsaredisplayedtoohigh.mostcannotevendisplayproperlyans9value.suchinaccuratescalesandmeters areuselessfordisplayingtruesignallevels,onlytrendsofweakeningorstrengtheningsignals! Signallevelsdependonthebandwidthvaluesdisplayed.Theprofessionalapproachistoalwaysrefertoa bandwidthofonehertz:dbm/hzordbmv/hz.becauseofthewaydecibelsarecalculated,theconversion becomeseasyforotherbands.let'stakeadrmsignalof10khzbandwidth(10,000hertzor40db/hz).so,if theinputpower(shownonsmeterdisplay)whenusinga10khzfilter,isforexample50dbm,thenitisrelative to1hz.thatresultsinasignalofonly90dbmor90dbm/hz. ThePerseusreceivercannowindicatetwomeasurementsforsignaldisplay:

3 TheSmetershowsthesignallevel,asitlieswithinthechosenbandwidth.Thislevelwillvarywithinthe filterbetweentherangeofapproximately20hzand50khz. Themarkers,however,revealadifferentlevelonthedisplay(regardlessofwhetherthewaterfallor spectrumisshown)seefigure3.thisiscalledresolutionbandwidth(rbw)anddependsonsampling rate,chosenspan,andzoomlevel.thusitcanbechosenindicatebetween0.03hzand1953.1hz. Figure3:Thelevelsofthemarkersshowsresolutionbandwidth(RBW),whichisdisplayedinHertzinawindowon theleftofperseus. Thebestrangetomeasureandnormalizeto1Hzalsodependsonthemodulationofthesignal.Hereareafew considerationsandrecommendations: AM(amplitudemodulation)usuallyconsistsofatransmittedcarrierwithconstantpowerplusthetwo sidebands.thelattercover25percentofthenominalpowereachatmaximum(=peakmodulation).thus,if yousetamarkeronacarrierofsuchasignal(withpeaksearch),itresultsinalevelmoreorlesscorresponding toabandwidthof1hz(dbm/hz)(independentfromtheactualbandwidth,whichmaybedifferent,e.g.50hz). Incontrast,thisisnotapplicabletonoiseandnoiselikesignals(suchasDRM),whereyouhavetonormalizethe measuringbandwidthto1hz. InSSBmode,thecarrierisattenuatedmostlytosuchadegree,notevenseeableatthereceiver.Hereyouhave torelytothemodulationonly.thus,youmustmeasureatabandwidth,approachingthebandwidthofthe modulationitself.asperseus widestmeasuringbandwidth(=resolutionbandwidth/rbw)is2khz,youshould usethisvalue.especiallywithshortwavecommunications,(audio)frequencyofconsiderablyabove2khz,don t contributetoomuchtothesignalstrength,andcanbeomitted.measuringtheexactlevelofssbsignalsseems difficult.thisisjustacoarseapproach.bestis,tocombinethiswithset"average"(avg)quitehightogetthe peaks.ontheotherhand,youlosetheinfluenceoffading. DRMisanoiselikesignalwiththreepilotcarriers.Youmeasureapilotcarrierwithasmallmarker(below10 Hz),whichcorrespondstothedisplayofabandwidthof1Hz.Anotherwayistomeasurethenoiselikepartof thesignalwiththemaximumrbwof1953.1hz.becausethisrbwrepresentsonlyafifthofthebandwidthof thewholesignal(10khzwide),youhavetoadd3.7dbtothesevalues(because1:5=3.7db).seefigure6. Noisecanalsobemeasured,toshowthesignaltonoiseratio,forexample.Here,thedisplayedpowerisalways convertedto1hz. Note:Withnarrowbandmeasurements,youshouldbeawareofextremelydeep,yetshortdipsinsignallevel. Thisisduetoselectivefadingwhichrunsthroughthesignallikeadeeptrench.Itcanbeshownbestwithnoise likesignals,e.g.atdrmbroadcastingstations.

4 Figure4:RadioFardainAMfromThailandon7520kHzisbroadandstronglymodulated.Anaverageshortwave AMsignalisshownatMrk2(VOATinang).ManyDXstationsoftenproduceagoodsignal,butaremodulatedso weakthattheyarebarelyaudibleangola4950khzisanotoriousexample. Figure5:ThesignaloftheRAFradioSSBtransmitterinDraytonon5450kHzisinuppersideband.Thecarrier (Mkr1)issuppressedcomparedwiththestrongestmodulationfrequency(Mkr2)to35.6dBanexcellentvalue. Theanalysisofsuchsignalscanonlysucceedifwewouldputa3kHzwidemarker(correspondingtothe modulationwidthofthesignal)inthemidstofthesignal,whichhereistheuppersideband.asperseusprovides roughly2khzaswidestresolutionbandwidth,youshouldadd1.2dbtocompensateforthedifferenceof2khzto 3kHz.

5 Figure6:ADRMsignaloftheBBC/Sineson13590kHz,measuredwith15.26HzRBW,showsthecenter frequency(mkr1),thethreepilottones(mkr3tomkr5)andthelowercutofffrequency.inaddition,theaverage levelofthepskmodulatedcarrier(mrk2)andthenoise(mrk7)isshown.exceptforthelasttwomarkers,all equatetodbm/hzvalues.butforthe"noisemarkers"mrk2andmrk7,youhavetoadd12db,tonormalize theirresolutionbandwidthof15.6hzto1hz(for:15.26hz/1hzcorrespondtothis12db).afteraddingthis12 db,youhavenormalizedthereadingsoftheselasttwocarrierstodb/hz. Howoftenshouldyoumeasure? Inadditiontothefrequencyresolution,thetimeresolutionisimportant.Thesoftwareoffers2.1h(software settings/mkrloginterval)between0,1and5secondspracticalwaystomeasureshorttermchanges,aswellas longtermseefigure7. Figure7:Thetimeresolutioncanbeselectedinthesoftwaresettingsinthepopupmenu"Mkrloginterval" between100millisecondsand5seconds.

6 Whenobservingfadeinorfadeoutusingtwelvereadingsperminute(i.e.,everyfiveseconds),thisisalmosttoo frequent.veryshorttermdetection,however,isimportantforthedocumentationofflutterfading,for example. Notes:Thesmoothingfunctionofthemaindisplay(slider:AVGMain)alsohassomeimpactonthescreenandin thestoredvaluesofthe"markers.log"file.withshortsampletimes,youshouldturnofftheavgmainslider, becauseotherwisethe"softwaresettings"settimeresolutionwillbeoverruled.anysmoothingcanbemade laterinotherprograms,withcontrolledandtraceableresults. TheAGCsetting(Fast/Med/Slow/Off)hasnoconsequencesonthedata.Allright,isitallsetupcorrectly? Yes,thenwecanstart!Eitherfromlivereception,orevenfromaWAVrecording: Withthemouseontheappropriatesignal,clicktherightmousebuttoninsuccessiontosetuptoeight markers.ifyouhaveenabledthebutton"peaksrc',themarkerwillautomaticallybewithinacertain capturerangeanditgetssettothestrongestfrequency.thisisidealifyouwanttoobservethecarrier ofanamradiostation. Pressthebutton"MkrLog",andaSavetoFilewindowopensformarkers.logseeFigure8.Click"OK", andthefilemarkers.logwillbefilledwiththeappropriatevalues.thedisplay"mkrlog"lightsupatthis time. Toturnofftheloggingfeature:clicktheMkrLogbuttonagain.The"markersavedtofile"markers.log opens;thenclick"ok". Note:thelogwillthenagainstarttofunction,andthepreviousfilewillbeoverwrittenwithoutwarning! Figure8:Eightmarkersarepreparedforlogging.Yourcurrentfrequenciesandlevelsareright.Atthesametime theircarriers1to8characterizedinthespectrum.clickagainon"ok"andthenpressthe"mkrlog"button.the MkrLogindicatorlightsupstartstherecording.

7 Whatdoyoudowithitnow? Sonowwehavealogfilewiththemarkers.Whatareyousupposedtodowithit?Thepossibilitiesareendless anddependonyourinterestandknowledge.buttwothingsyouwillinevitablyendupwith:avisual representationandathinningofthedatausingstatisticalmethods.thedeepermeaningistofindsome patterns,hiddeninavastamountofdata;notjustthinning,butthinningbythesenseofaknownalgorithm. Thus,onehastotrypatternrecognitionbystatisticalmethods.Iwouldliketogivesomeexamplesofbothand alsoavoidobstaclesintheway,suchastheformattingofthedataseefigure9. Figure9:Whenyouopenthefile"markers.log"withatexteditor,itisclearthateightmarkers(0to7)were recordedeverysecond. Idecidedtousethemarkers.logwiththefreesoftwareSciDAVis. 2 IthasWindows,Mac,andLinuxversions availableandiseasiertoworkwiththanmicrosoftexcel.butinprincipleyoucanuseanyspreadsheetwitha statisticsfunction.soevenmicrosoftexcel(orsunopenoffice),applenumbers,andabovealltheorigin softwareprobablyoffersthemostoptions. 3 Theeasiestwayistoimportalogfilewithonlyonemarker.Oncethereismorethanonemarker,allmarkersare listedunderthesamesampletimeoneafteranother.theyaremarkedfrom"0"formarker1to"7"formarker 8inthecolumn"MkrId".Figure10showstheimportwiththeappropriatesettings,andFigure11isasectionof anongoingrecordingof"markers.log"in"scidavis"importedrecord.

8 Figure10:WithSciDAVisyoucanevenimportdatafromthelogfilewhileplayingarecording.Whileignoringthe firstsixrowsandselecttheseparator"space"option. Figure11:HowtheresultslookinSciDAVis,whichadmittedlystillneedsediting.

9 Thisinturnallowsdatatobeseparated,soyoucancopythevaluesseparatelyforeachmarkerintoaseparate column.tosortthetableaccordingtothemarkernumbers: selectthewholetable(allcolumnsandrows) Clickmenu:Table>SortTable Sortcolumns:"Together" Order:"Ascending" LeadingColumn:theonecontainingthenumberoftheMarkers(MarkerID,max.from0to7) Thiswillsortallcompleterowsaccordingtothemarkernumbers,e.g.all(!)valuesformarker0arefollowedby allvaluesformarker1,andsoforth.thenyouneedtocopythevaluesofallothermarkersotherthanmarker0 intotheneighboringcolumns.thus,youhaveforeachtimesample(=row)thevaluesofthedifferentmarkers alsointhisrow,butindifferentcolumns.afterthat andnamingthetitlesofthecolumnsappropriately the tableshouldlooklikewhatisshowninfigure12. Figure12:Thedataisadjusted,thelevelsofthemarkerarenexttoeachother,andtheheadersarefilledwith thefrequencies.nowwecanproceed! Note:ThePerseusmarkerslogfunctionrecordsinseconds,butnottheabsolutetime.Therefore,Ipreferto replacethevaluesinthe"time"column(e.g.5.001,10.003, )justbythenumbersoftherow(reading: 1,2,3 ): Selectthefirstcolumn Menu:Table>FillSelectionwith>RowNumbers Afterthat,youcanletSciDAViscalculateeventheabsolutetimebyinsertingaformulaforallrownumbersin thefirstcolumn: Selectthecolumn Open"Formula"

10 Inserttheappropriateformula.Example:Ifyouhavesampledevery5seconds,e.g.row12willrepresent thevaluefor1minuteafterstart,androw720willrepresentthevalue1hourafterstart.thusthe formula"col(1)/12"willreturntheminutes,whereas"col(1)/720"willreturnthehours.ofcoursethey areindecimalnotation.togettheabsolutetime,youhavetoaddtotheformulathenumberof minutes/hourssincemidnight. Irecordedforsixminutes,giving6x60=360valuesperstation.Eightmarkersresultinatotalof2880numbers. That sahugenumber,callingforavisualizationoroverview.thisisdonebyjustaclickonthemenu"plot", showninfigure13. Figure13:Eightnewchannelsrecordedoversixminutesinthe31mb.Prettyconfusing. Thisisactuallytoomuchinformation.Weneedtoreduceoraverageitinameaningfulway.Thisdonewiththe helpofstatistics.it'snotmathtrickery,butactuallyhighlightstheimportantdatafromtheunimportantdata, andshowstrends.first,iconvertedthedatafromimage13intoa"boxplot".thisisdonewithjustaclickofa buttoninscidavis(plot>statisticalgraph>boxplot);seefigure14.

11 Figure14:TheBoxPlotisastatisticalmethodthatcreatesorder.Fordetailsseetext. ThelevelcharacteristicofeachfrequencyineachcaseissummarizedinacolumnatthebottomoftheXaxis, correspondingtothefrequency.360valuesateachfrequencyareeachdividedintoseveralgroups: Minimumandmaximumofeachsignalwithinthesixminutesismarkedbyanupperandlower"X" Therectangle(box)itselfincludesallthevaluesthatlieat±25percentaroundthemeanvalue.Thisis markedbythesmallsquare.upperandlowersidesoftheboxdenotethe25and75thpercentiles Thetopandbottomshort,horizontallinesegmentsmarkthe5and95thpercentiles Istheinformationclearertous?Yes,wecanassessthereliabilityofthereceptionsincewegetanoverview aboutthefading,evenwithselectivefading.forexample,thisseemsparticularlymeaningfulon9535khz,since thedistancefromthehighesttolowestvalueinjustsixminutesisabout50db.wethusgetanoverviewnot onlyforamoment,butwithareliableviewoftheoverallperiod.theseareinsightfulmethodswhichhavenever beenavailablebeforetoshortwavelistenersorradioamateurs. Ifthisdiagramseemstoocrowded(Figure13),youcanshoweachtraceseparatelyoranytracescombined. Figure15showsthisforthetwotracesfrom9.505kHz(flatfading)and9535kHz(vividfading).Buttakecare:in thisdiagram,alllevelshavebeen"normalized".thisis:thelevelsdon trepresenttheirabsolutevalueindb,but theirrelativevalues.thehighestvalueofeachtraceis"1",whereasthelowestvalueshows"0".whether"1" means20dbm(andalocalstation)or80dbm(adxstation)cannotbeseenfromsuch"normalized"traces. However,thereisabigadvantageofnormalizedvalues:foryoucancomparethestructureofthefading, regardlessoftheabsolutelevelofthesignals. SciDAViscannormalizeonlypositivenumbers.Aswefacenegativenumbers(like73dBm),wehavetoaddto eachlevelthenumberofthelowestlevelofeachmarker.example:thevaluesforthemarkerrangebetween

12 50dBm(maximum)and70dBm(minimum)youhavetoadd70.Thus,70dBmwillbecome"0",and50dBm willbecome"20".afternormalization,"0"leaves"0",whereas"20"willget"1".and"60dbm"willget"10"in thefirststage,andafternormalization0.5. Figure15:Thenormalizedaxisdoesnotexhibittheabsolutelevel,butalevelrelativetoeachonascalefrom01. Buttheimageisstilltoodetailed.That stherightcircumstancewhere"smoothing"comesintoplay.just imagineitasmedianvaluesofadefinednumberofneighboringvalues.ifyouincludeonlytwoneighboring values,smoothingisweak.thebiggerthenumberofneighboringvalues,thestrongertheeffectof"smoothing", showingnotdetails,butthegeneraltendencyoffading.figure16showsthisforsixneighboringvalues,namely 0to5.At"0"thereisnosmoothingeffect,whereasat"5"itisquitestrong,asseeninFigure16.

13 Figure16:Theoriginalcurve"Smoothed0"willbesmoothedatvariousstrengths.Detailsareprogressivelylost, butfadingtendenciesandpatternsemergemoreclearly. Withthisapproachyoucaneasilycomparevarioussmoothedcurves,andunderstandthedifferences. Figure17:Herewefindmanyrelativelysmallsignals,asshowninthishistogram. Thehistogramisaninterestingcurveforthesecomparisons.Hereisadiagramshowingthefrequenciesandthe signallevelgroupings(teninthiscase).figure17showsawiderangeofsmallersignals;thereceptionhereis lessstablethanthesignalshowninthehistogramoffigure18.acompletelystablesignalwouldhaveonlya singlecolumn.

14 Figure18:Inthismorestablesignal,thelargerlevelisconcentratedinasmallerwidth. ThedistributionofthelevelisdifferentfromthefamousbellshapedGaussiancurve(allvaluesrandomly distributedaroundameantogivethesymmetricalappearanceofabell).whenitcomestofadingthough,we haveaflatterprofileinthedirectionoflowersignalstrengthandasteeperprofileinthedirectionofstrong signals.butwhydothesignalsappearontheleftsideofunlimitedflatdiscontinuedandlimitedtotheright side? Thisdependsonthefactthatmostsignalsarriveatleasttwodifferentwaystous.Atthereceiver,therearetwo extremeoptions:theymingle"inphase"(thenthesignalisdoubled(+6db),ortheyminglewith"opposite phase"(thentheyabsorbeachother).theyareattenuatingeachother,ineffecttotallyextinguishingthewhole signal,thustheattenuationis"infinitedb".thisextremeisoccurringonlyifthephaseoftwopathsdiffersby exactly180 pluseachpathdeliveringexactlythesameleveltotheantennajack.however,bothconditions almostneverconvergeintoonemoment.inpractice,theattenuationrarelyisinfinite,butintheregionofsome 10dB.Butitisapproaching"infinitedB"asymptomatically.Ontheotherhand,theupperlimitisanexactfigure: +6dB,whentwopathsareexactly"inphase",andofthesamestrength.Thistypeofdistribution(oneside asymptomatically,theothersteepwithafixedend)iscalled"rayleighdistribution".thereareseveralsiblingsof thisdistribution,butingeneralweencounterrayleighdistributionwhendescribingthecharacterofmultipath fading. 4 Suchthingsareindispensabletotheprofessionalplanningofshortwavebroadcasts.DXersaremoreinterested inwhetherasignalisheard,andforhowlong,andwhenthesignalisthebest.again,themarkersprovideevery possibility. ThusweseeinFigure19thecourseofthewintersignalWWCR/Nashville5070kHzandRadioRebelde/Cuba 5025kHzbetween0600UTCand1200UTC,shortlyafterWWCRsignoff.ThesunriseatthereceiverinNorthern Germanyis0730UTC,thesunriseinCubais1155UTC,andinNashville,thesunevengoesonuntilabout1259 UTC.Weseethatbothsignalsstartalmostequal,butthenthemorenortherlyNashvillestrengthenscompared tocuba.evenbeforesunriseatthereceivinglocation,thesignalfromcubatravelsalongdistanceindaylight,

15 anditsmoresubduedsignalisevident.infigure20(fromdxatlas),onecanalsoseethedecember30th grayline1000utc. Figure19:ShowsthesmoothedlevelsofNashvilleandHabanaovertime.Theystartatalmostsamesignal strength.butaroundreceiver ssunrise,theyseparatefromeachother.ashabanatakesamoresoutherlypath, thissignalismoreinfluencedbytheattenuatingdlayer,buildingupduetosunshine.abiggerpartofthispath liesunderthesun. Figure20:ShowsthepositionofthegraylineonDecember30that1000UTC,globeprojection.Nashvilleand Habanaareshownbypushpinicons,andthereceiverlocationisindicatedbyaYagiantennaicon.

16 IfsuchexperimentsdoguideustoexceptionalDX,theyareverymuchwelcomedbyeventheaverageDXer. Theycanprovideausefultracewhereyoucanseethetimeswithbestsignal/noiseratioataglance.Figure21is aclearexample. Figure21:ThereceptionofSIBCHoniaraonDecember24,2009at1500UTCshowstheoptimumreceptiontime. OnChristmasDay2009,DXerWolfgangBueschelannouncedthatSIBCHoniara/5019.7kHzwasheardonce again,afteratransmitterrepair.whenireadthenewsinchristophratzer'sadxlist,iimmediatelypressedthe recordbuttonofperseusandcaptured1330to1900utcinwavfiles.rightfromthestartsibcwasaudible, anditincreasedto1500utc,andfadedshortlyafter1600utc.thesignalstrengthenedabitafterthat,but neverreacheditspriorlevel.mylocalsunsetwas1509utc,almostexactlythetimeofthestrongestreception. 5 Thesewerejustafewpossibilitiesandideasonusingthemarkersandmarker.logfileinPerseus.Yourother ideasarewelcome!germantext&images 2010:NilsSchiffhauer,DK8OK Footnotes Footnote1: Footnote2: Footnote3: Footnote4:Forfurtherexamples: Footnote5:TwoSamples14:00to15:00UTC:

17 APPENDIX Markers ResolutioninaNutshell For(semi)scientificpurposesitisimportanttoknow,whatexactlyyouaremeasuringbythemarkers.They havetwodimensions: timeand level Forboth,resolutiondependsonacoupleoffactors,someoftheminterdependent. Ingeneral,themarker slogdocumentswhatyouseeonthescreeninthebigwindow,spectrumpreferredover waterfall. Regardingtime,Perseus SoftwareSettings doofferachoicefrom0.1to5seconds.obviously,theactualtime resolutionalsodependsfromthe Span,andthe ResolutionBandwidth/RBW.Let sshowthiseffect,when receivingtimesignalstationmsfon60khz. 1 Each normal minutestartswith atleast100ms off andends withatleast700mscarrier,asthefactsheetofthenationalphysicallaboratoryputsit. 2 FiguresAtoDhaveall beenmadewitharesolutionof0.1seconds(perseus SoftwareSettings).Pleaserefertothecaptions. FigureA:Thisisthediagram,wedoexpectfromatimesignalstationonlongwave.Weclearlyseetheseconds, markedby carrieroff foratleast100milliseconds.thedatarefertoa span of100khz,anda resolution bandwidth of122hz.ifwemagnifythisdiagram,thisleadsusto

18 FigureB: whereeach100millisecondsampleismarkedbyabullet.becausestartingofthe100mssamples cannotbesynchronizedwiththetimeoftransmitting,yousometimesseemorethanonebulletmarkinga carrierofftime ofexactly100ms. FigureC:Exactlythesamesituation,asshowninFigureA.Butrecordedwitha span of1600khz,anda resolutionbandwidth of1953,1hz.thisobviouslyprovidesuswithabettertimeresolution.

19 FigureD:AmagnifiedpartofFigureC,showingabettertimeresolution.SeeforsomedBoffadingevenduring the900millisecondsof carrieron. Thefiguresshowthatthebiggerthespanandthebiggertheresolutionbandwidth,thegreateristheresolution intime. 3 Thenextstepwastofindout,whatasamplingrateofe.g. 5seconds reallymeans:willitreturntheaverage level(powerofvoltage)overfiveseconds,orwillitgivejustaflashlightpictureeachfiveseconds? Obviously,Perseusiscollectingsamplesviatheflashlightmethod.Otherwise,FiguresEandFwon tshow samplesofsuchlowlevels.again,ireceivedmsftimeticks.overfiveseconds,itscarriershouldbe on forat leastfoursecondsor80%ofthetime.thus,whenaveraged,thedistributionofthesamplewouldbewithinjust acoupleofdb,butnotupto50db.thus,thediagramsseemtoshowthesynchronizationbetweenthetime, wherethesamplesare flashlighted,andthesecondticksofthetransmitter.ifitwouldbepossibleto synchronizethestartjustwithin carrieroff,thediagramwouldshowalmostasimplelinearound100dbm.in case,startedwithin carrieron,itwouldshowalmostalinebetween90and80dbm. 3 Sorryfordon tprovidingtheunderlyingmath;willhavetoasknicoforthat.

20 FigureE:WhensampledMSFwithfiveseconds,aspanof1600kHzandaRBWof1953Hz,thedifferencesofthe samplescomeuptomorethan15db.thissuggeststhateachfiveseconds,thesoftwareplacesaflashlightonto thesignal.sometimes,atthismoment,itseesacarrier(90dbm),sometimethecarrierisoff. FigureF:Showstheeffectofsynchronization,800seconds,100kHzspanand122Hzresolution.

21 Averagingthesignallevel,willgiveusmorerealisticresults.Thiscanbedonebytheslider AVGMain.Youcan seetheeffectfromfigureg,comparingwithfiguree. FigureG:Averagingshowstheaveragelevelofthetimesignalstationfor100secondsatthesamescale (Level/Time)asFigureE. Aswedon tknowbyexactnumberstheeffectofthisaveraging,amorepreciseaveragingcanbealsodoneby statisticalmethods(e.g. AveragingWindow ). Somuchfor timesandsamples.nowforthemarkers level.aslaidoutinthearticle,theleveldependson ofcourse thesignalandonthe resolutionbandwidth/rbw.signalswithaconstantlytransmittedcarrier, whichisstrongcomparedtothemodulation(aswithmostbroadcastingstations),areeasilytomeasure:largely notinfluencedbytheresolutionbandwidth,themarker(setontothecarrier:pksrc)automaticallyshowsthe levelindbmordbuvat1hz. Tomeasurenoiseornoiselikesignals(likeDRM),youhavetotakethe resolutionbandwidth intoaccount. ThisisnotalwaysassimpleasjustaddingorsubtractingdB,inorderto normalize abandwidthtothatof1hz. Mostoftenonshortwave,youhavetotakeintoaccountthefactorofselectivefading. FigureHshowsthelevelsofthethreepilotcarriersofaDRMsignal.Theyaretransmittedwiththesame constantpower.butwereceivethemwithoftendifferentlevels.

22 FigureH:ThethreepilotcarriersofaDRMsignalat+750Hz,+2250Hzand+3000Hz(inreferencetothecarrier frequency)haveasimilarshape,butnotexactlythesame.duetoselectivefading,theydifferabitintime,as wellasinlevel. Evenmeasuringpilotcarriers,withDRMsignal,youhavetoobservetheresolutionbandwidth,seeFigureI. FigureI:OneDRMpilotcarrierunderthemicroscope(Mkr1).Itisonlyroughly8dBstrongerthantheotherPSK carriers(mkr2),peakinginadistanceofonly±43hz.thus,insuchanenvironment,oneshouldmeasurethe carrieronlyata resolutionbandwidth lowerthanabout30hz Mkr3markstwo notches 16Hzapartfrom thepilotcarrier.asasharpselectivefadingcanleadtoapilotcarrierwellbelow(some10db)belowthepsk carriers,youneverknow,whatexactlyyouaremeasuringwithawider resolutionbandwidth.

23 Thegraphical(not:numerical)settingofmarkersisveryeasyandintuitivetodo,butleavesuswithtwo problemsinratherspecialcases: tomeasuree.g.adrmsignalwithseveralmarkersofawide resolutionbandwidth (theycannotbe placedexactly) tomeasureatverylow resolutionbandwidths,e.g.separatecarriersononemediumwavechannel, differingbyonlyafewhertz.triedtoseparatee.g.urumchi,bksaryadhandgoldukfromeachother on1521khz,butfailedtodoso. RTTYsignals(FSK)shouldbemeasuredwitha resolutionbandwidth,widerthantheirshift. Text&figures:NilsSchiffhauer,DK8OK, 2010