Specifications

Section-5 Maintenance
October 17, 2013
5‐10
Copyright©2013,HarrisBroadcast
WARNING:Disconnectprimarypower priortoservicing. 888‐2693‐004
RecallfromtheforwardpowercalprocedurethattheLPUFWDsampleinputisalsoapproximately0dBmatfull
systemoutputpower.ThiswasbydesigntoallowtheFWDsampletobeusedasaconvenientsignalsourcefor
reflectedcalibration.
Inge
neral,thecalibrationisperformedbyconnectingapowermetertotheforwardcouplerusedinthesystem
forwardcali brationandthenraisingthesystemoutputtofullpower.Therequiredlevelwillbeindicatedonthe
calibrationscreen:itisthesameasthehighcalibrationpointinthefo
rwardcalibration(e.g.61dBmina1.0kW
digitalsystem)asindicatedonthemeter.TheuserwillthenremovetheRFLDsampleinputcablefromtheactive
LPUandconnecttheFWDsampleinitsplace‐‐througha20dBpadforthelowpointanddirectlyforthehighpoin
t
‐‐thusprovidingthedesired‐20dBmand0dBmlevels,respectively.
5.4.4 SystemReflectedCalibrationProcedure
STEP 1 ZeroandcalibrateyourRMSpowermeter,followingthemanufacturer’s
proceduresforyours pecificmodel.
STEP 2 Locatethesystemforwardcalibrationsample,whichshouldhavebeen
measuredandlabeledatthefactorywiththecouplingfactorforyour
frequencyofoperation.Thiswilleitherbeaforwardportonthepre‐filter
directionalcouplerwhichisleftavailableforthispurposeinastandalone
(i.e.non‐ra
cked)configuration,orthefrontbulkheadPREFILTERforward
powersampleinarackedconfiguration.Ifthecouplingfactorisinquestion,
orifthefrequencyhaschanged,theapplicableforwardcouplerportshould
besweptwithanetworkanalyzertodeterminethecorrectcouplingfactor
tobeused.Remembertoincludeth
elossintheroutingcablesinthis
networkanalyzermeasurementwhencharacterizingthebulkhead
measurementpoint.
STEP 3 Oncethecouplingvalueisdetermined,enterthisvalueasanoffsetinyour
powermeter,setthemeter’sdisplaytoreadindBm(3digitsissufficient,i.e.
xx.xdBm),andconnectthemeter’ssensortothisport.
Note
Please ensure that the sample level present at this point (max system output, in dBm, minus the coupling
factor) does not exceed the maximum input range of your particular power sensor.
STEP 4 Enterthereflectedpowercalibrationmenu,eitherfromthefrontpanel
(SETUP>XMTRPOWERSETTINGS>POWERCAL>REFLECTED)orfromthe
WebGUI.See’SystemCali bration’(leftside)Figure5‐3onpage5‐6.
STEP 5 UsetheapplicableRaise/Lowerbuttons(dependingonwhetheryouare
calibratingfromthefrontpanelorWebGUI)toadjustthetransmitter
outputpoweruntilthepowermeterindicatesthevaluerequestedonthe
calibrationscreen.Thiswillbethefullsystemoutputpowervalue,thesame
asthehighcalibrationpo
intintheforwardcalibrationprocedure,(e.g.
61dBmina1kWdigitalsystem).Onceastablereadinghasbeenobtainedon
thepowermeter,proceedtothelowpointcalibration.
STEP 6 Lowpointcalibration:RemovetheFWDandRFLDsamplecablesfromthe
activeLPU(thecablesarelabeledFWDandRFLDontheirrespectiveheat
shrinktubinglabels).Ifdesired,useapowermetertomeasurethelevel
presentontheFWDsamplecableandverifythatitisapproximately0dBm.
ConnecttheFWDsampleca
ble,througha20dBattenuatorpad,totheREF
PWRinput.PresstheSavebuttontostorethevalueinmemoryandproceed
tothehighpointcalibration.RefertoFigure5‐6.