Specifications

Maxiva UAX
October 17, 2013
5‐33
888‐2693‐004 WARNING:Disconnectprimarypower priortoservicing.
Copyright©2013,HarrisBroadcast
5.7 Pre‐correctionforAnalogTV
Theprecorrectionforananalogtransmitterisafixednonlinearpredistortionandlinearequalizationwithautomatic
setup.Theproceduredescribedbelowautomaticallycalculatestheprecorrectionforaninstalledsystem.Oncethe
precorrectioniscalculated,itcanbestoredinthesetupmemoryoftheexciter.Theprecorrectionisappliedby
settingboththeLinearRTACmodeandtheNonlinearRTACmo
detoSTORED(seeFigure5‐14onpage5‐23).
Assumptions:
• Transmitterpeakpowerlevelisknownandautomaticpowerregulationhasbeenactivated.
• Asignalsampleisavailablefromaforwardcoupleraftertheamplifierandpriortothemaskfilter.
• Asignalsampleisavailablefromaforwardcouplerafterthemaskfilter.
• Transmitterisalreadyconfiguredforthecorrectcarrierfrequencyandmodulationstandard(M,B/G,D/K,
etc).
EquipmentandTo
olsRequired:
• TektronixTG700VideoSignalGeneratorPlatformorequivalent
• TektronixVM700TVideoMeasurementSetorequivalent
• SpectrumAnalyzer
5.7.1 PrecorrectionSetup Procedure–(AnalogTV)
CalculatingNonlinearPredistortion(trainingperiod):
STEP 1
VerifythatthenonlinearandlinearRTACmodesaresettoBYPASS.
STEP 2 Applyanappropriate1Vp‐p,black,nosetup,videotestsignal.
STEP 3 Turntransmitteronatdesiredpowerlevel.
STEP 4 Verifythataforwardpowersamplefromtheafterthefinalamplifierbut
beforethefilterisconnectedtothePRE‐FILTERportonthebackoftheLPU.
Thermslevelofthesampleshouldideallybeapproximately‐5dBm.
STEP 5 Verifythatthenonlinear(Pre‐Filter)samplelevelisslightlybelowtheblack
lineindicator(transmitteratfullpower)ontheRTACstatusscreen.
STEP 6 Switchonthesoundcarrier.Readjustoutputpowerto100%.
STEP 7 Confirmthatthesoundcarrierlevelis10dBbelowvisualpeakofsynclevel
onthespectrumanalyzer.
STEP 8 Demodulateasampleofthesystemoutputusinganappropriate
demodulator.Connectthevideooutputsignaltoavideomeasurement
system/waveformmonitor.
STEP 9 Measurethesynclevelandadjustsyncoffsettoachieve300mV(40IRE).
Readjusttheaurallevelto‐10dBasnecessary.
STEP 10 Applytheappropriatemodulatedrampvideo signal.
STEP 11 Measurethedifferentialgain/differentialphaseonthevideomeasurement
system/waveformmonitor.
STEP 12 SetthenonlinearRTACmodetoADAPT.
STEP 13 VerifythatthenonlinearRTACattemptandsuccesscountersincrement
abouteverytwentyseconds.
STEP 14 Afteroneortwoadaptations,switchtheRTACnonlinearmodetoHOLD.
STEP 15 Savethiscurrentcorrectioninoneofthefourslots(SeeStoring
Precorrection).NOTEthatsincetheLinearRTACisinBYPASSatthistime,no
linearcorrectionwillbestored.
LinearEqualizer:
STEP 16
Linearequalizationrequiresthatnonlinearitieshavebeenlinearized.This
conditionistrueafterthenonlinearcorrectionhasbeenapplied.