User's Manual

8 3 6 A 2 k W UHF Tr a nslat or , I nt erna lly Diple x ed Det ailed Alignm e n t Pr oce dur e
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Lin e a rit y Correct or Adjust m e n t
The I F linearit y correct ion function consist s of three non- linear cascaded st ages, each having
adj ust able m agnit ude and threshold or cut - in points locat ed on the ALC Board. The t hreshold
adj ust m ent determ ines at w hat I F signal level t he corresponding correct or st age begins t o increase
gain. The m agnit ude adj ust m ent determ ines t he am ount of gain change for t he part of t he signal
which exceeds t he corresponding t hreshold point. Refer t o t he UHF Excit er Tray Assem bly Drawing
( 1265- 5300) , or t he Assem bly Draw ing for ( A8) ALC Board (1265-5305) , t o locate the adj ust m ents
for the first t hrough t hird linearit y correct or st ages. Because t he stages are cascaded, t he order
of correct ion is im portant. The first st age should cut - in near whit e level, wit h the cut - in point of
the next st age t ow ard black and wit h the last st age prim arily st ret ching sync.
To adj ust t he linearit y correctors from scratch. Ensure that t he Translat or is operat ing at full
power with the desired A/ V Rat io. Check that t he Jum per W1 on J4 on t he ALC Board is Enabled,
bet ween Pins 1 & 2. Check t hat the ALC Volt age is set to + 0.8 VDC as m onit ored on the Front
Panel Met er in the ALC Posit ion.
I nsert a m odulat ed ram p video t est signal int o the Translator. Dem odulat e t he out put signal of the
Translat or and observe the waveform on a Waveform Monit or while also looking at t he signal on a
Spect rum Analyzer. On the I F ALC Board ( 1265-1306), preset t he Pot s R34, R37 & R40 ( Threshold)
full CCW, and t he Magnit ude Adj ust m ents R13, R18 & R23 full CW. On t he I F Phase Correct or
Board ( 1227- 1250) , preset the Pot s R7, R15, R23 & R35 full CW, and R3, R11, R19 & R31 full CCW.
Lin e a rit y Correct or Adjust m e n t - Cont inued
Set t he Waveform Monitor t o Different ial St ep Filt er and the Volt s/ Division scale t o .1V. Cent er
the display around Blanking.
Gradually adj ust pot s R3, R11 and R19 Clockwise on t he I F Phase Correct or Board as needed t o
m inim ize t he observed t hickness of the int erm od as seen on t he display.
Adj ust the pot s R34, R37 and R40 Clockwise on the I F ALC Board needed to give correction at
Sync or at low lum inance levels, which are view ed at the rightm ost edge of the Waveform Monit or.
The interm od beat product s bet ween the Color Burst and the Aural Carrier at 920 kHz above Visual
Carrier should also be observed on the Spectrum Analyzer while perform ing t he preceding
adj ust m ent s. The frequency will vary for PAL Syst em s. When the adj ust m ents are perform ed
properly, t he int erm od product s on the Spect rum Analyzer should be at least - 52 dB down, wit h a
Red Field input, from peak visual carrier and the I nt erm od Dist ortion as displayed on the Waveform
Monitor should be no m ore t han 1 I RE. The pot R31 on t he I F Phase Correct or Board is used for
any extra I nt erm od correct ion that m ay be needed.
I t should be not ed that any adjust m ent of the above pot s affect s ot her visual param et ers and
som e slight adj ustm ent s of all t he pot s m ay be needed t o m eet all specificat ions sim ult aneously.
I f the Translat or is being driven very hard, it m ay not be possible t o get enough Sync St ret ch
while m aintaining a flat different ial gain. I n this case, som e Video Sync St ret ch m ay be used from
the Sync Tip Clam p/ Modulat or Board. The Sync St ret ch adj ust m ent is R48 locat ed on the Sync
Tip Clam p/ Modulat or Board. Swit ch the Translator to Standby.
Phase a n d Gain Adjust m e n t of t he UHF Am plifier Trays