User's Manual

1 1 7 B 2 0 W at t V H F H igh Band Transla t or Syst e m Align m ent Procedu r e
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To adjust t he linearity correction from scrat ch, preset t he Linearit y Correct or pots R5, R16 and R26
( t hreshold) to CCW and Linearity Corrector pots R2, R11 and R22 (m agnit udes) CW. I nsert a 3.58
MHz m odulat ed st aircase or ram p video t est signal int o t he Tray and m onitor the different ial gain of
the output . Swit ch the ALC Aut o/ Manual Sw it ch (S1) located on ( A10) t he ALC/ AGC Board to
Auto ALC. This com plet es t he ALC loop.
Adj ust the ALC Reference Pot (R47) , or t he Front Panel Power Adj ust , to obtain a Detect ed I F
Out put Volt age Level of + 2.0 VDC at TP3 of the ALC/ AGC Board. The Front Panel Met er in the ALC
Reference Voltage position should also read + 2.0 VDC. Switch the ALC Auto/ Manual Swit ch (S1)
located on ( A10) the ALC/ AGC Board t o Manual ALC and adj ust t he Manual ALC Pot (R17) t o obtain
a Detect ed I F Output Volt age Level of + 2.0 VDC at TP3 of the ALC/ AGC Board. Swit ch the ALC
Auto/ Manual Swit ch ( S1) located on ( A10) the ALC/ AGC Board t o Auto ALC. The ALC will now
operat e t o m aintain the corresponding peak power level following t he correct ors. Therefore, t he
linearity adj ust m ent procedure should be repeat ed to achieve t he correct different ial gain
predist ortion. A positive aspect of linearity adj ust m ent with ALC and AGC enabled is that t he
cont rol m ovem ents will not affect peak power. This com plet es the preset st eps.
While observing Different ial Gain, adj ust the first linearit y stage and advance t he Threshold # 1
Cont rol ( R5) CW t o stret ch t he signal above the Whit e and Mid- Lum inance region. Back off on t he
corresponding Magnit ude # 1 Control ( R2) as required. Next , advance the Threshold # 2 Cont rol
( R16) to st ret ch the Black and Sync levels, then back off on the Magnit ude # 2 Control ( R11) as
required. Adj ust the Threshold # 3 Control ( R26) t o furt her st ret ch the Black and Sync levels.
Back off on t he corresponding Magnitude # 3 Control ( R22) as required. Go back t hrough the White
through Black and Sync correct ors t o t ouch up the effect s of ALC Level changes during t he
adj ust m ent. I f t he am plifier is being driven very close t o saturation, it m ay not be possible to get
enough Sync St ret ch while m aint aining a flat different ial gain. The I F linearit y correct ors, when
properly adj ust ed, will provide excellent lower sideband suppression and m inim um frequency
response change vs. level. These result s are achieved by generat ing int erm od product s which
cancel wit h t hose produced by the am plifier, an effect which is not possible with video correct ion.
FI NAL AGC ADJUSTMENT
Check t hat the ALC Volt age is set t o + 2.0 VDC at TP3. Switch the front panel Met ering Switch,
located on the Front Panel of t he VHF Upconverter/ Am plifier Tray, t o the % Visual Output Power
position and adj ust the AGC Aut o Gain pot ( R96) located on t he ALC/ AGC Board to 100% on the
m et er. Switch t he AGC Switch (S2) t he Manual Position and adjust the AGC Manual Gain pot
( R101) , located on t he ALC/ AGC Board, also for 100% on t he m eter. Swit ch S2 back t o Autom at ic.
The Front Panel Meter of the Upconvert er/ Am plifier Tray in the AGC Det ect or Volt age position
should read (.3 VDC) and in t he ALC Reference Voltage Position ( 2 VDC) , but t he exact values are
writ t en on t he Final Test Data Sheet for your Syst em .
This com plet es t he Syst em Alignm ent Procedure for t he 117B.