User's Manual

1 1 7 B 2 0 W a t t VHF High Band Transla t or Upconve rt er/ Am plifie r Tray
Circuit Descript ion
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The VHF Upconverter/ Am plifier Tray t akes the m odulated Visual + Aural I F input from the Modulator
or Receiver Tray and m ixes it wit h a generat ed L.O. t o produce t he desired VHF High Band Channel
Frequency out put. The Tray then am plifies t he VHF signal t o t he 20 Wat t peak of Sync Visual
Out put power level.
I F SI GNAL PATH
The input of t he Upconvert er/ Am plifier Tray is a m odulat ed I nt ernally Diplexed I F signal. The I F
input net work for the Tray is a sim ple bandpass filt er located on ( A10) the ALC/ AGC Board
( 1067- 1116) which elim inates harm onics on t he input signal. The signal is next adj ust ed in level by
the pin at t enuat or/ ALC circuit ry and sent to ( A11) the Linearit y Corrector Board (1161- 1116) . The
Linearit y Correct ors com pensat e for the am plit ude non- linearities of the final am plifiers by providing
an opposit e am plit ude transfer funct ion. The shape of this t ransfer funct ion is set by t he
potentiom et ers located on this board. The correct or circuit s can also be bypassed by the
switches locat ed on the board.
The out put of the Linearit y Correct or Board is sent back to t he ALC/ AGC Board where an AGC
circuit com pares a detect ed sam ple of the I F wit h a det ect ed sam ple of the RF Out put and adj ust s
the I F out put t o m aintain a const ant gain aft er the first sam ple point . This correct s for any
tem perat ure drift that m ay occur in the am plifier devices. ( A9) The AGC Control Board (1137-
1201) provides adj ust m ents of t he AGC feedback from t he Transm it t er Control Board t o t he VSWR
Cutback circuit located on the Transm itt er Cont rol Board.
The ALC and AGC cont rolled I F signal from J4 on the board is fed t o Jack ( J2) located on ( A16) t he
Mixer/ Am plifier Enclosure, which cont ains ( A16-A1) a Filter/ Mixer Board and ( A16- A2) a
Filt er/ Am plifier Board. The I F Signal (- 3 dBm Visual - 13 dBm Aural) connect s t o Jack J7 of ( A16-
A1) t he Filter/ Mixer Board (1150- 1102) and is wired t o t he Mixer st age Z1. The Mixer m ixes t he I F
wit h the local oscillator signal, that connects t o J3 on the board, to produce the desired VHF
output signal.
L.O. SI GNAL PATH
The local oscillator signal is derived from a cut t o channel cryst al, locat ed in an oven set at 45° C.
This oscillat or circuit , which is part of (A14- A1) the Channel Oscillator Board (1145- 1201) , is a
m odified Colpitt s circuit . The Channel Oscillat or Board is m ount ed in ( A14) a Channel Oscillator
Assem bly (1145- 1202) that has a separat e oven set at 50° C for im proved st ability. The out put of
the Oscillat or Assem bly at J1 is fed t o ( A15) a x4 Mult iplier Board ( 1174-1112) . The x4 Mult iplier
cont ains t wo doubler circuit s which m ult iply the L.O. signal to t he required frequency needed for
m ixing wit h the I F to produce t he VHF High Band Channel Frequency. The L.O. Signal ( + 5 dBm )
from J2 on the board is connect ed Jack J1 of ( A16) the Mixer/ Am plifier Enclosure which is cabled t o
Jack ( J3) of (A16- A1) the VHF Filt er/ Mixer Board ( 1150-1102). The L.O. Signal is am plified by U2
and connect ed to J4 of the Board. The am plified L.O. Signal at ( + 14 dBm ) is j um pered t o ( J5) t he
L.O. I nput Jack t o the Mixer Z1.
RF SI GNAL PATH
The L.O. input and the I F input are m ixed to produce an out put of the Mixer at Jack ( J6) (- 14 dBm )
which cont ains t he unwanted Mixer product s along wit h the desired VHF Channel signal. These
signals are j um pered from J6 to J1 the RF I nput Jack of the VHF Filt er/ Mixer Board.
RF SI GNAL PATH - CONTI NUED