Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-32
DC blocking for the output signals. The
RF signals connect to L7, which consists
of UT-141 coaxial cable. L7 combines
the RF back to a single-RF output at a
50-Ω impedance and sends it to L8,
which provides a sample of the RF. The
main path through L10 is to J5, the RF
output jack of the board (+10 to +20
dBm). The sample of the RF connects
to a splitter that provides a sample
output (0 dBm) at J6 of the board. The
other output of the splitter connects to
a peak-detector circuit consisting of
CR3 and U3, which provides a DC level
at J7 that represents the RF output of
the UHF exciter to the front panel
meter. R29 sets up the calibration of
the front panel meter for 100% in the
UHF Exciter position when the output
power of the exciter is at +17 dBm
peak visual or +10 dBm average for
digital applications.
The board is powered by ±12 VDC that
is produced by an external power
supply. The +12 VDC enters the board
through J8, pin 3, and is filtered and
isolated by RF choke L9 and shunt
capacitors C24 and C33. This circuit
isolates the RF signals from the board
away from those of other devices
connected to the same +12 VDC line
external to the UHF upconverter board.
The +12 VDC is then applied to the rest
of the board.
The -12 VDC enters the board through
J8, pin 5, and is filtered and isolated by
RF choke L11 and shunt capacitors C34
and C35. This circuit isolates the RF
signals from this board away from
those of other devices connected to the
same -12 VDC line external to the UHF
upconverter board; the -12 VDC is then
applied to the rest of the board.
4.2.18 (A1) Power Entry Module
Assembly (1227-1206;Appendix D)
The power entry module assembly
provides overvoltage and surge
protection for the input AC lines that
connect to the exciter tray. The AC
input plug connects to J14; J14 is part
of the power entry module on the rear
panel of the exciter tray.
The module assembly contains two
130-VAC varistors and one 250-VAC
varistor that connect across the AC
lines and to ground. The module also
contains two 4-amp fuses for
overcurrent protection, one in each
input line.
4.3 (A4 and A5) Variable
Phase/Gain Trays (1245-1200;
Appendix C)
The Variable Phase/Gain Tray sets the
phase and gain adjustments of the RF
to provide maximum output when the
outputs of the two Amplifier Arrays are
combined. There are two Variable
Phase/Gain Trays in the 837B UHF
Translator, each controlling the phase
and gain of one of the two Amplifier
Arrays.
The Tray is made up of (A4) a Variable
Phase/Gain Assembly (1245-1204),
which contains (A4-A1) a Variable
Phase/Gain Board (1245-1201), (A5) a
Metering Board (1245-1202) and (A3)
a +15V/-12V Power Supply Board
(1245-1203).
4.3.1 (A4-A1) Variable Gain/Phase
Board (1245-1201; Appendix D)
The RF Input signal connects to the
rear panel of the Tray at J1 and is
cabled to J1 on (A4-A1) the Variable
Phase/Gain Board (1245-1201) that is
mounted inside (A4) the Variable
Phase/Gain Assembly (1245-1204) for
RFI and EMI protection. The Variable
Phase/Gain Board contains two main
circuits, one for ALC and one for Phase
adjustment of the RF signal. A front
panel mounted ALC adjust Pot (A8)
connects through (A5) the Metering
Board (1245-1202) to J5 on the Board
which controls the output level to the
tray. A front panel mounted Phase