User's Manual

Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT835A, Rev. 1 4-26
front panel meter. Another input to the
(A9) Dual Peak Detector Module is the
Forward Sample from the Side A
Amplifier Array which is peak detected
and connected to the (A15) front panel
meter.
4.5.4 (A18) Detector Threshold
Board (1245-1402; Appendix D)
The Detector Threshold Board consists
of three identical signal paths. One
path uses a detected Reflected sample
from Side A, another the detected
Reflected sample from Side B and the
final path uses a detected Combined
Reflected sample. These samples are
compared to the threshold settings,
20% Reflected level, and provide an
output to cut back the transmitter if the
reflected level of any of the input
samples increase above 20%.
A Sample of the Side A Reflected level
enters the board at J1-1. The level is
split and one path connects to J1-2 to
be used as a Side A Remote Reflected
output. The other path connects to the
Operational Amplifier U1A whose turn
on level is controlled by the setting of
R5. R5 is set to cause U1A to conduct
if the reflected sample input increases
above the 20% level. The output, at
J2-1 and also J2-5 through the jumper
W1 on J4, connects to the Transmitter
Control Board, located in the UHF
Exciter, where it cuts back the
transmitter using the VSWR cut back
circuits.
A Sample of the Side B Reflected level
enters the board at J8-1. The level is
split and one path connects to J8-2 to
be used as a Side B Remote Reflected
output. The other path connects to the
Operational Amplifier U1B whose turn
on level is controlled by the setting of
R12. R12 is set to cause U1B to
conduct if the reflected sample input
increases above the 20% level. The
output, at J2-5 and also J2-1 through
the jumper W1 on J4 connects to the
Transmitter Control Board, located in
the UHF Exciter, where it cuts back the
transmitter using the VSWR cut back
circuits.
A Sample of the Combined Reflected
level enters the board at J7-1. The
level is split and one path connects to
J7-2 to be used as a Remote Combined
Reflected output. The other path
connects to the Operational Amplifier
U1C whose turn on level is controlled
by the setting of R19. R19 is set to
cause U1C to conduct if the combined
reflected input sample increases above
the 20% level. The output, at J6-1 and
also J2-5 through the jumper W2 on J5
connects to the Transmitter Control
Board, located in the UHF Exciter,
where it cuts back the transmitter using
the VSWR cut back circuits
4.5.5 (A1) Power Entry Module
Assembly (1227-1206; Appendix D)
120/240 VAC connects to the Tray at J8
on (A1) the Power Entry Module
Assembly. Jumpers on the Power Entry
Module are set for the desired AC
Voltage Input. The assembly contains
an On/Off Switch, two 4 Amp Fuses
and three Varistors for AC line
protection. The AC is connected to
(A2) a step down Toroid that supplies
an 18 VAC output thru TB1 to the ±12V
Power Supply Board.
4.5.6 (A3) ±12V Power Supply
Board (1062-1013; Appendix D)
The ±12 VDC needed to operate the
Boards in the Metering Panel are
provided by the ±12 VDC Power Supply
Board (1062-1013).
The 18 VAC, from an external step-
down Transformer, is directed to the
Board thru J5 Pins 1 & 4, with Pin 2
connected to the center tap of the
secondary of the Transformer.
The +12 VDC is produced by using a
Full-Wave rectifier circuit consisting of
CR1 and CR2 whose output is filtered