User's Manual

300-Watt Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT830A, Rev. 1 4-19
J8-12, which can light any remote
receiver fault indicator that is connected
to it.
4.1.10.5 Metering
The front panel meter connects to J3-1(-)
and J3-2(+) on the board; this is the
output of switch S3. The front panel
meter has four metering positions that
are controlled by switch S3: % Forward
Power, % Reflected Power, % Exciter,
and ALC.
The reflected sample connects to the
board at J2-9 and is connected through
buffer amplifier U1B and 100-Ω resistor
R84 to position 3 of switch S3. The
forward sample connects to the board at
J2-5 and is connected through buffer
amplifier U1D and 100-Ω resistor R86 to
position 4 of switch S3. The exciter
sample connects to the board at J2-3 and
is connected through buffer amplifier U1A
and 100-Ω resistor R87 to position 2 of
switch S3. The ALC sample connects to
the board at J6-1 and is connected
through buffer amplifier U2C; R15, the
ALC calibration pot that adjusts the
output of U2A, pin 1; through 100-Ω
resistor R18; and to position 1 on switch
S3.
Typical readings on the meter are:
• % Reflected = <5%
• % Forward Power = 100%
• % Exciter = The level on the meter
needed to attain 100% output power
from the transmitter
Refer to the test specifications sheet for
the transmitter for the actual readings for
the items shown below:
• ALC = .8 VDC
Samples of the exciter at J1-10, the
visual at J8-26, the aural at J8-27, and
the reflected at J1-5 are provided for
remote metering.
U6 is a temperature sensor IC that gives
the operator the ability to measure the
temperature inside the tray by measuring
the voltage at TP1. The sensor is set up
for +10 mV equals 1° F (for example,
750 mV equals 75° F).
4.1.10.6 Operational Voltages
The +12 VDC needed for the operation of
the board enters the board at jack J4, pin
3. C28, L1, and L3 are for the filtering
and isolation of the +12 VDC before it is
split and applied to the rest of the board.
The -12 VDC needed for the operation of
the board enters at jack J4, pin 5. C29
and L2 are for the filtering and isolation
of the -12 VDC before it is split and
applied to the rest of the board.
When the +12 VDC is connected to the
board, it is split. Four of the +12 VDC
outputs are fed out of the board at J8-16,
J8-17, J8-18, and J8-19 through diode
CR7, CR8, CR9, or CR10 and resistor
R50, R51, R52, or R53 to any external
amplifier trays for use in their logic
circuits. The resistors are for current
limiting and the diodes are to prevent
voltage feedback from the external
amplifier trays.
4.1.11 (A3)+12V(4A)/-12V(1A)
Power Supply Board (1265-1312;
Appendix D)
The ±12-volt power supply board
consists of three separate power
supplies, two of which produce the +12
VDC and one for the -12 VDC needed to
power the circuit boards in the exciter
tray.
4.1.11.1 +12 VDC Power Supply
The 18 VAC from the external step-down
toroid in the tray connects to J1, pins 7
and 8. The 18 VAC connects through 7-
amp fuse F2, for over-current protection,
to two full-wave bridge rectifier circuits.
CR1, CR2, CR3, and CR4 rectify the AC
that is then filtered by C2 and connected