User's Manual

300-Watt Digital UHF Transmitter Chapter 4, Circuit Descriptions
DT830A, Rev. 1 4-23
4.2.7 (A10) DC Power Supply Board
(1047033; Appendix D)
The DC power supply board generates
both positive and negative 12 and 5 VDC,
as well as positive 3.3 VDC, at a current
level that is sufficient to operate the
other boards in the modulator tray.
Visual indicators, using LEDs, are
provided on the board to show the
normal operation of each voltage
regulator.
The DC outputs (+15, +5, and -15 VDC)
from the switching power supply
(1049886) are directed to jack J1. The
voltages are then filtered by C1 to C6
and fed to voltage regulators U1 to U7.
The outputs are protected from over-
current conditions by the regulators. The
regulators are designed to fold back the
voltage if a short-circuit condition occurs
external to the board and will continue to
do so until the short is eliminated. If a
short appears, the on-board LED
associated with that regulator will
extinguish with the loss of the output.
4.2.8 (A8) VSB IF Filter Board
(1047976; Appendix D)
The VSB IF filter board performs the
low-pass filtering of frequencies above
63 MHz.
The board receives the output IF signal
from the vector modulator board at J1.
The input signal is fed through the 50-Ω
matching circuit of R1, R2, and R3. The
signal is then filtered by low-pass filter
circuit L1 to L5 and C2 to C6. The signal
is amplified by U1 and fed to SMA
connector J2. The signal is also fed
through the IF sample circuit of U2 and
associated components to J4, the IF
sample. This sample is fed to the front
panel sample port.
The board is supplied by an external
+12-VDC source.
4.2.9 (A4) VSB Symbol Generator
Board (1049396; Appendix D)
The symbol generator board takes the
MPEG data and clock signals from the
interface card and performs the digital
signal-processing functions outlined in
the ATSC specification for 8-VSB
modulation. These functions involve
data randomization, the Reed Solomon
encoder, the data interleaver, and the
trellis encoder. These functions are
implemented in the programmable logic
chip U1 on the symbol generator card.
In addition, this card performs the linear
equalization function. This function is
implemented in U14.
The output of this card is symbol data
that has been equalized. The data is
available at J25 in the form of ten data
lines and a 32.28-MHz clock. In addition,
the microcontroller data and address
bus is available at this output connector.
The LCD display and the switch panel
are also controlled by the symbol
generator card. The interface to the LCD
display is provided at J20 and the
interface to the switch panel is provided
at J21. The RS-232 interface to Port A is
provided at J19 on this card. This
interface is wired to the rear of the tray
and is used to load the linear equalizer
and perform adaptive equalization. The
Port B serial interface is wired through
connector J4 on this card.
4.3 (A6 and A7, A8 and A9 with
upgrade) UHF Amplifier Trays
(1294-1112, 1294-1113 or 1294-
1114; Appendix C)
4.3.1 (A3) 1-Watt Amplifier Board
Assembly (1227-1319; Appendix D)
The 1-watt UHF amplifier board assembly
provides radio frequency interference
(RFI) and electromagnetic interference
(EMI) protection, as well as the heatsink,
for the 1-watt UHF amplifier board
(1227-1303) that is mounted inside the
module assembly. Depending on the