User's Manual

300-Watt Digital UHF Transmitter Chapter 2, System Description
DT830A, Rev. 1 2-1
Chapter 2
System Description
The DT830A is a complete 300-watt
(average) UHF solid-state digital
television transmitter that operates at a
nominal average output power of 300
watts.
2.1 System Overview
The DT830A consists of the assemblies
and trays listed in Table 2-1.
Table 2-1. DT830A Major Assemblies and Trays
MAJOR ASSEMBLY NUMBER TRAY/ASSEMBLY NAME
A4 UHF digital exciter tray
A6 and A7 UHF amplifier trays
A11 Coupler assembly
A2 AC distribution assembly
A19 8-VSB modulator tray
A12 Input and remote interface assembly
A8 UHF “tee”
2.1.1 (A19) 8-VSB Modulator Tray
(1075164; Appendix C)
The 8-VSB modulator accepts an MPEG-
2 transport stream input and outputs an
8 VSB IF signal centered at 44 MHz. To
operate the modulator, the MPEG is
connected to one of the three
connectors on the rear panel, depending
on the format of the MPEG data stream.
The formats presently available are
SMPTE 310M, Differential Serial TTL, and
ECL. In addition, the modulator has an
internal test source that can generate an
MPEG data stream for test purposes.
This signal is then modulated to a 44
MHz IF and fed to the output at J1.
2.1.2 (A4) UHF Digital Exciter Tray
(1294-1111; Appendix C)
The output from the modulator connects
to J6 on the rear of the UHF exciter tray,
which is wired to J18 on the IF delay
equalizer board, 44 MHz (1072090) and
exits the board at J10. The processed
digital IF signal is then wired to the ALC
board (1265-1305) at J32. With digital IF
input selected, the jumper W11 on J29 is
connected between pins 2 and 3 on the
ALC board; the digital IF is wired through
the K3 and K4 relays to the rest of the
ALC board. The LED DS5, digital IF
modulator enable, should be lit. The ALC
board has the capability to switch
between two different IF inputs; in this
case, only the digital IF input is used.
The output of the ALC board (0 dBm
peak) connects to (A11) the UHF
upconverter board (1265-1310) in the
upconverter section of the UHF digital
exciter. The upconverter takes the LO
and heterodynes it with the IF; the signal
is then filtered to produce the RF on-
channel output.
The (A15-A1) UHF generator board
(1565-1109) is mounted in the UHF
Generator Enclosure (1519-1144) for EMI
and RFI protection. The board contains a
VCXO circuit and additional circuitry to
multiply the VCXO frequency by eight.
The output is split and provides an input
to the x8 multiplier circuitry as well as a
sample for the PLL board.
The amplified eighth harmonic is then fed
to the SMA output jack of the board at J3.
Typical output level of the signal is +16
dBm nominal.