User's Manual

Digital UHF Transmitter Chapter 2, System Description and
Customer Remote Connections
DT835A, Rev. 1 2-3
A4, A5 & A6) UHF amplifier trays, (A7) a
4 to 6-way combiner, (A8) an output
coupler, (A10) an AC distribution
assembly, and (A11) an interface panel.
The RF input from the variable
phase/gain tray connects to J1 on (A11)
the interface panel in the amplifier array
assembly. The RF is connected to the
COM input of the 8-way splitter, which
splits it eight ways, with six of the
outputs connected to J1, the RF input on
each of the UHF amplifier trays and the
other two outputs terminated with 50Ω.
The UHF amplifier trays amplify the RF
signals to the power needed to produce
a maximum of 300 watts 64 QAM or 8-
VSB digital per tray.
The outputs of the four, five or six UHF
amplifier trays are combined in the 4, 5
or 6-way combiner. This provides
approximately half of the power needed
to generate the full 8-VSB digital output
of the transmitter. The RF output is
connected to the output coupler
assembly. The output coupler assembly
supplies a forward and a reflected power
sample of the output from the amplifier
assembly to the metering panel in the
single exciter assembly.
In each UHF amplifier tray, the forward
power and reflected power samples from
the 4-way combiner board are
connected to the dual peak detector
board, single supply, that provides peak
detected samples to the amplifier control
board. The amplifier control board then
supplies DC voltages to the front panel
meter of the UHF amplifier tray. Before
exiting each UHF amplifier tray, the RF
is fed through a circulator for the
protection of the tray from high VSWR
conditions.
2.1.5 Transmitter Output
Assemblies
The outputs of the amplifier array
assemblies connect through (A5 and A6)
1-5/8” to 3-1/8” adapters to (A4) a
hybrid combiner (55223A) that
combines the output from the amplifier
assemblies into a single output. The
reject output of the hybrid combiner is
connected to (A7) an output coupler that
provides a reject sample from J3 to the
metering panel in the single UHF exciter
assembly for monitoring purposes. The
output of the (A7) directional coupler
connects to (A8) a 2500-watt reject load
that dissipates any reject power
produced during the combining process.
A (A8-A1) thermal switch is mounted on
the 2500-watt reject load that connects
to the overtemperature fault circuit on
the transmitter control board in the UHF
exciter tray. This fault circuit shuts down
the transmitter if an overtemperature
fault occurs. The overtemperature is
normally caused by a large reject power
being dissipated by the reject load due
to the malfunctioning of one of the
amplifier arrays.
The output of the (A4) hybrid combiner
at J3 is fed to (A11) the output coupler
assembly. The filtered signal is
connected to (A11) an output coupler
assembly that provides combined
forward and reflected power samples to
the metering panel in the single UHF
exciter assembly. The forward sample is
processed to provide peak detected
visual and aural power output samples
to the front panel meter on the metering
panel. The reflected power sample is
also peak detected and wired to the
front panel meter.
2.1.6 Control and Status
Information on the control and status of
the transmitter is provided by the
indicators on the metering panel and the
variable phase/gain trays. There are also
control, status, and LED indicators on
the front panel of the UHF exciter tray.
The functions of these control and status
indicators are shown in the following
tables. The switches and LED indicators,
which are mounted so that the switches
and LEDs can be operated or viewed
from the front panel of the UHF exciter,
are part of the transmitter control board.