System Description Chapter 2

3-kW UHF Transmitter Chapter 2, System Description
835-3, Rev. 0 2-4
The RF input from the UHF exciter tray connects to J1 on (A11) the interface panel in
the amplifier assembly. The RF is connected to the COM input of (A9-A1) the 8-way
splitter which splits it eight ways; six of the outputs are connected to J1, the RF input on
each of the 600-watt amplifier trays (1227-1300), and the other two outputs are
terminated with 50-
Ω
loads. Each of the 600-watt amplifier trays amplify the RF signals
to the power needed to produce a total of 3000 watts peak of sync, with a maximum of
600 watts.
In each 600-watt amplifier tray, a forward power sample and a reflected power sample
from the 4-way combiner board are connected to the dual peak detector board, single
supply. This board provides peak-detected forward samples to the amplifier control
board that supplies the samples to the front panel meter of the 600-watt amplifier tray.
Before exiting each 600-watt amplifier tray, the RF is fed through a circulator for the
protection of the tray from high VSWR conditions. The reject port of the circulator
provides a reject sample to the 4-way combiner board. The 4-way combiner board
supplies the reflected sample to the dual peak detector board, single supply, in the tray
that connects to the front panel meter.
The outputs of the six 600-watt amplifier trays are combined in (A7) the 6-way
combiner that provides the 3000 watts peak of sync output with a maximum of 3600
watts. The 6-way combiner has six reject outputs that connect to (A12) a reject load
assembly (1278-1312). The reject load assembly provides loads for any reject power
generated due to mismatch in the combing process. The assembly provides a heatsink,
(A12-A3 and A12-A5), two fans, and (A12-A4) a thermal switch. The thermal switch is
mounted on the heatsink for the reject load assembly and connects to the
overtemperature fault circuit on the transmitter control board in the UHF exciter tray;
this shuts down the transmitter if an overtemperature fault occurs. The combined RF
output for the transmitter is at the 1-5/8” hardline connector from the 6-way combiner.
2.2.2 3-kW Transmitter Output Assemblies
The output of (A2) the amplifier assembly connects through a 1-5/8” to 3-1/8” adapter
to (A9) a bandpass filter, (A10) an output trap filter assembly, and then to (A11) the
output coupler assembly (1020-1002). The bandpass filter and trap filter are tuned to
provide high out-of-band rejection of unwanted generated products. The filtered signal
is connected to (A11) an output coupler assembly that provides two combined forward
and a combined reflected power sample to the metering panel in the UHF exciter
assembly.
2.3 Control and Status
The forward samples are processed to provide peak-detected visual and aural power
output samples to the front panel meter of the metering panel. The reflected power
sample is also peak detected and wired to the front panel meter.
The control and status of the 3-kW transmitter is provided by the meter indications on
the UHF exciter tray. The switches and LED indicators, which are mounted so that the
switches and LEDs are operated or viewed from the front panel of the UHF exciter, are
part of the transmitter control board (1265-1311). On the UHF exciter tray, switch S1 is
an Operate/Standby switch that provides the Operate command (enable), when in
Operate, to the amplifier array at J4-15 and J4-16, where it is split six ways and
connected to each 600-watt amplifier tray. The enable is needed to turn on the
switching power supplies in the 600-watt amplifier trays. When the UHF exciter is in
Operate, the green LED DS2 is on and, when in Standby, the amber LED DS1 is on.