System Description Chapter 2

500-Watt VHF Low Band Transmitter Chapter 2, System Description
325A, Rev. 0 2-2
In the VHF 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, that provides peak-
detected forward samples to the amplifier
control board that supplies the samples
to the front panel meter of the tray.
2.2 Control and Status
Control and status information for the
transmitter is provided by the meter and
LED indicators on the front panel of the
VHF exciter. The switches and LED
indicators are part of the (A17)
transmitter control board that is mounted
so that the switches and LEDs are
operated or viewed from the front panel
of the VHF exciter.
Switch S1 is an Operate/Standby switch
that controls the output of the
transmitter by providing the Enables
that, when the transmitter is in Operate,
are needed to turn on the switching
power supplies in the two VHF amplifier
trays. In Operate, the green LED DS2 is
on and in Standby the amber LED DS1 is
on. If the transmitter does not switch to
Operate when S1 is switched to Operate,
check that a dummy jumper plug, with a
jumper between pins 23 and 24, is
connected to jack J11 on the back of the
tray. The jumper plug must be connected
to (A12-J9) when the (optional) remote
interface panel is used. This jumper
provides the interlock needed for the
transmitter to operate. If the interlock is
present, the green LED DS5 should be lit.
Switch S2 is an Automatic/Manual switch
that controls the operation of the
transmitter by the presence of the video
input signal. When the switch is in
Automatic, the green LED DS3 is lit and,
if the video input signal to the
transmitter is lost, the transmitter will
automatically switch to Standby. When
the video input signal returns, the
transmitter will automatically switch back
to Operate. In Manual, the amber LED
DS4 is lit and the operation of the
transmitter is controlled by the front
panel switches. During normal operation
of the transmitter, switch S2 should be in
the Auto position. The front panel of the
VHF exciter also has LEDs that indicate a
Video Fault (Loss; red LED DS9) and
VSWR Cutback (amber LED DS7).