User's Manual

350-Watt Digital VHF LB Transmitter Chapter 2, System Description, Maintenance &
Remote Control Connections
DT325B, Rev. 0 2-2
2.2.1: (A4) Exciter Control/
Power Supply Assembly, LXB,
220VAC (1310835; Appendix C)
The (A4) Control/Power Supply
Assembly is made up of a System
Controller Board (1310089), a Power
Protection Board (1302837) and a LCD
w/Switches Board (1307977). The
Assembly also contains a switching
power supply that provides ±12 VDC to
the rest of the modules in the chassis
and +32 VDC to the Power Amplifier
module if needed.
The Assembly provides all transmitter
control and monitoring functions. The
Front panel LCD allows monitoring of
system parameters, including forward
and reflected power, transistor currents,
module temperatures and power supply
voltages.
Table 2-2: Controller/Power Supply Display
DISPLAY FUNCTION
LCD
A 4 x 20 display providing a four-line readout of the internal
functions, external inputs, and status. See Chapter 3,
Controller/Power Supply Display Screens, for a listing of displays.
Table 2-3: Controller/Power Supply Status Indicator
LED FUNCTION
OPERATE
( green )
When lit it indicates that the transmitter is in the Operate Mode. If
transmitter is Muted the Operate LED will stay lit, the transmitter
will remain in Operate, until the input signal is returned.
FAULT
( red or green )
Red indicates that a problem has occurred in the transmitter. The
transmitter will be Muted or placed in Standby until the problem is
corrected.
DC OK
( red or green )
Green indicates that the switchable fuse protected DC outputs that
connect to the modules in the transmitter are OK.
Table 2-4: Controller/Power Supply Control Adjustments
POTENTIOMETER DESCRIPTION
DISPLAY CONTRAST Adjusts the contrast of the display for desired viewing of screen.
2.2.2: (A5) Upconverter Module
(1310226) and (A1) Downconverter
Module (1311157)
NOTE: More information and the
drawings on the Axciter Modulator Tray
(1305842) and the Upconverter Module
(1310226) and Downconverter Module
(1311157) are found in the separate
Axciter Manual.
The output from the Axciter modulator,
which is an 8-VSB IF signal centered at
44 MHz. that is -6 dBm in level, is cabled
to J68 on the rear panel of the
Driver/Amplifier Chassis Assembly. The
IF input is connected to the upconverter
module assembly through the backplane
board in the chassis assembly. The 44
MHz IF signal is upconverted to the
desired channel frequency by the
upconverter module. The resulting RF
signal is amplified and wired to a Pin
Diode Attenuator which adjusts the gain
of the module that is controlled by an
Automatic Gain Control circuit. The AGC
maintains a constant power out of the
upconverter, and also the transmitter,
that connects to the power amplifier
module. The gain controlled output of the