User's Manual

300-Watt Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures
DT830A, Rev. 1 5-7
(A8) the amplifier control board (1265-
1414), to the AGC On position.
To align (A6) the UHF amplifier tray,
switch on CB3 on the AC distribution
panel. Move the transmitter Operate/
Standby switch on the UHF exciter to
Operate and observe the power supply
metering position on the UHF amplifier
tray. It should read +26.5 VDC when the
tray is switched on and the transmitter is
in Operate. The (A12) ASTEC America
+26V/2000W switching power supply
(VS3-L6-B6-21) is factory set for the
+26.5 VDC and has no customer-needed
adjustments.
Switch the tray to the % Output Power
Meter position and adjust the front panel
gain pot on that amplifier tray to 100%
on the meter. Back off the gain pot to the
reading on the Test Data Sheet. Switch
the transmitter to Standby and reconnect
the UHF amplifier tray.
To align (A7) the UHF amplifier tray,
switch off CB3 and switch on CB4 on the
AC distribution panel. Move the
transmitter Operate/Standby switch on
the UHF exciter to Operate and observe
the power supply metering position on
the UHF amplifier tray. It should read
+26.5 VDC when the tray is switched on
and the transmitter is in Operate. The
(A12) ASTEC America +26V/2000W
switching power supply (VS3-L6-B6-21)
is factory set for the +26.5 VDC and has
no customer-needed adjustments.
Switch the tray to the % Output Power
Meter position and adjust the front panel
gain pot on that amplifier tray to 100%
on the meter. Back off the gain pot to the
reading on the Test Data Sheet. Switch
the transmitter to Standby and reconnect
the UHF amplifier tray.
Switch the transmitter to Operate. The
output power reading on the front panel
meter of UHF exciter should be 100%.
Check that the ALC voltage, as read on
the front panel meter, is set to .8V. The
voltage can be adjusted by using the
power screwdriver adjust pot on the front
panel of the UHF exciter tray. The
amplifier tray can then be adjusted as
needed to achieve the 100% output.
As shipped, the exciter was preset to
include linearity (gain vs. level) and
phase (phase vs. level) pre-distortion.
The pre-distortion was adjusted to
approximately compensate the
corresponding non-linear distortions of
the amplifier. Move the jumper W1 on J4
of the ALC board to the corrector enable
position. Refer to the Test Data Sheet for
the final test readings on the amplifier
tray. Adjust the phase pot on the front
panel of the UHF amplifier tray to obtain
maximum % Output Power on the front
panel meter of the UHF exciter. Adjust
the gain pot on the UHF amplifier tray to
obtain 100% Output Power on the front
panel meter of the UHF exciter.
5.2.1 Phase and Gain Adjustment of
the UHF Amplifier Trays
The following procedure was completed
at the factory and should only be
repeated if one of the UHF amplifier trays
is replaced.
Preset the phase and gain potentiometer
on each UHF amplifier tray full CCW. Turn
off the A6, A7 amps at the AC
distribution panel. Switch the transmitter
to Operate and adjust the gain pot on
each tray for 25% Output Power. Adjust
the phase control CW on the left, bottom
UHF amplifier tray. If the % Visual
Output Power goes up, continue to adjust
the phase control until either the peak is
reached or the end-of-travel is reached.
If the % Output Power goes down, reset
the phase control on the UHF amplifier
tray full CCW and repeat the above
procedure with the phase control of the
other amplifier tray.
If the end-of-travel is reached on the
phase adjust, reset the phase control
CCW and add a 2-inch length of cable to
the output of the (A5) splitter module
that connects to the affected UHF
amplifier tray at J1. Readjust the phase