User's Manual

3300-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
335B, Rev. 0 5-8
Reflected Power. Be careful not to
increase Reflected Power on the other
Amplifier Trays. The Amplifier Trays
should interact in such a way that the
phasing of any one amplifier tray will
affect the Reflected on the other amplifier
trays.
Raise or lower the output power of each
tray as needed to achieve 100% Output
Power. The output power of each tray
should be 90% to 100%.
5.8 Calibration of the Forward
Output Power Level of the
Transmitter
NOTE: Only perform the following
procedure if the forward power
calibration is suspect.
Switch the transmitter to Standby and
preset R51, the aural null pot on the
visual/aural metering board (1265-
1309), fully CCW. Adjust R48, the null
offset pot on the visual/aural metering
board, for 0% Visual Output. Perform
the following adjustments with no aural
present. This is accomplished by
removing jumper cable W1, the aural IF
loop-through, that is connected to J16 on
(A5) the sync tip clamp/modulator board
(1265-1302). Connect a sync and black
test signal to the video input jack of the
VHF exciter tray. Switch the transmitter
to Operate.
Next, set up the transmitter for the
appropriate average output power level:
• Sync + black 0 IRE
setup/wattmeter=1190 watts
• Sync + black 7.5 IRE
setup/wattmeter=1090 watts
NOTE: The transmitter must have 40 IRE
units of sync.
Adjust R28, visual calibration, on (A19)
the visual/aural metering board (1265-
1309) for 100% on the front panel meter
in the % Visual Output position.
With the spectrum analyzer set to the
zero span mode, obtain a peak reference
on the screen. Reconnect jumper cable
W1 to J16 on (A5) the sync tip
clamp/modulator board. While in the
Visual Output Power position, adjust L3
for a minimum visual power reading.
Turn the power adjust pot on the front
panel until the original peak reference
level is attained. Peak L1 and C8 for a
maximum aural power reading and then
also adjust R20 for a 100% Aural Power
reading. Switch the transmitter to the
Visual Output Power position and adjust
R51, the aural null pot, for 100% Visual
Power.
5.9 Calibration of the Reflected
Output Level of the Transmitter
NOTE: Only perform the following
procedure if the reflected power
calibration is suspect.
Check that the transmitter is at 100%
forward power. Switch the transmitter to
Standby and move the reflected cable to
the other Incidental port on the A16
Coupler. Switch the transmitter to
Operate and adjust R39 on the
visual/aural metering board (1265-1309)
for a 10% reading in the Reflected Power
position. At this 10% reference power
reading, the VSWR LED mounted on the
front panel of the exciter should be
illuminated. If this LED is not lit, adjust
R22 on the transmitter control board in
the VHF exciter tray until the VSWR LED
just turns on. Turn the power adjust pot
slightly CCW and the LED should go out.
Turn the pot CW until the LED just turns
on. The reflected output power is now
calibrated.
Switch the transmitter to Standby. Move
the cable on A16 Coupler back to the
Reflected port.
Switch the transmitter to Operate and
adjust the front panel power pot for a
100% Visual Power reading.