User's Manual

2650 Watt VHF High Band Transmitter Chapter 5, Detailed Alignment Procedures
435B, Rev. 0 5-15
located in the VHF exciter. Connect a
sync and black test signal to the video
input jack of the VHF exciter tray. Switch
the transmitter to Operate.
Set up the transmitter for the appropriate
average output power level: sync + black
0 IRE setup/wattmeter=595 watts; sync
+ black 7.5 IRE setup/wattmeter=545
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.
5.7 Calibration of the Reflected
Output Level of the Transmitter
On the meter, in the Visual Power
position, turn the power adjust pot to
20%. Check that the jumper is in Manual
on (A11-A3) the VHF filter/amplifier
board (1064252), located in the VHF
exciter. Reverse the cables on A9, J3
and J4, and adjust R39 on the (A19)
visual/aural metering board (1265-
1309), in the VHF exciter, for a 20%
reading in the Reflected Power position.
At this 20% 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 (A17)
transmitter control board (1265-1311) 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 cables on A9, J3 and J4, to their
original positions. Switch the transmitter
to Operate and adjust the front panel
power pot for a 100% Visual Power
reading.
5.8 (A8) 2-Way Combiner Assembly
(1219-1006; Appendix C)
There are no adjustments to (A8) the
VHF combiner assembly (1219-1006).
5.9 (A9) Bandpass Filter Assembly
NOTE: The bandpass filter is a pre-tuned
vendor item and should not be tuned
without the proper equipment. If tuning
is required, consult the Axcera Field
Support Department before attempting
to make any adjustments.
This completes the alignment procedure
for the 435B Transmitter. If a problem
occurred during alignment, please
contact Axcera field service department
at 724-873-8100.