User's Manual

2650 Watt VHF High Band Transmitter Chapter 5, Detailed Alignment Procedures
435B, Rev. 0 5-1
Chapter 5
Detailed Alignment Procedures
The 435B transmitter was aligned at the
factory and should not require additional
alignments to achieve normal operation.
This transmitter operates using the
baseband audio and video inputs or, if
the (optional) 4.5-MHz composite input
kit is purchased, either a single
composite video + 4.5-MHz input or
separate baseband video and audio
inputs.
Check that the RF output at J2 of (A9)
the bandpass filter assembly is
terminated into a dummy load of at least
1000 watts. While performing the
alignment, refer to the Test Data Sheet
for the transmitter and compare the final
readings from the factory with the
readings on each of the trays. They
should be very similar. If a reading is off
by a significant amount, the problem is
likely to be in that tray.
Switch on the main AC and the VHF
exciter circuit breakers on the AC
distribution panel behind the rear cabinet
door.
5.1 (A4) VHF High Band Exciter Tray
(1070901; Appendix C)
5.1.1 VHF High Band Exciter Tray
with Baseband Video and Audio
Inputs
The (A4) VHF high band exciter tray
(1070901) has adjustments for video
levels, audio modulation levels, and other
related parameters.
Connect an NTSC baseband video test
signal input (1 Vpk-pk) to the transmitter
video input jack J2 on the (A12) remote
interface panel. Jacks J1 and J2 on the
VHF exciter tray are loop-through
connected and the unused jack can be
used as a video source for another
transmitter by removing jumper W4 on
jack J3 on (A5) the sync tip clamp
modulator board (1265-1302). Connect a
baseband audio input (+10 dBm) to the
balanced audio input terminal block TB1-
1 (+), TB1-2 (-), and TB1-3 (ground). If
stereo/composite audio is provided,
connect it to BNC jack J6, the composite
audio input jack on the remote interface
panel. Jacks J3 and J13 on the rear of
the exciter panel are loop-through
connected and the unused jack can be
used as an audio source for another
transmitter by removing jumper W1 on
jack J15 on the aural IF synthesizer.
Look at the front panel meter on the VHF
exciter tray. In the Video position, the
meter indicates active video from 0 to 1
Vpk-pk. The normal video input level is 1
Vpk-pk on the meter. If this reading is
not at the proper level, the overall video
level can be changed by adjusting video
level control R12 on the sync tip clamp/
modulator board.
Switch the meter to the Audio position to
show the audio deviation (modulation
level) of the signal from 0 to 100 kHz.
The aural IF synthesizer board was
factory set for a ±25 kHz deviation with a
balanced audio input of +10 dBm. If the
reading is at not the correct level, adjust
balanced audio gain pot R13 on the aural
IF synthesizer board, as needed, to attain
the ±25 kHz deviation. The aural IF
synthesizer board was factory set for a
±75 kHz deviation with a composite
audio input of 1 Vpk-pk. If this reading is
not correct, adjust composite audio gain
pot R17 on the aural IF synthesizer
board, as needed, for the ±75 kHz
deviation.
5.1.2 VHF H.B. Exciter Tray with the
(Optional) 4.5-MHz Composite Input
Kit
With the 4.5-MHz composite input kit,
the (A4) VHF exciter tray (1070901) is