User's Manual

3300-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
335B, Rev. 0 5-1
Chapter 5
Detailed Alignment Procedures
The 335B 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 (A16)
the coupler is terminated into a dummy
load of at least 3300 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 circuit breaker for
the transmitter and the VHF exciter
circuit breaker located on the rear of the
tray.
5.1 (A4) VHF Low-Band Exciter Tray
(1070820 or 1304463 w/P.F;
Appendix C) with Baseband Video
and Audio Inputs
NOTE: The 1304463 VHF Exciter is used
with the precise frequency system and
will contain the VCXO Assembly (1145-
1206), in place of the Channel Oscillator
Assembly (1145-1202), and the IF VCXO
Board (1248-1131), in place of the IF
Oven Oscillator Assembly (1191-1404).
The (A4) low-band VHF exciter tray 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 J2 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 VHF exciter tray are loop-through
connected and the unused jack J13 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 the
video level control R12 on the sync tip
clamp/ modulator board.
Switch the meter to the Audio position,
which shows 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 the 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.