User's Manual

3300-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
335B, Rev. 0 5-12
10. Move jumper W7 on J4 to the
Clamp Enable position. Readjust pot
R152, depth of modulation, for the
correct depth of modulation.
11. Set the waveform monitor to
display ICPM. Preset R53 fully CCW,
adjust C78 for the greatest effect at
white on the ICPM display, and then
adjust R53 for minimum ICPM.
12. Recheck the depth of modulation
and, if necessary, adjust R152,
depth of modulation.
13. On a spectrum analyzer, adjust pot
R70 for a level of approximately -10
dBm at J18.
14. Remove the input video test signal.
Place the front panel meter in the
video position and, while monitoring
the meter, adjust pot R144, zero
adjust, for a reading of zero.
15. Replace the input video test
signal (the 5-step staircase).
Turn the front panel meter to
the video position and adjust
R20 on the transmitter control
board for a reading of 1 volt
(10 on the 0 to 10 scale). This
board does not have sync
metering.
16. Reconnect the plug to J18 and
move the spectrum analyzer test
cable to the 41.25 IF output jack
J16. Tune C59 and L17 to L20 to
maximize the 41.25-MHz aural IF
signal and minimize the out-of-
band products. Adjust pot R97 for
-20 dBm at J16.
17. Reconnect the plug to J16 and
move the spectrum analyzer test
cable to IF output jack J20. Preset
R62, the visual IF gain pot, to the
middle of the range. Insert a
multiburst test signal into the
transmitter and observe the visual
frequency response with the
spectrum analyzer set at 1
dB/division. Tune R63 and C30,
the IF frequency response
adjustments, for a flat-frequency
response (±0.5 dB).
18. While still monitoring J20 with a
spectrum analyzer, readjust R62,
visual IF gain, for a 0 dBm visual
output level. Adjust R85, A/V ratio,
for a minus 10 dB aural-to-visual
ratio or to the desired A/V ratio.
Reconnect the plug to J20.
19. Using an input video test signal (the
5-step staircase) with 100 IRE
white level, monitor TP2 with an
oscilloscope. Set control R24, the
sync clip, just below the point
where sync clipping begins to occur.
Similarly, set R20, the white clip, to
just below the point at which the
white video begins to clip.
5.12.7 (A4) Aural IF Synthesizer
Board, 4.5 MHz (1265-1303;
Appendix D)
1. To set up the test equipment for
this board:
A. Connect the 600Ω balanced
audio output from an audio
oscillator to the balanced audio
input terminals of the tray at
TB1-1 (+), TB1-2 (-), and TB1-
3 (ground) on the rear chassis.
B. Connect the combined IF
output at J21 (IF sample) on
the clamp modulator board to
the input of an IF splitter.
Connect one output of the
splitter to the video
demodulator and the other
output to the spectrum
analyzer.
C. At the front of the
demodulator, connect a short
cable from the RF-out jack to
the IF-in jack.