Data Sheet Chapter 5

500-Watt VHF Transmitter Chapter 5, Detailed Alignment Procedures
425A, Rev. 0 5-10
by the baseband video and audio inputs
with baseband has been selected by the
4.5-MHz composite input kit, the
composite 4.5-MHz filter board and the
4.5-MHz bandpass filter board are not
used.
The tray has been factory tuned and
should not need any alignments to
achieve normal operation. To align the
tray for the 4.5-MHz composite input,
apply the 4.5-MHz composite input, with
the test signals used as needed, to the
video input jack (J1 or J2 [loop-through
connections]) on the rear of the tray.
Select the 4.5-MHz composite input by
removing the baseband select from J18-6
and J18-7 on the rear of the tray.
To align the exciter using baseband video
and audio inputs, apply the baseband
video, with the test signals used as
needed, to the video input jack (J1 or J2
[loop-through connections]) and the
baseband audio to the proper baseband
audio input on the rear of the tray. For
balanced audio input, connect TB1-1(+),
TB1-2(-), and TB1-3 (GND). For
composite/stereo audio, connect the
composite audio input jack (J3 or J13
[loop-through connections]) and connect
a baseband select from J18-6 and J18-7
on the rear of the tray.
5.12.2 Delay Equalizer Board (1227-
1204; Appendix D)
The jumper W1 on J5 of the sync tip
clamp/modulator board, if present, must
be in the Enable position between pins 2
and 3.
Note: This board has been factory
tuned and should not be retuned
without the proper equipment.
To tune this board:
1. Connect a sinX/X test signal into
jack J1-2 on the delay equalizer
board.
2. Monitor the video output of the
board, at the video sample jack J2,
with a video measuring set, such as
the VM700, adjusted to measure
group delay.
3. Tune the four stages of the board
using the variable inductors (L1-L4)
and potentiometers (R7, R12, R17,
and R22) until the signal attains the
FCC group delay curve. The stages
are arranged in order of increasing
frequency. Adjust R29, as needed,
to attain the same level out of the
board as into the board.
5.12.3 (A24) Composite 4.5-MHz
Filter Board (1227-1244;
Appendix D)
This board is part of the 4.5-MHz input
kit and will only function properly with a
4.5-MHz composite input signal and the
4.5-MHz composite input selected. To
align this board:
1. Connect the test signal from an
envelope delay measurement set to
the video input of the tray at J1 or
J2.
2. Connect an oscilloscope to jack J7,
video out, between the J7 center
pin and pin 1 or 3 (ground). Adjust
C21, frequency response, if needed,
for the best frequency response.
Adjust R32, video gain, for a signal
level of 1 Vpk-pk on the
oscilloscope.
The output at J6 and J7 on the board
should be video only, without the 4.5-
MHz aural subcarrier.
5.12.4 (A25) (Optional) 4.5-MHz
Bandpass Filter Board (1265-1307;
Appendix D)
This board is part of the 4.5-MHz input
kit and will only function properly with a
4.5-MHz composite input signal and the
4.5-MHz composite input selected. To
align this board: