User's Manual

2650 Watt VHF High Band Transmitter Chapter 5, Detailed Alignment Procedures
435B, Rev. 0 5-4
The output at J6 and J7 on the board
should be video only, without the 4.5-
MHz aural subcarrier.
5.1.4.1.2 (Optional) (A25) 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:
1. Adjust the filter with L2, C3, L4,
and C7 for a frequency response of
no greater than ±0.3 dB from 4.4
to 4.6 MHz.
2. Adjust C19 for an overall peak-to-
peak variation of less than ±0.3 dB
from 4.4 MHz to 4.6 MHz.
2. Recheck the frequency response; it
may have changed with the
adjustment of the envelope delay.
If necessary, retune the board.
5.1.4.2 (A6) 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.
5.1.4.3 (A7) IF Carrier Oven
Oscillator Board (1191-1404;
Appendix D)
To align this board:
1. While monitoring J3 with a
spectrum analyzer, observe the
45.75-MHz visual IF (typical +5
dBm).
2. Connect a frequency counter to J3
and adjust C17 for 45.750000 MHz.
3. Connect a frequency counter to J1
and check for 50 kHz, which is the
aural phase lock loop reference.
5.1.4.4 (A5) Sync Tip
Clamp/Modulator Board (1265-
1302; Appendix D)
To align this board:
1. Determine if jumper W4 on jack J3
is present. Jumper W4 terminates
the video input into 75Ω. Remove
jumper W4 if a video loop-through
is required on the rear chassis at
jacks J1 and J2.
2. Set the controls R20, the white clip,
R24, the sync clip, and R45, the
sync stretch cut-in, to their full
CCW position. Set R48, the sync
magnitude, fully CW and place the
jumper W7 on jack J4 to the
Clamp-Off, Disable, position.
3. Connect a 5-step staircase video
test signal to the input of the
transmitter.