Data Sheet Chapter 5
500-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
325A, Rev. 0 5-9
Switch on the tray and adjust the front
panel meter, in the Reflected Output
Power position, to a 100% reading using
R53, the reflected power meter adjust on
the AGC control board. Adjust the
reflected output power to a 20% reading
using R5 on the AGC control board.
Adjust R59, the VSWR cutback adjust on
the AGC control board, until the red
VSWR Cutback LED DS4 on the front
panel lights. This sets up the VSWR
cutback circuitry.
Readjust R5 for 100% on the meter to
achieve a 500 watts peak of sync output
+ 50 watts aural power. However, if the
system requires less output power per
amplifier tray, adjust each tray by the
same amount to give the desired total
output power.
Switch off the tray and return the J5 and
J8 cables on the 3-way combiner
assembly back to their original positions.
If the tray was originally operating below
100% output power, the AGC fault adjust
was set for 20% below the operational %
Output Power of the tray. See the Test
Data Sheet for the transmitter for the
actual readings for the tray. Place S1 on
the AGC control board in the AGC
position. This is the normal operating
position after the setup is completed.
There is a spare 1-amp and 10-amp fuse
on the top, right-hand side of the tray.
These are replacements for fuses on the
current metering board.
The VHF amplifier tray is aligned,
calibrated, and ready for normal
operation.
5.12 Board Level Alignment
Procedures
5.12.1 (Optional) 4.5-MHz
Composite Input Kit
If the (optional) 4.5-MHz composite input
kit is purchased, the tray is capable of
operating by using either the 4.5-MHz
composite input or the baseband audio
and video inputs. The kit adds the (A24)
composite 4.5-MHz filter board (1227-
1244; Appendix D) and the (A25) 4.5-
MHz bandpass filter board (1265-1307;
Appendix D) to the transmitter. When the
4.5-MHz intercarrier signal generated by
the 4.5-MHz composite input has been
selected by the 4.5-MHz composite input
kit, the 4.5-MHz generated by the aural
IF synthesizer board is not used. When
the 4.5-MHz intercarrier signal generated
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.