Data Sheet Chapter 5

500-Watt VHF Transmitter Chapter 5, Detailed Alignment Procedures
425A, Rev. 0 5-8
C19 for peak output with the best
linearity across the spectrum.
5.11.7 (A3-A3) 4-Way Splitter Board
(1219-1101; Appendix D)
There are no tuning adjustments for (A3-
A3) the 4-way splitter board (1219-
1101). The board takes the +36 dBm
input and splits it into four equal +30
dBm inputs.
5.11.8 (A4-A1, A4-A2, A4-A3, and
A4-A4) High-Band Amplifier Board
(1218-1201; Appendix D)
Each of the (A4-A1, A4-A2, A4-A3, and
A4-A4) high-band amplifier boards
(1218-1201) have 20 dB of gain and are
biased at 2 amps of idling current when
they are used as a visual, or visual +
aural, amplifier or 1 amp of idling current
when they are used as an aural amplifier,
no RF drive applied. To set the bias for
the final amplifier board (A4-A1), remove
the RF drive and switch the front panel
current meter to the I
1
position. Preset
bias adjust pots R5 and R9 CCW. Slowly
tune bias adjust pot R5 for 1 amp on the
meter for a visual, or visual + aural,
amplifier or .5 amps on the meter for an
aural amplifier. Adjust R9 for 2 amps on
the meter for a visual, or visual + aural,
amplifier or 1 amp on the meter for an
aural amplifier.
To set the bias for the final amplifier
board (A4-A2), remove the RF drive and
switch the front panel current meter to
the I
2
position. Preset bias adjust pots R5
and R9 CCW. Slowly adjust bias adjust
pot R5 for 1 amp on the meter for a
visual, or visual + aural, amplifier or .5
amps on the meter for an aural amplifier.
Adjust R9 for 2 amps on the meter for a
visual, or visual + aural, amplifier or 1
amp on the meter for an aural amplifier.
To set the bias for the final amplifier
board (A4-A3), remove the RF drive and
switch the front panel current meter to
the I
3
position. Preset bias adjust pots R5
and R9 CCW. Slowly adjust bias adjust
pot R5 for 1 amp on the meter for a
visual, or visual + aural, amplifier or .5
amps on the meter for an aural amplifier.
Adjust R9 for 2 amps on the meter for a
visual, or visual + aural, amplifier or 1
amp for an aural amplifier.
To set the bias for the final amplifier
board (A4-A4), remove the RF drive and
switch the front panel current meter to
the I
4
position. Preset bias adjust pots R5
and R9 CCW. Slowly adjust bias adjust
pot R5 for 1 amp on the meter for a
visual, or visual + aural, amplifier or .5
amps on the meter for an aural amplifier.
Adjust R9 for 2 amps on the meter for a
visual, or visual + aural, amplifier or 1
amp on the meter for an aural amplifier.
Connect a spectrum analyzer to output
jack J2 of the board and adjust C1 for
peak output.
5.11.9 (A5-A1) 4-Way Combiner
Board (1219-1102; Appendix D)
There are no adjustments to the (A5-A1)
4-way combiner board (1219-1102). The
four +49.5 dBm inputs are combined to
produce the 600 watts peak of sync
output at J5 for a visual amplifier, 300
watts peak of sync plus aural for
common amplification, or the 400 watts
for an aural amplifier.
5.11.10 Calibration of the Visual Plus
Aural Output Power and VSWR
Cutback
Check that a dummy load of at least 300
watts is connected to the output of the
tray that is to be calibrated. Place switch
S1 on the AGC control board in the
Manual position before beginning the
setup.
To adjust the visual output power levels:
1. Remove the J16 cable from (A5) the
sync tip clamp/modulator board
(1265-1302) in the exciter tray. Set
Manual AGC switch S1, on the (A13)
AGC control board (1142-1601) in the