User's Manual

2650 Watt VHF High Band Transmitter Chapter 5, Detailed Alignment Procedures
435B, Rev. 0 5-10
2. Adjust C3 and C6 to determine
the center frequency. Use C2 and
C7 to locate the upper and lower
channel-edge shaping. C4 is used
to determine the channel
bandwidth.
5.1.4.12 (A11-A3) High-Band VHF
Filter/Amplifier Board (1064252;
Appendix D)
The filter/amplifier board has been
factory swept and adjusted for a 6-MHz
bandwidth.
NOTE: This board should not be tuned
without the proper equipment.
The filtered output connects to J1 of the
board and is amplified by U1 to a
nominal +12 dBm visual and +2 dBm
aural level by adjusting R9. The output at
J2 is fed to J4 on the A11 enclosure and
from there to J15 on the rear of the tray.
To align the board, use a multiburst or
sweep video signal inserted into the
exciter tray.
Reconnect the cable from J6 to J1 on the
filter/amplifier board. Monitor J2, the RF
output of the board, and peak C17 for
the maximum signal level. Tune manual
gain adjust R9 for a +12 dBm peak
visual output.
The VHF exciter tray is aligned and ready
for normal operation.
5.2 (A6 and A7) VHF High Band
Amplifier Tray (1301169; Appendix C)
The (A6 and A7) VHF high-band amplifier
tray has been adjusted at the factory to
meet all specifications, including phase
adjustment to match the multiple trays in
an amplifier array when they are
combined. The tray should not need to
be adjusted to attain normal operation.
Any adjustments to the boards in this
tray should be performed in the Manual
Gain position, with S1 on (A13) the AGC
control board (1142-1601) in Manual.
The idling current for the amplifier boards
are adjusted with no RF drive applied. S1
should be in the Auto AGC position for
the normal operation of the transmitter.
Connect a dummy load with a rating of a
least 750 watts to J2, the RF output jack
of the tray.
5.2.1 (A13) AGC Control Board
(1142-1601; Appendix D)
Using a calibrated wattmeter, check that
the tray is operating at the rated power.
Remove cable connected to the forward
power sample input jack J4 on the (A13)
AGC control board (1142-1601). The
output power level should drop to 20%
because of the VSWR cutback setting and
the VSWR LED DS4 should be
illuminated. The front panel Module
Status LED should not be lit.
Reconnect J4 on A13 and adjust R59 on
the AGC control board to begin cutting
back on the output power level when the
reflected level increases above 20%.
In the Power Supply Voltage position, the
front panel meter is calibrated to
+28 VDC by adjusting pot R86 on the
AGC control board.
5.2.2 (A1-A1) Phase Shifter Board
(1198-1602; Appendix D)
There are no adjustments to (A1-A1) the
phase shifter board (1198-1602). The
front panel has adjustments for phase
that are made during the amplifier array
setup procedure.
5.2.3 (A2-A1) VHF Filter/Amplifier
Board (1301178; Appendix D)
The (A2-A1) VHF filter/amplifier board
has approximately 5 dB of gain. Tune
the channel filter capacitors C20 and C29
(loading), C23 and C26 (center
frequency), and C24 (coupling) at J6 on
the board for the best response.