Data Sheet Chapter 5
500-Watt VHF Low Band Transmitter Chapter 5, Detailed Alignment Procedures
325A, Rev. 0 5-15
5. Adjust the front panel power adjust
control A20 for 0.5 VDC at TP4. If
the (optional) remote power
raise/lower kit is present, move
switch S1 on the board to mid-
range and then adjust (A20) the
front panel power adjust control for
0.8 VDC at TP4.
6. Disconnect the plug that is on J12
(IF output) and monitor J12 with a
spectrum analyzer. Verify an output
of approximately 0 dBm. If
necessary, adjust R99 to increase
the output level. If less of an output
level is needed, move jumpers J27
and J28 to pins 2 and 3 and then
adjust R99. Reconnect J12.
7. Move W2 on J5 to the Cutback
Enable position. Remove the input
video signal and verify that the
output of the transmitter drops to
25%. Adjust R71, the cutback level,
if necessary. Restore the input
video.
Note: The following step affects the
response of the entire transmitter
.
8. Connect a video sweep signal to the
input of the tray. Monitor the
output of the system with a
spectrum analyzer. Adjust C71 with
R103 and C72 with R106, as
needed, to flatten the response.
C71 and C72 adjust for the
frequency of the correction notch
being applied to the visual response
of the transmitter. R103 and R106
are used to adjust the depth and
width of the correction notch.
9. Refer to Section 5.5 of this chapter
for the system alignment
procedures for the linearity
correctors. Controls R13, R18, and
R23, the magnitude controls,
should be set fully CW. Controls
R34, R37, and R40 are the linearity
cut-in adjustments.
5.12.11 (A14-A1) Channel Oscillator
Board, Dual Oven (1145-1201;
Appendix D)
This board is mounted in (A14) the
channel oscillator assembly (1145-1202).
To align the board:
1. Connect the main output of the
channel oscillator (J1) to a
spectrum analyzer, tuned to the
crystal frequency, and peak tuning
capacitors C6 and C18 for
maximum output. Tune L2 and L4
for maximum output. The output
level should be about +5 dBm. The
channel oscillator should maintain
an oven temperature of 50° C.
If a spectrum analyzer is not
available, connect a digital
voltmeter (DVM) to TP1 on the x4
multiplier board. Tune capacitors C6
and C18 for maximum voltage,
then also tune L2 and L4 for a
maximum voltage output at TP1.
2. Connect the sample output of the
channel oscillator (J2) to a suitable
counter and tune C11, coarse
adjust, and C9, fine adjust, to the
crystal frequency.
Note: Do not repeak C6, C18, L2, or
L4. This may change the output
level.
Note: While adjusting C9 and C11 to
the crystal frequency, the peak
voltage monitored at TP1 of the x4
multiplier board should not
decrease. If a decrease does occur,
there may be a problem with the
crystal. Contact Axcera Field
Support for further instructions.
Note: If the VCXO board (1145-
1204) in the VCXO assembly (1145-
1206) is used, the fine-frequency
adjust C9 is not located on the VCXO
board. Use R9 on the FSK with
EEPROM board.