Data Sheet Chapter 5

500-Watt VHF Transmitter Chapter 5, Detailed Alignment Procedures
425A, Rev. 0 5-16
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 ADC 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.
3. Reconnect the main output (J1) of
the channel oscillator to the input
(J1) of the x4 multiplier.
5.12.12 (A11-A1) x4 Multiplier Board
(1174-1112; Appendix D)
While monitoring the board with a DC
voltmeter, maximize each test point
voltage by tuning the broadband
multipliers in the following sequence:
1. Monitor TP1 with a DVM and tune
C4 for maximum voltage. Monitor
TP2 with a DVM and tune C6 and
C10 for maximum voltage.
Monitor TP3 with a DVM and tune
C12; repeak C4, C6, and C10 for
maximum voltage.
2. Connect a spectrum analyzer,
tuned to four times the crystal
frequency, to the x4 multiplier
output jack J2. While trying to
keep the out-of-band products to
a minimum, monitor the output
and peak the tuning capacitors for
maximum output.
Connect a spectrum analyzer to J6 on
board. Adjust C23 and C26 to determine
the center frequency. Use C2 and C7 to
locate the upper and lower channel-edge
shaping. C24 is used to determine the
channel bandwidth.
The output of the x4 multiplier connects
to (A11-A1) the filter/mixer board.
5.12.13 (A11-A2) VHF Filter/Mixer
Board (1150-1102; Appendix D)
To align the board:
1. Monitor J4, the LO output of the
board, with a spectrum analyzer
and adjust C12 and C18 for
maximum output (+14 dBm) at