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f.
On the unit display, set the TX CAL field to CALIBRT. If the current reading on the DMM
increases more than 50mA, send the unit to troubleshoot.
g.
SLOWLY Adjust the PA digital pot value until 28V current is between 200 and 300mA.
h.
Make note of the PA digital pot value and turn it back to 00.
i.
SLOWLY Adjust the DRVR until 28V current is between 50 and 75mA.
j.
Make note of the DRVR digital pot value and turn it back to 00.
k.
Place the TX CAL field on the display back to normal mode.
l.
Adjust the DRVR and PA settings to the values obtained in h and j.
m. Scroll the display to the Store Calibration? field and press ENT on the CDI.
n.
Tune the comm to 127.000 MHz.
o.
Adjust the DRVR and PA settings to the values obtained in h and j.
p.
Scroll the display to the Store Calibration? field and press ENT on the CDI.
q.
Tune the comm to 136.975 MHz.
r.
Adjust the DRVR and PA settings to the values obtained in h and j.
s.
Scroll the display to the Store Calibration? field and press ENT on the CDI.
3.4 Receiver IF Alignment
For –03 and higher comm boards, the receiver IF alignment of section 3.4 is not required.
3.4.1 IF Alignment – 8.33 KHz Mode
a.
Recall saved State 2 on the HP8920A/B.
State 2 on Radio Test Set:
•
RX Mode
•
RF GEN Freq = 118.000 MHz
•
RF GEN amplitude = 25µV
•
AF GEN1 to FM
•
FM DEVIATION = 7.0 KHz
•
AF GEN1 FREQ = 1 KHz
•
ohm/emf = emf on config page
•
RF Level Offset ON - configuration page
•
RF In/Out = -0.3 dB - configuration page
b.
Set the COMM frequency to 118.005 MHz, 8.33 KHz mode.
c.
While monitoring the IF AGC voltage on the test panel with a DMM, adjust the HP8920A/B
RF GEN amplitude until the DMM reads 5.0 ± 0.1 VDC.
d.
Adjust T200 until maximum IF AGC voltage is achieved.
e.
Adjust T201 until maximum IF AGC voltage is achieved.
f.
Adjust L200 until maximum IF AGC voltage is achieved.
g.
Adjust L202 until maximum IF AGC voltage is achieved.
3.4.2 IF Alignment - 25 KHz Mode
a.
Recall saved state 2 on the HP 8920A/B as in section 3.4.1. Change the FM deviation to
20.0 KHz
b.
Set the channel spacing to 25 KHz.
c.
Set the COMM frequency to 118.000 MHz, and the HP8920A/B RF GEN Freq to 118.000
MHz.
d.
While monitoring the IF AGC voltage on the test panel with a DMM, adjust the HP8920A/B
RF GEN amplitude until the DMM reads 5.0 ± 0.1 VDC.
e.
Adjust L201 until maximum IF AGC voltage is achieved.
f.
Adjust L203 until maximum IF AGC voltage is achieved.
g.
Install the cover on the RF section.
GNC 400 COMM TRANSCEIVER ALIGNMENT PROCEDURE
P/N 005-00051-55 REV. T
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