Service manual

8000 SERIES RECEIVER DECODER MODULE (RDM)
2-6
March 2000
Part No. 001-3139-502
2.8.6 FRONT END ALIGNMENT
Front end helicals L6-L11 are adjusted using the
peak/dip method. Proceed as follows:
Figure 2-4 TEST PROBE DIAGRAM
1. Fabricate the probe shown in Figure 2-4 and connect
it to an RF voltmeter or spectrum analyzer.
2. Set the signal generator on the channel frequency
and connect it to either antenna jack on the back of
the drawer. Set diversity control switch S1 to the
antenna being used (ANT 1 or ANT 2).
3. Insert the probe in the hole adjacent to the L6 heli-
cal. Increase the signal generator output (unmodu-
lated) to obtain a reading on the RF voltmeter. (A
250 mV input signal produces about 10 mV at the
test probe.)
4. Insert a shorting rod (heavy piece of bare wire) into
the hole adjacent to the L7 helical and lightly touch
the helical coil.
5. Adjust L6 for a peak on the RF voltmeter.
6. Move the shorting rod to L8 and adjust L7 for a dip
on the RF voltmeter (the probe remains in the L6
cavity).
7. Move the shorting rod to L9 and adjust L8 for a peak
on the RF voltmeter.
8. Move the shorting rod to L10 and adjust L9 for a dip
on the RF voltmeter.
9. Move the shorting rod to L11 and adjust L10 for a
peak on the RF voltmeter.
10.Remove the shorting rod and adjust L11 for a dip on
the RF voltmeter. Remove the probe from L6.
2.8.7 IF ALIGNMENT
NOTE: A signal generator stable to ±0.1 PPM or bet-
ter is required to properly tune the IF stages. Refer to
Section 2.8.2 for more information.
1. Connect a DC voltmeter to TP1. Preset the cores of
L12, L13, L14, T1, T2, T3 and T4 near the top of the
can.
2. Set the signal generator to the channel frequency,
modulated with 1 kHz at ±1.5 kHz deviation.
Adjust the output level for a meter reading of
approximately 1.5V DC.
3. Adjust L12, L13, L14, T1, T2, T3 and T4 for
maximum DC voltage (keep readjusting the signal
generator output to keep the voltage at TP1 below
2.5V DC). Repeat this step.
4. Increase the signal generator output to -60 dBm
(220 µV).
5. Connect a DC voltmeter across TP2 and TP3 (both
voltmeter inputs must be floating). Adjust T5 for
0V across TP2 and TP3.
6. Connect a distortion analyzer to the front panel
AUDIO TEST jack. Increase the generator
output to -47 dBm (1 mV) and ±2.5 kHz deviation.
Adjust T1, T2 and T5 for lowest distortion.
2.8.8 DIVERSITY AND SQUELCH ADJUST-
MENT
1. Preset R87 fully clockwise and set S1 to the antenna
jack being used (ANT 1 or ANT 2). Connect an AC
voltmeter to the front panel AUDIO TEST jack.
2. With no RF signal input, note the meter reading to
establish a 0 dB reference.
3. Switch S1 to the center "DIV" position and increase
the unmodulated signal generator output to obtain
7 dB quieting.
4. While listening to the audio from the speaker (adjust
the LOCAL VOL control as required), turn R87
counterclockwise until the audio just squelches.