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2. If an FM signal cannot be demodulated, perform the Demodulator Adjustment procedure.
If the output of A4C707 cannot be adjusted as described in the Demodulator Adjustment
procedure, troubleshoot the FM Demodulator or Audio MUX circuits on A4.
4.8
kHz
IF
Filters
Refer to function block N of A4 Log Amplifier Schematic Diagram (sheet 3 of 4) in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
Problems with the 4.8 kHz filters can result in spurious signals appearing 2.88 kHz to
3.52 kHz above the frequency of the desired response. Also, ERR 536 RBW
<300
may occur
when problems exist with the 4.8 kHz IF filters.
Measure the
passband
of the 4.8 kHz IF filters as described in the following procedure.
1. On the HP 85623 spectrum analyzer, press [CAL), IF
Al3J
UFF
, (SPAN), and 600 (Hz.
2. Disconnect W27 from A4J3 and inject a 10.7 MHz signal of -20
dBm
into
A4J3.
3. Fine-tune the frequency of the signal generator to center the signal on the screen. Set the
signal generator to sweep one 2 kHz span about this center frequency. Press
(mSWP)
on
the HP 85623 spectrum analyzer.
4. Set another spectrum analyzer, such as the HP
8566A/B,
to 4.8 kHz center frequency and
2 kHz span.
Caution
If a dc block is not used, damage to the HP
8566A/B
results. The
HP
8566A/B
and many other spectrum analyzers have dc-coupled inputs and
cannot tolerate dc voltages on their inputs.
5.
Connect the VIDEO OUTPUT (
rear panel) of the HP 85623 spectrum analyzer through a
20 dB attenuator and dc block to the input of the HP
8566A/B.
Set the sweep time of the
HP
8566A/B
to 10 seconds.
6.
Set the HP
8566A/B
t
o single trigger and press TRACE A CLEAR-WRITE . Trigger a sweep
of the HP
8566A/B
and the signal generator simultaneously. The HP
8566A/B
shows the
passband
of the 4.8 kHz IF filters. The 3 dB bandwidth of the filters should be 1.2 kHz.
The
passband
of the filters should be flat within 2 dB over 800 Hz.
7.
Reconnect W27 (coax 3) to A4J3.
10.7
MHz
IF
Filters
1.
2.
3.
4.
5.
Press (PRESET], (FREQUENCY), 300
(MHz),
(SPAN), 600 (Hz), (CAL), and IF
BDJ
OFF.
Disconnect W29 (coax 7) from A5J3. Set the signal generator for a 10.7 MHz signal at
-50
dBm
and connect it to
A5J3.
Fine tune the frequency of the signal generator to center the signal on the HP 85623
spectrum analyzer display. Set the signal generator to sweep one 2 kHz span about this
center frequency.
On the HP 85623 spectrum analyzer, press
(-1.
Disconnect W27 (coax 3) from
A5J5.
Connect a test cable from A5J5 to the input of an
HP
8566A/B.
IF Section 9-17