Frequency Counter Prescaler/Conditioner; Am/Fm Demodulator; 4.8 Khz If Filters - HP 8560A Service Manual

9. Reconnect cables W54 to A4J6 and W52 to A4J8.

Frequency Counter Prescaler/Conditioner

Refer to function block Q of A4 Log Amplifier Schematic Diagram (sheet 4 of 4) in the
HP 856OA/61B/63A Spectrum Analyzer Component Level Information
The Frequency Counter Prescaler/Conditioner divides the frequency by two, and then
attenuates it. The circuit consists of frequency divider (U703A) and an output attenuator.
The frequency divider turns on only when the instrument is counting.

AM/FM Demodulator

Refer to function block R of A4 Log Amplifier Schematic Diagram (sheet 4 of 4) in the
HP 856OA/61B/63A Spectrum Analyzer Component Level Information
The demodulator circuitry on the A4 Log Amplifier produces a low-level audio signal. This
audio signal is then amplified by the A4 Audio Amplifier. The FM demodulator demodulates
narrowband FM (5 kH z deviation) signals.The detector demodulates AM signals.
1. If demodulation problems occur when the spectrum analyzer is in the frequency domain,
perform the Frequency Span Accuracy performance test and, if necessary, the YTO
Adjustments procedure.
2. If an FM signal cannot be demodulated, perform the Demodulator Adjustment procedure.
If the output of A4C707 cannot be adjusted for 50 mVp-p as described in the Demodulator
Adjustment procedure, troubleshoot the A4 FM Demodulator or Audio MUX circuits.

4.8 kHz IF Filters

Refer to function block N of A4 Log Amplifier Schematic Diagram (sheet 3 of 4) in the
HP 856OA/61B/63A 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, error message 536 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 spectrum analyzer, press
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. Set the spectrum
analyzer to single sweep.
4. Set the HP 8566A/B to 4.8 kHz center frequency and 2 kHz span.
5. Connect the VIDEO OUTPUT (rear panel) of the spectrum analyzer through a 20 dB
attenuator and dc block to the input of the HP 8566A/B. Set the sweep time of the
10 seconds.
HP 8566A/B to
ADJ OFF , w), 600 (Hz.
IF
binder.
binder.
binder.
IF Section 8-17