HP 8560A, Service Manual

Page: 299 / 450

9. Reconnect cables W54 to and W52 to
Frequency Counter
Refer to function block Q of A4 Log Amplifier Schematic Diagram (sheet 4 of 4) in the
HP Spectrum Analyzer Component Level Information
binder.
The Frequency Counter divides the frequency by two, and then
attenuates it. The circuit consists of frequency divider 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 Spectrum Analyzer Component Level Information
binder.
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 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 cannot be adjusted for 50 as described in the Demodulator
Adjustment procedure, troubleshoot the A4 FM Demodulator or Audio MUX circuits.
4.8 IF Filters
Refer to function block N of A4 Log Amplifier Schematic Diagram (sheet 3 of 4) in the
HP Spectrum Analyzer Component Level Information
binder.
Problems with the 4.8 filters can result in spurious signals appearing 2.88 to
3.52 above the frequency of the desired response. Also, error message 536 may occur
when problems exist with the 4.8 IF filters.
Measure the of the 4.8 IF Filters as described in the following procedure.
1. On the spectrum analyzer, press IF
ADJ OFF , 600 (Hz.
2. Disconnect W27 from and inject a 10.7 MHz signal of -20 into
3. Fine-tune the frequency of the signal generator to center the signal on the screen. Set the
signal generator to sweep one 2 span about this center frequency. Set the spectrum
analyzer to single sweep.
4. Set the HP to 4.8 center frequency and 2 span.
5. Connect the VIDEO OUTPUT (rear panel) of the spectrum analyzer through a 20
attenuator and dc block to the input of the HP Set the sweep time of the
HP to
10 seconds.
IF Section 8-17