Chapter 8 425
IF Section
Log Amplifier Assembly (P/O A4)
10.Reconnect cable W54 to A4J4.
Frequency Counter Prescaler/Conditioner
Refer to function block Q of A4 log amplifier schematic diagram (sheet 4
of 4) in the
HP 8560 E-Series 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 8560 E-Series Spectrum Analyzer Component Level
Information.
The demodulator circuitry on the log amplifier on A4 produces a
low-level audio signal. This audio signal is then amplified by the audio
amplifier on A4. The FM demodulator demodulates narrowband FM (5
kHz 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
as described in the Demodulator Adjustment procedure,
troubleshoot the FM Demodulator or Audio MUX circuits on A4.
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