460 Chapter8
IF Section
Cal Oscillator Assembly (P/O A4)
Sweep Generator
Refer to function block Z of A4 log amplifier schematic diagram in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
A properly operating sweep generator generates a series of
negative-going parabolas. Before the sweep, switches A4U802C and
A4U802D turn on, shorting A4C802 and A4C801 (the output is at 0
volts). These switches open to start the sweep. The output of A4U804A,
pin 1, is 0.35 V to 10 V, depending on the sweep width selected by
A4U802A and A4U803A. This voltage appears across A4R801.
Capacitor A4C801 integrates the current through A4R801. The output
of A4U804B is a straight, negative-going ramp. Capacitor A4C802 and
resistor A4R802 integrate the output of A4U804A which starts a
negative ramp (A4U804C) at the beginning of the sweep. The ramp
from A4U804B is added to the current in A4R802 via A4U803B.
Integrating this ramp results in the parabolic output waveform.
AM/FM Demodulation, Audio Amplifier, and Speaker
Refer to function blocks R, S, and T of A4 Log Amplifier Schematic
(sheet 4 of 4) Diagram in the
HP 8560 E-Series Spectrum Analyzer
Component Level Information.
If the audio circuits are not functioning use the following procedure to
isolate the problem:
1. Set an AM signal generator controls as follows:
Frequency ............................................................. 100MHz
Amplitude ................................................................−6dBm
Modulation type .................................................... 80%AM
Modulation frequency .............................................. 400Hz
2. Set the spectrum analyzer controls as follows:
Center frequency .................................................. 100MHz
Span.............................................................................. 0 Hz
Sweep time .................................................................50ms
Reference level ...........................................................0dBm
Resolution bandwidth ..............................................10kHz
Amplitude scale LINEAR
3. Adjust the spectrum analyzer reference level and center frequency to
display the 400 Hz modulation frequency eight divisions
peak-to-peak.
4. On the spectrum analyzer, press
AUX CTRL, AM/FM DEMOD, AM
DEMOD ON, and set the sweep time to 5 seconds.
5. Vary the volume and listen for the variation in speaker output level.
Clipping is normal at the highest volume levels.
6. If the audio is not working correctly, monitor the signal at A4U704
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