Sweep Generator; Am/Fm Demodulation, Audio Amplifier, And Speaker; Low-Pass Filter - HP 8560A Service Manual

Low-Pass Filter

Refer to function block AB of A4 Cal Oscillator Schematic Diagram in the
HP 856OA/61B/63A Spectrum Analyzer Component Level Information
1. Connect a DVM positive probe to A4J9 pin 4.
2. On the spectrum analyzer, press ICAL).
IF ADJUST STATUS: 300 kHz RBW and IF ADJUST STATUS: 3 kHz RBW. During this time
period, the voltage should be within a 2 to 10 Vdc range.
4. Observe the DVM reading while IF ADJUST STATUS: AMPLITUDE is displayed. The reading
should be within the 2 to 10 Vdc range.
5. If the DVM reading is outside the range in step 3 but inside the range in step 4, suspect
one of the filter reactive components.

Sweep Generator

Refer to function block Z of A4 Cal Oscillator Schematic Diagram in the
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 A4C801 and A4C802 (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
beginning of the sweep. The ramp from A4U804B is added to the current in A4R802 via

AM/FM Demodulation, Audio Amplifier, and Speaker

Refer to function blocks R, S, and T of A4 Cal Oscillator Schematic (sheet 4 of 4) Diagram in
HP 856OA/61 B/63A Spectrum Analyzer Component Level Information
the
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..lOOMHz
Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -6 dBm
Modulation Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80% AM
Modulation Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 Hz
2. Set the spectrum analyzer controls as follows:
CENTER FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 MHz
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz
SWEEP TIME . . . . . . . . . . . . . . . . . . . . .._............................ 50ms
REF LVL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0 dBm
RES BW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 kHz
SCALE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..LINEAR
8-40 IF Section
binder.
HP 856OA/61B/63A
binder.
binder.