HP 8560A, Service Manual

Page: 297 / 450

10. If log fidelity is poor near the bottom of the screen or the 1 MHz resolution bandwidth is
narrow, a fault might exist in the wide/narrow filter switch. Refer to function block G
of A4 Log Amplifier Schematic Diagram in the
HP Spectrum Analyzer
Component Level Information
binder. Check this switch as follows:
a. Monitor voltages on pins 1 and 7 while changing the spectrum analyzer
resolution bandwidth from 100 to 300
b. If the voltages do not come within a few volts of the V and -15 V supplies,
and are suspect.
c. Disconnect the digital multimeter and reconnect W27 to
Linear Amplifiers
Refer to function block C of A4 Log Amplifier Schematic Diagram (sheet 2 of 4) in the
HP Spectrum Analyzer Component Level Information
binder.
The Linear Amps consist of two variable gain stages, and as well as the buffer
amplifier and The linear amplifiers provide 0 to 40 of IF
gain in 10 steps. The gain of can be increased by 20 by turning on
and with the control line LIN_20B. The gain of can be increased by either
10 or 20 with the control lines LIN_10 or LIN_20A respectively. The gain can be
selected by setting the spectrum analyzers reference level.
IF Gain Application Guidelines
Power into Reference Level Gain of Gain of Total Gain
- 5 0 0
0
- 4 - 6 0 0
10 10
14dBm - 7 0 0
20
20
-24 - 8 0
20
10
30
-34
- 9 0
20 20 40
Total gain can be measured by injecting the specified power into and measuring the
total gain provided by and The following procedure provides a means of
troubleshooting the linear amplifiers.
1. On the spectrum analyzer press (PRESET), (SPAN), ZERO SPAN , 1
50 LINEAR,
MORE, AMPTD UNITS
, and
2. Disconnect W27 (coax 3) from and connect W27 to the output of a signal generator.
3. Set the signal generator controls as follows:
Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Simultaneously decrease the signal generator output and spectrum analyzer REF LVL in
10 steps to -90 At each step, the signal displayed on the spectrum analyzer
should be within one division of the previous position.
5. If a problem exists, isolate it by comparing the actual gain of and with
those listed in the above gain guidelines.
6. Reconnect W27 (coax 3) to
IF Section 8-15