3. Set the HP 85623 spectrum analyzer to log mode, with a resolution bandwidth of 300
l&z
and single sweep.
4. Using the DMM, check the voltage at
U503
pin 6.
5. Verify that this level is about -700 mV.
6. Adjust the source amplitude to place the signal at the reference level.
7. Reduce the input signal level in 10 dB steps, down to -60
dBm,
while noting the voltage
displayed on the DMM. The voltage should increase (become less negative) at a rate of
30
mV
for each 10 dB decrease in input power. Troubleshoot the A4 assembly if the signal
does not decrease properly.
8. Set the HP 85623 spectrum analyzer resolution bandwidth to 100 kHz to place the
wide/narrow filter in narrow mode.
9. Repeat steps 2 through 7.
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
8560
E-Series Spectrum Analyzer
Component Level Information.) Check this switch as follows:
a. Monitor voltages on A4U302 pins 1 and 7 while changing the HP 85623 spectrum
analyzer resolution bandwidth from 100 kHz to 300 kHz.
b. If the voltages do not come within a few volts of the
+15
V and -15 V supplies,
U103
and
U302
are suspect.
c. Disconnect the digital multimeter and reconnect W27 to
A4J3.
Linear
Amplifiers
Refer to function block C of A4 Log Amplifier Schematic Diagram (sheet 2 of 4) in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
The linear amplifiers consist of two variable gain stages, U2OlC and U201E as well as the
buffer amplifier A4U201B, A4U201D, and A4Q201. The linear amplifiers provide 0 to 40 dB
of IF gain in 10 dB steps. The gain of A4U201C can be increased by 20 dB by turning
on A4CR201 and A4CR210 with the control line LIN-20B. The gain of A4U201E can be
increased by either 10 dB or 20 dB with the control lines
LIN-10
or
LIN-20A
respectively.
The gain can be selected by setting the HP 85623 spectrum analyzer reference level.
IF Gain Application Guidelines (ATTEN=lO
dB)
Power into
A4J3
Reference Level
Gain of A4U201C
Gain of
A4U201E
(Pin
8
in; Pin
3
out) (Pin
3
in; Pin
10
out)
+6
dBm
-50
dBm
0
dB
0
dB
-4
dBm
-60 dBm
0
dB
10
dB
-
14dBm
-70
dBm
0
dB
20
dB
-24
dBm
-80
dBm
20
dB
10
dB
-34
dBm
-90 dBm
20
dB
20
dB
I
9-14 IF Section
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