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Total gain can be measured by injecting the specified power into
A4J3
and measuring the
total gain provided by A4U201C and A4U201E. The following procedure provides a means of
troubleshooting the linear amplifiers:
1. On the HP 85623 spectrum analyzer, press
c-1,
(SPAS3),
ZEXQ
SF&N,
a),
TP
ADJ
OFF, (FREQUENCY), 1
(GHz),
(m),
-50
dBm,
LINW,
MORE, AMFTD UNITS,
[dem,
and [AMPLITUDE).
2. Disconnect W27 (coax 3) from A4J3 and connect the output of a signal generator to A4J3.
3. Set the signal generator controls as follows:
Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+6
dBm
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7MHz
4. Simultaneously decrease the signal generator output and HP 85623 spectrum analyzer
REF LVL in 10 dB steps to -90
dBm.
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 A4U201C and A4U201E with
those listed in the above gain guidelines.
6. Reconnect W27 (coax 3) to
A4J3.
Video
Off
set
Refer to function block P of A4 Log Amplifier Schematic Diagram (sheet 3 of 4) in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
The circuit provides a programmable video offset, with a step size of 5
mV,
from -300 mV to
i-900 mV.
1. On the HP 85623 spectrum analyzer, press (PRESET),
(SPAN),
ZEND
SPAN,
(-1,
1
m),
@iZiiKZ),
-50
dBm,
(CAL), IF AD3 OFF.
2. Disconnect W27 (coax 3) from A4J3 and connect a signal generator to A4J3.
3. Set the signal generator controls as follows:
Amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+lOdBm
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.7MHz
4. Simultaneously decrease the signal generator output and HP 85623 spectrum analyzer
reference level in 10 dB steps down to -110
dBm.
At each step, the signal displayed on the
spectrum analyzer should be close to the reference level.
5. Reconnect W27 (coax 3) to A4J3 and cycle the spectrum analyzer power. Press
STOP
NJ?<CN
when it appears.
6.
On the HP 85623 spectrum analyzer, press
(K),
SINGLE, (CAL), and IF
A1)J
DFF
.
7. The offset DAC, A4U102 pin 2, should now be at its default value of approximately
t2.45
V. The voltage at
U601
pin 3 should be approximately 0 V for a DAC output
of 2.45 V.
8. If this default offset voltage is incorrect, DAC
U102
is the most probable cause.
IF Section 9-15