HP 8901B Operation And Calibration Manual page 422

Model
8901B
Adjustments
NOTE
If the frequency of the power reference i s already within the proper limits,
do not attempt to adjust the frequency to exactly 50
MHz.
To do
so
m a y
unnecessarily affect the level.
4.
Reinstall the A32 assembly. (The thumb screw need only be finger tight.)
5.
With the H P 432A Power Meter switched off and the thermistor interconnect cable connected
to
it but not to the thermistor mount, measure the resistance between the center conductor of the
rear-panel VRF' connector and pin 1 (the first pin
to
the right of the key slot) on the thermistor
end of the interconnect cable. Record the value of the mount resistance for future reference.
(It
should be approximately 2000.)
Mount Resistance (R):
R
6. Connect the equipment as shown in Figure 5-8. The input of the digital voltmeter should be
floating. The positive input of the voltmeter should be connected to the rear-panel VCOMP
connector of the H P 432A Power Meter, the negative input
to
the VRF connector. Switch the
equipment on and let it warm up for
at
least 30 minutes.
HP 8901B
MODULATION ANALYZER
POS VCOMP
0
0
: : : : :
000000
0000
0
0 0 0
0000
0
HP 432A
POWER METER
0000
DIGITAL VOLTMETER
0
0 0
nnoooo
00000
0
NEO
VRF
I
CALIBRATION
RF P W E R OUTPUT
HP 478A
THERMISTOR
MOUNT
Figure
5-8.
Power Reference Adjustment Test Setup
7. On the Modulation Analyzer, key in 45.0
SPCL to switch the power reference o f f .
8. Set the H P 432A Power Meter RANGE to COARSE ZERO and adjust the front-panel COARSE
ZERO
to obtain a zero meter indication.
9. Fine zero the H P 432A Power Meter on the most sensitive range, then set the RANGE switch to
1 mW (0 B m ) .
10. Observe the voltage reading on the voltmeter. If the reading is greater than 400 pV, press and
hold the FINE ZERO switch on the HP 432A Power Meter and adjust COARSE
ZERO
so that
the voltmeter reads less than 200 pV then release the
FINE
ZERO switch. Record the voltmeter
reading.
V c o ~ p
-
VRF
with No Power
(Vo):
Vdc
11. Connect the voltmeter to read VCoMp (with respect to chassis ground) on the HP 432A Power
12. On the Modulation Analyzer, key in 45.16 SPCL. Record the voltmeter reading.
Meter. (The voltmeter's negative input should connect to chassis ground.)
V c o ~ p with 1 mW Vdc
13. Reconnect the voltmeter leads as shown in Figure 5-8 (where VRF
is
connected to the negative
input of the voltmeter).
Adjustment 19
5-31