HP 8901B Operation And Calibration Manual page 204

Model 8901B
Special Function
103,0212, 490
S
5
102,0212,490
S
5
101.0212.490 S 5
Operation
Variable Name
vz3, vz4, v z 5
vz2
Vzl
Voltmeter Reading in V
5.
6.
7.
8.
9.
10.
11.
12.
NOTE
For best accuracy on the most sensitive range (range
I),
the zero offset
voltage (Vzl) should be averaged for many voltmeter measurement cycles.
This
i s
most easily done via aprogrammable voltmeter under HP-IB control.
Key in 10.0 SPCL then CALIBRATE. Key in 49.0, S, 5, SPCL. Record the voltmeter reading
(Vc). Select SAVE CAL (Blue Key and CALIBRATE key)
to
calibrate the Modulation Analyzer's
display. The display should read
1
mW.
Select SPCL twice. Record the least-significant digit (the tenth digit) on the display (Re). (This
digit indicates the RF Power range for the calibration.)
Select AUTOMATIC OPERATION. Select CALIBRATE
to
turn off the Recorder Output Mode.
Connect the signal source to the power sensor's input. Allow the Modulation Analyzer to make a
normal RF power measurement.
Key in 0.212 SPCL Key
in
49.0, S, 5, SPCL and record the voltmeter reading (Vp).
Select SPCL twice. Record the least-significant digit (the tenth digit) on the display (Rp). (This
digit indicates the RF Power range.)
Compute the RF power (P, in mW) from the following formula:
v c
= V
Rc
=
vp =
V
Rp
=
CFC Vp-VzRp
CFp VC-VzRp
p=-
X
x
10(Rp - Rc)
where
CFc is the reference (50 MHz) calibration factor from the chart on the power sensor;
CFp is the calibration factor at the signal frequency from the chart on the power sensor;
VzRc is the voltage from step 4 for range Rc;
VzRp is the voltage from step 4 for range Rp.
Begin subsequent RF power measurements at step 2 as long as the results of step 4 exhibit drift;
otherwise, begin at step 9.
COMMENTS
More Information
Internal Voltmeter Offset
For further details on Special Functions 49 and 50, refer to Service Special finctions in Section
8.
The RF power circuits do not zero to OV. Instead they "zero" to between 0.5V and 0.8V which permits
the internal dc voltmeter to operate over its most linear range The internal controller subtracts this
offset
from subsequent power readings.
Recorder Output
3-89