Fm Calibration - HP 8901B Operation And Calibration Manual

Model 8901B Operation
FUNCTIONS
CALIBRATE, SAVE CAL, Function 12 (FM Calibration), Special Function 17 (FM Calibration Factor)
DESCRIPTION
The accuracy of the Modulation Analyzer's FM demodulator can be checked with the internal
FM calibrator. The calibration process generates a calibration factor to
compensate for the FM
measurement error (within the accuracy limits of the FM Calibrator). The calibration factor can then
be enabled to automatically correct the measured FM error in subsequent measurements using the
SAVE CAL key or Special h c t i o n 17. With the calibration factor enabled, FM measurements
can
be
made with an accuracy typically better than 0.5%. The calibration factor can be enabled, disabled, or
displayed at any time.
Other instruments in the HP 8901 and 8902 RF signal analyzer family can be calibrated or cross
checked with the Modulation Analyzer's FM calibrator using Special b c t i o n 12.
PROCEDURE
Self-Calibration
To determine the measurement error of the Modulation Analyzer's FM demodulation circuits, first
allow at least a half-hour continuous operation before calibration, then perform the following steps:
1. Connect the CALIBRATION AMFM OUTPUT
to
the RF INPUT with a 50Q cable (or a sensor
2. Press the CALIBRATE key. After several seconds, the FM calibration factor is displayed in
%
The instrument displays 100.00%
if
no error is measured.
A
display of 100.17% means the FM
demodulator in the Modulation Analyzer is reading 0.17% high. As long as the CALIBRATE
key light is on and the cable is connected, calibration repeats and the FM calibration factor is
updated approximately every 17 seconds. To turn off the calibrator, select CALIBRATE or any
Measurement key.
module with an internal switch such as the HP 11722A) and select FM.
and stored (but not enabled unless already enabled).
NOTE
For optimum accuracy, the instrument should be continuously operating for
at least one half hour before calibration
is
performed. In addition, the first
two
FM
Calibration Factors received after instrument power-up should not
be used even if the instrument
is
already warm, since the circuits in the
audio chain may not be fully settled.
Correcting Measurements with the FM Calibration Factor
Once a calibration factor has been determined, the instrument retains that value in its non-volatile
memory. This factor can be enabled
to
automatically correct FM measurements. The calibration factor
can also be disabled or displayed.
Selecting 7% CAL FACTOR (Blue Key, MHz) or 16.2 SPCL displays the Calibration Factor being used.
FM Calibration
3-155