HP 8901B Operation And Calibration Manual page 248

Model 8901B Operation
7. To use this AM calibration factor to correct AM measurements made with the RF signal analyzer,
enter the value as a ratio reference and use the Ratio function in the RF signal analyzer.
The Special b c t i o n codes are summarized in the table below:
Special
Function
Code
Function
Program Code
Display computed peak
AM
DisDlav demodulated peak residual
AM
13.0 SPCL 13.0SP
13.1 SPCL 13.1SP
Display demodulated peak
AM
HP-IB PROGRAM CODES
13.2 SPCL 13.2 SP
HP-IB codes for enabling, disabling, or displaying the internal AM calibration factor are provided in
"Procedures". The HP-IB codes for the AM Calibrator Special Function used to calibrate another
RF
signal analyzer are also provided as part of "Procedures".
AM
=
M1
CALIBRATE off = C O
CALIBRATE on = C1
SPCL
=
SP
INDICATIONS
Self-Calibration
When the CALIBRATE key is pressed, approximately 17 seconds pass during which the instrument
configures itself and tunes to the calibrator's signal. The display indicates four dashes
(-
- -
-)
and lights
the 9% annunciator. Once the AM Calibration Factor has been computed, it is displayed. Subsequent
updates occur approximately every 17 seconds.
Correcting Measurements with the AM Calibration Factor (Self-Calibrated)
When the calibration factor is enabled, the
AM
depth measurement is always a corrected measurement.
If
%
CAL FACTOR (Blue Key, MHz) is selected, and the AM calibration factor is enabled, the AM
calibration factor is displayed. If
%
CAL
FACTOR (Blue Key, MHz) is selected, and the AM calibration
factor is disabled, 100% is displayed. (Note the resolution of
1%)
Calibrating Another RF Signal Analyzer
The Modulation Analyzer displays the computed AM depth (Special Function 13.0), but shows two
dashes
(- -)
throughout the rest of the procedure.
MEASUREMENT TECHNIQUE
When AM and then CALIBRATE are selected, the FM Calibrator sends an unmodulated 10.1 MHz
carrier to the AM Calibrator.
The AM Calibrator contains two identical modulators in parallel whose outputs are summed. When
the calibration operation is initiated, each modulator is turned on and each individual output level is
measured, via
an
on-board detector, to compute AM depth.
While one of the modulators is on, the residual AM of the calibrator (very low) and the AM demodulator
(more significant) are characterized and weighted (refer to Residual
N o i s e
Effects on page 3-191).
AM Calibration 3-
143