HP 8901B Operation And Calibration Manual page 260

Model 8901B
The Special Fbnction codes are summarized in the table below:
Display computed peak
FM
Display demodulated peak residual
FM
Display demodulated peak
FM
Operation
12.0 SPCL 12.0SP
12.1 SPCL 12.1SP
12.2 SPCL 12.2 SP
Function
Program Code
Special
Function
Code
HP-I8
PROGRAM CODES
HP-IB codes for enabling, disabling, or displaying the internal FM calibration factor are provided in
"Procedures". The HP-IB codes for the FM Calibrator Special Function used
to
calibrate another RF
signal analyzer are also provided as part of "Procedures".
FM = M2
CALIBRATE on
=
C1
CALIBRATE
off =
C O
SPCL =
SP
I N D I CAT1 ONS
Self -Calibration
When the CALIBRATE key is pressed, approximately 17 seconds pass during which the instrument
conSgures itself and tunes
to
the calibrator's signal. The display indicates four dashes
(----)
and lights
the % annunciator. Once the FM Calibration Factor
has
been computed, it is displayed. Subsequent
updates occur approximately every 17 seconds.
Correcting Measurements with the FM Calibration Factor (Self-Calibrated)
When the calibration factor is enabled, the FM deviation measurement is always a corrected
measurement.
If
% CAL FACTOR is selected, and the FM calibration factor is enabled, the FM calibration factor is
displayed. If % CAL FACTOR is selected, and the FM calibration factor is disabled, 100% is displayed.
(Note the resolution of 1%)
Calibrating Another RF Signal Analyzer
The Modulation Analyzer displays the computed FM deviation
(
Special Function 12.0), but shows two
dashes
(--)
throughout the rest of the procedure.
MEASUREMENT TECHNIQUE
When FM is selected and CALIBRATE is selected, a 10.1 MHz voltage controlled oscillator (VCO)
within the calibrator
is
driven to one end of its nominal tuning range. The frequency of the VCO is
counted, and the oscillator is driven to the opposite end of its tuning range where it is counted again.
The peak FM deviation is computed from these measurements.
While the VCO is
at
one end of its range, the residual FM of the calibrator (very low) and the
FM Demodulator (more significant) are characterized and weighted. (Refer to Residual Noise Effects
on page 3-191.) The VCO is frequency modulated by a 10 kHz modulation oscillator, and the FM
FM Calibration
3-157