HP 8901B Operation And Calibration Manual page 256

Model 8901B
Operation
HP-IB PROGRAM CODES
All HP-IB codes for setting range limits for FM measurements are provided in "Procedures".
FM = M2
SPCL
=
SP
MEASUREMENT TECHNIQUE
The FM on the IF is demodulated by a frequency discriminator. The amplitude of the discriminator's
output is proportional to
the frequency deviation. The demodulated signal is filtered, audio detected,
and displayed as kHz deviation.
FM de-emphasis equalization can be inserted ahead of the audio detectors and display circuitry by
selecting PRE DISPLAY. The demodulated FM signal always passes through the FM de-emphasis
"network" before it appears at the output of MODULATION OUTPUT/AUDIO INPUT.
FM Measurement Block Diagram
COMMENTS
Input/Output Status
The demodulated FM is present at MODULATION OUTPUT/AUDIO INPUT (unless AUDIO
INPUT has been selected). The demodulated FM is usually present at the rear-panel FM OUTPUT
connector. If the RF input signal drops too low for accurate FM demodulation, the FM measurement
is automatically squelched (muted, turned
off)
except for the FM OUTPUT. (Refer
to
FM Output on
page 3-163.)
Relative FM Deviation Measurements
If FM deviation is to be displayed relative to a reference, enter the value as
a
ratio reference using the
RATIO key. (Refer to Ratio on page 3-215.)
FM
3-153