HP 8901B Operation And Calibration Manual page 270

Model 8901B Operation
@M
FUNCTIONS
OM, Special finction 2 (Audio Range)
DESCRIPTION
The @M key enables the Modulation Analyzer to measure the phase deviation of the tuned input signal.
The demodulated OM is present at MODULATION OUTPUT/AUDIO INPUT.
The OM measurement is specified only for RF carriers from 10 to
1300 MHz; however,
OM
measurements can be performed on carriers from 150
kHz to
10 MHz.
The @M measurement is only specified for modulation rates from 200 Hz to 20 kHz; however, the low
frequency 3
dB
limit is typically 7
H z .
The following figure shows the display resolution for different combinations of peak phase deviation
and modulation rate.
RESOLUTION
0.001 RADIAN
RESOLUTION
200 Hz
500 Hz 1 kHz
2
kHz
5 kHz 10 kHz 20 kHz
MODULATION RATE
PROCEDURE
To make a OM measurement, first tune the instrument to the input signal by selecting AUTOMATIC
OPERATION. Select OM.
Select an audio detector: PEAK+, PEAK-, PEAK
*
/2, AVG, or RMS. (The RMS detector, selected
by pressing the Blue Key and the
RMS
key, is less accurate in measuring OM and is typically only
used for audio distortion measurements.)
OM 3-169