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Model 8902A
Operation
FUNCTIONS
cPM, Special Function 2 (Audio Range)
DESCRIPTION
The @M key enables the Measuring Receiver to measure the phase deviation of the tuned input
signal. The demodulated OM is present at MODULATION OUTPUT/AUDlO INPUT.
The OM measurement is specified only for RF carriers
from
10 to 1300 MHz; however, @M
measurements can be performed
on carriers
from 150 kHz to 10 MHz.
The OM 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.
400
40
4
0.1 RADIAN
RESOLUTION
0.01 RADIAN
R
ESO LUTl
ON
0.001 RADIAN
R ESO LUT ION
L
I
I
I
I
I
I
200
Hz
500 Hz 1 kHz
2 kHz
5
kHz 10 kHz
20
kHz
MODULATION RATE
PROCEDURE
To make a OM measiirement, first tune the instrument to the input signal by selecting AUTOMATIC
OPERATION. Select
OM.
Select an audio detector: PEAK+. PEAK-, PEAK
3t
/2. AVG, o r RMS. (The RMS detector, selected
by pressing the Blue Key and the
RMS
key, is less accurate in measuring
cPM and is typically only
used for audio distortion measurements.)
3-197
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