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Model 8902A
Operation
MEASUREMENT TECHNIQUE
The QM on the IF is first demodulated by a frequency discriminator. The amplitude of the
discriminator's output is proportional to the frequency deviation. The demodulated signal is filtered
and passed through an integrator, which extracts the phase information. The integrator's output is
detected and displayed as phase deviation in radians. The integrator's output is made available at the
MODULATION OUTPUT/AUDIO INPUT.
@M Mi>autrcmcnf Block Diagram
COMMENTS
Frequency and Distortion Measurements.
The demodulated signal's frequency and distortion can also be measured. (Refer to
A iici'io
MuasirrtJ-
ments
which begins on page
3-225.)
Relative Measurements.
If iPM deviation is to be displayed relative to a reference, enter the value
as
a ratio reference using
the RATIO key. (Refer to Rafiu on page 3-245.)
Peak Detector. The PEAK+ detector always detects the upward carrier phase excursion while
the PEAK- detector always detects the downward carrier phase excursion. The PEAKf/2 detector
sums the upward and downward phase-excursion readings and divides the total by two to provide
an average
of
the two peak values.
(Do
not confuse this "average" value with the detected average
value.)
Inverted Output Signals.
When operating with carrier frequencies below 2.5 MHz, the output signal at MODULATION
OUTPUT/AUDIO INPUT is inverted unless the 455 kHz IF is selected. When operating with carrier
frequencies above 2.5 MHz
or
when using the 455 kHz IF, the upper limit of the modulation rate is
that o f the >20 kHz LP FILTER.
3-
199
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