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Operation
BLOCK DIAGRAM
Model 8902A
~
MODULATION OUTPUT/
AUDIO INPUT
AUOIO PEAK
DETECTOR
DISTORTION
AUOIO RMS
ANALYZER
DETECTOR
AUDIO
COUNTER
AN0 COUNTER
DISPLAY
A itdio
FiI1sr.s Block Diagram
COMMENTS
Filter Selection Affects Modulation Output.
T h e selected filters are always in the path of the demodulated signal independent of the selection of a
modulation measurement. Thus, unless turned off, the output of MODULATION OUTPUT/AUDIO
INPUT is filtered. In addition, the selected filters remain in effect when switching between
modulation measurements.
Automatic Filter Selection.
Under certain conditions, filters are inserted automatically. When the 455 kHz IF is used, o r when
the RF input is less than
2.5 MHz,
the 15
kHz
low-pass filter is inserted inl less another low-pass
filter has been selected. (The ALL OFF >200
kHz
low-pass filtering cannot be selected.) T h e 15 kHz
low-pass filter selected when operating with the
455
kHz IF is automatically turned off when the 1.5
MHz IF is selected.
Bandwidth Limitations.
With n o filters selected, the post-demodulation bandwidth is from less than 20 Hz to greater than
200
kHz.
(These frequencies refer t o the limits over which measurement accuracy is specified, not
the 3 dB bandwidth.) However. the IF circuits and demodulators impose more severe bandwidth
3-208
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