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Service
Model 8901B
For near-identical modulators the formula can be written in the form
100%
%AM
=
-
3--E
where
E
is a small error term which need not be determined with great accuracy. Note that if Modulators
A and
B
are identical,
E
approaches zero, and the formula reduces to 100%/3 or 33.33%.
A measurement of residual AM is also made on the unmodulated RF and entered into the calculation
of the
AM
calibration factor. The AM signal is then measured and the calibration factor is calculated
and shown on the display.
To
prevent ringing of the demodulated signal in the audio circuits, the modulation squarewave is given
a slow risetime by the Current Sources. Special Function 13 controls the AM Calibrator and permits
its use with another Modulation Analyzer or Measuring Receiver.
8D-28
Service Sheet BD3
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