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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