Operation Model 8901B
demodulator makes another FM measurement. (Both peak detectors are
used
and the average
is
computed.)
The Modulation Analyzer compares the deviation (static measurements) with the demodulated
FM
(toggled measurements) and computes
its
accuracy error
as
follows:
x
100
Demodulated FM
-
Demodulated Residual FM
Computed FM
FM Calibration Factor
(%)
=
All segments
of
the calibration are carefully monitored.
If
any segment
is
out
of
limits, the calibration
is
aborted and Error
08
is
displayed.
r
10.1
MHz
VOLTAGE
CONTROL LED
OSCILLATOR
OUTPUT AM
BUFFER CALIBRATOR
I
OUTPUT
I
COUNTER
AN0 DISPLAY
BUFFER CONTROLLER
-
Simplified
Block
Diagram
of
the
FM
Calibrator
COMMENTS
Default Calibration Factor
If
the instrument’s non-volatile memory is erased, 100.00%
is
used
as
the default calibration factor.
Updating the FM Calibration Factor
Whenever FM calibration
is
performed, the instrument updates the stored FM calibration factor.
Special Function Cancellation
Performing calibration cancels most Special finctions.
When Using the
FM
Calibrator to Calibrate Other Signal Analyzers
The modulation waveform of the FM Calibrator
is
a rounded trapezoid.
An
signal analyzer, which uses
it
as
a calibration standard, must have demodulation and audio processing circuits which preserve the
full
fidelity
of
the waveform.
Automatic
FM
Ranging
When used
to
calibrate an RF signal analyzer, Special Functions 12.1 and 12.2 set the FM deviation
range
to
that
of
0
to
40
kHz
(Special Function
2.2).
Upon exiting the FM Calibrator Special Function,
the audio ranging
is
not returned
to
automatic but remains fixed (thus leaving the SPCL light on).
Key in 2.0 SPCL
to
return the audio ranging to automatic.
3-158 FM Calibration
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