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Operation
Model
890214
Residual Noise Effects
DESCRIPTION
To make the most accurate peak-modulation measurements,
it is necessary
to
measure and correct
the effects of residual noise, that is, noise not on the baseband signal, but modulating the R F carrier,
The following procedure describes the measurement technique.
PROCEDURE
The following procedure enables the user to correct for the effects of residual noise on peak-
modulation measurements.
NOTE
This procediire applics to sinewavc modirla!ion only.
1. Set up and make a normal peak-modulation measurement. The displayed measurement result
will include the signal plus its noise,
(S
+
N ) # , k .
2. Press the Range Hold key to prevent autoranging. If filtering and/or de-emphasis was used in
step 1, make all the following measurements with the same settings.
3. Remove the modulation from the signal and measure the remaining peak-residual noise,
Npkr
on the carrier.
4.
Select AVG. Measure the average residual noise,
Nau.
5. Compute
6. Use the following nomograph to determine the percent,
N%,
of the peak-residual noise level,
Npk, to be subtracted from the original, peak-signal-plus-noise
measurement, (S
+
N ) $ , k .
7. Compute the corrected, peak modulation
where
N%
is expressed as a ratio (rather than in
Y o ) .
3-219
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