Model
8901B
Operation
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
RF
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
procedure applies
to
sinewave modulation only.
1.
Set up and make
a
normal peak-modulation measurement. The displayed measurement result
will
2.
Press the Range Hold key
to
prevent autoranging.
If
filtering and/or de-emphasis
was
used in
3.
Remove the modulation from the signal and measure the remaining peak-residual noise,
Npk,
on
4.
Select
AVG.
Measure the average residual noise,
Nav.
5.
Compute
include the signal plus
its
noise,
(s
+
N)pk.
step
1,
make
all
the following measurements with the Same settings.
the carrier.
6.
Use
the following nomograph
to
determine the percent,
N%,
of the peak-residual noise level,
Npk,
to
be subtracted Erom the
original,
peak-signal-plus-noise
measurement,
(S
+
N)pk.
7.
Compute the corrected, peak modulation
where
N%
is
expressed as a ratio (rather than in
7%).
Residual Noise Effects
3-191
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