Model
8901B
FM
Operation
FUNCTIONS
FM, Special F’unction
2
(Audio Range)
DESCRIPTION
The Modulation Analyzer can measure the FM deviation of the tuned input
signal.
(Special
F’unction
2
enables the instrument
to
set limits on the range of FM deviation
that
can be measured.)
FM Measurements are specified for rates from
20
Hz
to
10
kHz
for carrier frequencies
10
MHz and
below
(or
whenever the
455
kHz
IF
is
used) and from
20
Hz
to
200
kHz
for carrier frequencies from
10
to
1300
MHz
(1.5
MHz
IF
only). The corresponding
3
dB
audio bandwidths are approximately
0.5
Hz
to
15
kHz for carriers
10
MHz and below
(or
with the
455
kHz
IF)
and approximately 0.2 Hz
to
260
kHz for carriers from
10
to
1300
MHz
(1.5
MHz
IF
only). Peak deviations up
to
40
kHz can be
measured on carriers below
10
MHz, and peak deviations up
to
400
kHz
can be measured on carriers
above
10
MHz.
The demodulated
signal’s
frequency and distortion can
also
be
measured. (Refer
to
Audio
Measure-
ments
on page
3-197.)
PROCEDURE
To
make an FM measurement, first tune the instrument
to
the input signal
by
selecting Automatic
Operation. Press the FM key.
Select an audio detector: PEAK+, PEAK-, PEAKf/2, AVG,
or
RMS. (The RMS detector, selected
by pressing the Blue Key and AVG key,
is
accurate in measuring FM,
has
a reduced bandwidth, and
is
usually only used for less audio distortion measurements.)
FM
3-151
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