Advertisement
Model 8902A
Operation
COMMENTS
Input/Output Status.
The demodiilated AM is present at MODULATION OUTPUT/AUDIO INPUT (unless AUDIO
INPUT has been selected). The demodulated AM is usually present at the rear-panel AM
OUTPUT
connector. (Refer to AM
Oiitpirl
on page 3-173.)
PeakflP Detector.
The PEAK+ detector always detectsthe peak of the carrier envelope while the PEAK- detector
always detects the trough. The PEAKzt/2 detector sums the peak and the trough readings and divides
the total by two to provide an average of the two peak values.
(Do
not confhse this "average" value
with the detected average value.)
Automatic Range Selection.
The routine which automatically selects the modulation range contains a region of overlap between
35 and
40°/o
AM (peak detected). When using the average o r RMS detectors, ranging occiirs at
readings lower than these. In general, if the modulation is reduced from above 40% into the
overlap region, only
0.1%
resolution
is
ordinarily displayed although
0.0
1% resolution is available.
To
display the increased resolution, press the AM key a second time. Audio Range has more detailed
information on the modulation ranges that can be set.
Automatic Filter Selection.
When operating above 2.5 MHz, while using the
455
kHz IF, the upper limit of the demodulated
signals modulation rate is that of the >20 kHz LP Filter. The 15 kflz LP Filter is automatically selected
when operating below 10 MHz
o r
whenever the 455
kHz
IF is selected. However, this filter may be
overridden by selecting another LP Filter. The lower limit of the modulation rate is determined by
the ALC response time selected. (Refer
to AM ALC Rcsponse
Time
on page 3-165.)
Inverted Output Signal.
The signal at the rear-panel AM Output is inverted relative to the Modulation Output signal.
Potential Inaccuracies.
AM conditions that cause the carrier signal to disappear (such
as
1000/0 AM
or
pulse modulation)
will cause inaccuracies in measurement of FM, RM. or input frequency, o r they could cause Error
05 (FM squelched) to be displayed when these measurements are selected.
Increased Accuracy.
Accuracy
of
AM readings may be improved by calibrating the AM measurement (refer to AM
Cc'lihralion on page 3-167) and by taking into account the effects of residual noise (refer to Rt.sidira/
Noisc EjJ2ct.s on page 3-2 19).
Relative AM Depth Measurements.
If AM depth is to be displayed relative to a reference, enter the value as
a
ratio reference using the
RATIO key. (Refer to Ratio on page 3-245.)
3-163
Advertisement
Chapters
