HP 8901B Operation And Calibration Manual page 242

Model 8901B
AM
Display
Resolution
( O h
1
Program
Code
Spec i a I
Function
Code
Detector
Selected
Modulation
Range
Peak?
(YO)
FUNCTIONS
AM, Special Function 2 (Audio Range)
M 0 D U LATl ON
OUTPUT
Sensitivity
(Vac/O/o AM)
D ESCR I PT I ON
Automatic Selection
1 4
RMS
140 Pk,
Avg
140 Pk, Avg,
RMS
5100
Pk, Avg,
HMS
Operation
2.0 SPCL 2.0SP
Automatic Selection
2.4 SPCL 2.4SP 0.001 0.1
2.4 SPCL 2.4SP
0.01 0.1
2.1 SPCL 2.1 SP
0.01
0.1
2.2 SPCL 2.2SP
2.3 SPCL 2.3SP
or
or
0.1
0.01
Selecting AM enables the Modulation Analyzer to measure the AM depth of the tuned RF input signal.
(Selecting Special Function 2 sets measurement limits on the range of AM depth at the same time a
specific display resolution is set.)
AM 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 100 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 0.5 Hz to
260 kHz for carriers from 10 to 1300 MHz (1.5 MHz IF only). (Special Function 6.1 will modify the
lower frequency.) Modulation depths
to
99% can be measured.
The demodulated signal's frequency and distortion can
also
be measured. (Refer
to Audio Measure-
ments section which
starts
on page 3-197.)
PROCEDURE
To make an AM measurement, first tune the instrument to the input signal by selecting AUTOMATIC
OPERATION. Select AM.
Select an audio detector: PEAK+, PEAK-, PEAKf/2, AVG, or RMS. The RMS detector (Blue Key,
AVG) is less accurate than the other detectors in measuring AM, has a reduced bandwidth, and is
typically only used for audio distortion measurements.
The following table lists the different measurement range limits that can be selected with Special
hnction 2:
To filter the demodulated signal, select the desired filter. (Refer to Audio Filters on page 3-179 for
more information about filters.)
AM 3-135