Model 8901B Adjustments
Adjustment
12
FM
DISTORTION AND INCIDENTAL
AM
-
1.5
MHZ
IF
0
Service Sheet
5
Description
The AMFM
test
source is frequency modulated
at
a
100 kHz rate with
400
kHz peak deviation. The
peak deviation
is
measured with both the positive and negative peak detectors when the Modulation
Analyzer
is
tuned
first
to
the signal and then
to
its
image. The
IF
is
adjusted
so
that the difference
between the detector readings
is
the same
for
both signals. This method permits proper adjustment
of
distortion even in the presence of
a
small amount of distortion from the FM source. The incidental AM
is measured on an FM signal modulated at a
1
kHz rate and
50
kHz peak deviation. The instrument
is adjusted for minimum AM.
Equipment
AM/FM Test Source
.............................................................
HP 11715A
Audio Analyzer
...................................................................
HP 8903B
HP
8901B
MODULATION ANALYZER
HP
11715A
AM/FM TEST SOURCE
I
0
INPUT
FYS4
OUTPUT
I
AUDIO
AUDIO ANALYZER
OUTPUT
Figure
5-5.
FM
Distortion and Incidental AM
-
1.5 MHz Adjustment
IF
Test Setup
Procedure
1.
Connect the equipment
as
shown in Figure
5-5.
(The AMFM
test
source output can be connected
2. Set the audio analyzer's oscillator
to
100 kHz
at
4V.
On the AMFM
test
source, set the
test
3.
On the Modulation Analyzer, press the blue key then press INSTR PRESET (the AUTOMATIC
4.
Tune the AM/FM
test
source's carrier frequency
to
approximately
400
MHz.
5. On the Modulation Analyzer, press MHz
to
center
its
tuning. Press
FM.
Adjust the audio
analyzer's oscillator level for a display of
400
kHz peak deviation on the Modulation Analyzer.
6.
On the Modulation Analyzer, switch the DETECTOR between PEAK+ and PEAK- and note
the difference between the
two
readings. Adjust A18R23
(FM
DISTN
1.5
MHZ
IF)
for
equal
readings between PEAK+ and PEAK-.
either
to
a
sensor module or directly
to
the Modulation Analyzer's INPUT.)
mode
to
FM.
OPERATION key)
to
preset the instrument. Set the
HP
FILTER
to
50 Hz.
Adjustment 12
5-19
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