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Adjustments
Model 8902A
Adjustment 12-FM
Distortion and Incidental AM-1.5
MHz IF
Reference
Service Sheet 5.
Description
The AM/FM test source is frequency modulated at
a 100
kHz rate with 400 kHz peak deviation. T h e
peak deviation is measured with both the positive and negative peak detectors when the Measuring
Receiver is tuned first to the signal and then to its image. T h e IF is adjusted so that the difference
between the detector readings is the same for both signals. This method permits proper adjustment o f
distortion even in the presence of a small amount o f distortion from the F M source. T h e incidental
AM
is
measured o n an
FM
signal modulated at a 1 kHz rate and
50
kHz peak deviation. T h e
instrument is adjusted for minimum AM.
Equipment
AM/FM Test Source
............................................................
H P
1 17
15A
Audio Analyzer.
.................................................................
H P 8903B
HP 8902A
I
MEASUR
I
NG RECE I VER
HP 11715A
AM/FM TEST SOURCE
I
AUDIO
INPUT
AUDIO ANALYZER
I
Figure
5-5.
FM
Distortion
and Incidcwal
AM-1.5
M f f z Anjustmen.nl
IF
Ttw
Stviip
Procedure
1.
Connect the equipment as shown in Figure 5-5. (The AM/FM test source output can be con-
nected either to a sensor module or directly t o the Measuring Receiver's INPUT.)
2.
Set
the audio analyzer's oscillator to 100 kHz at 4V. On the AM/FM test source, set the test
mode to FM.
3. On the Measuring Receiver. press the blue
key then press INSTR PRESET (the AUTOMATIC
OPERATION key) to preset the instrument. Set the HP FILTER to 50
Hz.
4.
Tune the AM/FM test source's carrier frequency to approximately 400 MHz.
5. On the Measuring Receiver, press
MHz t o center its tuning. Press FM. Adjust the audio ana-
lyzer's oscillator level for a display of
400
kHz peak deviation on the Measuring Receiver.
6. On the Measuring Receiver, switch the DETECTOR between PEAK+ and PEAK- and note
the difference between the two readings. Adjust A18R23 (FM DlSTN 1.5
MHZ
IF) for equal
readings between PEAK+ and PEAK-.
7. On the Measuring Receiver, key in 3000
4
kHz to time the Measuring Receiver
to
the signal
image. Again switch between PEAK+ and PEAK-. T h e difference between the t w o readings
should
be less
than
1.6
kHz. If it is not, adjust A18R23 again to diminish the difference by o n e
half. Now note the reading for PEAK+ (PKl+) and PEAK- (PKI-). Press
fi
kHz. Note the
reading for PEAK+ (PK2+) and PEAK- (PK2-). The instrument is adjusted properly when
5-20
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