Model
8901B
Adjustment
16
HP
89016
(Step
4)
I
MODULAT
I
ON ANALYZER
Adjustments
OUTPUT
FM
DISTORTION AND INCIDENTAL AM
-
455
KHZ
IF
0
Service
Sheets
5
and
8
I
!
INPUT
?l;u&
(step
1)
Description
MODULATION
OUTPUT/
:E8
0
(Step
41 INPUT
-
AUDIO
INPUT
AUDIO ANALYZER
;;:E;
000000
O
0000
0
00
0
0
0
000000
0
0000
0
The signal generator
is
set
to
2.45
MHz and frequency modulated at
a
1
kHz
rate
with
10
kHz
peak
deviation. The incidental AM on the signal
is
measured and the instrument
is
adjusted for minimum
AM.
At
2.45
MHz the signal
is
not down converted by the Modulation Analyzer but goes directly into
the
IF.
The adjustment alters the rolloff characteristic of
a
2.5
MHz IF low-pass filter, which
is
the
principal source of the incidental
AM.
For the
455
kHz
IF,
the AM/FM
test
source
is
frequency modulated
at
a
10
kHz
rate
with
10
kHz
peak deviation. The demodulated FM
is
measured with
a
distortion analyzer
and
FM distortion
is
adjusted for a minimum. The incidental AM
is
measured with FM
set
for a
1
kHz
rate
and
5
kHz
peak
deviation. The instrument
is
adjusted for minimum AM.
Equipment
AMFM Test Source
.............................................................
HP
11715A
Audio Analyzer
...................................................................
HP
8903B
Signal Generator.
.................................................................
HP
8640B
SIGNAL GENERATOR
r
HP
11715A
AM/FM TEST SOURCE
I
FW3Z
OUTPUT
rl
:oo:o
AUD
IO
INPUT
Figure
5-7.
FM Distortion and Incidental
AM
-
455
kHz
IF Adjustment Test Setup
Procedure
NOTE
In the following procedure the RF modulation source can be connected
either to a sensor module (which
is
connected to the Modulation Analyzer)
or
directly to the Modulation Analyzer’s INPUT connector. The procedure
is
written for the latter case.
1.
Set the signal generator to
2.45
MHz at
0
dBm with
10
kHz peak FM deviation
at
a
1
kHz rate.
Connect
its
RF output
to
the Modulation Analyzer’s INPUT
as
shown
in
Figure
5-7.
2.
On
the Modulation Analyzer, press the blue key and then press INSTR PRESET (the
AUTOMATIC OPERATION key)
to
preset the instrument. Key in
34.0
SPCL
to
measure the
IF
frequency. The
IF
should be approximately
2.45
MHz.
If
it
reads approximately
0.455
MHz,
tune the frequency down slightly until a reading of
2.45
MHz
is
obtained.
Adjustment
16
5-25
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