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Model
8902A
Adjustments
OSCILLOSCOPE
VERTICAL
INPUT
S I QNAL GENERATOR
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8 8 8 : :
0
P
0
0
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Adjustment 23-Narrow
455 kHz IF Filter
C A L l ~ R A T l O N
INPUT
RF
POWER
OUTPUT
SWEEP
OUTPUT
(Stop
20)
REFERENCE
W R
I
ZONTAL
INPUT
Service Sheet 6 .
DESCRIPTION
An
x-y plot of the frequency response of the narrow 455
kHz IF
filter is obtained by sweeping the IF
with a
signal
generator and looking at the response on an oscilloscope with its x axis driven by the
sweep output of the signal generator. The filter's overall response
is
checked and adjustments are made
only if the filter is out of limits. The overall IF gain is
also
adjusted.
Adjustment of the filter begins by adjusting overall flatness and slope. If the adjustment is inadequate,
then the first stage of the filter
is
observed as succeeding stages
are
shorted out and adjustments made
to the filter components to
bring about responses of a particular given shape.
EQUIPMENT
Figure 5-1 0. Narrow
455 kHz IF Filter Adjustment Test Setup
PROCEDURE
1.
Perform Adjustment 16-FM Distortion
and
Incidental
2.
Connect the equipment as shown in Figure 5-10. (Con-
nect the vertical input of the oscilloscope directly to
A55J1 (IF OUT).)
3. Set the signal generator to 0 dBm and set
its
frequency
to sweep from 430 to 480 kHz (that is, 455f25 kHz).
4. On the Measuring Receiver, press the blue key then
press INSTR
PRESET
(the AUTOMATIC OPERA-
TION key) to preset the instrument. Key in 0.2 S (Shift)
26 SPCL and 0.2 S 30 SPCL to set the gain of the IF
amplifiers to 0
dB
and to insert the narrow 455 kHz IF
filter.
AM-455 kHz IF.
rev.21 SEP87
5-39
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