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Model 8902A
Operation
Minimum
47.5
FM
De-emphasis Check
26. Press the FM key. Press the RATIO key. If the display is in dB, press the LOG/LIN key to
display
Yo.
The instrument should display between 99.8 and 100.2% REL. The oscilloscope
should show a sinusoidal waveform with a peak-to-peak amplitude between 0.9 and
1.1V
and
a period of 1 ms.
27. Press the LOG/LIN key. Press the RATIO key. Press the PRE-DISPLAY key.-Set the FM rate
as listed in the following table. For each setting, perform the following steps:
a. Set the FM DE-EMPHASIS o f f if it is on. (Leave PRE-DISPLAY on.)
b. Set the signal generator's FM modulation rate to a value approximate to that listed in the
c. Press the RATIO key to establish a reference of 0 dB.
d. Press the FM DE-EMPHASIS time constant key listed in the table.
e. Adjust the modulation rate (but not the level) until the displayed modulation is -3.0 dB.
f. Press the
S
(Shift) key then press the AUDIO FREQ key (the AM key). The Measuring
Receiver should display a rate within the limits listed. Also, the oscilloscope waveform
should change proportionately with the display. (Allow for a times 10 amplitude at the
output of MODULATION OUTPUT/AUDIO INPUT when FM DE-EMPHASIS is set to
750
ps.)
table.
Maximum
52.5
Approximate
FM Modulation Rate
285
2 850
14 250
80 000
FM DE-EMPHASIS
Time Constant
( A
25
50
75
750
3 1 5
3 150
15
750
140 750
I
Frequency Limits (Hz)
I
205.8
21
8.7
Audio Frequency and Audio Filters Check
28. Set FM DE-EMPHASIS and PRE-DISPLAY o f f . Set the FM rate as listed in the following table.
For each setting, perform the following steps:
a. Set the HP FILTER and LP FILTER to ALL OFF.
b. Set the signal generator's FM rate as listed in the table.
c.
Press the FM key then press the RATIO key to establish
a
reference
of 0
dB.
d. Set the HP or LP FILTER as listed in the table, and fine adjust the FM rate for
a
reading
e. Press the S (Shift) key then the AUDIO FREQ
key and note the FM rate. The Measuring
of -3.0 dB REL.
Receiver should display a rate within the limits listed.
Approximate
F M Modulation Rate
300
3 000
15 000
90 000
HP or
LP
Filter
50 Hz HP
300
Hz HP
3
kHz
LP
15
kHz LP
>20
kHr LP
3-53
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