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HP 492A Operating And Service Manual page 33

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Section V
Paragraphs 5-41 to 5-44
~DEL
618B/
620A/
~DEL
492A/
494A
TWT AMPLIFIER
Model 492A/494A
~DEL
4000
VACUUM TUBE VM
626A
SIGNAL GENERATOR
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co
420A
CRYSTAL
DETECTOR
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INPUT
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(8)
RF OUTPUT
(
RO
Figure 5-5. Test Setup for Hum and Spurious Modulation Performance Check
5-41. For Model 494A proceed as for Model 492A,
except, the generator to be used in figure 5-4 is to
be set at a frequency of 9.7 gc. The value from which
the attenuator dial reading is
to
be subtracted, is
-76.7 dbm for the Model 494A.
5-42. HUM AND SPURIOUS MOOULATIO
CHECK.
5-43. For Model 492A proceed as follows:
a. Connect test setup as shown in figure 5-5.
b. Set the generator to 8 gc and
to
square wave
modulation, 1000 pps.
5-8
c. Set the twt HELIX control to position 5, and
position the GRID BIAS control
to
full counterclockwise.
d. Adjust the generator attenuator until the output
is indicated as a -20 db on the 4000.
e. Switch the generator to cw operation.
f. Record the reading on the 4000.
g. Take the difference, in db's, in the readings
in steps d and f and add to it 8 db. The sum of
these two numbers should be greater than 45 db.
5-44. For Model 494A proceed as for Model 492A,
except, the generator to be used in figure 5-5 is to
be set at a frequency of 12.4 gc.
00144-2

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