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Performance Checks; Output Power Check; Noise Figure Check - HP 492A Operating And Service Manual

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Model 492Aj494A
Section I
Paragraphs 5-32 to 5-44
5-32. PERFORMANCE CHECKS.
5-33. GAl
CHECK.
5-34. For Model 492A proceed as follows:
d. Set the two HELIX control to position 5, and
position the GRID BIAS control to full counterclockwise.
e. Adjust the output power of the generator until
the 430C reads 2 miIIiwatts.
a. Set the twt HELIX control to position 5, and
position the GRID BIAS control to full counterclockwise.
f. Repeat steps c through e throughout the fre-
quency band of the twt amplifier, up to 8 gc.
b. Connect test set up as shown in figure 5-4.
c. Set the generator attenuator to -30 dbm, with
a frequency output of 4 gc, in cw operation.
d. The 430C should read greater than 0 dbm.
5-38. For Model 494A as for Model 492A, except,
generator to be used in figure 5-4 to have a frequency
range from 7 to 12.4 gc, and the test should start at
7 gc and end at 12.4 gc.
e. Change the frequency of the generator to 8 gc,
maintaining the same power level.
5-39. NOISE FIGURE CHECK.
f. The 430C should read greater than 0 dbm.
5-40. For Model 492A proceed as follows:
a. Connect test set up as shown in figure 5-4.
5-35. For Model 494A proceed as for Model 492A,
except, generator to be used in figure 5-4 to have a
frequency range from 7 to 12.4 gc, and the test should
be made at these frequencies.
b. Set generator to 6 gc, in cw operation.
c. With generator output power turned off, adjust
the twt HELIX control for a maximum dbm indication
on the 43OC. Record this reading.
5-36. OUTPUT POWER CHECK.
5-37. For Model 492A proceed as follows:
a. Connect test set up as shown in figure 5-4 and
insert a 10 db attenuator between the twt amplifier
and the 477B Thermistor Mount.
b. Set the 430C to the 3 mw range.
c. Set the generator to a frequency output of 4 gc,
in cw operation.
d. With generator output power turned on, adjust
the generator attenuator to obtain a reading on the
430C that is 3 db greater than that recorded in step c.
e. Record the reading on the generator attenuator
dial.
f. Take the reading obtained in step e and sub-
tract it from -78 dbm, for the Model 492A. The re-
sult is the noise figure for this 492A.
~
MODEL
430C
POWER METER
~
MODEL
492A/
494A
TWT AMPLIFIER
~
MODEL
6188/
620A!
626A
SIGNAL GENERATOR
§]
rg
©
M o ! l
©
©
©
a
©
4778
THERMISTOR
MOUNT
~
0
(0
INPUT
OUTPUT
RF OUTPUT
(
0
0
RO
)
MODEL
X281A
ADAPTER
MODEL
X4878
THERMISTOR
TO
REPLACE 477B
AT
FREQUENCIES
ABOVE
IOGC.
Figure 5-4. Test Setup for Gain, Output Power, and Noise Figure Performance Checks
00144-2
5-7

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