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the space between module Al0 and the
ceiver test setup (para 102 and fig. 79.7),
brass wheel-like part of the coupling.
except disconnect test cabIe No. 9 from
the 1066A output- and connect it to the
(3) Adjust RT-505/PRC-25 to a frequency
50-kc higher than its current setting.
AN/USM-44 output. Monitor the RF
(4) Momentarily set the RT-505/PRC-25
voltage at A21J3 with RF Millivoltmeter
function switch to OFF, then back to
Hewlett-Packard Model HP-411A (HP-
ON, and verify receiver audio output by
411A).
observing the oscilloscope and the TS-
(2)
Adjust the AN/USM44 for a 41.00-mc cw
723A/U (used as a vacuum-tube voltmeter)
output at approximately 100 UV.
indications.
(3)
Tune the AN/USM-44 for a maximum
(5) Repeat the procedures given in (3) and (4)
indication on the HP-411A.
above until a frequency setting produces
(4)
Increase the RF output of the AN/USM-
no audio output within 3 seconds, or
44 to the point where limiting just starts
until a frequency of 31.95 mc is reached.
(where an increase in the AN/USM-44
Record the maximum frequency that pro-
output does not increase the reading on the
duces an audio output,
HP-411A.)
(6) Adjust the RT-505/PRC-25 to 31.50 mc
(5)
Reduce the AN/USM-44 RF output for
and repeat the procedures given in (3) and
an indication on the HP411A that is 6
(4) above except reduce the frequency by
db below the limiting level. Sweep the
50 kc for each successive step until the
ANT/USM-44 frequency across the selec-
audio output is not obtained or until a
tivity pass band and select the frequency
frequency of 31.00 mc is reached. Record
that provides the highest peak. Readjust
the minimum frequency that produces an
the AN/USM-44 output level so the
audio output.
selected peak is 6 db below the limiting level.
(7) Withdraw the decoupling tool and rotate
(6)
Determine the pass-band irregularities and
the kilocycle frequency selector to 50
the 6-db-down points.  The pass-band
to re-engage the coupling.
irregularities should be within 2 db and
(8) Adjust the RT-505/PRC-25 to 51.50 mc
the 6-db-down points should be at least
and disengage the coupling ((2) above).
32-kc apart.  Use the AN/USM-26 to
(9) Repeat the procedures given in (3) and
determine the AN/USM-44 frequency at
(4) above until a frequency produces no
the 6-db points. Disconnect test cable No.
audio output within 3 seconds or until a
9 from the dummy antenna input and
frequency of 51.95 mc is reached. Record
reconnect cable No. 9 to the AN/USM-26
the maximum frequency that produces an
input. Increase the AN/USM-44 output
audio output.
level sufficiently to drive the AN/USM-26.
(10) Adjust the RT-505/PRC-25 to 51.50 mc
(7)
Set the AN/USM-44 to the frequency of
and repeat the procedures given in (3) and
the highest peak of the selectivity pass
(4) above except reduce the frequency for
band and to an output level 6 db above the
each successive step until the audio output
noise level. (Read the noise level on the
is not . obtained or until a frequency of
HP-411A with the AN/USM-44 output
51.00 mc is reached. Record the minimum
at zero; then increase the AN/USM-44
frequency that produces an audio output.
RF output until a 6-db increase is indi-
(11) Withdraw the decoupling tool and rotate
cated by the HP-411A.)
the kilocycle frequency selector to 50 to
reengage the coupling.
(8)
Increase the AN/USM-44 output level 60
(12) Evaluate the test results. At both test
db and locate the two frequencies that
frequencies (31 .50 and 51.50 me), the mini-
produce the same output level (6 db above
mum acceptable catching range is 650
noise) as read on the HP-411A ((7) above).
kc with at least 250 kc on each side of the
Determine and record the frequencies by
test frequency.
use of the AN/USM-26. The two re-
f. Selectivity Test.
corded frequencies are the 60 db-down
(1) Perform the selectivity test with the
points. They should be less than 100-kc
equipment connected in a standard re-
apart.
18
TAGO
8344-A


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