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|  maintain the pattern reasonably
output to the AF INPUT and AF
steady on the cathode-ray tube face.
INPUT RETURN terminals on the
(3) Record the height of the pattern
audio test box.
from peak to peak and from valley
(3) Connect the audio test box 10-pin
to valley.
connector to either AUDIO recep-
(4) Repeat procedures (2) and (3) above
tacle on the rt unit front panel.
for channel settings of 300.0 mc
(4) Connect a 600-ohm load between
and 225.0 mc.
the SPEAKER and AF OUTPUT
(5) Calculate the modulation percent-
RETURN terminals on the audio
age as follows:
test box.
Modulation percentage =
(5) Connect the feedthrough crossarm
of Variable Attenuator CN-318/U
between the ANT. jack on the rt
unit and Radio Frequency Watt-
x 100
meter AN/URM-43A.
(6) Connect the variable adjustment
(6) The modulation percentage must
leg of the CN-318/U directly to the
be between 70 and 100 percent.
input of Transfer Oscillator CM-
d. Broadband Audio Test Procedure.
77/USM.
(1) Remove the rt unit from its case
(7) Connect Oscilloscope AN/USM-50
and set switch S801 to BB. Replace
to the output of the CM-77/USM.
the rt unit in its case. (Refer to
b. Preliminary Adjustments.
TM 11-5820-222-20 for procedure
(1) Tune the rt unit to 399.9 mc.
and location of S801.)
(2) Key the transmitter by connecting
(2) Make the connections given in a
a lead between the RADIO CONT
above, except omit the dummy
LINE and CONT LINE RETURN
microphone and connect the TS-
terminals on the audio test box.
382/U and the ME-30B/U between
(3) Set the CN-318/U for minimum
terminal B of BROADBAND jack
J704 and the AF INPUT RETURN
(4) Set the AN/USM-50 MULTIPLIER
terminal of the audio test box.
switch to 1, the VERTICAL GAIN
(3) Perform the preliminary adjust-
control to midrange, and the
ments given in b above.
SWEEP TIME control to 1,000
(4) Set the TS-382/U to 1,000 cps; set
microseconds.
the signal level to an amplitude
(5) Tune the CM-77/USM for maxi-
(approximately 8 volts as indicated
mum pattern height on the AN/
on the ME-30B/U) sufficient to
USM-50. Adjust the AN/USM-50
begin wave from clipping (as viewed
VERTICAL GAIN control to main-
on the AN/USM-50).
tain the pattern height within the
(5) Record the waveform amplitudes
cathode-ray tube face.
and calculate the modulation per-
(6) Adjust the CN-318/U so that a 6-db
centages as described in c (3), (4),
increase (twice the rf input) or de-
and (5) above.
crease (half the rf input) in the rf
(6) The modulation percentages must
input to the CM-77/USM causes a
be between 70 and 100 percent.
6-db change (twice or half the
height) of the pattern on the AN/
USM-50.
c. Normal Audio Test Procedure.
guide.
(1) Set the TS-382/U to 1,000 cps; set
(1) Connect Audio Oscillator TS-382/
the signal level for 0.1 volt on the
U to the dummy microphone input.
ME-30B/U.
(2) Connect the dummy microphone
(2) Adjust the AN/USM-50 SWEEP
TIME FINE and SYNC controls to
output to the AF INPUT and AF
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