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Resettability Tests
TM-11-5820-222-35 Radio Sets AN/VRC-24 and AN/TRC-68 Manual
Audiofrequency Response Characteristics

253) volts ac (AN/TRC-68), or at 22 and
(3) Tune the rt unit to 225.0 mc.
(4) Set the TS-497/URR to a test fre-
30 volts dc (AN/VRC-24). The input signal
required to deactivate the squelch must be
quency of 225.0 mc. Set the METER
between 0.5 and 17 microvolt for maxi-
switch to S-METER and tune the
TS-497/URR for a maximum indi-
mum sensitivity, and between 4.5 and 280
microvolt for minimum sensitivity.
cation on the meter.
h. Tune the rt unit to 399.9 mc. Set the
Modulate the TS-497/URR output
TS-497/URR at the same frequency. Turn
signal at 30 percent with a 1,000-
the METER switch to S-METER and read-
cycle audiofrequency.
just the TS-497/URR for a maximum S-
Adjust the MICROVOLTS control
METER indication. Turn the MICROVOLTS
on the TS-497/URR until the ME-
dial to 6. Adjust the SQUELCH control for
30B/U indicates 12.25 volts across
the minimum setting that will deactivate
600-ohm load.
the squelch. Turn the MICROVOLTS dial
Recycle the rt unit to 399.9-mc and
to the minimum setting that will operate
then back to the test frequency. The
the squelch. The signal input voltage ratio
M E - 3 0 B / U indication should be
between the unsquelched and the squelched
within 10 percent of 12.25 volts.
condition must not exceed 2 to 1.
R e p e a t (7) above for test fre-
quencies of 300 and 235 mc.
149. Signal Plus Noise-to-Noise Ratio
148. Squelch Test
Connect the AN/VRC-24 or AN/TRC-68
Connect the equipment as shown in figure
to the test equipment as shown in figure
115. Connect the ME-30B/U and variable
autotransformer or the ME-26/U and po-
a. Set the TS-497/URR to the same fre-
tentiometer as shown in figure 114.
quency as the rt unit and tune the TS-497/
a. Tune the rt unit to 399.9 mc.
URR for a maximum indication on the S-
b. Set the SQUELCH control to the maxi-
mum sensitivity position (fully counter-
b. Adjust the TS-497/URR for a 10,000-
clockwise to the stop but not to OFF).
microvolt output modulated 30 percent with
c. Turn the METER switch to S-METER
a 1,000-cycle audio signal.
and tune the TS-497/URR for a maximum
c. Adjust the rt unit VOLUME control
indication of the S-METER.
f o r a 24.5-volt root-mean-square (rms)
d. Adjust the TS-497/URR for the mini-
indication on the ME-30B/U. Record the
mum setting of the MICROVOLTS control
indication on the corresponding db scale.
that will deactivate the squelch (as indi-
d. Turn the modulator switch on the TS-
cated by the lighting of the CALL LIGHT
497/URR to OFF. The decrease in db as
indicated on the ME-30B/U must be not
not exceed 3 microvolt.
less than 35 db.
e. Turn  the  SQUELCH  control  fully
clockwise  (minimum  sensitivity).  The
150. Receiver Audio Output Test
squelch must deactivate with an input sig-
nal of not less than 25 microvolts nor more
Connect the test equipment to the AN/
VRC-24 or AN/TRC-68 as shown in figure
than 50 microvolt without readjustment of
116. Do not connect the ME-26/U, the AN/
the SQUELCH control.
f. Perform b through e above at test
USM-50, the TS-723A/U, or the AN/URM-
frequencies of 309.9 and 225.0 mc. The
a. Tune the rt unit and the TS-497/URR
to any convenient frequency.
the squelch must be between 1.5 and 6
b. Set the METER switch to S-METER
microvolt for maximum sensitivity, and
and adjust the TS-497/URR frequency for
between 12.5 and 100 microvolt for mini-
a maximum S-METER indication.
mum sensitivity.
g. Perform b through f above with sup-
c. Adjust the TS-497/URR for a 100-
microvolt rf signal modulated 30 percent
ply voltages of 103 (or 207) and 127 (or

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