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|  UG-274B/U to the connector o n
(2) Connect the handset to either
the other end of the dummy an-
AUDIO connector.
tenna.
b. Performance Test.
(6) Set the AN/URM-48 frequency to
(1) Press the handset push-to-talk
switch.
30,000 mc as indicated on the AN/
(2) Set the ME-26 B/U to the 300-volt,
USM-26. Adjust the deviation for
dc range. Normal indication at J3
10kc at 1,000 cps.
is +125 volts; normal indication at
(7) Set the receiver-transmitter front
J2 is -45 volts dc.
panel controls as follows:
c. Faulty Part Isolation.
(a) BAND switch at 30-52.
Note: Make all measurements with respect to
(b) Tuning knobs at 30.00 mc.
ground unless otherwise specified.
(c) Function switch at ON.
(1) Measure the dc resistances at the
b. Bandwidth Test.
points listed below and compare
(1) Connect the 411A between pins 1
and 4 of A2J1.
them with the normal resistances.
(2) Adjust the output of the AN/URM-
48 for a 25-millivolt indication on
the 411A.
(3) Disconnect the 411A from pins 1
and 4 of A2J1 and connect it be-
tween pins 2 and 3 of A2J1. The
411A should indicate 4.5 db less
than the indication not e d in (2)
above. (This value, -4.5 db, is the
input-to-output voltage ratio.)
(4) Adjust the AN/URM-48 level to
obtain a 0-db indication on the
411A.
(5) I n c r e a s e the AN/URM-48 fre-
(2) After replacing a faulty part, re-
quency until the 411A indicates a
peat the procedures given in b
3-db decrease. Record this fre-
above.
quency.
(6) D e c r e a s e the AN/URM-48 fre-
quency to obtain a 0-db indication
on the 411A.
a. Preparation.
(7) Further decrease the AN/URM-48
(1) Prepare the following equipment:
frequency until the 411A indicates
a 3-db decrease. Record this fre-
(b) Frequency Meter AN/USM-26.
quency.
(8) Return the AN/URM-48 frequency
(d) Adapter UG-274B/U.
to obtain a 0-db indication on the
411A.
(2) Connect a Cord CG-530/U (part of
(9) Compute the difference between
the AN/USM-26) between ANT con-
the frequencies recorded in (5) and
nector J2 on the receiver-trans-
(7) above. The freqpency difference
mitter and one end of the dummy
is the 3-db bandwidth, which should
be 400 kc.
(3) Connect the output of the AN/URM-
(10) Adjust the AN/URM-48 frequency
48 to a male connector of the UG-
to 52.950 mc as indicated by the
274B/U.
AN/USM-26.
(4) Connect the AN/USM-26 to the
(11) Repeat (1) through (9) above. The
other male connector of the UG-
input-to-output voltage ratio noted
274B/U.
in (3) should be -3.0 db; the 3-db
(5) Connect the female connector of
bandwidth
c o m p u t e d in the
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