Specifications

CHAPTER 1
THEORY
1. Scope
a. This manual covers field (fourth
echelon) and depot mainteriance for Test
Set, Radio AN/VRM-l. It includes in-
structions appropriate to fourth and fifth
echelon for troubleshooting, testing, align-
ing, and repairing the equipment. Detailed
functions of the AN/VRM-1 are covered in
this chapter.
b. The complete technical manual for
this equipment includes TM 11-6625-496-
12, TM 11-6625-496-20P. and TM 11-6625-
45P.
c. Forward comments concerning this
manual to the Commanding Officer, U. S.
Army Signal Materiel Support Agency,
ATTN: SIGMS-MPP-4, Fort Monmouth,
N.J.
Note: For applicable forms and records, refer to
paragraph 2, TM 11-6625-496-12.
d. Refer to DA Pamphlet 310-4 to de-
termine what Changes to or revisions of
this publication are current.
2. Block Diagram
(fig. 37)
Test Set, Radio AN/VRM-1 is a portable
equipment for testing plug-in modules of
Receiver, Radio R-442/VRC and Receiver-
Transmitters,
Radio RT-246/VRC and
RT-524/VRC. Signal paths are shown in
the block diagram and are discussed in a
through c below. The complete circuit is
shown in the overall schematic diagram
(fig. 39).
a. Selector Witch.
The setting of the
20-position selector switch, S7902, is de-
termined by the type of test to be made.
The routing of the voltages under test is
determined by the selector switch position.
b. Rf Signals.
The radiofrequency (rf)
signals under test are amplified by the
test probe rf amplifier and routed by
S7902A to the 5.65-mc filter, to an ap-
propriate attenuator network, or directly
to S7902B and S7902C. The latter switch
2
sections apply the signal to one of three rf
amplifiers:
11.5-megacycle (mc), 5.65-
mc, or 47. O-mc. The amplified signals
are rectified and applied through S7902D
to the Schmitt trigger circuit (e below).
c. Audio signals. The audio signals
from the test probe are routed by S7902B
or S7902C either through an appropriate
attenuator network or directly to the audio
amplifier. The amplified signal is rectified
and applied through S7902 D to the Schmitt
trigger circuit (e below).
d. Dc Voltages.
The dc voltages under
test are routed either through an appro-
priate attenuator or directly to S7902B or
S7902C. The latter switch sections apply
the voltage to either the voltage divider
or the voltage supply limits sensing cir-
cuit. The voltage supply limits sensing
circuit senses whether the voltage under
test is between minimum and maximum
tolerances. The direct-current (de) volt-
age from the voltage divider or voltage
supply limits sensing circuit is connected
through S7902D to the Schmitt trigger cir-
cuit (e below).
e. Schmitt Trigger. The Schmitt trigger
circuit operates in conjunction with two
indicator lamps. In the absence of a signal
or when a signal is not within tolerances,
the RED indicator lamp lights. When a
signal is within tolerances, the GREEN
indicator lamp lights.
f. Power.
Power is supplied to the TS-
1777/VRM-l from a 26-volt dc power
source, such as a vehicle electrical sys-
tem. The power source is connected to a
16-volt dc regulator circuit and a line volt-
age sensing circuit. The output of the
16-volt dc regulator circuit is connected
to the line voltage sensing circuit. When
the power source voltage is above 22 volts
dc (minimum limit), the output of the 16-
volt dc
voltage
lamps,
voltage
regulator is switched by the line
sensing circuit to the indicator
the Schmitt trigger circuit, the
supply limits sensing circuit, and