CHAPTER 1
THEORY
1. Scope
sections apply the signal to one of three rf
a m p l i f i e r s : 1 1 . 5 - m e g a c y c l e (mc), 5.65-
a. T h i s m a n u a l c o v e r s f i e l d ( f o u r t h
mc, or 47. O-mc. The amplified signals
echelon) and depot mainteriance for Test
are rectified and applied through S7902D
S e t , Radio AN/VRM-l. It includes in-
to the Schmitt trigger circuit (e below).
structions appropriate to fourth and fifth
c. Audio signals. T h e a u d i o s i g n a l s
echelon for troubleshooting, testing, align-
from the test probe are routed by S7902B
ing, and repairing the equipment. Detailed
or S7902C either through an appropriate
functions of the AN/VRM-1 are covered in
attenuator network or directly to the audio
this chapter.
amplifier. The amplified signal is rectified
b. The complete technical manual for
and applied through S7902 D to the Schmitt
this equipment includes TM 11-6625-496-
trigger circuit (e below).
12, TM 11-6625-496-20P. and TM 11-6625-
d. Dc Voltages. The dc voltages under
45P.
test are routed either through an appro-
c. Forward comments concerning this
priate attenuator or directly to S7902B or
manual to the Commanding Officer, U. S.
S7902C. The latter switch sections apply
A r m y Signal Materiel Support Agency,
the voltage to either the voltage divider
A T T N : SIGMS-MPP-4, Fort Monmouth,
or the voltage supply limits sensing cir-
N.J.
c u i t . The voltage supply limits sensing
N o t e : For applicable forms and records, refer to
circuit senses whether the voltage under
paragraph 2, TM 11-6625-496-12.
t e s t is between minimum and maximum
d. Refer to DA Pamphlet 310-4 to de-
t o l e r a n c e s . The direct-current (de) volt-
termine what Changes to or revisions of
age from the voltage divider or voltage
this publication are current.
supply limits sensing circuit is connected
through S7902D to the Schmitt trigger cir-
2. Block Diagram
cuit (e below).
e. Schmitt Trigger. The Schmitt trigger
circuit operates in conjunction with two
Test Set, Radio AN/VRM-1 is a portable
indicator lamps. In the absence of a signal
equipment for testing plug-in modules of
or when a signal is not within tolerances,
Receiver, Radio R-442/VRC and Receiver-
t h e RED indicator lamp lights. When a
T r a n s m i t t e r s , R a d i o RT-246/VRC and
s i g n a l is within tolerances, the GREEN
RT-524/VRC. Signal paths are shown in
indicator lamp lights.
the block diagram and are discussed in a
f. Power. Power is supplied to the TS-
through c below. The complete circuit is
1 7 7 7 / V R M - l from a 26-volt dc power
s h o w n in the overall schematic diagram
source, such as a vehicle electrical sys-
tem. The power source is connected to a
a. Selector Witch. The setting of the
16-volt dc regulator circuit and a line volt-
20-position selector switch, S7902, is de-
a g e sensing circuit. The output of the
termined by the type of test to be made.
16-volt dc regulator circuit is connected
The routing of the voltages under test is
to the line voltage sensing circuit. When
determined by the selector switch position.
the power source voltage is above 22 volts
b. Rf Signals. The radiofrequency (rf)
dc (minimum limit), the output of the 16-
s i g n a l s under test are amplified by the
volt dc regulator is switched by the line
t e s t probe rf amplifier and routed by
voltage s e n s i n g circuit to the indicator
S7902A to the 5.65-mc filter, to an ap-
l a m p s , t h e Schmitt trigger circuit, the
propriate attenuator network, or directly
v o l t a g e supply limits sensing circuit, and
to S7902B and S7902C. The latter switch
2
