CHAPTER 2. CIRCUIT FUNCTIONING

TM 11-5820-498-35

CHAPTER 2

CIRCUIT FUNCTIONING

Section I. RADIO, AND RADIO WITH INTERCOM,

CIRCUIT FUNCTIONING

2-1. General

RT-841/PRC-77. Those that are identical in both

a. The radio sets include a receiver-transmitter

receiver-transmitters have the same reference

(RT-505/PRC-25 or RT-841/PRC-77), a whip

designation (for example: dc to dc converter A10

antenna (AT-912/VRC or AS-1729/VRC), the

and speech amplifier limiter A22). Those modules

MT-1029/VRC, and OA-3633(*)/GRC. An audio

that are functionally identical but have internal

accessory, interconnecting cables, and mounting

circuit differences are identified with different

hardware to mount the radio sets in a vehicle are

reference designations. For example: squelch

provided in the installation unit (kit) applicable

relay control A24 and receiver audio amplifier

to the radio set installation (SB 11-131).

A25 in the RT-505/PRC-25 are the same, as

b. The OA-3633(*)/GRC converts the nominal

squelch relay control A54 and receiver audio am-

24-volt vehicular battery to operating voltages

plifier A55 in the RT-841/PRC-77. In this man-

(13, 2.6, and 3 volts dc) for itself and the re-

ual those functionally similar modules are identi-

ceiver-transmitter. It also has provision for lis-

fied thusly: A24/A54, A25/A55, A22/A22, etc.

tening on a loudspeaker to the signals received on

2-2.

Radio and OA-3633(*)/GRC, Circuit

the receiver-transmitter, and for matching the

Functioning Without Crewmember Con-

output of the receiver-transmitter to the whip an-

tenna matching network.

trol Boxes

(fig. 4-3)

c. The radio sets are also capable of operating

When the radio configuration does not include

with a vehicular radio-intercommunication (inter-

c r e w m e m b e r control boxes, t h e radio and

com system. The intercom system includes a cen-

OA-3633/(*)GRC circuit functioning are given in

tral audio and power control (Amplifier, Audio

a through d below. Figure 4-3 shows the circuits

Frequency AM-1780/VRC), and crewmember

in radio standby mode; that is, neither transmit-

control boxes (Controls, Intercommunication Set

ting or receiving a radio signal.

C-2296/VRC (located on the rear outside the ve-

a. Circuit Setup. For this radio configuration,

hicle), C-2297/VRC (for vehicle driver), and

the following conditions are required:

C-2298/VRC (for other crewmembers)). The ra-

(1) The link in the MT-1029/VRC must be

dio-intercome boxes, interconnecting cables,

set for local control of the dc power to the equip-

mounting hardware, and audio accessories re-

ment.

quired for the radio set with an intercom system

(2) On the AM-2060(*)/GRC, the POWER

are provided in the installation kit applicable to

circuit breaker switch is set to ON, and the ANT.

the vehicle in which the equipment is used (SB

FREQ. CONTROL switch is set to a position that

11-131). The crewmembers can talk either on the

includes the frequency at which the receiver-

intercom system or over the receiver-transmitter

transmitter is tuned. The SPKR switch is set to

in the radio set.

d. The internal circuit functioning of the re-

ON.

(3) On the receiver-transmitter, the func-

and

ceiver-transmitters,

whip

antennas,

tion switch S1 is set to ON, and the frequency

RT-1029/VRC as well as the intercom system

selector switches MC and KC (not shown in fig.

control boxes is provided in the manual asso-

4-3) are set to the desired operating frequency.

ciated with the particular equipment. Refer to

paragraph 1-1b and c for the associated publica-

An audio accessory (such as the H-189/GR,

H-161/U, or equal) is connected to one of the re-

tions.

ceiver-transmitter AUDIO receptacles FL1 or

e. The module circuits in the RT-505/PRC-25

FL2.

a r e functionally the same as those in the

2-1