Section II. FUNCTIONAL OPERATION OF ELECTRONIC CIRCUITS

TO 31R2-2GRC171-2

TM 11-5820-815-14

NAVELEX 0967-LP-544-5010

SECTION II

FUNCTIONAL OPERATION OF ELECTRONIC CIRCUITS

switches (S3 through S7) for remote frequency select

4-35.

GENERAL.

and two spst switches (S1 and S2) for remote power

on/off and squelch on/off of the receiver-transmitter. It

4-36. This section provides a detailed circuit descrip-

also contains a potentiometer (R1) for control of audio

tion of Radio Set Control C-7999/GRC-171 and of each

level from the receiver-transmitter and a ready lamp

module of Radio Receiver-TransmitterRT-980/GRC-

(DS1) that indicates the radio set is tuned and ready for

171. The description of each module includes a func-

use.

When off, the lamp indicates the receiver-

tional description that is supported by a block diagram

transmitter is in the process of tuning or that there has

and a detailed description of electronic circuits that is

been a circuit malfunction. The panel lights provide

supported by simplified schematic and complete

illumination for labeling on the front panel of the C-

schematic diagrams.

7999/GRC-171.

4-37. In this section reference is made to logic 0 and

4-40. The frequency select switches develop bcd

logic 1 voltage levels. A logic 0 voltage level is defined

frequency select information in accordance with table 4-

as a voltage between 0 and +0.4 V dc. A logic 1 voltage

1. When applied to the 15-frequency select lines to the

level is defined as a voltage between +2.4 and +5.5 V dc.

receiver-transmitter, the bcd frequency select information

tunes the radio set to the frequency displayed on the

4-38.

RADIO SET CONTROL C-7999/GRC-171.

thumb-wheel switches. Diodes CR1 through CR15

provide isolation between the frequency select switches

4-39. Refer to the schematic diagram of figure FO-17.

of the C-7999/GRC-171 and the switches of the local

The C-7999/GRC-171 contains five thumb-wheel

frequency select located on the

Table 4-1. Radio Control Frequency Select Coding

4-7