Section IV. PRINCIPLES OF OPERATION

TM 11-5820-882-23/TM 06827A-23/2

All sealing surfaces (module cover and battery case)

always be used to stop the module travel and oppose the

prying force.

should have a thin film of silicone grease (NSN 6850-

c. Always inspect frame sockets for damage before

00-177-5094) applied to hepl preserve watertightness

inserting a module. .4 normal socket should have four

and keep the rubber seals pliable. If a handset is used

spring leafs visible. If a spring leaf is pushed over to the

with the radio set, a small amount of silicone grease

wrong side of a socket, it can be pushed back into place

should also be applied to the "O" ring in the connector

with a sharp pointed tool (pin, needle, scribe, etc.). If

to facilitate insertion.

the leaf breaks off or is smashed into the bottom of the

socket, the socket should be replaced if possible.

3-13. Placing in Service

However, the socket will still make good contack with

After the radio set has been repaired, the unit must be

the module pin after the damaged leaf is removed from

checked out completely with the minimum performance

the socket. The radio set is still operational until repairs

test (table 3-2). Upon the completion of the test, the

can be made at a higher level.

radio set should be set to some predetermined frequency

3-12. Lubrication

and properly aligned before being returned to service.

Section IV. PRINCIPLES OF OPERATION

3-16. Receive Operation

3-14. General

The receiver is packaged in three modules. These

Radio Set AN/PRC-68 consists of eight plug-in

modules are:

modules, a frame assembly, and battery assembly. Prin-

a. Converter Module (1A6). The converter

ciples of operation of the radio set is limited to descrip-

module consists of two bandswitched, varactor-tuned rf

tion of the modules and their interfacing with each

other. Refer to figures 2-1 and 2-2 for module loca-

amplifiers and the receiver 1st mixer which converts the

tions.

operating frequency to the first i-f of 12 MHz. The low-

band rf amplifier tunes the frequency range from 30 to

3-15. Circuit Functioning

54 MHz while the high-band tunes 54 to 80 MHz. The

settings of the frequency select switches (A, B, and D,

Circuit functioning of the radio set (fig. FO-1) can be

broken down into modules that comprise separate func-

on synthesizer module, and preset CHAN switch) deter-

tions (receive and transmit) and modules that are used

mine the operating frequency of the rf amplifier and the

for both functions (synthesizer and voltage controlled

local oscillator injection frequency to the first mixer.

oscillator). The battery saver circuitry, tone tuning, and

This injection signal is provided by the voltage controll-

150 Hz squelch tone signal are also discussed.

ed oscillator (VCO) module. For the low-band (30 to 54

Figure 3-11. Pin Straightening procedure.

3-17