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ARMY TM 11-5820-882-23MARINE C O R P S TM 06827A-23/2

TECHNICAL MANUAL

ORG ANIZATIONAL AND DIRE CT SUP P ORT

MAINTENANCE MANUAL

RADIO SET AN/PRC-68

(NS N 5820-01-079-9260)

This copy is a reprint which includes current

pages from Changes 1

DE P AR TMEN TS OF TH E ARMY AND TH E N AVY,19 J ANU AR Y 1981

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CHANGE)

)No. 1 )

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

Cl

HEADQUARTERS DEPARTMENT OF THE ARMYHEADQUARTERS US MARINE CORPS

Washington, DC,30 June 1981

ORGANIZATIONAL AND DIRECT SUPPORTMAINTENANCE MANUAL

RADIO SET AN/PRC-68

(NSN 5820-01-079-9260)

TM 11-5820-882-23/TM 06827A-23/2, 19 January 1981, is changed as follows:

1. New or chan ged mater ial is indicat ed by a vertical bar in th e ma rgin.

2. Remove and insert pages as indicated in the page list below:

Remove Insert

i and ii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i and ii1-1an d 1-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1a nd 1-22-3 th rough 2-10 . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 through 2-103-15 an d 3-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15 and 3-16A-1 and A-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1 and A-2B-3 through B-5 . . . . . . . . . . . . . . . . . . . . . . . . . . B-3 through B-5

3. File this chan ge sheet in front of th e man ua l for r eference purposes.

B y O r d e r o f t h e S e c r e t a r y o f t h e A r m y :

Official:

ROBERT M. J OYCE

B r i g a d i e r G e n e r a l , U n i t e d S t a t e s A r m y

T h e Ad j u t a n t G e n e r a l

EDWARD C. MEYER

G e n e r a l , U n i t e d S t a t e s A r m y

Chief of S taf f

DISTRIBUTION:T o r e d i s t r i b u t e d i n a c c or d a n c e w i t h S p e c i a l L i st .

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TECHNICAL MANUAL

No. 11-5820-882-23

No. 06827A-23/2

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

HEADQUARTERS DEPARTMENT OF THE ARMHEADQUARTERS, US MARINE CORPS

W A S H I N G T O N , DC 19 January 1981

ORGANIZATIONAL AND DIRECT SUPPORTMAINTE NANCE MANUAL

RADIO SET AN/PRC-68

(NSN 5820-01-079-9260)

REPORTING ERRORS AND RECOMMENDING IMPROVEMENTS

You con help improve this manual . If you f ind any mis takes or i f you know

of a way to improve the procedures , please le t us know. Mail your le t ter , or

DA Form 2028 (Recommended Changes to Publicat ions and Blank Forms), or

DA F orm 2028-2 loca ted in back o f th i s m anua l d i rec t to : Com m ander , US

Arm y Com m unica t ions -E lec t ron ic s Com m and , ATTN: DRS EL-ME-MQ, F or t

Monmouth, New Jersey 07703. Marine Corps uni ts should submit a NAVMC

10772. A reply will be furnished to you.

CHAPTER

SECTION

CHAPTER

SECTION

CHAPTER

SECTION

APPEN DIX

APPEN DIX

SECTION

1.

I.

II .

III.2.

I.

II .

III.

IV .

V.

VI.

3.

I.

II .

III.IV .

A

B

I.

II .

III.

IV .

Paragraph

HOW TO USE THIS MANUAL ----------------------------------------------

INTRODUCTION

General information --------------------------------------------- 1-1

Equipment description and data ------------------------------ 1-6

Principles of operation ------------------------------------------ 1 -9ORGANIZATIONAL MAINTENANCE

Repair par ts, special tools, TMDE, and su pport

equ ipm en t ------------------------------------------------------- 2 -1

service upon receipt --------------------------------------------- 2-4

Preventive maintenance checks and services

(PMCS)---------------------------------------------------------- 2-9

Troubleshooting -------------------------------------------------- 2-10

Ma int en an ce pr ocedur es ---------------------------------------- 2-13

Preparation for storage or shipment ------------------------- 2-19

DIRECT SUPPORT MAINTENANCE

INSTRUCTIONS

Repair pa rts, special tools, TMDE, an d su pport

equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 1

Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

Maintenance procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10Prin ciples of opera tion ----. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

MAINTENANCE ALLOCATION

Introduction-------------------------------------------------------------------------

Maintena nce allocation chart for Radio set

AN/P RC-68---------------------------------------------------------------------

Tool and test equipment requirements for Radio

set AN/PRC-68----------------------------------------------------------------

Rem ar ks -----------------------------------------------------------------------------

Page

0-1

1-1

1-1

1-2

2-1

2-2

2-8

2-10

2-13

2-14

3-1

3-3

3-153-17

A-1

B-1

B-3

B-4

B-5

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APPENDIX C

SECTION I

INDEX

Figure

1-1

1-2

1-3

1-4

2-1

2-2

2-3

2-4

2-5

2-6

3-1

3-2

3-33-4

3-5

3-6

3-7

3-8

3-9

3-10

3-11

FO-1

Number

2-12-2

2-3

2-4

3-1

3-2

3-3

3-4

Paragraph

EXPENDABLE SUPPLIES AND MATERIALSLIST

In tr du ction -------------------------------------------------------------------------

Expendable supplies and materials list -----------------------------------------II----------------------------- ------------------------------------ ------------------- ------

LIST OF ILLUSTRATIONS

Title

Ra dio Set AN/P RC-68 -------------------------------------------------------------------------

Radio Set, Major Components ----------------------------------------------------------------

Receiver Oper at ion, Sim plified Block Diagr am -------------------------------------------

Transmitter Operation, Simplified Block Diagram ----------------------------------------

Radio Set Component Locations, Front View ---------------------------------------------

Radio Set Component Locations, Rear View ----------------------------------------------

Ba t te r y Tes t ---------------------------------------------------------------------------------------

Transmitter Power Output Test ---------------------------------------------------------------

Sen sit ivit y Tes t ------------------------------------------------------------------------------------

Radio Set Packaging Diagram----------------------------------------------------------------

Maintenance Kit MK-()/PRC-68-----------------------------------------------------------

Receiver Troubleshooting Test Setup --------------------------------------------------------

Tra ns mit ter Trou blesh ooting Test Set up ---------------------------------------------------Receiver Fault Isolation Test Setup ----------------------------------------------------------

Receiver Fault Isolation Test Setup (Alternate Procedure)-----------------------------

Tra ns mit te r Fa ult Isola tion Test Set up ------------------------------------------------------

Module Socket Test Point Location, Front ------------------------------------------------

Module Socket Test Poin t (E Nu mbe rs ) Location , Fr ont -------------------------------

Module Socket Test Point Location, Rear--------------------------------------------------

Modu le Rem ova l ---------------------------------------------------------------------------------

Pin Straightening Procedure -------------------------------------------------------------------

Radio Set Block Diagram (2 Sheets)---------------------------------------------------------

LIST OF TABLES

Title

Fr equ ency Cha rt (Pr int ed on ba tt ery )-------------------------------------------------------Frequency Chart (Switch Code)---------------------------------------------------------------

Organizational Preventive Maintenance Checks and Services --------------------------

Troubleshooting Procedures ------------------------------------------------------------------

Maintenance Kit MK-( )/PRC-68 Description -------------------------------------------

Radio Set Minimum Performance Test -----------------------------------------------------

Fa u lt Is ola ti on Tes t ------------------------------------------------------------------------------

Synthesizer Test Voltages and Frequencies -------------------------------------------------

Page

C-1

C-2

I-1

Page

1-0

1-3

1-4

1-4

2-1

2-2

2-10

2-11

2-11

2-15

3-1

3-2

3-33-7

3-7

3-8

3-8

3-9

3-9

3-163-17

Page

2-32-4

2-10

2-12

3-2

3-4

3-11

3-15

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HOW TO USE THIS MANUAL

q Army maintenance levels and related Marine Corps maintenance levels are asfollows:

Operator/Crew Echelon 1 MaintenanceOrganizational Echelon 2 MaintenanceDirect Suppor t Echelon 3 Maintenance

General Support Echelon 4 MaintenanceDepot Echelon 5 Maintenance

q This manual contains all the necessary information to service Radio Set AN/PRC-68 at the organizational (echelon 2) and direct (echelon 3) supportmaintenance levels.

q Use the MAC (located in Appx. B) to determine the proper maintenance levels.

q To service Radio Set AN/PRC-68 at organizational (echelon 2) maintenancelevel, consult chapters 1 and 2.

q To service Radio Set AN/PRC-68 at direct support (echelon 3) maintenancelevel, consult chapters 1 and 3.

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Figure 1-1. Radio S et AN/ PRC-68.

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CHAPTER 1

INTRODUCTION

Section I. GENERAL INF ORMATION

1-1. Scope

This manual describes Radio Set AN/PRC-68 (fig. 1-1)and provides instructions for organizational and directs u p p o r t m a i n t e n a n c e . M a i n t e n a n c e a l l o c a t i o n c h a r t

(MAC) i s inc lud ed in appendix B.

1 -2 . Ma in t e n a n c e Fo r m s , R e c o r d s , a n d

Rep o r t s

Department of the Army forms and procedures used forequipment maintenance will be those prescribed by TM

38-750. The Army Maintenance Management System.Marine Corps units should refer to the current editionof TM 4700-15/1.

1 -3 . D e s t r u c t i o n o f Ar m y M a t e r i e l t o P r e -

v e n t E n e m y Us e

Demolition and destruction of electronic equipment willbe under the direction of the commander and in accor-dance with TM 750-244-2.

S e c t i o n I I . E Q U I P M E N T

1 - 6 . Eq u ip m e n t C h a r a c t e r i s t i c s , C a p a -

b i li t ie s , a n d F e a t u r e s

Radio Set AN/PRC-68 (radio set) is a ha nd-heldreceiver-transmitter that provides ground-to-groundvoice communications in the 30 megahertz (MHz) to 79.

95 MHz band. The unit is capable of secure speechoperation when it is used with the secure voice module(svm). The radio set can be used with a short or longantenna, with a standard military handset such as H-138/U, H-189/U or H-250/U, or with its built-in spea k-er-microphone.

1 -8 . Eq u ip m e n t D a ta

1 -4 . P r ep a r a t io n for S to r ag e o r Sh ip m en t

Refer to Chapter 2, section VI for administrative

storage instructions.

1 -5 . R e p o r t i n g E q u i p m e n t I m p r o v e m e n t

R e c o m m e n d a t i o n s ( E IR )

EIR can and must be submitted by anyone who is aware

of an un satisfactory condition with t he equipm ent

design or u se. It is not n ecessar y to show a new design or

list a better way to perform a procedure, just simply tell

why the design is unfavorable or why a procedure is dif-

ficult. EIR maybe submitted on standard Form (SF) 368

(Quality Deficiency Report). Mail directly to Comman-er, US Arm y Commu nications - Electronics

Comnand, ATTN: DRSEL-ME- MQ, Fort

Monmouth, NJ 07703. Marine Corps units mail to Com-

manding Gereral, Marine Corps Logistics Base (P840),

Albany, GA 31704. A reply will be furnished to you.

DESCRIPTION AND DATA

1-7 . Loca t ion an d Desc r ip t ion o f Majo r

C o m p o n e n t s

Figure 1-2 shows the major components of the radioset. The unit consists of: the rt unit, which contains the

eight modules and all necessary operating controls and

connectors; the module cover, held by two captive

screws to the chassis frame, which also holds the fre-

quency changing and alignment tool; the battery, which

snaps onto mating connectors on chassis frame; the bat-

tery case, held on by two latches; and the short antenna.

GENERAL

Frequency -------------------------------------------------30.00 MHz79.95 Long antenna ------------------------------------------ 1 mile ( 1.6 Kilo-

MH z meters)Available channels--------------------------------------1000 Oper at ing t emp era tu re r an ge ------------------------- - 40F to + 159F

Ch an ne l sp acin g -----------------------------------------50 kH z (-40C to +

Preset channels-------------------------------------------10 65C)

Pr ese t ch an ne l spa cing----------------------------------200 kH z Weight (including battery and an tenna ,

Modu lat ion ------------------------------------------ frequ en cy modu la- no headset)---------------------------------------------- 40oz. (1.30 kg)

tion (fro) S ize. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . 8.35 in (212.0 mm )

Range x 3.80 in (96.0

Sh ort an te nn a -----------------------------------------330 yards (300 m m )

meters) x 1.52 in (38.6

mm)

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Fr equ en cy st ab ility -------------------------------------- 0 .005 per cent

Spu rious a nd ha rm onics ra diat ion--------. ----------50 dB below rf car-

rier level

Modu lat ion limit ing ------------------------------------- 1 5 k Hz devia tion

(maximum)

Sque lch ton e (2.53.5 kHz deviat ion) -------------- 148 to 15 2 H z

RECEIVER

Adjacen t cha nn el r ejection ---------------------------- 60 dB

Image rejection ------------------------------------------- 40 dB

q SINAD = Signal + N oise + Distort ion

Noise + Distort ion

Sen sit ivity- . . . . . . . . . . . .. . . .0.5 uV for 10 dB

SINAD*

Squelch sensitivity ---------------------------------------0.5 uV

Selectivity: 6 dB down------------------------------bandwidth greater

than 15 kHz

60 dB down------------------------------bandwidth less than

50 kHzResp ons e to s pu riou s sign als -------------------------- 60 dB

Fr equ en cy st ab ility -------------------------------------- 0.00 5 per centAudio out pu t ---------------------------------------------less th an 10 per cent

distortion at 20

m W

Se c t ion I I I . P RIN CIPLE S O F O PE RATIO N

1-9. Gener al In for ma t ion

The radio set contains eight plug-in modules which pro-vide all the circuitry necessary for receive and transmitoperation. These operations can be broken down intotwo basic functions, described below.

1-10. Receiver Op r at ion ( fig. 1-3)

When the radio set is turned on (PWR OFF/ON/SQUELCH DIS switch in the ON position), the unit isin the receive mode (squelch is on, no receiver noise pre-sent). Signals entering the antenna are routed throughthe antenna coupler to the converter stage. The frequen-cy synthesizer and voltage controlled oscillator (vco)

provide a mixer frequency for the coverter stage. This

mixer signal is determined by the setting of the frequen-cy select switches (three located on the synthesizermodule and one located on the top panel of the radioset). After the incoming signal is converted to a 12.0MHz s ignal, it is routed to th e filter /i-f module foramplification and a second conversion to 6.5 MHz andthen to the i-f/a-f module. The intermediate frequencyan d a udio frequ ency (i-f/a-f) module det ects an damplifies the signal and connects it to the built-inspeaker/microphone or external handset.

1 -1 1. T r a n s m i t t e r O p e r a t i o n (fig.1-4 )

When the radio set is in the transmit mode (unit turned

on and PUSH TO TALK switch depressed), the speaker/

microphone is used as a microphone to apply a voice

signal to the modulator/mixer. Here the signal is fre-

quency modulated on a carrier singal determined by the

synthesizer and voltage controlled oscillator (controlled

by the frequency select switches). The output of the

modulator/mixer goes to the transmitter module where

it is amplified to 1 watt minimum. The antenna coupler

matches the t ransmitter circuit impedance to the ant en-

na (long or sh ort) for maximum power t ran sfer.

1-12. Secu r e Voice Ope r a t ion

Secure voice operation may be utilized on the radio set

by connecting the secure voice module (svm) to the bot-tom of the rt unit. The battery case and battery must be

removed first. The svm connector (located next to the

battery connector) has a small black shorting plug in-stalled. This plug must be removed to install the svm inits place. If the radio set is not being used with securevoice equipment, the shorting plug must be installed in

the svm connector for normal set operation. The re-tainer (attached to SVM plug) must be wrapped around

the connector before installation of plug to preventdamage to retainer line.

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Figure 1-2. Rad io set, m ajor com ponents.

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Figure 1-3. Receiver operation, simplified block dia gram.

Figure 1-4. Transmitter operation simplified, block diagram.

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CHAPTER 2

ORGANIZATIONAL MAINTENANCE

Sec t ion I REPAIR PARTS, SPECIAL TOOLS, TMDE, AND SUPPORT EQUIPMENT

2 -1. Co m m o n To o l s a n d Eq u ip m e n t for tools and equipment to be used at the organizational

For authorized common tools and equipment refer to maintenance level. Refer to applicable T/F (table of

the Modified Table of Organization and Equipment equipment) for Marine Corps units.

(MTOE) applicable to your unit. 2-3 . Repa i r Pa r t s

2-2 . Specia l Tools , TMDE, and Support Repair parts are listed in the Repair Parts and Special

E q u i p m e n tTools List (TM 11-5820-882-23P) covering organiza-tional and direct support maintenance for this equip-

Refer to the maintenance allocation chart (Appx. B), ment.

Figure 2-1. Radio set component locations, front view.

2-
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Section II. SERVICE UPON RECEIP T

2-4. C h e ck i n g U n p a c k e d E q u i p m e n t

a. Inspect the equipment for damage incurred dur-ing shipment. If the equipment has been damaged,report the damage on DD Form 6, Packaging Improve-ment Report.

b. Check the equipment against the packing slip tosee if the shipment is complete. Report all discrepanciesin accordance with the instructions of TM 38-750.Marine Corps units should refer to current edition ofTM 4 700-15/1.

c. Check DA PAM 310-7 to see whether there are

any modification work orders pertaining to this equip-

ment .

2-5. D is a s se m b l y I n s t r u c t i on s

To disassemble the radio set for battery replacement or

channel changing and a lignment (fig, 1-2), perform th e

following:

a. Unfasten latches on battery case and remove bat-

tery case. (Handle case carefully as damaged case will

not seal properly).

b. Remove battery by disconnecting snap ter-

minals.

c. Remove module cover by tu rning t he t wo captive

screws counterclockwise (located on bottom of module

cover).

NOTE

Make sure that the svm shorting plug (located

next to the battery terminal connector in the rt

unit , fig. 22), is installed and in good condi-

tion. The rad io set will not work un less the

shorting plug or svm is installed.

2 - 6 . R e a s s e m b l y I n s t r u c t i o n s

To reassemble the radio set, perform the following:

a. Apply a thin coat of silicone grease (NSN 6850-00-177-5094) to top edge of the module cover. Slide

module cover over r t u nit a nd secure with the t wo cap-

tive screws located on t he bottom of the cover (tur n

clockwise),

b. Atta ch battery t o batt ery connector on rt unit,

c. Apply a thin coat of silicone grease to the top edgeof the batt ery case an d att ach battery case and securewith the two latches,

Figure 2-2. Radio set component locations, rear view.

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2 - 7 . F r e q u e n c y C h a n g in g a n d A l ig n -

m e n t P r o c ed u r e s.

The ten position (0 through 9) CHAN switch on the

front panel provides ten preset sequent ial channels spac-

ed 200 kHz apart over a 2 MHz bandwidth. Any portion

of the 30.00 MHz to 79.95 MHz range can be selected by

changing the three switches (A, B, and D) on the syn-

thesizer module and the CHAN switch on the top panel

of the radio set. (Refer to table 2-1 or table 2-2 for fre-

quencies and their respective switch settings). Whenever

the frequency of a radio set is changed (excluding the

ten preset channels), the transmitter module and anten-

na coupler module must be realigned to ensure proper

matching and maximum power transfer of the radio set

to the antenna.

a. Changing Frequency. To change the frequency

of the radio set, perform the following:

(1) Disassemble unit (para 2-5).

(2) refer to figure 2-2. Set synthesizer switches,

with the enclosed alignment tool (or JFD 5284 align-ment tool), and the top panel CHAN switch, to th e new

frequency using table 2-1 or table 2-2, as applicable.

N O T E

The frequency chart shown in table 2-1 is

printed on the battery. Table 2-2 is a complete

listing of all frequencies including degraded

(low sensitivity) channels.

(3) Set the transmitter switch and antenna coupler

switch (fig. 21) with the enclosed alignment tool to th e

same position as switch A on the synthesizer module.

(4) Connect battery.

b. Alignment. After the frequency of the radio set

has been changed, perform the following procedures for

radio set alignment (fig. 2-1 ):

(1) Install antenna (either short or long).

(2) Set CHAN switch to 5.

(3) Preset Cl on the transmitter module fully

clockwise (use enclosed alignmen t tool of JF D 5284).

(4) Set PWR OFF/ON/SQUELCH DIS switch to

ON .

(5) Press push-to-tune switch (on side of radio

set) and adjust VOL control for comfortable level.

(6) Using the alignment tool, adjust C1 on the

transmitter module counterclockwise for the lowest

tone.

(7) Release push-to-tune switch.

(8) The antenna coupler adjustment (L1) must be

made using Test Set TS3354/PRC-68 (test set),

(a) Remove cover from test set.

(b) Install test set antenna.

(c) Set FUNCTION switch to FSM position.

(9) Hold radio set so the antenna is approximately

6 to 24 inches from FSM antenna on test set.

(10) Press PUST TO TALK switch on radio set

and use alignment tool to adjust L1 (located on ant enna

coupler) for maximum (peak) indication on the test Se

meter .

(11) Release PUSH TO TALK switch.

(12) With alignment tool, adjust squelch (SQ

ADJ) cont rol on i-f/a-f module coun te rclockwise unt

noise is hear d.

(13) Slowly tu rn SQ ADJ contr ol clockwise u nt

receiver quiets, then advance control one full turclockwise.

(14) Return CHAN switch to channel originall

selected.

(15) Set PWR OFF/ON/SQUELCH DIS switc

to PWR OFF.

(16) Remove battery.

(17) Reinstall alignment tool on module cover.

(18) Reassemble unit (para 2-6).

c. Frequency Chart (Battery). To use the chart i

table 2-1, select the frequency value for each synthesize

switch in turn, that comes closest to (but not over) th

desired frequency. Then add the values of the switche

(A, B, CHAN (C), and D) to determine the operatinfrequency. By using the proper combination, any fr

quency between 30.00 to 79.95 MHz (in 50 MHz steps

may be selected.

Table 2-1. Frequency Chart (Printed on Battery)

d . F r e q u e n c y C h a r t ( S w i t c h C o d e ) . T h e f o l l o w i n

c h a r t s i n t a b l e 2 - 2 m a y b e u s e d t o d e t e r m i n e a

o p e r a t i n g f r e q u e n c y f r o m t h e s y n t h e s i z e r s w i t c h c o d e

or the synthes izer switch codes from a known frequen

c y . ( E a c h c h a r t c o v e r s a 2 M H z b a n d ) . T o f i n d t h

C ha nge 1 2 -

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opera t ing f requency ( in MHz) f rom the swi tch codes ,

f i n d t h e n u m b e r s t h a t c o r r e s p o n d t o t h e A , B , C H A N

and D pos i t ions .

Example: Switch code is 3412, where:

A = 3

B = 4

CHAN = 1

D = 2

(1) F ind the chart which has A = 3 and B = 4 a t

the top left hand corner.

(2 ) Nex t loca te 1 in the CHAN co lum n.

(3 ) Read ac ros s un t i l you com e to the f requency

num ber unde r the 2 in the D co lum n.

( 4 ) A n s w e r s h o u l d b e 6 2 . 3 0 M H z .

T o f i n d t h e s y n t h e s i z e r s w i t c h c o d e s w h e n t h e

frequency ( in MHz) is known, f ind the frequency in the

c h a r t a n d r e a d o f f t h e A , B , C H A N , a n d D s w i t c h

codes .

E x a m p l e : F r e q u e n c y i s 5 3 . 1 5 M H z

( 1 ) F i n d t h e c h a r t w h i c h c o n t a i n s t h e f r e -

q u e n c y .

(2) Read the upper lef t hand comer codes (A,

B,) first (2, 6).

(3 ) Go to the CHAN co lum n and loca te the

n u m b e r t h a t c o r r e s p o n d s t o f r e q u e n c y ( 5 ) .

( 4 ) R e a d t h e n u m b e r i n t h e D c o l u m n t h a t c o r -

responds to the frequency (3) .

(5 ) The syn thes ize r swi tch code i s 2653 .

Table 2-2. Frequency Char t(Switch Code)

2-4 Cha nge 1

q See Notes at foot of table.

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Table 2-2. Frequency ChartContinued

(Switch Code)

Cha n ge 1 2 -

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( S w i t c h C o d e )

2-6 Cha nge 1

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Table 2-2. Frequency C h a r t - C o n t i n u e d

(Switch Code)

Cha nge 1 2 -7

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(Switch Code)

2-8 Change 1

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(Switch Code)

Sect ion I I I . PR EVENTIVE MAINTENANCE CH ECKS AND SER VICES (P MCS)

2-8. Genera l

To insure that the radio set is always ready for opera-

tion, it must be inspected systematically so that defects

may be discovered and corrected before they result in

serious damage or failure. Organizational preventive

maintenance procedures are designed to help maintain

equipment in serviceable condition. They include what

items should be checked and how to check them. These

checks and services are to be made at specific (W) week-

ly, (M) monthly, (Q) quarterly, (S) semiannually, and

(A) annual intervals.

2-9. P MCS Ta ble

Table 2-3 des cr ibes the o rgan iza t iona l p reven t ive

maintenance checks and services for the radio set.

Routine checks like CLEANING, DUSTING, WASH-

ING, CHECKING FOR FRAYED CABLES, STOW-

ING ITEMS NOT IN USE, COVERING UNUSED

R E C E P T A C L E S A N D C H E C K I N G F O R L O O S E

NUTS AND BOLTS are not listed as PMCS checks.

They are th ings that you should do anytime you see th ey

must be done. If you find a routine check like one of

those listed, in your PMCS, it was listed because other

operators reported problems with this item.

WHEN YOU ARE DOING ANY PMCS OR

ROUTINE CH ECKS, KEEP IN MIND THE

WARNINGS AND CAUTIONS.

W ARNING

Adequate ventilation should be provided while

us ing TRICHLOROTRIFLUOROETHANE.

Prolonged breathing of vapor should be avoid-

ed. The solvent should not be used near heat or

open flames; the products of decomposition

are toxic and irritating. Since TRICHLORO-

TRIFLUOROETHANE dissolves natural oils,

prolonged contact with skin should be avoid-

ed. When necessary, use gloves which the sol-

vent cannot penetrate. If the solvent is taken

internally, consult a physician immediately.

Compressed air is dangerous and can cause

serious bodily harm if protective means or

methods are not observed to prevent a chip or

par ticle (of wha tever size) from being blown into

the eyes or unbroken skin of the operator or

other personnel. Compressed air shall not be

used for cleaning purposes except where reduc-

ed to less than 30 p.s.i.g. and then only with

effective chip guarding and personel protective

equipment. Do no use compressed air to dry

parts when trichlorotrifluoroethan has been

used.

C hange 1 2 -9

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Table 2-3. Organizational Preventive Maintenance Checks and Services

Section IV. TROUBLESHOOTING

2 - 1 0 . V i s u a l I n s p e c t i o n m a l f u n c t i o n i s s t i l l n o t l o c a t e d , h i g h e r l e v e l t r o u b l e -

2-11. Troubleshoot ing Procedures 2-12. T e st E q u i p m e n t R e q u i r e d

If visual inspection does not locate the trouble, consult Test Set TS-3354/PRC-68 (test set) is u s e d to t roub le -troubleshooting table 2-4. Use the applicable section of shoot the radio se t . Refer to figures 2-3, 2-4, and 2-5

t h i s t a b l e a s d e t e r m i n e d b y t h e m a l f u n c t i o n , I f t h e f o r t e s t e q u i p m e n t h o o k u p s .

Figure 2-3. Battery t es t .

2-10

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Figure 2-4. Transmitter power output test.

Figure 2-5. Sensitivity test.

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2-12

para 2-18

para 2-17

paragraph 2-7

para 2-7

para 2-5figure 2-5

para 2-7fig. 2-1

para 2-6para 2-7

fig 2-1para 2-7

figure 2-4para 2-5

fig. 2-2

fig. 2-3

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

Table 2-4. Troublesh ooting Pr ocedur es

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para 2-6ara 2-7

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

Table 2-4. Troubleshooting ProceduresContinued

Sect ion V. MAINTENANCE PR OCEDURE S

2-13. Gen er a l

Maintenance procedures at the organizational level for Remove rust and corrosion from metal surfaces bythe radio set are limited to cleaning, painting, andreplacement of broken external parts (knobs and anten-na) and battery replacement.

2-14. Cleaning

Inspect the exteriors of the radio set. The exterior sur-

faces should be clean, free from dust, dirt, grease and

fungus.a. Remove dust and loose dirt with a clean soft

cloth, item 2, App. C.

WARNING

Adequate ventilation should be provided while

using TRICHLOROTRIFLUOROETHANE.

Prolonged breathing of vapor should be avoid-

ed. The solvent should not be used n ear heat or

open flame; the products of decomposition are

toxic and irritating. Since TRICHLOROTRI-

FLUOROETHANE dissolves natural oils,

prolonged contact with skin should be avoid-

ed. When necessary, use gloves which the sol-

vent cannot penetrate. If the solvent is taken

internally, consult a physician immediately.

b. Remove grease, fungus, and ground-in dirt from

the radio set; use a cloth dampened (not wet) with tri-

clorotrifluoroethane, item 6, App. C.

c. Remove dust or dirt from antenna and audio con-

nectors with a brush, i tem 1, App. C.

2-15. T ou c h u p P a i n t i n g I n s t r u c t io n s

lightly sanding them with fine sandpaper, item 4, App.

C. Brush two thin coats of paint on the bare metal toprotect from further corrosion, items 3 and 7, App. C.Refer to SB 11-573 and 43-0118.

2-16. Knob Replacement

The th ree knobs on t he ra dio set ar e held onto th eir

shafts by setscrews. If knob replacement becomesnecessary:

a. Loosen setscrew with an appropriate wrench.

b. Remove defective knob.

c. Install new knob.

d. Tighten setscrews (if knob has two setscrews,

tighten the setscrew that engages the flatted shaft first).

2-17. An ten n a R eplacem ent

Remove damaged antenna from connector by turning

an ten na coun ter clockwise. Check conn ector on ra dio

set for corrosion or thread damage. Remove and signs

of corrosion. If connector is damaged, refer radio set to

higher level of maintenance. Insert new antenna into

conn ector a nd h an d tighten clockwise.

2-18. Ba t t e r y Rep lacemen t

Remove battery case by unfastening latches on side of

radio set case and sliding case off. (Handle case careful-

ly as damaged case will not seal properly). Detach old

battery from bat tery connector a nd a ttach n ew battery

to connector. Apply a thin coat of silicone grease, item

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5, App. C, to the top edge of the battery case (to In order to prevent water seepage make sure

facilitate O ring sealing). Reinstall battery case and battery case and rubber gasket are n ot dam ag-

fasten latches. ed. Make sure battery case and module cover

CAUTION are properly aligned before fastening latches.

Sec t ion VI . PREPARATION FOR STORAGE OR SHIPMENT

2-19. Packaging, Marking and Shipping can be readied for mission performance within 24

R e q u i r e m e n t s hours. Before placing an item in administrative storage,the next scheduled preventive maintenance checks and

Refer to figure 2-6 for packaging diagram.services s hould be perform ed, all k nown deficiencies

2-20. T y p e o f S t o r a g e corrected, an d a ll curr ent modification work orders ap-

Short t erm (adm inistra tive storage) = 1 to 45 days. Ad-plied. The a dministra tive storage site should provide re-

quired protection from the elements and allow accessministrative storage covers storage of equipment which

for visual inspection and exercising when applicable.

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Figure 2-6. Radio set packaging diagram.

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CHAP TER 3

DIRECT SUPPORT MAINTENANCE INSTRUCTIONS

Se c t ion I . REPAIR PARTS, SPECIAL TOOLS, TMDE, AND SUPPORT EQUIPMENT

3-1 . Common Tools an d Eq uip men t tools and equipment to be used at direct support

For authorized common tools and equipment refer to maintenance level.

th e Modified table of Organization a nd Equipmen t3-3. Main ten an ce Kit

(MTOE) applicable to your unit.Figure 3-1 shows Main ten an ce Kit MK-( ) /PRC-68 us

3-2. Spe cial Tools , TMDE, an d Su pp or t ed with the test equipment to troubleshoot the radio setE q u i p m e n t Table 3-1 provides a brief description of the contents o

Refer to the maintenance allocation chart (App. B), for the kit .

Figu re 3-1. Main ten an ce Kit MK-( )/PRC-68.

3-

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Figure 3-2. Receiver troubleshooting test setup.

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

Table 3-1. Maint enan ce Kit Description MK-( ) /PRC-68

3-2

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3-4 . Repa i r P ar t s

R ep a ir pa r t s a r e li st e d in t h e r ep a ir p a r t s organizational and direct support maintenance for this

and special tools list (TM 11-5820882-23P) covering equipment.

Sec t ion I I . TROUBLESHOOTING

3-5. Troubleshoot ing Procedures isolation test, as outlined in table 3-3. This table will

Troubleshooting instructions for the radio set contained isolate a problem down to a particular module whichin this section are separated into two procedures. The will then be replaced. If module replacement does not

first procedure consists of a minimu m per forma nce test, repair unit, higher level maintenance is required.

as outlined in table 3-2. This ta ble will be used to deter-3-6 . Tes t Equ ipme nt Se t up s

mine the general nature of the malfunction and, after a

repair has been made, to ensure the radio set is working The test setup requirements for performing the

properly for all functions. Minimum perform an ce of troubleshooting procedures are shown in figures 3-2

the radio set may also be performed using the test set and 3-3. The maintenance kit required for the test

(table 2-4). The second procedur e consist s of a fau lt setups is described in table 3-1.

Figure 3-3. Transmitter troubleshooting test setup.

3-3
http://050400.pdf/http://050400.pdf/

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figure 3-2

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

Table 3-2. Radio Set Minimum Performance Test

Table 3-3, steps 1 through 11

Table 3-3, steps 1 through 11.




3-4

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figure 3-3

figure 3-3

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

Table 3-2. Radio Set Minimum Performance TestContinued



Table 3-3,steps 12 through 21.




Table 3-3, s teps 2 through 21.

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Table 3-2. Radio Set Minimum Performance TestContinued

3-7. Fa u l t Isota t ion Test

Table 3-3 is a fault isotation test for the radio set. By us-

ing these tests and the associated test equipment, theradio set may be fault isolated to a defective module. Ifthe problem cannot be located to a defective module orother DS level maintenance, then higher level mainte-nance is required. In all cases, after a defective module

has been replaced or a repair made to the radio set, the

minimum performance t est (table 32), or minimum per-

formance check using the test set (table 2-4), must be

performed to ensure the radio set is fully operational.

3-8. Fa ul t Isolat ion Test Equ ipmen t Set -

u p s

Figure 3-4 and 3-6 show the equipment setups necessary

t o perform the fault isolation tests.

3-9. Test P oint Locat ions

Figures 3-7 and 3-8 show the t est point locat ions u sed in

fault isolation testing. Test point connections are made

by a special rf cable assembly 565461-801 (part of Main-

ten an ce Kit MK-( ) /PRC-68). In a ll cases where t his

cable is used, the center conductor is connected to the

test point called for, and the shield is connected to the

nearest ground point on the printed circuit board. The

BNC connector end mates with the applicable test

equipment un it, when called for.

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Figure 3-4. Receiver fault isolation test setu p.

Figure 3-5. Receiver fault isolation test set up (alternate procedure.3-7

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3-8

Figure 3-6. Transmitter fault isolation test setup.

Figure 3-7. Module socket test point locat ion, front.

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Figur e 3-8. Module socket test point (E nu mbers) locat ion, front.

Figure 3-9. Module socket test point location, rear.

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Table 3-3. Fault Isolation Test

3-10

table 3-3figures 3-5 and 3-8

para 2-5fig. 2-1

figure 3-4 para 3-10

fig. 3-7

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para 2-5fig. 2-1

para 3-10

fig. 3-7

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

Table 3-3. Fault Isolation TestContinued

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3-12

fig. 3-8

fig. 3-8

figure 3-8

fig. 3-8

para 2-5fig. 2-1

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figure 3-6para 3-10

fig. 3-7

table 3-4

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


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para 2-5

para 3-10

table 3-4table 3-4

table 3-4

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


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Table 3-3. Faul t Iso la t ion TestCont inued

Table 3-4. S ynth esizer Test Voltages and Frequencies

S e ct i on I II . M AI NT E NAN CE P R O C ED UR E S

3 - 1 0 . R e m o v a l a n d R e p l a c e m e n t o f (2 ) Inset c o r n e r of s c r e w d r i v e r t i p i n t o f o r w a r dModules

.

The following procedures are used for removal and in -

sertion of the modules in the Radio Set. The Special in-

structions in paragraph 3-11 should also be observed toprevent secondary damage and failures, Refer to

paragraph 2-5 for disassembly instructions.

a. Converter Module.

(1) Hold radio in left hand with control panel

toward palm, thumb over converter module and fingers

over radio on opposite side.

(panel end) pry slot on converter module. Extend left

thumb over converter module to stop module travel and

pry up this end of the module (see fig. 3-10). Movescrewdriver to other slot on the converter module and

pry up. Remove module from radio with fingers.

(3) To insert converter module, align module pins

with frame sockets and gently press module into place,

b. I-f/ A-f Module.(1) Hold radio in left hand with bottom side (bat-

tery connector s ide) in pa lm a nd left t hu mb over i- f/a-f

module and fingers on back side of radio.

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(2) Inser t screwdriver int o side slot n ear est bot-

tom side (battery side) of radio and pr y up m odule using

the left t hum b to restrict t ravel. Move screwdriver to the

middle slot on if/af module and pry up. Remove

module with fingers by using slight side to side rocking

motion of modu le.

(3) To inset i-f/a-f module, align module pins

with frame sockets and gently push module into place.

c. Filter/ I-F Module.

(1) First remove the i-f/a-f module.(2) Hold radio in left hand with bottom side (bat-

tery connector side) in palm and left thumb over anten-

na coupler module (rear part of thumb should be over

the filter/i-f module). Carefully pry up the i-f/a-f end

of the filter/i-f module with the screwdriver. Then pry

up the opposite end of filter/if module and remove

module with your fingers.

(3) To insert filter/i-f module, align module pins

with frame sockets and gently push module into place.

d. Transmitter Module.

(1) First remove the i-f/a-f and convertermodules.

(2) Hold radio in left hand with transmitter

module facing up. Remove module with r ight th um b

an d forefinger on en ds. Use a top (panel) -to-bott om

rocking motion to loosen the module in the frame

sockets.

(3) To insert the module, align module pins withframe sockets a nd gently push module into place.

e. Antenna Coupler Module.

(1) Firs t r emove i-f/a-f and convert er m odules.

(2) Hold the radio in left hand with antennacoupler module facing up. Remove module with right

thu mb an d forefinger on t he ends. Use a top (panel) -to-

bottom rocking motion to loosen the module in the

sockets.

(3) To insert antenna coupler module, align

module pins with frame sockets and gently push

module into place.

f. Vco, Modulator MixerJ

and SynthesizerModules.

(1) Hold radio in left h an d with m odules facingup. Insert screwdriver into slots in fram e and gently pr y

up the removable circuit board with the three modules

at tached.

modules from frame sockets and pull it away from the

radio panel to expose the CHAN switch cable connec-

tor. Pull removable circuit board far enough away from

panel (approximately 3/4 inch) to grip the cable connec-

tor with the thumb and forefinger of the left hand; then

unplug the connector by gently pulling away with the

removable circuit board assembly.

(3) The three modules may be removed now by

pulling them up from th e rem ovable circuit board withthe fingers.

(4) To insert the vco, modulator/mixer, or syn-

thesizer module, align the module pins with the socketson the removable circuit board. Gently push the moduleinto place. When all three modules are installed on the

removable circuit board, connect th e synt hesizer cable

assem bly. Align th e rem ovable circuit board p ins withthe fram e sockets and gently push the removable circuitboard into place. Make sure the modules and removable

circuit board are properly seated.

3-11. Spec ia l In s t r uc t ions

a. Always inspect a module for bent or broken pins

before inserting it into the frame sockets. To straighten

bent pins, use needle-nose or long-nose pliers with

smooth jaws. Position the jaws so that the whole pin isstraightened simultaneously (see fig. 3-11 ).

b. When inspecting for bent pins, the pins shouldappear to be reasonably vertical in relation to the

module bottom surface. Bent pins usually result when

excessive prying force is applied to only one end or side

of a module. The th um b of the opposite ha nd sh ould

Figure 3-10. Module removal.

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always be used to stop the module tra vel and oppose the

prying force.

c. Always inspect frame sockets for damage before

inserting a module. .4 normal socket should have four

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

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

with a sha rp point ed tool (pin, needle, scribe, etc.). If

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

socket, the socket should be replaced if possible.

However, the socket will still make good contack with

the module pin after the damaged leaf is removed from

the socket. The radio set

can be ma de at a h igher

3-12. Lub r ica t ion

3-14. General

is still operational until repairs

level.

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

All sealing sur faces (module cover an d bat ter y case)

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

00-177-5094) applied to hepl preserve watertightness

and keep the r ubber seals pl iable. If a han dset is used

with th e rad io set, a sm all amoun t of silicone greas e

should a lso be applied to th e O ring in th e conn ector

to facilitate insertion.

3-13. P lac in g in Ser vice

After th e radio set has been repaired, the un it must be

checked out completely with the minimum performance

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

radio set should be set t o some predeter mined frequency

and properly aligned before being returned to service.

Sec t ion IV . P RINCIP LES OF OPE RATION

3-16. Receive Opera t ion

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

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

ciples of operation of the radio set is limited to descrip-tion of the modules and their interfacing with each

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

tions.

3 -1 5. C ir c u i t F u n c t i o n i n g

Circuit fu nctionin g of th e ra dio set (fig. FO-1) can be

broken down into modules that comprise separate func-

tions (receive and transmit) and modules that are used

for both functions (synthesizer and voltage controlled

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

150 Hz squelch tone signal are also discussed.

The receiver is packaged in three modules. These

modules are:

a. Converter Module (1A6). The convertermodule consists of two bandswitched, varactor-tuned rfamplifiers an d th e receiver 1st mixer which converts t he

operatin g frequency to th e first i-f of 12 MH z. The low-

band rf amplifier tun es the frequency range from 30 t o

54 MHz while the high-band tu nes 54 to 80 MHz. The

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

on synthesizer module, and preset CHAN switch) deter-

mine the operating frequency of the rf amplifier and the

local oscillator injection frequency to the first mixer.

This injection signal is provided by the voltage controll-

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

Figure 3-11. Pin Straightening procedure.

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MHz), it is 12.000 MHz above th e rf input frequencies;

for the high-band (54 to 80 MHz), it is 12.000 MHz

below the rf input frequencies.

b. Filter/ I-f Modu le (1A3). The filter/i-f modulecont ains a 12 MH z crysta l filter, 12 MHz if amplifier,

18.5 MHz crystal oscillator, and a 6.5 mixer/amplifier

(2nd mixer), The output of the second mixer (6.5 MHz)

is the difference of the 12.0 MHz input and 18.5 MHzinput from the crystal oscillator.

c. I-f/ A-f Module (1A2). The i-f/a-f modulecont ains a 6.5 MH z i-f amp lifier/discriminat or, squelch

circuits, a udio amp lifier, an d a low-pass filter. Oth er

functions contained within the module are a tone tuner

circuit and battery saver switch. The input signal to the

if/a-f module is th e 6.5 MHz frequ ency modulat ed sig-

na l from t he filter/i-f module. The signal is det ected

and routed th rough the low-pass filter to th e audio

amplifier. When a handset of other audio accessory is

conn ected t o the AUDIO connector of the r adio set, the

speaker mute circuit electronically switches off the

audio signal to the speaker and routes it to the handset.

The squelch threshold is adjusted by a potentiometer

located in the module. The squelch circuit is normally

on when the radio set is turned on. However, squelch

can be disabled by turning the function switch to the

SQUELCH DIS position.

3-17. Tra nsm i t Oper a t ion

The transmit ter is packaged in three modules. These

modules are:

a. Modu lator/ Mixer Module (1A8). The modulator/mixer module conta ins a speech amplifier a nd filter, 150

Hz (squelch tone) buffer, 12 MHz deviation oscillator rf

mixer, and two bandswitched, varactor-tuned rf pream-plifiers. The sp eech am plifier increases th e level of the

microphone signal sufficiently for clipping action. The

output of the amplifier passes through a low-pass filter

before it is superimposed upon a 12 MHz deviation os-

cillator. The 150 Hz squelch tone from the synthesizer

is also routed to the deviation oscillator after passing

through a buffer and the speech filter network. The fre-

quency modulated output of the oscillator is combinedin a varactor-tuned mixer stage with the frequency syn-

thesizer output signals to create th e desired rf outpu t

frequency. The rf output is amplified by two bandswit-

ched, varactor-tuned rf preamplifiers. For frequencies

in the low-band (30 to 54 MHz), the output frequency is12.000 MHz below the synthesizer frequency; and for

the high-band (54 to 80 MHz), the output frequency is

12.000 MHz above the synthesizer frequency.

b. Transmitter Module (1A4).. The transmittermodule contains an rf preamplifier, driver, final power

amplifier and low-pass band filters. The output from

the modulator is applied to the preamplifier for ampli-

fication to approximately 1 vrms. The output of the

driver stage is approximately 100 mw. This stage has a

tuned circuit which tunes the output of the transmiter.

Tuning is accomplished by using the built-in tone tuner

and adjusting C1 on t he module. The tone tun er cir-

cuitry is located in the i-f/a-f module and converts the

variation in the collector currents of the transmitter

stages to a tone frequency when the tone tu ner but ton(located on the side of the frame assembly) is depressed.

The fina l out put (approximately 1.5 watt s) is routed

through one of four band-selected low-pass harmonic

filters to the antenna coupler (1A5).

c.Antenna Coupler Module (1A5). The antennacoupler module contains the rf transmit/receive diode

switching circuits and the antenna matching circuit. Pin

diodes in the module provide transmit/receive switching

functions to the antenna matching network. These di-

odes also isolate the transmit/receive circuitry to pre-

vent the transmitted signal from entering the receiver in-

put. The antenna matching network provides an imped-

ance match between the antenna and transmitter circuits

(between 50 ohms an d 100 ohms). The ma tching ran ge is

determined by the position (1 through 4) of the rotary

switch located on the module (set the same as the A

switch on the synthesizer). Optimum tuning is ac-

complished by using the field strength meter on the test

set and adjusting L1 on the coupler module (tune for

maximum indication).

3 - 8 . F r e q u e n c y S y n t h e s i z e r ( 1 A 7 a n d

1A8)

The radio set frequency synthesizer consists of the vco

module (1A7) and the synthesizer module ( 1A9). Thefuncton of the frequency synthesizer is to generate the

required mixer injection frequency and tuning voltage

for the converter and modulator modules when a given

operating frequency is selected. The frequency syn-

thesizer also determines which band (low or high) is ac-

tive depending upon selection of the operating frequen-

cy.

a. The frequency range of the synthesizer is from

42.000 MHz to 67.950 MHz which corresponds with a

generated tuning voltage range from 2.0 vdc to 11.0 vdc

respectively. The frequency synthesizer is programmable

in 50 kHz steps with the frequency select (A, B. and D)

switches on the synthesizer module and the CHAN (C)switch on the panel of the radio set.

b. The frequency range of the synthesizer isgenerated twice to provide low-band radio set operation

from 30,000 MHz to 53.950 MHz (positions 1 and 2 of

the A switch), and high-band radio set operation from

54.000 MHz to 79.950 MHz (positions 3 an d 4 of the A

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switch). The two bands are required to cover the 30 to

80 MHz ran ge of the radio set with vara ctor t uning.

c. The basic purpose of the frequency synthesizer is

to generate the discrete channel frequencies with an ac-

curacy of 25 ppm. This is accomplished by phase lock-

ing a voltage controlled oscillator (VC O) to a standard

crystal controlled reference frequency. The reference

frequency of the synthesizer is 12.5 kHz crystal oscilla-tor by a factor of 800, or dividing the output of the 12.5

MHz crystal oscillator by a factor of 1000. The division

factor is determined by the position of the A switch. The

reference divider ( K) consists of an injection locked

oscillator which divides by 4 (10 MHz) or 5 (12.5 MHz),

an d a fixed divide r at io (200) digital coun ter. Th e 12.5kHz outpu t of the reference divider is r out ed to th e

phase comparator (detector).

d. To achieve pha se locking, th e outpu t of the vco(42 to 68 MHz) must be frequency translated and divid-

ed douwn to 12.5 kHz for phase comparison with the 12.

5 kHz reference frequency. Because the vco must pro-

vide 520 discrete frequencies spaced 50 kHz apart, avariable frequency divider is r equired t o divide each one

of these discrete frequencies down to 12.5 kHz. The

variable divider ( N) ratio is determined (program med)

by setting the synthesizer switches to the code cor-

responding with the desired operating frequency. Once

the N ratio is programmed, the vco can phase lock on-

ly at that frequency which translates down to 12.5 kHz.

e. Because the maximum counting speed of the

cmos program ma ble divider is 5 MHz, th e 42 to 68 MHz

range of the vco must be frequency translated down to

less th an 5 MHz. This is a ccomplished by first dividing

the output frequency of the vco with t he 4 pr escaler in

the vco module. The prescaler output is routed to the

mixer in the synthesizer module. The output of the mix-

er is the difference frequency of the prescaler input and

th e 10 MH z or 12.5 MHz r eference oscillat or.

f. Because th e capt ure ra nge of th e phase detector is

narrow (approximately 500 kHz at the vco frequency),

the vco must be swept over its frequency range to a fre-quency within this capture range. When this occurs, the

phase detector output control voltage (superimposed on

the sweep voltage) pulls the vco into phase-lock with the

reference frequency of the synthesizer.

g. The sweep voltage is a sawtooth staircase

waveform consist ing of add itive coarse t un e volta ge

steps over a voltage range from 1.5 vdc to 13.0 vdc. The

ramp sweeps the vco over its frequency range by stepp-

ing up from 1.5 vdc to the coars e tu ne volta ge required

to put the vco frequency within the capture range of the

phase detector. Once phase lock is achieved, the ramp

stops and holds at that coarse tune voltage. The tune

voltage output from t he synth esizer is th e phase detectorcontrol voltage superimposed on the ramp coarse tune

voltage. The level of the phase-locked tuning voltage is

proportional to the selected operating frequency, and

varies from 2.0 vdc to 11.0 vdc.

h . The loop filter attenuates the 12.5 kHz reference

frequency to minimize frequency modulation of the

Vco.

i. The synthesizer also generates the battery savertiming waveform and the 150 Hz squelch tone wave-

form, Both of these signals are derived from the crystal

reference frequency with digital frequency dividers.

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APPENDIX A

REFERENCES

A-1. S c o p eThis appendix lists the forms and publications tha t a re referenced in th is man ual or th at conta in information a p-

plicable to the operation and maintenance of Radio Set AN/PRC-68.

A - 2 . F o r m s

DA Form 2028

DA Form 2028-2

NAVMC 10772 (USMC)

SF 364

SF 368

TM 4700-15/1 (USMC)

A-3. Publicat ions

DA Pam 310-4SB 11-573

SB 38-100

SC 5180-91 -CL-R07SC 5180-91 -CL-R13

TB 43-0118

TM 11-5820-882-10

TM 11-5820-882-23P(To Be Published)

TM 11-5965-257-l5

TM 11-5965-280-15

TM 11-6130-247-15

TM 11-6625-255-14

TM 11-6625-400-12

TM 11-6625-444-15

TM 11-6625-524-14

TM 11-6625-586-12

TM 11-6625-683-15

Recommended Changes to Publications and Blank Forms

Recommended Changes to Equipment Technical Publications

Suggested Recommendations and Improvements for Marine Corps

Technical Manuals

Report of Discrepancy (ROD)

Quality Deficiency Report

Forms and Records Procedures

Index of Technical PublicationsPainting and Preservation Supplies Available for Field Use for Elec-

tronics Command Equipment

Preservation, Packaging, Packing and Marking Materials, Supplies

and Equipment Used by the Army

Tool Kit, Electronic Equipment TK-105/G (NSN 5180-00-610-8177)

Tool Kit, Electronic Equipment TK-101/G (NSN 5180-00-064-5178)

Field Instructions for Painting and Preserving Electronics Command

Equipment Including Camouflage Pattern Painting of Electrical

Equipment Shelters

Operat ors Manu al: Radio Set AN/PRC-68 (NSN 5820-01-079-9260)

Organizational and Direct Support Maintenance Repair Parts and

Special Tools Lists for Radio Set AN/PRC-68

Operat ors, Organizational, Direct Su pport, General Sup port an dDepot Ma intenan ce Manu al (Including Repair Pa rts and Special

Tools Lists): Ha nds et H -138/U (FSN 5965-892-0972)

Operators, Organizational, Direct Support, General Support, and

Depot Ma intenance Manu al (Including Repair P art s an d Special

Tools Lists): Ha ndset H-189/GR (NSN 5965-00-069-8886)


Depot Maintenance Manual for Power Supply PP-3940/G

Operators, Organizational, Direct Support, and General Support

Maintenance Manual: Spectrum Analyzer TS-723A/U,

TS-723B/U, TS-723C/U, and TS-723D/U (NSN 6625-00-668-9418)

Operat ors and Or ganizat iona l Maintena nce Manu al for Meter, Modu-

lation ME-57/U

Operators, Organizational, Direct Support, General Support, andDepot Maintenance Manual: Digital Voltmeter AN/GSM-64

Operat ors, Organizat iona l and F ield Maint ena nce Manu al: Volt-

meter Electronic AM/URM-145

Operator and Organizational Maintenance Manual: Generator ,

Signal AN/URM-103


Depot Maintenance Manual: Signal Generator AN/URM-127

(NSN 662540783-5965)

Ch an ge 1 A-
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APPENDIX B

MAINTENANCE ALLOCATION

S e c t i o n I INTRODUCTION

B - l . G e n e r a l

This appendix provides a summary of the maintenanceoperations for AN/PRC68. It authorizes categories of

maintenance for specific maintenance functions on

repaira ble items an d components a nd th e tools and

equipment required to perform each function. This ap-

pendix may be used as an aid in planning maintenance

operations.

B - 2 . M a i n t e n a n c e F u n c t i o n

M a i n t e n a n c e fu n c t i on s wil l be l imi ted to an dde f i ned a s fol lows:

a. Inspect. To determine the serviceability of anitem by comparing its physical, mechanical, and/or

electrical characteristics with established stan dardsthrough examination.

b. Test. To verify serviceability and to detect inci-pient failure by measuring the mechanical or electrical

characteristics of an item and comparing those charac-

teristics with prescribed standards.

c. Service. Operations required periodically to

keep an item in proper operating condition, i.e., to

clean (deconta mina te), to preserve, to drain, t o paint, or

to replenish fuel, lubricants, hydraulic fluids, or com-

pressed air su pplies,

d. Adjust. To maintain, within prescribed limits,by bringing into proper or exact position, or by setting

the operating characteristics to the specified parameters.

e. Align. To adjust specified var iable elements ofan item to bring about optimum or desired perfor-

mance.

f. Calibrate. To determine and cause correctionsto be made or t o be adjusted on instru ment s or test

measuring and diagnostic equipments used in precision

measurement. Consists of comparisons of two instru-

ment s, one of which is a certified stan dard of known ac-

curacy, to detect and adjust any discrepancy in the ac-

curacy of the instrument being compared.

g.Install. The a ct of emplacing, seat ing, or fixing

into position an item, part, module (component orassembly) in a manner to allow the proper functioning

of the equipment or system.

h. Replace. The act of substituting a serviceablelike type part, subassembly, or module (component orassembly) for an unserviceable counterpart.

Repair. The application of maintenance services(inspect, test, service, adjust, align, calibrate, replace)

or other maintenance actions (welding, grinding, rivet-

ing, straightening, facing, remachining, or resurfacing)

to restore serviceability to an item by correcting

specific damage, fault, malfunction, or failure in a

part, subassembly, module (component or assembly),

end item, or system.

j Overhaul. That ma inten an ce effort (service/act-ion) necessary to restore an item to a completely ser-

viceable/operational condition as prescribed by mainte-

nance standards (i.e., DMWR) in appropriate technical

publications. Overhaul is normally the highest degree of

maintenance performed by the Army. Overhaul does not

normally return an item to like new condition.

k. Rebuild. Consists of those services/actionsnecessary for the restoration of unserviceable equip-

ment to a like new condition in accordance with

original manufacturing standards. Rebuild is the highestdegree of materiel maintenance applied to Army equip-

ment. The rebuild operation includes the act of return-

ing to zero those age measurements (hours, miles, etc.)

considered in classifying Army equipments/com-

ponents.

B-3 . Co lumn En t r ie s

a. Column 1, Group Number. Column 1 listsgroup numbers, the purpose of which is to identify com-

ponents, assemblies, subassemblies and modules with

the next higher assembly,

b. Colum n 2, Com ponent/ Assem bly. Column 2

contains the noun names of components, asemblies,subassemblies, and modules for which maintenance is

authorized.

c. Column 3, Maintenance Functions. Column 3lists the functions to be performed on the item listed in

column 2. When items a re l isted without maintena nce

functions, it is solely for purpose of having the group

numbers in the MAC and RPSTL coincide.

d. Colum n 4, Main tenance Category. column 4specifies, by the listing of a work time figure in the

appropriate subcolumn (s), the lowest level of mainte-

nance authorized to perform the function lis ted in

column 3. This figure represents the active time requiredto perform tha t m aintenan ce function a t t he indicatedcategory of maintenance. If the number or complexity

of the tasks within the listed maintenance function vary

at different maintenance categories, appropriate work

time figures will be shown for each category. The

number of task-hours specified by the work time

figure represents the average time required to restore an

item (assembly, subassembly, component, module, end

item or system) to a serviceable condition under typical

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field operat ing conditions. This time includes prepar a-

tion time, troubleshooting time, and quality assurance/

quality control time in addition to the time required to

perform the specific tasks identified for the maintenance

functions aut horized in the maint enan ce a llocation

chart. Subcolumns of column 4 are as follows:

COperator/Crew

OOrangizational

FDirect Support

HGeneral Support

DDepot

e. Column 5, Tools and Equipment. Column 5specifies by code, those common tool sets (not in-

dividual tools) and special tools, test , and supportequipment required to perform the designated function.

f. Column 6, Remarks. Column 6 contains analpha betic code which leads to the rema rk in section IV,

Remarks, which is pertinent to the item opposite the

particular code.

B -4 . To o l a n d Te s t Eq u ip m e n t R e q u i r e -

men ts (Sec t I I I )

a . Tools or Equipment Reference Code. Th e

numbers in this column coincide with the numbers used

in th e tools an d equipmen t column of th e MAC. The

numbers indicate the aplicable tool or test equipment

for the maintenance functions.

b. Maintenance Category. The codes in t his COl-umn indicate the maintenance category allocated the

tool or test equipment.

c.Nomenclature, This column lists the noun nameand nomenclature of the tools and test equipment re-

quired to perform the maintenance functions.

d. National/ NAT O Stock Nu m ber. This columnlists the National/NATO stock number of the specific

tool or test equipment.

e. Tool Number. This column lists the manufac-tu rers pa rt nu mber of the tool followed by th e Federa l

Supply Code for manufacturers (5-digit) in parentheses.

B-5. Rem ar ks (See IV)

a . Reference Code, This code refers to the ap-

propriate item in section II, column 6.b . Re m ark s . This column provides the required

explanatory information necessary to clarify items ap-

pearing in section II.

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SECTION II MAINTENANCE ALLOCATIN CHART

Change 1 B-3

(1)GROUP

NUMBER

00

01

0101

T M 1 1 - 5 8 2 0 - 8 8 2 - 2 3 / T M 0 6 8 2 7 A - 2 3 / 2

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S E C T I O N I V . R E M A R K S

1981-703-029/1260 Change 1 B-5/ (B-6 b lank)

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APPENDIX CEXPANDABLE SUPPLIES AND MATERIALS LIST

Sec t ion I INTRODUCTION

1. S c o p e

This appendix lists expendable supplies and materialsyou will need to operate and maintain Radio Set AN/

PRC-68. These items are authorized to you by CTA 50-

970, Expandable Items (Except Medical, Class V, Re-

pair Parts, and Heraldic Items).

2 . Ex p la n a t i o n o f C o lu m n s

a. Column 1Item Number. This number isassigned to the entry in the listing and is referenced in

the narrative instructions to identify the material (e.g.,

Use cleanin g compound, item 5, App. C).

b. Column 2Level. This column identifies thelowest level of maintena nce that requires th e listed item.

(enter as applicable)

COpoerator/Crew

OOrganizational Maintenance

FDirect Support MaintenanceHGeneral Support Maintenance

c. Column 3National Stock Number. This is the

Nat ional st ock nu mber a ssigned to the item ; use it to re-

quest or requisition the item.

d. Column 4Description. Indicates the Federalitem name and, if required, a description to identify the

item. The last line for ea ch item indicates the part

number followed by the Federal Supply Code for Manu-

facturer (FSCM) in parentheses, if applicable.

e. Column 5 Unit of Measure (UM), Indicatesthe measure used in performing the actual maintenancefunction. This measure is expressed by a two-character

alphabetical abbreviation (e. g., ea, in, pr). If the unit ofmeasure differs from the unit of issue, requisition thelowest unit of issue that will staisfy your requirements.

( Ne x t p r i n t e d p a g e i s C -2 )

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I N D E X

S U B J E C T Para

Alignm ent pr ocedur es . . . . . . . .. . . .. . . . . . . ... . . . 2-7

Ancillary equipment . . . . . . . . . . . . . . . . . . . . . . . 1-6

Ant enn a r epla cemen t . . . . . . . . . .. . . . . . . . . . . . . . 2-7

Battery

Freguency chart . . . . . .. . . . . . . . . . . .. ... . . 2-7cRepla cemen t . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 2-18

Clea nin g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .2-14

Common t ools and eq uipm ent . . . . . . . . . . . . . . . . . . . . . . .. . . . .. .. . 2-1

Compone nt location . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .. . . .. . 1-7

Da ta , ta bula ted . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 1-8

Destruction to prevent enemy use . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .1-3

Disa ssem bly inst ru ctions . . . . . . . . . . . . . . . . . . . . . .. . . .2-5

Equipment capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 1-6

Equ ipment im provement r ecommen dat ions .. .. . . . . . . . .. . . . . 3-7

Fau lt isolation . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . .. . . . . . .. . . .. 3-7

Knob r epla cemen t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16

Lubrication

Gasket seal -----------------------------------------------------------6-6

Maintenance

Direct support . . . . . . . . . . . . . . . ... . . . . ... . . . . . . . . . . . . . . . 3-1

Kit-------------------------------------------------------- --3-3

Organzational------------------------------------------------------2-13

Pr even tive . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . ..2-8

Modules

Pin str aigh ten ing . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .3-11

Removal a nd r epla cemen t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

P ai n ti n g-----------------------------------------------------------------2-15

Reassem bly instr uctions .. . . . . .. . . . . . . . . . . .. . . . . . . . . . 2-6

Receiver operation

Orgn tia tion al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

Direct sup port . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .3-16

Repair parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-3

St orge --------------------------------------------------------------2-19

SVM opera tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-12

Switch code . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7d

Synt hesize r oper at ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

Test point locations . . . . . . . . . . . . . . . . . . . . . .. . . . . . .3-9

Test set . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2-12

Tools

Comm on . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. .. 3-1

Specia l . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. 3-2

Transmitter operation

Orgn izat ional . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. . 1-11

Direct Support . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .. . . . . . . . .. 3-17

Troubleshooting procedures

Organizational --------------------------------------------------- --2-11

Direct s upp ort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 3-5

q U.S. GOVERNMENT PRINTING OFFICE : 1995 0 - 388-421 (01391) Index-1

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Figure FO-1. Radio Set Block Diagram (Sheet 1 of 2).

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Figure FO-1. Radio Set Block Diagram (Sheet 2 of 2).

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By Order of the Secretary of the Army and the Navy:

Official:

J. C. PENNINGTON Major General, United States Army

The Adjutant General

E. C. MEYERGeneral, United States Army

Chief of Staff

H. A. HATCH Major General, US Marine Corps

Deputy Chief of Staff for Installations and Logistics

Distribution:

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Documents