GE MASTR II Maintenance Manual

. - -

•

~

_._MOBILE

RADIO

®

MASTRO

MAINTENANCE

25·50

MHz,

100-WATT

TRANSMITTER

MANUAL

(MOBILE)

-'""'t:::l

tr.i!l>

c

'1:1

ro

1-1

(/l

<D

a.

ro

(/l

t""b

b:JJ:%:1

H::0

~

0'\

Ot::;l

0~

'-'

w

t-'

Vl
Vl

I»

-=

t-,3

::t>

-·

~

=

....

H

t"" CD

J:%:1

=

I»

~

0

=

n

CD

-=

I»

=

I»

=

-

r-

111::1:1

-

~

CD

ca

CD

'"

SPECIFICATIONS *

Frequency
Power

Crystal

Frequency

Spurious

Modulation

Modulation

Audio

Distortion

Deviation

Duty

Maximum

(2

Range

Output

Multiplication

Stability
5C-ICOM
5C-ICOM
2C-ICOMS

Frequency

Cycle

to 8 channels)

with
or

and

Harmonic

Sensitivity

Symmetry

Frequency

EC-ICOM

EC-ICOM

Emission

Characteristics

Spread:

Factor

25-50
100

to
MHz)

3

±0.0005%
±0.0002%

±0.0002%
At
Adjustable

taneous
80
Within

emphasis
Post

Less
Less

0.5

EIA

Full

MHz

Watts

50

MHz,

least

to

120

limiter
than

than

kHz

20%

Specifications

(Adjustable

and

(-40°C
(0°C
(-40°C

85

dB

from 0 to

modulation

Millivolts

+1

dB

to

from

filter

2%

(1000

3%

(300

maximum

Intermittent

from

to

to

to

below

-3

300

from

75

to

+70°C)

+55°C)

+70°C)

full

±5

kHz

limiting.

dB

of a 6-dB/octave

to

3000

per

FCC

Hz)

to

3000

1 dB

50

to

100

Watts

rated

swing

Hz

per

and

Hz)

Degradation

100

power

with

EIA

EIA.

Watts

at

25

output

instan-

pre-

standards.

to

at

30

30

25-30
30-36
36-42
42-50

*These

specifications

are

MHz
MHz
MHz
MHz

intended

primarily

for

the

use

of

the

serviceman.

Refer

.160
.200
.240
.280

to

MHz
MHz
MHz
MHz

the

appropriate

Specification

.320
.400
.470
.540

Sheet

MHz
MHz
MHz
MHz

for

the

complete

specifications.

LBI4898

TABLE

OF

CONTENfS

SPECIFICATIONS

................................................................

.

Cover

DESCRIPTION

.................................................................•..

1

CIRCUIT ANALYSIS

..............................................................

.

1

Exciter

..................................................................

.

1

ICOMs

...............................................................

.

1

Audio

IC

............................................................

.

3

Frequency

Divider

...................................................

.

4

Phase

Modulators,

Amplifiers

and

Multipliers

........................

.

4

Power

Amplifier

..................................•........................

5

RF

Amplifiers

.......................................................

.

5

Power

Control

Circuit

...............................................

.

6

Carrier

Control

Timer

....................................................

.

6

MAINTENANCE

...................................................................

.

6

Disassembly

...............................................•...............

6

PA

Transistor

Replacement

................................................

.

7

Alignment

Procedure

......................................................

.

9

Test

Procedures

..........................................................

.

10

Power

Output

........................................................

.

10

Tone

Deviation

......................................................

.

10

Voice

Deviation

.....................................................

.

10

Troubleshooting

..........................................................

.

11

OUTLINE

DIAGRAM

...............................................................

.

12

SCHEMATIC

DIAGRAMS

(with

voltage

readings)

Exciter

..................................................................

.

14

Power

Amplifier

..........................................................

.

15

PARTS

LIST

AND

PRODUCTION

CHANGES

Exciter

..................................................................

.

13

Power

Amplifier

..........................................................

.

16

-

18

ILLUSTRATIONS

Figure

l -

Block

Diagram

......................................................

.

Figure

2-

Typical

Crystal

Characteristics

....................................

.

Figure

3 -

Equivalent

!COM

Circuit

............................................

.

Figure

4 -

Simplified

Audio

IC

................................................

.

Figure

5 -

Disassembly

Procedure

(Top

View)

...................................

.

Figure

6-

Disassembly

Procedure

(Bottom

View)

................................

.

Figure

7 -

PA

Transistor

Lead

Identification

......................•............

Figure

8 -

PA

Transistor

Lead

Forming

.........................................

.

Figure

9-

Frequency

Characteristics

Vs.

Temperature

..........................

.

Figure

10-

Power

Output

Setting

Chart

.........................................

.

1

2

3

4

7

7

8
8

9
9

WARNING

----------------------------------------,

ii

Although

the

highest

DC

voltage

in

MASTR

II

Mobile

Equipment

is

supplied

by

the

vehicle

battery,

high

currents

may

be

drawn

under

short

circuit

conditions.

These

currents

can

possibly

heat

metal

objects

such

as

tools,

rings,

watchbands,

etc.,

enough

to

cause

burns.

Be

careful

when

working

near

energized

circuits!

High-level

RF

energy

in

the

transmitter

Power

Amplifier

assembly

can

cause

RF

burns

upon

contact.

KEEP

AWAY

FROM

THESE CIRCUITS

WHEN

THE

TRANSMITTER

IS

ENERGIZED!

,.

•

•

•

•

•

•

DESCRIPTION

MASTR

II

transmitters

are

crystal-con-

trolled

phase

modulated

and

designed

for

one-

through

eight-frequency

operation

in

the

25

to

50

megahertz

band,

The

solid

state

transmitter

utilizes

both

integrated

circuits

(ICs)

and

discrete

components,

and

consists

of

the

following

assemblies:

•

Exciter

Board;

with

audio,

modulator,

amplifier

and

multiplier

stages,

•

Power

Amplifier

Assembly;

with

ampli-

fier,

driver,

PA,

power

control,

fil-

ter

and

antenna

switch.

CIRCUIT

ANALYSIS

EXCITER

The

exciter

uses

nine

transistors

and

two

integrated

circuits

to

drive

the

PA

assembly,

The

exciter

can

be

equipped

with

up

to

eight

Integrated

Circuit

Oscillator

Modules

(ICOMs). The

ICOM

crystal

freq-

uency

ranges

from

approximately

8,33

to

16,67

megahertz,

and

the

crystal

frequency

is

multiplied

three

times

(divided

by

four

---

---

I

EXCITER

MOD

I

~-fOJUST

I

I
I

I

Ehf"'~

QIQJ

I

I

I

I

-)

I

POWER

I

F2

~-~

POWER

ADJUST

I

I

YI02

J

0211

·Q217

'--•

I

I

---.

I

F8

!l

..J

AMPL·!

DRIVER

I

I

YIOB

I

0204

0205

!...--

I XTAL FREQ•

L_

LBI-4898

and

multiplied

by

12

for a multiplication

·factor

of

three)

•

Audio,

supply

voltages

and

control

functions

are

connected

from

the

system

board

to

the

exciter

board

through

P902.

Centralized

metering

jack

Jl03

is

pro-

vided

for

use

with

GE

Test

Set

Model 4EX3All

or

Test

Kit

4EX8Kl2. The

test

set

meters

the

modulator,

multiplier

and

amplifier

stages.

ICOMS

Three

different

types

of

ICOMs

are

available

for

use

in

the

exciter.

Each

of

the

ICOMs

contains

a

crystal-controlled

Colpitts

oscillator,

and

two

of

the

ICOMs

contain

compensator

ICs,

The

different

ICOMs

are:

•

•

•

AMP

5C-ICOM -

contains

an

oscillator

and

a 5

part-per-million

(±0.0005%)

com-

pensator

IC,

Provides

compensation

for

EC-ICOMs.

EC-ICOM -contains

an

oscillator

only,

Requires

external

compensation

from

a

5C-ICOM.
2C-ICOM -

contains

an

oscillator

and

a

2

PPM

(±0,0002%)

compensator

IC,

Will

not

provide

compensation

for

an

EC-ICOM

•

2506A

I

I

I

I

I

I

J

Figure

1 -

Transmitter

Block

Diagram

1

LBI4898

CIRCUIT

ANALYSIS

The

lCOMs

are

enclosed

in

an

RF

shielded

can

with

the

type

!COM

(5C-ICOM,

EC-ICOM

or

2C-ICOM)

printed

on

the

top

of

the

can.

Access

to

the

oscillator

trimmer

is

obtained

through a hole

on

the

top

of

the

can.

Frequency

selectaon

is

accomplished

by

switching

the

ICOM

keying

lead

(terminal

6)

to

A- by means

of

the

frequency

selector

switch

on

the

control

unit.

In

single-fre-

quency

radios,

a

jumper

from

H9

to

HlO

in

the

control

unit

connects

terminal 6 of

the

!COM

to

A-.

The

oscillator

is

turned

on

by

applying a keyed

+10

Volts

to

the

exter-

nal

oscillator

load

resistor.

RF

bypassing

is

provided

for

all

unused

keying

loads

in

eight

frequency

radios.

In

two

frequency

radios

the

six

unused

keying

leads

are

shorted

to

ground.

r---------------

CAUTION

--------------~

All

ICOMs

are

individually

compen-

sated

at

the

factory

and

cannot

be

repaired

in

the

field.

Any

attempt

to

repair

or

change

an

ICOM

fre-

quency

will

void

the

warranty.

In

standard

5

PPM

radios

using

EC-ICOMs,

at

least

one

5C-ICOM

must

be

used.

The

5C-ICOM

is

normally

used

in

the

receiver

Fl

position,

but

can

be

used

in

any

transmit

or

receive

position.

One

5C-ICOM

can

provide

compensation

for

up

to

15

EC-ICOMs

in

the

transmit

and

receiver.

Should

the

5C-ICOM

compensator

fail

in

the

open

mode,

the

EC-ICOMs

will

still

maintain 2 PPM

frequency

stability

from

0°C

to

55°C

(+32°F

to

131°F)

due

to

the

regulated

compensation

voltage

(5

Volts)

from

the

10-Volt

regulator

IC.

If

desired,

up

to

16

5C-ICOMs

may

be

used

in

the

radio.

The 2C-ICOMs

are

self-compensated

at

2

PPM

and

will

not

provide

compensation

for

EC-ICOMs.

Oscillator

Circuit

The

quartz

crystals

used

in

ICOMs

ex-

hibit

the

traditional

"S"

curve

character-

istics

of

output

frequency

versus

operating

temperature.

At

both

the

coldest

and

hottest

tem-

peratures,

the

frequency

increases

with

increasing

temperature.

In

the

middle

tem-

perature

range

(approximately

0°C

to

+55°C),

frequency

decreases

with

increasing

temper-

ature.

Since

the

rate

of

change

is

nearly

linear

over

the

mid-temperature

range,

the

output

frequency

change

can

be

compensated

by

choosing a parallel

compensation

capa-

citor

with a temperature

coefficient

appro-

ximately

equal

and

opposite

that

of

the

crystal.

2

Fig~re

2 shows

the

typical

performance

of

an

uncompensated

crystal

as

well

as

the

typical

performance

of a crystal

which

has

been

matched

with a properly

chosen

compen-

sation

capacitor.

::::!:

Cl..
Cl..

+5

-15" +10" 26.5"

+42"

65"

DEGREES

CENTIGRADE

Figure

2 -

Typical

Crystal

Characteristics

At

temperatures

above

and

below

the

mid-range,

additional

compensation

must

be

introduced.

An

externally

generated

com-

pensation

voltage

is

applied

to a varactor

(voltage-variable

capacitor)

which

is

in

parallel

with

the

crystal.

A

constant

bias

of 5 Volts

(provided

from

Regulator

IC

U901

in

parallel

with

the

compensator)

establishes

the

varactor

capa-

city

at a constant

value

over

the

entire

mid-

temperature

range.

With

no

additional

com-

pensation,

all

of

the

oscillators

will

pro-

vide 2 PPM

frequency

stability

from

0°C

to

55°C

(+32°F

to

131°F).

Compensator

Circuits

Both

the

5C-ICOMs

and

2C-ICOMs

are

tem-

perature

compensated

at

both

ends

of

the

temperature

range

to

provide

instant

freq-

uency

compensation.

An

equivalent

!COM

cir-

cuit

is

shown

in

Figure

3.

The

cold

end

compensation

circuit

does

not

operate

at

temperatures

above

0°C.

When

the

temperature

drops

below

0°C,

the

circuit

is

activated.

As

the

temperature

decreases

the

equivalent

resistance

decreases

and

the'

compensation

voltage

increases.

The

increase

in

compensation

voltage

decreases

the

capacity

of

the

varactor

in

the

oscillator,

increasing

the

output

fre-

quency

of

the

ICOM.

•

•

•

•

•

•

CIRCUIT

ANALYSIS

LBI4898

NOT PRESENT

IN

EC-ICOM

REG

COMPENSATION

IOV

15V

.----\---------{l\----------{2~-------------------,

COMPENSATION

I

IC

Ul

COLD

END

COMP

~~

I

I HOT

END

COMP

I
I

I

-l

I

I

24K

I

I

COMPENSATOR~

OUTPUT

24K

I

I

I

I

OSCILLATOR

CIRCUIT

+IOV

FREQ

SELECT

L

__

L

__

Figure

3 -

Equivalent

ICOM

Circuit

The

hot

end

compensation

circuit

does

not

operate

at

temperatures

below

+55°C.

When

the

temperature

rises

above

+55°C,

the

circuit

is

activated.

As

the

temperature

increases,

the

equivalent

resistance

de-

creases

and

the

compensation

voltage

de-

creases.

The

decrease

in

compensation

vol-

tage

increases

the

capacity

of

the

varactor,

decreasing

the

output

frequency

of

the

ICOM.

SERVICE

NOTE:

Proper

ICOM

operation

is

de-

pendent

on

the

closely-controlled

input

vol-

tages

from

the

10-Volt

regulator.

Should

all

of

the

ICOMs

shift

off

frequency,

check

the

10-Volt

regulator

module.

AUDIO

IC

The

transmitter

audio

circuitry

is

con-

tained

in

audio

IC

Ul02.

A

simplified

drawing

of

the

audio

IC

is

shown

in

Figure

4.

Audio

from

the

microphone

at

pin

12

is

coupled

through

pre-emphasis

capacitor

Cl

to

the

base

of

Ql

in

the

operational

amplifier-

limiter

circuit.

Collector

voltage

for

the

transistorized

microphone

preamplifier

is

supplied

from

pin

11

through

microphone

col-

lector

load

resistor

Rl8

to

pin

12.

The

operational

amplifier-limiter

cir-

cuit

consists

of

Ql,

Q2

and

Q3.

Q3

provides

limiting

at

high

signal

levels.

The

gain

of

the

operational

amplifier

circuit

is

fix-

ed

by

negative

feedback

through

Rl9,

R20

and

the

resistance

in

the

network

(pin

9).

The

output

of

Q3

is

coupled

through

a

de-emphasis

network

(RlO

and

C3)

to

an

active

post-limiter

filter

consisting

of

C4,

C5, C6,

Rll,

Rl2,

Rl3,

Rl5,

Rl7,

and

Q4.

Following

the

post-limiter

filter

is

class A amplifier

Q5.

The

output

of

Q5

is

coupled

through

MOD

ADJUST

potentiometer

Rl27

to

the

phase

modulators.

SERVICE

NOTE:

If

the

DC

voltages

to

the

Audio

IC

are

correct

and

no

audio

output

can

be

obtained,

replace

Ul02.

For

radios

equipped

with

Channel

Guard,

tone

from

the

encoder

is

applied

to

the

phase

modulators

through

CHANNEL

GUARD

MOD

ADJUST

potentiometer

Rl28,

and

resistors

RllO,

Rl21

and

Rl24.

Instructions

for

set-

ting

Rl28

are

contained

in

the

modulation

adjustment

section

of

the

Transmitter

Align-

ment

Procedure

•

3

LBI4898

CIRCUIT

ANALYSIS

OPERATIONAL

AMP-

LIMITER

4

MIC

A+

Rl8

REG

+IOV

POST-LIMITER

FILTER

.RIO

Rll

..

Q4

C4

C5

C3

11~--------~~~-4----~~~----._--~

AMPLIFIER

MIC

LO

Rl7

R20

Rlt

401(

40K

Rl5

10

9

OECOUPLER

NETWORK

A-

RC-2445A

Figure

4 -

Simplified

Audio

IC

FREQUENCY

DIVIDER

IC

The

output

at

pin 3 of

the

selected

ICOM

is

coupled

through

buffer

amplifier

QlOl

to

frequency

divider

UlOl,

which

di-

vides

the

oscillator

frequency

by

4.

The

divider

consists

of

two

J-K

flip-flops

con-

nected

as a binary

counter.

When

the·transmitter

is

not

keyed

(no

ICOMs

on),

QlOl

is

saturated

(turned

on)

with

its

collector

voltage

near

zero.

Key-

ing

the

transmitter

starts

one

of

the

ICOMs,

and

its

output

cuts

QlOl

on

and

off

once

each

cycle.

As

QlOl

turns

off

during

each

cycle,

the

drop

in

collector

voltage

causes

the

left

flip-flop

to

change

state.

Assume

the

flip-flop

was

in

the

"O"

state

(the

output

at

''Q"

near

A-).

The

first

cycle

of

the

oscillator

output

causes

it

to

switch

to

the

"1"

stage

(output

at

''Q"

approxi-

mately 5 Volts}.

The

second

cycle

will

cause

the

flip-flop

to

switch

back

to

the

"O"

state.

Therefore,

it

requires

two

os-

cillator

cycles

to

switch

the

left

flip-

flop

through

one

complete

cycle

from

"0"

4

to

"1"

and

back

to

"0"•

When

the

left

flip-flop

switches

from

"1"

to

"O",

it

causes

the

right

flip-flop

to

change

state.

It

requires

two

cycles

of

the

left

flip-flop

to

switch

the

right

flip-flop

from

"O"

to

"1"

and

back

to

"0".

Therefore,

four

cycles

of

the

oscillator

output

are

required

for

each

cycle

of

out-

put

from

pin 9 of

UlOl.

If

UlOl was

operating

into a pure

re-

sistive

load,

its

output

would

be a square

wave. However,

the

modulator

circuit

pre-

sents a tuned

load

to

the

IC,

so

that

har-

monics

are

filtered

out

and

the

waveform

at

the

junction

of

Cl02

and

Cl03

(modulator

input)

is

essentially

a

sine

wave

at

one-

fourth

the

oscillator

frequency.

The

out-

put

of

the

frequency

divider

is

coupled

through

DC

blocking

capacitor

Cl02

to

the

first

modulator

stage.

PHASE

MODULATORS,

AMPLIFIER & MULTIPLIERS

The

first

phase

modulator

is

varactor

(voltage-variable

capacitor)

CVlOl

in

series

with

tunable

coil

LlOl.

This

network

appears

as a series-resonant

circuit

to

the

RF

output

of

the

oscillator.

An

audio

signal

applied

to

the

modulator

circuit

tbrougb

blocking

capacitor

Cll5

varies

the

bias

of

CVlOl,

resulting

in a phase

modulated

output.

A

voltage

divider

network

(Rl08

and

Rl09}

pro-

vides

the

proper

bias

for

varactors

CVlOl,

CV102

and

CV103.

The

output

of

the

first

modulator

is

coupled

through

blocking

capacitor

ClOG

to

the

base

of

Class A amplifier

Ql02.

The

first

modulator

stage

is

metered

through

a

metering

network

consisting

of

Rll5,

Rl50,

Cl07

and

CRlOl.

Diodes

CR102

and

CR103

remove

any

amplitude

modulation

in

the

modu-

lator

output.

•

•

•