Ge Mastr ii User manual

MASTRO

e

MAINTENANCE

MANUAL

25·50

MHz,

50-WATT

TRANSMITTER

SPECIFICATIONS

*

Frequency

Range

Power

Output

Crystal

Multiplication

Factor

Frequency

Stability

5C-ICOM

with

EC-ICOM

5C-ICOM

or

EC-ICOM

2C-ICOMS

Spurious

and

Harmonic

Emission

Modulation

Sensitivity

Audio

Frequency

Characteristics

Distortion

Deviation

Symmetry

Maximum

Frequency

Spread:

(2

to

8

channels)

25-30

MHz

30-36

MHZ

36-42

MHz

42-50

MHz

Duty

Cycle

RF

Output

Impedance

25-50

MHz

50

Watts

(Adjustable

from

15

to

50

Watts)

3

±0.0005%

(-40°C

to

+70°C)

±0.0002%

(0°C

to

+55°C)

±0.0002%

(-40°C

to

+70°C)

At

least

85

dB

below

full

rated

power

output

Adjustable

from

0

to

±5

kHz

swing

with

instantaneous

modulation

limiting.

80

to

120

Millivolts

Within

+1

dB

to

-3

dB

of

a

6-dB/octave

pre-

emphasis

from

300

to

3000Hz

per

EIA

standards.

Post

limiter

filter

per

FCC

and

EIA.

Less

than

2%

(1000

Hz)

Less

than

3%

(300

to

3000

Hz)

0.5

kHz maximum

Full

Specifications

.160

MHZ

.200

MHz

.240

MHz

.280

MHz

EIA 20%

Intermittent

50

Ohms

1

dB

Degradation

.320

MHZ

.400

MHz

.270

MHZ

.540

MHz

specifications

are

intended

primarily for

the

use

of

the

serviceman. Refer

to

th"

appropriate

Specification

Sheet

for

the

complete

opecificotions.

.:

D»

-·

=

....

CD

=

D»

=n

CD

.:

D»

=

M

-

LBI-4896

TABLE

OF

CONTENTS

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

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

13

Power

Amplifier

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

15

PARTS

LIST

AND

PRODUCTION

CHANGES

Exciter

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

.

Power

Amplifier

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

Figure

ILLUSTRATIONS

1 -

Block

Diagram

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

2-

Typical

Crystal

Characteristics

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

3 -

Equivalent

ICOM

Circuit

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

4 -

Simplified

Audio

IC

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

.

5 -

Disassembly

Procedure

(Top

View)

.•.......•...................•....•..

6-

Disassembly

Procedure

(Bottom

View)

....................•.............

7-

PA

Transistor

Lead

Identification

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

.

8 -

PA

Transistor

Lead

Forming

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

9-

Frequency

Characteristics

Vs.

Temperature

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

.

10

-

Power

Output

Setting

Chart

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

.

14

16

1

2

3

4

7

8

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-

controlled,

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

fre-

quency

ranges

from

approximately

8,33

to

16.67

megahertz,

and

the

crystal

frequency

is

multiplied

three

times

(divided

by

four

r---

MOO

EXCITER

LBI-4896

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

4EXSK12.

The

test

set

meters

the

modulator,

multiplier

and

ampli-

fier

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:

•

5C-ICOM -

contains

an

oscillator

and

a

5

part-per-million

(±0.0005%)

compen-

sator

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

.

I ADJUST

I

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

' • I I

I

1

I

'

Fl

h-

YIOI

AUDIO

Ul02

BUFFER

0101

~

I I I

,-

-~

I

I :

y~~2

j--1

',

~-

:

I

I I

-,

: I

I

F8

I I

I I YIOS

.-~

I

t..--.1

IXTAL

FRED•

OPERA~NG

-FRE_O_,_,_I_

PHASE

MOO

CVIOI

t

FREO

DIVIDER

H41

UIOI

POWER

ADJUST

204·0210

I

i

~

MOO

AMPL-1

0102

BUFFER

0105

I

•

AMPL-1

Q~OI

LIMITER MOO

AMPL-2

1-------t-

CRI02

1------t"

0(03

CRI03

MULT-I MULT-2

TRIPLER DOUBLER

0106 0107

POWER

AMP

PA

f----oo

DRIVER

r--

FINAL

0202 0203

1-----

f---.--

PHASE

MOO

CVI02

C\1103

MULT-3

DOUBLER

0108

LOW

PASS

FILTER

Figure

1 -

Transmitter

Block

Diagram

t--

r--

MOO

AMPL-3

0104

AMPL-1

0109

t.Nr

SWITCH

K201

LIMITER

,,_.

CRI05

CRI06

I

--1

I

RC-2417A

_j

1

L'll-4896

CIRCUIT

ANALYSIS

The

ICOMs

are

enclosed

in

a

dust-

proof,

RF

shielded

can

with

the

type

ICOM

(5C-ICOM, EC-ICOM,

or

2C-ICOM)

printed

on

the

top

of

the

can.

Access

to

the

oscil~

lator

trimmer

is

obtained

by

prying

up

the

plastic

tab

on

the

top

of

the

can.

The

tabs

can

also

be

used

to

pull

the

ICOMs

out

of

the

radio.

Frequency

selection

is

accomplished

by

switching

the

ICOM

keying

lead

(termi-

nal

6)

to

A-

by

means

of

the

frequency

se'Iector

switch

on

the

control

unit.

In

single-frequency

radios,

a

jumper

from

H9

to

HlO

in

the

control

unit

connects

terminal

6

of

the

ICOM

to

A-.

The

oscil-

lator

is

turned

on

by

applying

a

keyed

+10

Volts

to

the

external

oscillator

load

resistor.

RF

bypassing

is

provided

for

all

unused

keying

leads

on

eight

frequency

radios.

On

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

BC-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

SC-ICOM

can

pro-

vide

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

exhibit

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

temperature

range

(approximately

0°C

to

+55°C),

frequency

decreases

with

increasing

temperature.

Since

the

rate

of

change

is

nearly

lin-

ear

over

the

mid-temperature

range,

the

out-

put

frequency

change

can

be

compensated

by

choosing

a

parallel

compensation

capacitor

with

a

temperature

coefficient

approximately

2

equal

and

opposite

that

of

the

crystal.

Figure

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.

RC-2443

-~L-L---~~----~~--,_--~----;-------~~

-15. +IO•

26.5•

+~

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

t.he

varactor

ca-

pacity

at

a

constant

value

over

the

entire

mid-temperature

range.

With

no

additional

compensation,

all

of

the

oscillators

will

provide

2

PPM

frequency

stability

from

0°C

to

55°C

(32°F

to

131°F).

Compensator

Circuits

Both

the

SC-ICOMs

and

2C-ICOMs

are

temperature

compensated

at

both

ends

of

the

temperature

range

to

provide

instant

fre-

quency

compensation.

An

equivalent

ICOM

circuit

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

de-

creases

and

the

compensation

voltage

in-

creases.

The

increase

in

compensation

voltage

decreases

the

capacity

of

the

varactor

in

the

oscillator,

increasing

the

output

frequency

of

the

ICOM.

•

CIRCUIT

ANALYSIS

LBI-4896

NOT PRESENT

IN

EC-ICOM

REG

IOV

COMPENSATION

5V

~------------~2~----------------------------------~

--

-l

COMPENSATION

IC Ul I

COLD

END

COMP

'}

r

24K

I

-------,

COMPENSATOR~

HOT

END

COMP

\

I

L

__

24K

fREQ

SELECT

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

voltage

increases

the

capacity

of

the

var-

actor,

decreasing

the

output

frequency

of

the

ICOM.

SERVICE

NOTE:

Proper

!COM

operation

is

dependent

on

the

closely-controlled

input

voltages

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

contained

in

audio

IC

Ul02.

A

simplified

drawing

of

the

audio

IC

is

shown

in

Figure

4.

Audio

from

the

microphone

at

12

is

coupled

through

pre-emphasis

capacitor

Cl

to

the

base

of

Ql

in

the

operational

ampli-

fier-limiter

circuit.

Collector

voltage

for

the

transistorized

microphone

pre-

amplifier

is

supplied

from

11

through

microphone

collector

load

resistor

Rl8

to

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

fixed

by

negative

feedback

through

Rl9,

R20

and

Rl26.

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

coupked

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

Alignment

Procedure

•

3

LBI-4896

CIRCUIT ANALYSIS

OPERATIONAL AMP- LIMITER

--~~----~------.---------------------~--------------~4

Rl8

MIC

LO

R20

401(

10

9

Rl9

401(

DECOUPLER

NETWORK

TO

Cl50

POST-

LIMITER

FILTER

04

AMPLIFIER

Rl7

Rl5

REG

+IOV

A-

RC-2445A

Figure

4 -

Simplified

Audio

IC

FREQUENCY

DIVIDER

IC

The

output

at

3

of

the

selected

lOOM

is

coupled

through

buffer

amplifier

QlOl

to

frequency

divider

UlOl,

which

divides

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"

at

approxi-

mately

5

Volts).

The

second

cycle

will

cause

the

flip-flop

to

switch

back

to

the

"0"

state.

Therefore,

it

requires

two

oscillator

cycles

to

switch

the

left

flip-

flop

through

one

complete

cycle

from

"O"

to

"1"

and

back

to

"0".

When

the

left

flip-flop

switches

from

"1"

to

"0",

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

out-

put

are

required

for

each

cycle

of

output

from

9

of

UlOl.

4

If

UlOl

was

operating

into

a

pure

resistive

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,

AMPLIFIERS

AND

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

out-

put

of

the

oscillator.

An

audio

signal

applied

to

the

modulator

circuit

through

blocking

capacitor

Cll5

varies

the

bias

of

CVlOl,

resulting

in

a

phase

modulated

out-

put.

A

voltage

divider

network

(Rl08

and

Rl09)

provides

the

proper

bias

for

varactors

CVlOl,

CV102

and

CV103.

The

output

of

the

first

modulator

is

coupled

through

blocking

capacitor

Cl06

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

mod-

ulator

output.

•

CIRCUIT

ANALYSIS

LBI-4896

Following

Ql02

is

another

Class

A amp-

lifier,

Ql03.

The

output

of

Ql03

is

applied

to

the

second

modulator

stage.

The

second

modulator

consists

of

two

cascaded

modula-

tor

circuits

consisting

of

CV102,

Ll02,

Ll03

and

CV103.

Following

the

second

modu-

lator

is

a

Class

A

amplifier

Ql04.

The

output

of

the

second

modulator

stage

is

metered

through

Rl33,

Rl45,

Cll7

and

CR104,

and

is

applied

to

the

base

of

buffer

Ql05.

Diodes

CR105

and

CR106

remove

any

amplitude

modulation

in

the

second

modulator

output.

Buffer

Ql05

is

saturated

when no

RF

signal

is

present.

Applying

an

RF

signal

to

Ql05

provides

a

sawtooth

waveform

at

its

collector

to

drive

the

class

C

tripler,

Cl06.

The

tripler

stage

is

metered

through

Rl46.

The

output

of

Ql06

is

coupled

through

tuned

circuits

TlOl,

Tl02

and

Tl03

to

the

base

of

doubler

Ql07.

TlOl,

Tl02

and

Tl03

are

tuned

to

one-fourth

of

the

operating

frequency.

The

doubler

stage

is

metered

through

Rl47.

The

output

of

Ql07

is

coupled

through

tuned

circuits

Tl04

and

Tl05

to

the

base

of

second

doubler

Ql08.

Tl04

and

Tl05

are

tuned

to

one-half

the

operating

frequency.

Ql08

is

metered

through

Rl48.

The

output

of

QlOS

is

coupled

through

three

tuned

circuits

(Tl06,

Tl07

and

Tl08)

to

the

base

of

amplifier

Ql09.

The

cir-

cuits

are

tuned

to

the

transmitter

operating

frequency

•

Ql09

is

a

class

C

amplifier

with

a

col-

lector

feed

network

consisting

of

Cl39, Cl41,

Ll04,

Ll08

and

Rl43.

The

stage

is

metered

through

Rl49.

The

amplifier

collector

cir-

cuit

consists

of

Cl42,

Cl43,

Cl46

and

Ll05,

and

matches

the

amplifier

output

to

the

in-

put

of

the

power

amplifier

assembly.

POWER

AMPLIFIER

The

PA

assembly

uses

three

RF

power

transistors

and

seven

transistors

in

the

Power

Control

circuitry

to

provide

a

power

output

of

50

Watts.

The

broadband

PA

has

no

adjustments

other

than

Power

Control

potentiometer

R216.

Supply

voltage

for

the

PA

is

connected

through

power

leads

from

the

system

board

to

feedthrough

capacitors

C297

and

C298 on

the

bottom

of

the

PA

assembly.

C297,

C298

and

C299,

L296

and

L297

prevent

RF

from

getting

on

the

Power

leads.

Diode

CR295

will

cause

the

main

fuse

in

the

fuse

assem-

bly

to

blow

if

the

polarity

of

the

power

leads

is

reversed.

Centralized

metering

jack

J205

is

pro-

vided

for

use

with

GE

Test

Set

Model

4EX3All

or

Test

Kit

4EX8Kl2.

The

Test

Set

meters

the

Ampl-1

drive

(exciter

output),

Ampl-1

power

control,

Driver

and

PA

current.

RF

AMPLIFIERS

The

exciter

output

is

coupled

through

an

RF

cable

to

PA

input

jack

J203.

The

RF

is

coupled

through

DC

blocking

capacitor

C202

to

the

base

of

Class

C

amplifier

Q201

through

a

matching

network.

The

network

matches

the

50-ohm

input

to

the

base

of

Q201,

and

consists

of

C205,

C206,

C235,

L201,

L202

and

L203.

Part

of

the

RF

input

is

rectified

by

CR201

and

used

to

activate

the

Power

Control

circuit.

Another

portion

of

the

rectified

RF

is

applied

to

voltage

dividers

R223

and

R224

for

metering

the

Ampl-1

drive

at

J205.

Collector

voltage

to

Q201

(Ampl-1)

is

controlled

by

the

Power

Control

circuit,

and

is

applied

through

a

collector

stabil-

izing

network

consisting

of

L224

and

R225

and

collector

feed

network

L204

and

C207.

The

collector

voltage

of

Q201

is

metered

through

R235

at

J205.

The

output

of

Q201

is

applied

to

the

base

of

Class

C

driver

Q202

through

a

low-

pass

filter

matching

network

(C209,

C210,

L205

and

L206).

Resistors

R202,

R203

and

R204

lower

the

gain

of

Q202.

Collector

voltage

to

Q202

is

coupled

through

a

col-

lector

stabilizing

network

consisting

of

L225

and

R233

and

collector

feed

network

L208

and

C213.

Collector

current

for

Q202

is

metered

across

tapped

manganin

resistor

R230

at

J205

(Driver

Current).

The

reading

is

taken

on

the

one-Volt

scale

with

the

High

Sensi-

tivity

button

pressed,

and

read

as

10

am-

peres

full

scale.

Following

Q202

is

an

interstage

coup-

ling

network

(C214

through

C221,

L209

through

L211,

R206

and

R207.)

The

output

is

applied

to

the

base

of

the

class

C

PA

stage,

Q203.

Supply

voltage

is

coupled

through

a

collector

stabilizing

network

consisting

of

L226

and

R234

and

collector

feed

network

C222

and

L212.

Collector

current

for

Q203

is

metered

across

tapped

manganin

resistor

R231

at

J205.

The

reading

is

taken

on

the

one-Volt

scale

with

the

High

Sensitivity

button

pressed,

and

read

as

10

amperes

full

scale.

The

PA

output

is

coupled

through

an

output

matching

network

(C224,

C225,

C226,

L213

and

L214,)

to

an

M-derived,

constant

K

low-pass

filter.

C230

through

C233

pro-

vides

ground

isolation

for

±

ground

opera-

tion.

The

filter

output

is

applied

to

the

antenna

through

antenna

switch

K20l.

5

LBI-4896

'POWER

AMPLIFIER

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

WARNING

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

The

stud

mounted

RF

Power

Tran-

sistors

used

in

the

transmitter

contain

Beryllium

Oxide,

a

TOXIC

substance.

If

the

ceramic,

or

other

encapsulation

is

opened,

crushed,

broken

or

abraded,

the

dust

may

be

hazardous

if

inhaled.

Use

care

in

replacing

transistors

of

this

type.

POWER

CONTROL

CIRCUIT

When

the

transmitter

is

keyed,

recti-

fied

RF

from

CR201

is

applied

to

the

base

of

switch

Q204,

turning

it

on.

Turning

on

Q204

turns

on

voltage

regulator

Q206

which

supplies

a

constant

voltage

to

Power

Adjust

potentiometer

R216.

Q208, Q209

and

Q210

operate

as

an

amp-

lifier

chain

to

supply

voltage

to

the

col-

lector

of

Q201

(Ampl-1).

The

setting

of

R216

determines

the

voltage

applied

to

the

base

of

Q208, The

higher

the

voltage

at

the

base

of

Q208,

the

harder

the

amplifiers

conduct,

supplying

more

collector

voltage

to

Q201. The

lower

the

voltage

at

the

base

of

Q208,

the

less

collector

voltage

is

supplied

to

Q201.

Reducing

the

supply

volt-

age

to

Q201

reduces

the

drive

to

Q202

and

Q203,

thereby

reducing

the

power

output

of

the

PA. The

power

output

can

be

adjusted

by R216

from

approximately

15

to

50

Watts.

Temperature

protection

is

provided

by

Q205,

Q207

and

thermistor

RT201

which

is

mounted

in

the

PA

heatsink.

Under

normal

operating

conditions,

the

circuit

is

in-

active

(Q205

is

on

and

Q207

is

off).

When

the

heatsink

temperature

reaches

approxi-

mately

100°C,

the

resistance

of

RT201

de-

creases.

This·increases

the

base

voltage

applied

to

Q205,

turning

it

off.

Turning

off

Q205

allows

Q207

to

turn

on,

decreas-

ing

the

voltage

at

Power

Adjust

potentiom-

eter

R216.

This

reduces

the

base

voltage

to

Q208

which

causes

Q209

and

Q210

to.

con-

duct

less,

reducing

the

collector

voltage

to

Q201

(Ampl-1).

This

reduces

the

trans-

mitter

output

power,

keeping

the

heatsink

at

a maximum

of

approximately

100°C.

When

the

heatsink

temperature

decreases

below

100°C,

the

temperature

control

circuit

turns

off,

allowing

the

normal

transmitter

power

output.

CARRIER

CONTROL

TIMER

The

Carrier

Control

Timer

option

shuts

off

the

transmitter

on

each

transmission

after

a

one-minute

timing

cycle,

and

alerts

the

operator

that

the

transmitter

is

off

by

means

of

an

alarm

tone

in

the

speaker.

The

transmitter

can

be

turned

on

again

by

re-

leasing

and

rekeying

the

push-to-talk

switch

on

the

microphone.

6

The

timing

cycle

(transmitter

keyed

time)

is

normally

set

at

the

factory

for

a

duration

of

one

minute.

A

potentiometer

permits

the

timing

cycle

to

be

adjusted

from

approximately

15

seconds

to

3

minutes.

MAINTENANCE

DISASSEMBLY

To

service

the

transmitter

from

the

top:

1.

Pull

the

locking

handle

down,

then

pry

up

the

top

cover

at

the

front

notch

and

lift

off

the

cover.

To

service

the

transmitter

from

the

bottom:

1.

Pull

the

locking

handle

down

and

pull

the

radio

out

of

the

mounting

frame,

2.

Remove

the

top

cover,

then

loosen

the

two

bottom

cover

retaining

screws

and

remove

the

bottom

cover

(see

Figure

5).

3.

To

gain

access

to

the

bottom

of

the

~

iter

board,

remove

the

six

screws

A

holding

the

exciter

board

and

its

o

ttom

cover

to

the

module

mounting

frame,

and

remove

the

bottom

cover.

To

remove

the

exciter

board

from

the

radio:

1.

Unplug

the

exciter/PA

cable

~

•

2.

Remove

the

six

screws

~

holding

the

exciter

board

and

its

bottom

cover

to

the

module

mounting

frame

(see

Figure

6).

3.

Press

straight

down on

the

plug-in

ex-

citer

from

the

top

to

avoid

bending

the

pins

when

unplugging

the

board

from

the

system

board

jack.

To

remove

the

PA

assembly:

1.

2.

Remove

the

PA

top~ver

and

unplug

the

exciter/PA

cable

B ,

the

antenna,

receiver

and

PTT

c

les

(S}

.

Remove

the

four

side-rail

screws

~

,

and

unsolder

the

power

cables

from

the

bottom

of

the

PA

assembly

if

desired.

To

remove

the

PA

board:

1.

2.

3.

Remove

the

PA

top~ver

and

unplug

the

exciter/PA

cable

~

•

Unsolder

the

two

feedthro~

coils

~

and

the

thermistor

leads

~

•

Remove

the

PA

transistor

hold-down

nuts

and

spring

washers

on

the

bottom

of

the

PA

assembly.

•

4.

~

ave

the

four

PA

board

mounting

screws

•

G ,

th~ive

screws

in

the

filter

c

sting

H ,

and

the

retaining

screw

in

Q210 ,

and

lift

the

board

out.

•

MAINTENANCE

BOTYOM

COVER

RETAINING

SCREW

Figure

5 -

Disassembly

Procedure

Top

View

PA

TRANSISTOR

REPLACEMENT

WARNING

--------·------~

The

stud

mounted

RF

Power

Transis-

tors

used

in

the

transmitter

con-

tin

Beryllium

Oxide,

a TOXIC

sub-

stance.

If

the

ceramic

or

other

encapsulation

is

opened,

crushed,

broken

or

abraded,

the

dust

may

be

hazardous

if

inhaled.

Use

care

in

replacing

transistors

of

this

type.

To

replace

the

PA

RF

transistors:

1.

Unsolder

one

lead

at

a

time

with

a

50-Watt

soldering

iron.

Use

a

scribe

to

hold

the

lead

away

from

the

printed

circuit

board

until

the

solder

cools.

2.

Turn

the

transmitter

over.

3.

Hold

the

body

of

the

transistor

to

pre-

vent

it

from

turning.

Remove

the

tran-

sistor

hold-down

nut

and

spring

washer

through

the

hole

in

the

heatsink

with

an

11/32-inch

nut-driver

for

Q201

and

Q202,

and

a

3/8-inch

nut-driver

for

POWER

LEADS

4.

5.

LBI-4896

Figure

6 -

Disassembly

Procedure

Bottom

View

Q203,

Lift

out

the

transistor

and

remove

the

old

solder

from

the'printed

circuit

board

with

a

de-soldering

tool

such

as

a

SOLDA

PULLT®,

Special

care

should

be

taken

to

prevent

damage

to

the

printed

circuit

board

runs.

Trim

the

new

transistor

leads

(if

required)

to

the

lead

length

of

the

removed

transistor.

Cut

the

collector

lead

at

a

45°

angle

for

future

iden-

tification

(see

Figure

7).

The

let-

ter

"C"

on

the

top

of

the

transistor

indicates

the

collector.

Apply

a

coating

of

silicon

grease

around

the

transistor

mounting

surface

and

place

the

transistor

in

the

mount-'

ing

hole,

Align

the

leads

as

shown

in

the

Outline

Diagram.

Then

hold

the

body

of

the

transistor

and

re-

place

the

holding-down

nut

and

spring-

washer,

using

moderate

torque

(6.5

inch-pounds

for

Q201

and

Q202,

and

11

inch-pounds

for

Q203).

A

torque

wrench

must

be

used

for

this

adjust-

ment

since

transistor

damage

can

result

if

too

little

or

too

much

torque

is

used.

7

LBI-4896

MAINTENANCE

6.

7.

8

COLLECTOR

(:

: '

EMITTER

{-

,~

BASE

Figure

7 -

Lead

Identification

Make

sure

that

the

transistor

leads

are

formed

as

shown

in

Figure

8

so

that

the

leads

can

be

soldered

to

the

printed

.circuit

pattern,

starting

from

the

inner

edge

of

the

mounting

hole.

Solder

the

leads

to

the

printed

cir-

cuit

pattern.

Start

at

the

inner

edge

of

mounting

bole

and

solder

the

remaining

length

of

transistor

lead

to

the

board.

Use

care

not

to

use

excessive

heat

that

causes

the

printed

SOLDER

ENTIRE

LEAD FROM

~DGE

OF MOUNTING HOLE

TO

END

OF

LEAD

~

SOLDER LENGTH

~-~~_-LEAD

=::::r[===j=l:=~=

PRI

NTE:.

D

f-!OARD

f'

TRANSM

ITTE:.R

/t1

HEATSINK

HOLD-

DOWN

NUT

8

SPRING WASHER

Figure

8 -

Lead

Forming

wire

board

runs

to

lift

up

trom

the

board.

Check

for

shorts

and

solder

bridges

betore

applying

power.

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

CAUTION

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

Failure

to

solder

the

transistor

leads

as

directed

may

result

in

the

generation

of

RF

loops

that

could

damage

the

transistor

or

may

cause

low

power

output.

•

••

GE MASTR II User manual

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