Yaesu FT-223 Instruction Manual

THEOR

OPERA

TION

:;.ENERAL

i'unctional

operation

the

model

-223

VHF

IFM

transceiver

ìllustrated

the

Block

Diagram,

Figure

lefer

the

schematic

diagram

for

the

circuit

description.

['be

transceiver

consista

crystal

controlled

transmitter

and

:eceiver

operating

any

the

channels

within

the

frequency

:ange

144

148

MHz.

addition

channels

which

are

;elected

the

CHANNEL

selector

switch,

one

"most-often-used"

:hannel

may

preset

for

ease

operation.

Solid

state

circuitry

employed

throughout

and

the

transceiver

designed

operate

rom

13.5

Volt

+lO

o/o

negative

ground

power

source.

CRANSMITTER

SECTION

Che

transmitter

section

produces

(phase

modulation

method)

Jutput

signal.

Che

audio

signal

from

the

microphone

amplified

integrated

ircuit

Q201

(TA706IAP)

which

works

arnplifier

and

IDC

Instantaneous

Deviation

Contro!)

circuìt.

The

IDC

circuit,

clips

lOth

positive

and

negative

peaks

when

they

exceed

predetermined

evel

li.Init

the

maximum

deviation

the

transmitter.

The

IDC

:ontrol,

VR202,

permits

the

deviation

adjusted,

and

nominally

actory

set

fora

deviation

+5kHz.

When

wide

band

transmission

desired,

VR202

must

readjusted

provide

maximum

deviation

•f +10

kHz.

FT-

223

BLOCK

OIAGRAM

The

tone

signa!

passes

through

low

pass

filter

uni

t 11c

0501

and

fed

0502,

NE567.

When

the

tone

signal

has

same

frequency

preset

for

transmitting,

the

voltage

0502

becomes

low

causing

0504,

2SC372Y

'0FF".

proper

bias

voltage

applied

0119

for

normal

operation.

Without

proper

tone

signal,

Q504

conducts,

removing

the

prc

bias

from

0119

disable

the

audio

circuit.

the

conventional

carrier

squelch

circuit

operative

wher

the

tane

squelch

switched

in,

the

busy

lamp

lights

when

any

carrier

received.

l SIV A )

r--

--------

------------

----ì

l l

.---

-~~

(

EA.RT

---------------

(

TOJYE.

S W l

ICH)

TONE SQUELCH

<Pe

-r555A) OPTION

Figure

Downloaded

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frequency

modulated

146

148

MHz

signal

amplified

Q210,

:c741,

Q211,

2SC730

and

Q212,

MRF212

and

applied

through

two

age

pi-network

the

antenn

diode

D204,

1Sl88FM

rectifies

mall

portion

the

output

and

applies

the

resultant

voltage

the

meter

where

provid

indication

relat

power

output

the

ansm

itter.

The

meter

sensitivity

adjusted

VR204

set

for

indication

the

meter

scale

a t l O

watts

ohm

esisti

load.

the

transmitter

keyed

without

antenna

conn

ed,

ifa

high

\T'R

exists

the

antenna

syst

the

reflected

power

detected

rough

T210

and

diode

D207,

1Sl88FM

produces

voltage.

~15,

2SC372Y

conducts

with

the

voltage

applied

through

VR209

.uaing

Q216,

2SC3

72Y

decrease

its

collector

current.

Thus

emitter

voltage

Q217

2SA496(0)

lowered

causing

Ql,

:D313

decrease

current

and

the

supply

voltage

the

amplifier

low

ered

prevent

damage

the

transistor.

The

protection

vel

set

VR209.

This

circuit

also

used

switch

the

output

wer

down

watt

where

the

ID/LOW

switch

LOW

position.

amou

power

reduction

may

adjusted

VR208.

antenn

change

-over

circuì

consista

the

switching

diodes

~05

and

D206,

301.

~CEIVE

SECTION

146

148

MHz

input

signal

from

the

antenna

plified

QlOl,

3SK

40Mon

board,

and

applied

through

five

hi-Q

)t-coupl

resonators

the

first

mixer,

Q102,

3SK40M

...

Q ,

a..

Figure

Top

View

·t

Downloaded

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C'he

limited

audio

signa!

applied

through

low-pass

filter

2202,

2SC372Y

where

amplified

and

applied

the

phase

modulator

-aractor

diade

D20l,

1658.

The

low-

;

pass

filte:t

limits

the

transm.itt€

nodulation

spectr\.un

attenuating

frequencies

above

the

speech

range.

~he

oscillator,

Q203,

2SC372Y,

operates

the

crystal

frequency

generate

the

initial

signal.

The

crystal

frequency

the

·ange,

and

determined

follows:

Crysta1

Frequency

(MHz)

Output

Frequency

(MHz)

~rhnmer

capacitors

TC40l

through

TC423

permit

each

the

:rysta1s

individually

setto

frequency.

Output

from

Q203

.mplified

Q204,

2SC372Y,

and

applied

across

transformer

L203.

~he

audio

signal

from

Q202

varies

tl1.e

bias

applied

DZO l

and

>202,

turn

causing

the

capa

city

the

diodes

vary

accordance

rith

the

audio

voltage.

D201

and

T201

and

D202

and

T202

are

eries,

the

capacity

change

the

diade

effectively

changes

the

esonant

frequency

produce

phase

shift

audio

rate

:1e

input

Q205,

2SC372Y

the

exciter

stage.

'he

angu1ar

phase

shift

fronì

the

modulator

relatively

small,

1erefore

the

crystal

frequency

multiplied

twelve

times

obtain

desired

deviation

the

output

frequency

144

148

MHz.

'he

nìodulated

MHz

signal

applied

through

the

buffer

amplifier

~205,

2SC372Y

the

multiplier

chain

consisting

doubler

Q206,

SC710D,

tripler

Q207,

2SC710D,

and

doubler

Q208,

2SC710D

·here

the

necessary

frequency

m~ltiplicatio-n

provided.

r·

Downloaded

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PB-1539

(RX

CRYSTAU

r----

1 Tc:n:J

JOI--.J

L-

N()J?.

IOI

3SK'l0

PB-

8.C

· (RX)

0115

C372Y

0102

SK40

Oil6

CI04

7 0117 2

------

SC372Y

0202

2SC372Y

L----

---

----

----- -

J,.JDNJ70R

1Jf1-oJI

Downloaded

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NJ(J ,

...._;

ICJ

'-""""

.,-

zvtJ1i

r,r

NOTES.

ALL

RES1STORS

IN n

4\11

±.10%

UNLESS

OTH

ERW

I.SE

NOTE

21lLL

PACITORS

IN"F

UNLESS

OTHERWISE

HOTEO

+*=- 16\IIV

-·

-..,

223

CIR

CUIT

OIAGRAM

--==

........,

AN7

Downloaded

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