Sharp R-309B Instrucciones de operaciones descargar pdf (Pagina 31)

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Figure

4-7.

Multi-Oscillator

Board,

Block

Diagram

Its

frequency

is

set

to 10 MHz

with

the

FM

CAL.

control

FP-R5,

which

adjusts

the

voltage

to

Varicap

CR2 in

the

tuned

circuit

of

the

oscillator.

When

adjusted

to

exactly

10 MHz,

the

oscillator

fre-

quency

is

kept

constant

by

the

AFC

volt-

age

from

the

frequency-error-detector

circuit

in

the

Second

IF

and

Discriminator

board

which

is

also

applied

to

Varicap

CR2.

The

internally-generated

modulating

signal

(for

FM

signal

generation)

is

pro-

duced

by

the

I-kHz

oscillator.

Transistor

Q4 in

this

oscillator

circuit

is

energized

when

+20

volts

is

applied

by

turning

the

FM

MOD.

switch

to

the

INT.

position.

The

output

of

the

oscillator

is

fed

to

the

DEV.

ADJ

.

potentiometer,

which

provides

ad-

justment

for

the

amount

of

signal

being

delivered

to

Varicap

CR2

of

oscillator

Q7

and

via

amplifier

Q5

and

emitter

follower

Q6, to

the

I-kHz

OUT

connector.

The

Varicap

changes

capacitance

and

thus

frequency-modulates

the

10-

MHz

output

of

Q7.

To

produce

a

second-IF

signalof

100

kHz,

the

first

IF

of

10 MHz

is

mixed

with

a

9.9-MHz

signal.

This

signal

is

pro-

duced

by

crystal-controlled

oscillator

Q13.

The

9.9-1VIHz

crystal

is

not

installed

in

the

Crystal

Oven

Assembly

but

ope

ra

tes

at

am

bient

tempera

tures.

Trans

is-

tor

Q13

is

always

energized

except

when

the

4-11

5.601"0015

"1

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