Sharp R-309B Instruções de Operação descarregar pdf (Página 22)

A

signal

generated

with

the

CE-7

is

derived

from

the

same

sources

as

the

LO.

signal

with

which

an

incoming

signal

is

mixed

to

form

the

first

IF

and to

determine

fre-

quency

error.

Because

there

is

always

a

10-

MHz

difference

between

the

sele

cted

frequency

and

the

LO.

signal,

this

10-MHz

difference

must

be

removed

before

the

LO.

signal

can

be

used

as

a

signal-generator

output

of

the

selected

frequency.

The

re-

moval

of

this

difference

is

accomplished

by

mixing

a

10-MHz

signal

originating

on

the

Multi-Oscillator

board

with

the

LO.

sig-

nal

in

the

Signal

Generator

'Mixer :

For

both

CW

and

FM

signals,

this

10-MHz

sig-

nal

is

passed

through

a

step

attenuator

be-

fore

being

fed

through

the

Signal

Generator

Mixer

.

This

attenuator

permits

control

of

the

signal-generator

output

level,

but

the

calibration

is

only

valid

if

the

20-dB

fixed

attenuator

provided

with

the

CE-7

is

con-

nected

to

the

output

connector.

An

FM

signal

can

be

modulated

by

an

internally

generated

I-kHz

signal

or

a

modulating

signal

from

an

external

source

can

be

applied

at

the

FM

MOD.!l

kHz

bUT

connector.

The

amount

of

peak

FM

deviation

is

adjustable

by

the

DEV.

ADJ.

control

and

is

read

on

the

FM

Deviation

Meter

or

Oscilloscope

in

the

same

manner

as

when

monitoring

an

incoming

RF

signal.

When

the

FM

MOD.

toggle

switch

is

in

the

INT.

position,

the

I-kHz

signal

is

available

at

the

FM

MOD.

/1

kHz OUT

connector

for

external

use

and

the

output

level

is

ad-

justable

with

the

DEV.

ADJ.

control.

The

CE-7

can

be

used

as

a

generator

of

frequencies

that

are

usually

encountered

in

IF

stages

of

commercial

receivers

if

crystal-controlled

IF

oscillators

are

ob-

tained

for

installation

on

the

Multi-Oscillator

board.

Up to

ten

of

these

plug-in

units

can

be

used

at

one

time

and

crystals

with

any

frequency

between

250 kHz

and

13.5

MHz

can

be

made

available.

The

desired

fre-

quency

is

selected

and

the

signal

level

is

adj

usted

with

front-

panel

control

s .

The

output

is

available

at

the

1.

F.

GENERATOR

OUTPUT

cor.ne

ctor

.

5601"00)5

In

the

following

paragraphs

reference

.

will

be

made

to two

groups

of

figures.

The

first

group

consists

of

figures

numbered

4-1

through

4-7

which

are

interspersed

with

the

text;

the

second

group

consists

of

schematics

number

6-1

through

6-9

which

are

part

of

Section

6.

Each

schematic

in

Section

6

is

placed

adjacent

or

in

close

proximity

to

associated

parts

lists

and

parts

pictorials.

-

1-.

2

Second

IF

and

Discriminator

Board

II

Figure

4-2

is

a

block

diagram

and

r

~

Figure

6-1

is

the

schematic

diagram

of

the

Second

IF

and

Discriminator

board.

@

In

the

FREQ.

-DEV.

MEASURE

mode

the

first

IF

of 10

l\1Hz

from

the

Broadband

["!

@I

Mixer

or

Preselector

to

the

second

IF

and

Discriminator

board

is

amplified

by

IC1 and

mixed

in IC2

with

a 9. 9-l\1Hz

r;

second

local

oscillator

signal

from

the

l\Iulti-Oscillator

board

buffered

by

Ql.

The

resulting

100 kHz

second-IF

signal

'"

is

filtered

and

then

amplified

by Q2

and

r~

Q3.

The

square

wave

out

of Q3

is

dif-

ferentiated

by R20 and

C22

and

sent

to

pulse

shaping

network

CR1 and CR2.

Only

the

positive

alternations

are

used

to

trigger

Q-l:,

the

normally-off

side

of

the

one-shot

multivibrator;

Q4

turns

on

and Q

.5

turns

off.

The

multivibrator

re-

mains

in

this

state

for

5

microseconds

before

reverting

to

its

normal

state.

This

5

microsecond

period

is

constant

regardless

of

the

frequency

with

which

the

multivibrator

is

triggered

and

is

calibrated

by

adjusting

the

CAL.

control.

If

the

incoming

signal

is

on

frequency,

and

the

second-IF

signal

is,

therefore,

exactly

100 k Hz and

if

there

is

no

modu-

lation

on

the

second-IF

signal,

the

time

between

triggers

is

10

microseconds

and

square

waves

result

at

the

collectors

of Q4

and Q5.

Refer

to

Figure

4-3.

When

there

is

an

error

or

the

second-IF

signal

is

modulated,

then

the

time

between

triggers

will

be

longer

'0 1'

shorter

than

10

micro-

seconds.

\\'hen

the

time

between

triggers

is

longer

than

10

microseconds,

Q5

is

turned

ON

for

a

longer

period

than

it

is

[

.-

turned

OFF.

Whent

he

time

is

less

than

10

microseconds,

Q5

will

be

OFF

for

a

it-

[:

-.-

4-2

L

...

.,..

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