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SECTION 4

CIRCUIT DESCRIPTION

4.1

Introduction

The

circuits

of

the

Model

CE-7

Multi-

Channel

Fl\1

Communications

Monitor

are

on five

printed

circuit

boards:

the

Second

IF

and

Discriminator

board

(0054),

the

Power

Supply

board

(0100),

the

Frequency

Error

Meter

board

(010 1),

the

Harmonic

Generator

board

(0102), and

the

Multi-

Oscillator

board

(0103).

Figure

4-1

is

the

functional

block

diagram

of

the

CE-7.

The

115-vac-supply

fuse

RP-

F2,

is

on

the

inside

of

the

rear

panel.

The

CE-7

is

basically

a

multi-channel

superheterodyne

receiver

and a

signal

generator.

In

the

FREQ.

- DEV. MEASURE

mode

of

operation

the

RF

signal,

the

fre-

quency

and

frequency

deviation

of

which

are

to be

measured

is

applied

through

the

ANT.

connector

of

the

RF

plug-in

that

is

being

used

(a

Broadband

Mixer

or

one

of

the

three

Presel

ectcr

s) .

The

RF

signal

is

mixed

in

the

RF

plug-in

with

the

local-oscillator

signal

from

the

Harmonic

Generator

board

in

the

CE-7.

The

local

oscillator

signal

has

a

frequency

that

results

from

mixing

the

output

of

a

selected

crystal

oscillator

(associated

with

the

selected

channel)

with

the

out

put

of a

10-MHz

crystal

oscillator.

When an R F

signal

must

be

measured

for

carrier-frequency

accuracy,

the

frequency

that

has

been

assigned

to

the

transmitter

of

the

RF

signal

is

the

same

frequency

that

is

selected

on

the

CE-7.

Thus,

the

CE-7

can

only

monitor

a

signal

for

which

it

has

a

crystal

of

appropriate

frequency.

The

incoming

signal

is

mixed

with

the

internally

generated

"standard"

or

local-

.

oscillator

signal.

If

the

transmitter

of

the

incoming

signal

is

on-frequency,

the

result

of

this

mixing

will be an

IF

of

exactly

10

-MHz.

If

the

frequency

of

the

incoming

signal

is

not

correct,

the

IF

signal

will

be 10 MHz

plus

or

minus

the

frequency

error.

5601"0015

The

10-

MHz

signal

(±

frequency

e r ror )

is

fed to

the

Second

IF

and Di

scr

irninutor

board

where

it

is

amplified

and m

ixed

with

a

9.9-MHz

signal

from

the

Multi-Osc

illator

board

to

form

a

second

IF"and

100 k Hz

(±

frequency

error).

This

second-IF

s ig-

nal

is

amplified

and

applied

to

the

frequency-

error

detector.

A

squelch

detector

in

the

Broadband

Mixer

or

Preselector

rectifies

the

10-

i\IHz

signal.

The

resulting

de

voltage

is

ampli-

fied

and fed to

the

sign

al-level

detector

in

the

CE-7.

If

the

10-l\IHz

signal

exceeds

a

preset

level,

the

SIG:-\AL

LEVEL

lamp

lights

to

indicate

that

accu

ra

te me

asure-

ments

can

be

made

and

the

frequency-

error

detector

is

energ

ized

.

The

frequency-

error

detector

is

adjusted

to

give

a

zero

indication

on

the

FREQUENCY

meter

when

the

second

IF

signal

is

exactly

100 k Hz.

If

the

frequency

of

the

monitored

signal

is

above

or

below

the

frequency

selected

with

the

CARRIER

FREQUEf\'CY

SELECTOR,

the

input

to

the

frequency-error

detector

will

be

exactly

the

same

amount

above

or

below 100 k Hz .

The

detector

output

will

cause

the

FREQUE~CY

meter

to

deflect

toward

the

plus

(+)

or

minus

(-)

side,

in-

dicating

the

direction

and a mount of

fre-

quency

error.

If

the

monitored

signal

is

frequency

modulated,

the

modulation

will

be

present

in

the

output

of

the

frequency-error

detec-

tor.

This

output

is

demodulated

and a

sig-

nal

representing

the

modulation

is

amplified

and

fed to

either

the

Model 302 FM

Deviation

Meter

or

the

Model

301

Oscilloscope.

If

the

Model 302

is

used,

its

FM

deviation

meter

will

indicate

the

peak

deviation

of

the

FM

signal.

On

the

Model 301

Oscillo-

scope,

the

amount

of

deviation

and

frequency-

error

will

be

shown

on

the

CRT

.

The

CE-7

can

be

used

as

a C\V-

or

FM-

signal

generator

but

its

range

is

limited

to

the

frequencies

for

which

crystals

are

in-

stalled

(if

the

Model

l\1CO-6

Oven-Oscillator

is

used,

the

range

is

extended

to

include

the

auxili

ary

crystals).

4-1

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