MFJ MFJ-201 Manuale utente

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ITF]

1.5-250

MHz

DIP

METER

Model

MFJ-201

Operation

Manual

GENERAL

|

This

unit

is

a

transistorized:dip

meter

for

rapidly

checking

circuits

and

components

in

receivers,

transmitters,

antennas,

etc.;

in:

the

1.5

to

250MHz

range.

It

is

designed

for

many

applications

in

Amateur

Radio

stations

and-service:shops.

2.

SPECIFICATIONS

‘

Frequency

Range

2

1.5

to

250MHz

with

six

plugin

coils:

Band

Range

A

1.5-—

4MHz

B

3.3-

8MHz

c

6.8—

18MHz

D

18—

47MHz

E

45

—

110MHz

F

100

—

250MHz

Modulation

:

Approx.

2kHz;

sine

wave

Crystal

Oscillator

:

1-15MHz,

crystal

in

FT-243

holder

Power

Supply

:

Q

volt

battery

Current

Consumption

:

2mA,

maximum

Semiconductor

Complement

:

2

transistors

and

1

diode

3.

PANEL

CONTROLS

Frequency

dial

:

Six

frequency

scales

calibrate

according

to

bands

and

color

of

the

coil

in

use.

Meter

:

For

indicating

resonance

and

for

battery

check.

Function

switch

:

Three

positions

OSC:

For

use

as

a

dip

meter

or

absorption

wave-

meter.

MOD

:

Applies

2kHz

AM

to

the

carrier

output.

BATT

:

For

checking

condition

of

CHECK

internal

battery.

SENSITIVITY

:

Adjusts

the

output

level

of

the

oscillator;

at

OFF,

the

power

supply

is

cut

off

and

the

instrument

can

be

used

as

an

absorption

wavemeter.

Earphone

jack

:

For

monitoring

AM

signals

with

a

crystal

earphone

(not

supplied).

4.

CIRCUIT

DESCRIPTION

The

RF

oscillator

is

a

Colpitts

type

using

a

silicon

transistor.

The

RF

voltage

is

rectified

with

a

diode

and

the

current

is

indicated

on

the

meter.

When

the

dip

meter

frequency

is

in

resonance

with

the

external

circuit,

the

meter

pointer

will

dip.

The

strength

of

the

oscillator

output

is

controlled

2

with

the

SENSITIVITY

adjuster.

When

required,

amplitude

modulation

can

be

applied

to

the

RF

oscillator

output.

A

twin-

T

type

circuit

is

used

for

the

2kHz

source.

In

the

absorption

wavemeter

function,

the

RF

oscillator

Power

is

cut

off

and

the

tuned

and

diode-meter

circuits

are

used.

5.

PRECAUTIONS

IN

OPERATION

1.

During

standby

periods

or

when

the

dip

meter

is

not

in

use,

set

SENSITIVITY

adjuster

at

OFF

(clicked).

This

will

Prolong

battery

life.

Handle

the

coils

carefully

when

inserting

or

removing

same

from

the

socket.

During

measurements,

the

coil

should

be

loosely

coupled

to

the

test

circuit.

The

coupling

must

be

as

loose

as

possible

to

obtain

proper

meter

indication.

Close

coupling

will

in-

troduce

errors

in

measurement.

IMPORTANT!

When

checking

transmitting

equipment,

close

coupling

will

damage

the

diode

detector

by

overload.

Disconnect

the

battery

from

the

internal

circuit

when

the

dip

meter

is

not

in

use

for

long

periods.

6.

OPERATION

1.

Battery

Check

and

Replacement

1.

2.

3.

Set

FUNCTION

at

BATT

CHECK.

Advance

SENSITIVITY

to

power

a.

on.

The

meter

pointer

should

swing

to

the

BATT

OK

portion

on

the

scale.

If

not,

renew

the

battery.

NOTE:

To

install

or

replace the

battery,

remove

the

covers

as

follows:

Remove

the

two

screws

each

at

the

right

and

left

sides

of

the

instrument;

take

off

the

covers.

Loosen

the

battery

clamp

screw

at

center

of

the

chassis

and

take

out

the

battery.

Remove

the

snap

terminals

from

the

battery.

To

install;

reverse

steps.

Tighten

the

clamp

screw

and

put

on

the

side

covers.

After

this

check,

set

SENSITIVITY

at

OFF.

2.

Use

as

a

Dip

Meter

1.

2.

3.

Plug

the

coil

for

the

band

in

use

in

the

socket.

Set

FUNCTION

at

OSC.

Advance

SENSITIVITY

past

the

click

point

so

that

the

meter

pointer

swings

to

about

0.8.

NOTE:

When

the

“F”

coil

is

used,

there

will

be

some

variation

in

the

meter

deflection

as

the

frequency

dial

is

rotated.

This

effect

will

be

present

when

the

coil

is

not

coupled

to

the

test

circuit.

Care

must

be

taken

during

use

not

to

confuse

this

condition

with

the

actual

dip

caused

by

the

test

circuit.

4

|

4.

Couple

the

coil

loosely

to

the

test

circuit

and

rotate

the

frequency

dial

in

small

steps

until

a

dip

is

observed

on

the

meter.

(When

there

are

two

dips

close

together,

place

the

coil

farther

from

the

test

circuit.)

Adjust

the

frequency

dial

until

the

maximum

dip

is

obtained.

Note

the

frequency

on

the

frequency

dial.

Set

SENSITIVITY

at

OFF

after

the

tests.

.

Examples

of

typical

coupling

methods

are

shown

in

Fig.

1.

NOTE:

It

is

important

that

the

power,

if

applied,

to

the

test

circuit

is

turned

off,

aby

4

see

enon

Fig.

—1

Dip

meter

coupling

methods.

5

AandB_:

Director

or

link

types.

C_

:

For

shielded

circuits;

the

coupling

capacitor

should

be

as

small

as

possible.

D_:

Determination

of

resonant

frequency

of

an

antenna;

use

a

1-turn

coil

in

the

antenna.

(For

vertically

grounded

antennas,

do

not

forget

to

make

the

ground

connection.)

E

=

Determination

of

electrical

length

of

quarer-wave

and

half-wave

coaxial

feeders.

3.

Use

as

an

Absorption

Wavemeter

1.

2.

3.

4,

When

the

coil

is

coupled

to

the

coil

in

an

oscillator,

or

RF

tank

coil

in

a

transmitter,

the

Plug

the

coil

for

the

band

in

use

in

the

socket.

Set

SENSITIVITY

at

OFF.

Set

FUNCTION

at

OSC.

meter

pointer

will

swing

upward

when

tuned

to

resonance.

The

amount

of

the

swing

depends

on

the

strength

of

the

oscillations

and/or

coupling

distance.

NOTE:

In

checking

transmitters,

take

care

that

the

energy

picked

up

will

not

overload

the

instrument,

otherwise

the

diode

detector

will

be

damaged.

Further,

do

not

touch

any

of

the

high

voltage

points

within

the

transmitter;

safety

is

important.

Read

the

frequency.

Typical

application

are

shown

in

Fig.

2.

Fig.

—2

Absorption

wafemeter

applications.

Measurement

of

oscillator

frequency.

Measurement

of

frequency

at

the

transmitter

output.

To

check

for

harmonics

or

parasitics,

slowly

rotate

the

frequency

dial

for

the

indications;

change

the

coils

are

necessary.

The

meter

deflection

will

indicate

the

relative

strength

of

these

signals.

Neutralizing

adjustments

can

be

made

by

first

cutting

off

DC

supply

to

the

plate

and

screen

grid

circuits.

The

tank

circuit

is

then

tuned

for

maximum

indication.

Next

the

neutralizing

capacitor,

CN,

is

adjusted

for

minimum

indication.

7

D:

Use

as

a

field

strength

meter

is

shown.

A

short

antenna

is

coupled

to

the

coil

for

signal

pickup.

When

the

wavemeter

is

tuned

to

the

operating

frequency

and

at

different

positions

around

the

antenna,

the

relative

field

strength

will

be

indicated

on

the

meter.

4,

Short

Wave

Receiver

Testing

In

this

application,

the

dip

meter

is

used

as

a

simple

test

oscillator,

with

or

without

amplitude

modulation.

The

test

frequency

is

set

with

the

suitable

coil

and

frequency

dial.

The

dip

meter

is

placed

near

the

receiver;

the

“input

signal

strength”

can

be

varied

with

the

distance

between

the

dip

meter

and

the

receiver.

For

operation,

set

SENSITIVITY

for

RF

output.

Communications

receivers

with

best

oscillators

can

be

tested

by

setting

FUNCTION

at

OSC

for

the

CW

signal.

When

an

AM

signal

is

required,

set

FUNCTION

at

MOD.

A

tone

of

approximately

2kHz

will

be

heard

in

the

loudspeaker.

Adjustments,

as

required,

can

be

made,

with

the

respective

signals,

in

the

receiver

circuits,

5.

Monitoring

Phone

Signals

The

wavemeter

application,

see

Sect.

5.3,

can

be

used

for

monitoring

AM

phone

signals.

A

crystal

earphone

is

connected

to

the

earphone

plug

and

the

plug

is

inserted

in

the

PHONE

jack.

Tune

to

the

RF

test

frequency

using

the

proper

coil.

8

For

“remote”

indication

of

the

modulated

output,

the

meter

can

be

connected

to

the

ear-

phone

plug;

the

inner

contact

is

the

+

side.

.

Use

as

a

Crystal

Oscillator

In

place

of

the

coil,

a

quartz

crystal,

1

—

15Mhz,

in

the

FT-243

holder,

inserted

in

the

socket

will

produce

output

at

the

crystal

frequency.

Set

FUNCTION

at

OSC

and

SENSITIVITY

as

required

for

the

output.

The

frequency

dial

is

rotated

until

the

most

stable

condition

is

obtained.

Set

the

dip

meter

near

the

receiver

for

signal

pickup.

For

modulated

output,

set

FUNCTION

at

MOD.

.

Audio

Signal

Output

Set

up

the

instrument

for

dip

meter

operation,

see

Sect.

2,

with

coil

E

or

F

in

the

socket

(However,

the

RF

is

not

used.)

Set

FUNCTION

at

MOD.

Audio

output

at

approximately

2kHz

is

available

at

the

PHONE

jack.

The

plug

connections

are

as

follows:

Inner

contact

for

the

“hot”

side

and

the

sleeve

for

ground.

This

signal

can

be

used

for

checking

audio

circuits.

.

Inductance

and

Capacitance

Measurements

Unknown

inductances

and

capacitances

can

be

determined

with

use

of

the

dip

meter,

see

9