Metra Electronics DAT Combo Manual de usuario descargar pdf (Pagina 57)

Put the

two receivers

side

by

side

on

a

table.

Pick out

a

station

on the SW

dial,

then turn

the set's

volume down

to nil

but

not far

enough

to

turn the

power

off.

Now tune

the

LW

receiver

to

455. Lo and

behold

-there

is your

SW

station.

Why? Well,

because every

inexpensive

shortwave

rig

radiates

slightly

at

its inter-

mediate

frequency.

Whatever

it

picks

up

is

rebroadcast

at

455

kHz and

your

longwave

receiver

will

pick

this

up.

Of course

you'll

want maximum

IF

pickup.

To obtain

this,

the

two

receivers

should

he connected

to

a

common

antenna.

And

if this

still

doesn't

provide enough

pickup,

have

a qualified

technician

hitch

the

SW

1F's output

directly

into

the LW's

RF circuit.

But

we

emphasize

the

person

who does this

must

be

fully quali-

fied.

If

you

try it yourself,

the

results

could

he

"shocking."

Anyway,

in most

cases

the

common

antenna

will

do

the trick.

Pitfalls.

Now

in setting

up

this

system

there

are

a few

pitfalls

to avoid.

First

be

sure

the

LW

receiver

does

tune

to the

IF-

Military

-surplus

longwave

receiver

(above)

picks

up

the

IF radiation

and gives

added

selectivity

for

those

crowded

bands

devoted

to

brass

pounding.

BFO in

longwave

receiver

puts

the dits

and

dohs

back

into

the Morse

code

messages.

Short

wire

from

antenna

post

(right)

is

wrapped

around

outdoor

antenna

lead

for ca-

pacitive

coupling.

Direct

connection

to

last IF stage,

through

very

-small

-value

capacitor,

is better.

TO

ANTENNA

that is, it must

have

a

band

covering

the

400

through

500

kHz

range.

Next,

be sure

the

LW

rig you

buy

is

war surplus

and

not

a

new one,

otherwise you

could

wind up paying

more than

a regular

Ham

receiver

would

have cost.

Sometimes

the

hand

switches

on

these

old rigs

act

up,

however,

for

ama-

teur purposes,

once

the

receiver

is

on that

455

kHz

band, you

shouldn't

care

less.

On

the

other hand,

this

should

knock

down

that

price

still further.

For

more exact

details

on

price, pick

out the

appropriate

dealers

from

their

ads

in this

issue (and

Literature

Library), then

write

them.

There

is

one more

thing

to

look

out for.

We said that

the

two

receivers

should

be

connected

to a common

antenna.

But

some-

times

connecting

the

SW

receiver

on the

hookup

will badly

detune

the

LW antenna

circuit.

If this

does

happen,

simply

place

a

very

small capacitor

(not

bigger

than

50

µµf

but the

value is

not critical)

between

the

longwave

lead

and

main

antenna

which

in turn

is

attached

directly

to

the SW

rig.

This effectively

isolates

the two

tuning

cir-

cuits.

This

is

a

must

if you

decide

to con-

nect

into the

IF

amplifier

directly.

All Set.

So

now

you're

all set

for

CW

reception.

You're

also

ready

to

receive

single -sideband

transmissions

but these

will

require

much more

careful

tuning.

A SSB

signal

is just

like one

using

standard AM

(amplitude

modulation)

except

that

one

side -

band (which

you

won't miss)

and

the

car-

rier have

been

removed.

In

order

to hear

single -sideband

voice transmissions

in

an

in-

telligible

manner

you

must

produce

your

own carrier

within the

IF. The

BFO,

of

course,

makes

this

possible.

(Turn

pua )

ALL BAND

RECEIVER-'

INSULATED

WIRE

GIMMICK

LONGWAVE

RECEIVER

HIGH

IMPEDANCE

HEAD-

PHONES

FEBRUARY

-MARCH,

1967

63

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