Marantz 5220 User Manual download pdf (Page 49)

A note

about

capacitor C1

-any

surplus,

multi -gang

variable capacitor

may be used.

Total

maximum capaci-

tance

should

be

about

1200 pF.

As

of

press time, Fair

Radio Sales,

Box

1105, Lima, OH

45802, has several

suitable

models, with an

approximate

cost

of

$3.00.

If you have trouble

find-

ing

a capacitor

on

the surplus

market,

buy

three

365 -pF

AM tuning

capacitors

and

gang

their shafts

to-

gether.

After

installing all

compo-

nents, wire

the Control

Panel in ac-

cordance

with the schematic

(Fig.

2)

using

18 -gauge solid

hookup wire.

Try

to

keep all

leads as short as possible.

The

Control

Panel should

be

mounted in a cutout on

a

rotatable

platform

-a lazy susan

arrangement.

The

platform

should

be big enough

to

accommodate

your

AM receiver also,

since

it must be

rotated

in step

with

the

Loop.

Once

the

Panel is

mounted, drill a

7/32 -inch

(5.6

-mm)

hole

in the

support

bracket

3 /e" (9.5

mm) down

and 1" (2.54

cm) over

from the

un-

notched top

corner.

Then drill

7/32

-inch

(5.6

-mm)

holes along

the center

line 3/6" (9.5

mm)

from

each

end of

an

111/4"

x

1"

x

3/6"

(28.6 cm

x

2.5 cm

x

9.5

mm)

hardwood strip.

Attach one

end of

the

strip

to

the support

bracket

using a

10

-20

x

1"

hex head bolt,

a

hex nut as a

spacer

between

the strip and

bracket,

FRAME

BILL

OF

MATERIALS

2-42 inch

lengths

of /"

ID thin

-wall

aluminum

tubing

4-14

-inch lengths of

h"

wood doweling

3-23/4-inch

lengths of

3/4"

wood doweling

4-12 -inch lengths

of 1/2"

x

1/2" aluminum

U- channel

1 -Block

of

hardwood

4"

x

lL /a"

x

3/a"

I-Strip

of hardwood

111/4"

x

I"

x

W'

1 -10-32

x

111" bolt and

washer

l -3/4 -inch

spacer

to

fit above.

I- 1/4-20

x

1" bolt,

washers,

and

wing nut

4-6

-32

x

I" machine

screws,

flatwashers,

and nuts

4-No. 6

x

'h"

wood

screws

8-1/4" self

-tapping sheet

metal

screws

PARTS

LIST

BPI -5 -way

binding

post

C1-

1200

-pF (total)

multi -gang

variable

capacitor

J1,J2

-Uhf coaxial

jack, SO -239

J3-RCA

phono

jack

J4 Open-

circuit

stereo

headphone jack

L 1 -6 turns

of

16-

or

18 -gauge

copper

wire

wound on

loop

frame

PLI -Double

male

uhf coaxial

adapter

(Amphenol

83 -877,

Lafayette

42

69064

or

equivalent)

SI

-SPST

switch

Misc. -4.75"

square

1/16

-inch aluminum

plate, tuning

knob,

machine

hardware,

hookup

wire,

solder, etc.

ANTENNA

BLOCK

STEREO

PRONE

PL04

JACK

AAA

ROD

L ^ -3 °

FROM

¢

PARALLEL

TO

ANTE/VIVA

BLOCK

Fig.

4.

Control

panel

layout.

Proper orientation

of

receiver

rod antenna

is shown.

\

and wing

nut. Keep

the wing

nut

rela-

tively

loose.

Now secure

the other

end

of

the

strip

to the Loop

frame using

a

10 -32

x

11/2" bolt,

washer,

and a

3/4' (1.9

cm)

spacer.

Use

the

3/16

-inch

(4.8 -mm)

hole previously

drilled

above

the bot-

tom of

the vertical

tubing.

Attach

the Loop

frame to

the Con-

trol Panel

using PL1,

a double

male

uhf

coaxial

adapter

(Amphenol

83-

877), between

jacks

J1

and J2.

Then

connect

the

free end of

the

hookup

wire

from the

loop

to binding

post

BP1.

Tighten

the hardware

holding

the

hardwood strip.

Leave S1 open,

and position

your

AM

receiver below

the

Loop, orienting

its rod antenna

as

shown

in

Fig. 4.

The two coils should

be about

1" to 3" (2.5

cm

to 7.6 cm)

apart.

Using

the

Loop.

Tune the

receiver

down

to the

low end (540

kHz) of the

AM

Broadcast

Band.

Turn

Cl's

tuning

knob so

that the plates

are

fully

meshed.

Then, carefully

tune

in an au-

dible signal

using

the

receiver's

tun-

ing capacitor.

Slowly

unmesh

C/ 's

plates (reduce

capacitance)

until

the

signal

peaks strongly.

You have

now

tuned the

Loop

to resonance

at

this

frequency.

It's

possible

that

loading effects

by

the Loop

may "pull"

the

receiver off

its

dial calibration.

If

this occurs, just

continue

to adjust

both Cl

and

the

receiver's

tuning

capacitor

for

maximum

intelligibility.

You'll

proba-

bly

find

that the two controls

interlock,

but

with a

little practice

you'll

be

quickly

zeroing

in on

the station

you're

after.

Try rotating the

loop to

get

an even stronger

signal.

Best

re-

sults

will

be obtained

when

the

plane

of

the loop

extends

in the direction

of

the desired

signal.

You can

also

use

this directivity

to

null

out

an

interfer-

ing

station

on

the same

frequency-

turn

the

loop

broadside

to the offend-

ing signal.

With S1

open,

the Loop

can

be

tuned

just

about

to 1600

kHz.

It also

has maximum

gain

in this position.

But

there

are

times

when

a bit

more

selectivity

is

desirable

over

gain

-for

example,

when

two

fairly strong

sta-

tions

are

a

few kHz

apart.

This

is

par-

ticularly

true

when

trying

to work

the

"splits " -foreign

stations

operating

on odd

frequencies

not

multiples of

10

kHz.

In situations

like this,

close

Si.

This shorts

out

the

bottom

turn of

the

loop,

giving

a

higher Q.

It also gives

you a

bit

more "room"

on C1

at

the

top

end

of

the band.

Other

Suggestions.

The

"pulling"

action

mentioned

earlier

can cause

you

to

get

"lost"

in

terms of

frequency.

To

prevent

this, prepare

a

list of strong

signals

in your

area,

noting

them by

call

letter and

frequency.

You can

then

use

them as

frequency

markers

to

chart

your way

across

the band.

It's

also

a good

idea to

get

a complete

list

of

North

American

AM

stations

-

especially

if you

want to DX

the band.

Several

are available,

listing stations

by call

letters, power

output,

frequen-

cy,

and geographical

location.

Another system

variable

is the

amount

of

coupling

between

the

Loop

and

the

rod antenna.

This

should

be

varied to suit signal

strength,

but can-

not accurately

be predicted

without

experience

with

your

particular

re-

ceiver.

While

it

should

vary between

1

and 3

inches, experiment

for

best

re-

sults.

To make

tuning easier,

a

vernier

(0

to 100)

tuning

knob can

be used

with

Cl. Once you

have

properly

tuned

a

station

in, record

its frequency,

direc-

tion toward

which

the Loop

is turned,

position of

Si,

and

the amount of

capacitance

needed.

Keep all

this

in-

formation

for future

reference.

0,

MARCH 1976

53

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