Memorex CP8 TURBO UNIVERSAL REMOTE CONTROL Manual de usuario descargar pdf (Pagina 39)

100

windshield would reduce

visibility, Pontiac management

bought the

concept and

the

windshield

antenna

was

intro-

duced in production

shortly afterwards.

Ford

Motor Company

limed suit

with

the

introduction

the

windshield antenna

in the 1970

Thunderbird. While

the

antenna

itself was, for all practical

purposes, identical

to the

one used in the Grand

Prix, Ford's approach

to the

sensitivity problem

was

not the

same: there

was

be little, if

any, compromise

in the

overall performance

of the radio

system.

Since the Thunderbird

windshield antenna had the

identi-

cal

16 dB loss as compared

to the 56"

whip,

the task

was to

improve the

sensitivity of the

radio by the

same amount, if at

all

possible.

After

many trials and tribulations

-which

included adding

extra buffer

stage in the

amplifier,

higher impedance

antenna and RF coils,

and increased

number of turns

on the

secondary coupling

-the

radio AM

sensitivity,

when used in

conjunction

with a

windshield antenna,

became essentially

comparable to the

original

whip -antenna system.

Active

Antennas

Experiments

with "active"

or "integrated" antennas

be-

gan

in the mid -I960s

both in the United

States and

Europe,

but active antennas

did not

become commercially

available

until

the

early

1970s.

The basic concept

of the active

antenna is

quite simple. It

well

-known fact that,

independent

of the polarization

of the

broadcast

signal, the car

body distorts the electromagnetic

field and

creates

vertical

and

horizontal components.

The

vehicle's body acts as the

rod antenna ground

plane,

and

effectively

becomes

part of the antenna

system. The upper

part

of the

vertical

rod antenna,

however, extends

to an area

the electromagnetic

field

where it provides

very little to the

total received power.

Since the

rod antenna

is not effective

its upper part, it

would be ideal,

for

esthetic

well as

practical

reasons (garage

doors, car

washes),

shorten the

overall length of a rod

antenna.

Unfortunately, as the

overall length

rod antenna

directly proportional

to the available

signal to the

receiver

the AM

band, and should not be

shortened too much

to avoid

impedance

mismatches

in the FM

band, short, passive -rod

antenna

systems are

not

viable.

short-rod antenna associ-

ated with an amplifier

overcomes

that problem (see

Fig. 12).

Several active- antenna

systems

are

available today

which

are especially

designed to

produce a better

signal -to -noise

ratio than passive

antennas

such as the

whip.

Such

active

antennas

have

separate amplifiers

for AM and

FM, and

despite their

short length

of about 16" (40

cm), they typically

give

higher outputs

than 36"

whips. Their main drawback

overload at high

input levels.

Heated

Backlite Antenna

A system

which combines

the advantages

windshield

and

active antennas

known as

heated backlite

antenna,

HBA

for short. Designed

by B.S.H.

Electronics

of Swinton.

Manchester, England,

this

new

vandal -proof antenna

system

went on sale on September

30,

1983,

in Ford's Orion.

was

the

first high-

volume production

car

in Europe

with an anten-

in its rear -window

heating

element, eliminating

the need

for a conventional

rod antenna

(see

Fig. 13).

Basically,

the HBA

long -wire design

capable

of receiv-

ing a broad frequency

spectrum. It consists

of the

back

window

heater elements

suitably

designed

to allow connec-

SHORT ROD

ACTIVE ANTENNA

Fig. 12 -As

the

overall

length of a

rod antenna

directly proportional

to the

signal

they can

provide to

the

receiver, and since an antenna

should

not

be shortened

too

much lest impedance

mismatches

the

FM band creep up,

short, passive -rod

antenna systems

are not

viable. But

active systems

such as

that

shown

here are

very good.

ANTENNA

(HEATED

BACK LITE)

Fig. 13

-The

HBA is a long -wire design capable of

receiving

broad frequency range.

consists

of the

back

-window heater elements designed

allow

connection

an amplifier

module

counted

in a vertical

pillar.

tion to an amplifier

module mounted in

the ear's rear

vertical

pillar. The module

is in turn connected,

via coaxial cable,

the RF stage of the

radio receiver.

The back -window

heater pattern has a

specific design

for

its new dual

purpose role,

optimized for use

as a radio

receiving antenna.

The main

difference

over current designs

is the use of a

single- ended, power,

feed arrangement

that is

required to

provide the shortest possible

connection

leads

between the

isolated assembly module

(the "amplifier

") and

the heater

busbars on the

backlite glass. That

is an essential

condition for predictable

antenna

performance.

Besides improved

styling, the

performance of the HBA

comparable to the

rod antenna. Its

major disadvantage

is the

higher

system cost as compared

to the

whip,

which is more

than compensated

for by

its consistent performance.

Goes On

should be clear by now, automobile

antennas

have

been

used

every

conceivable place

in the car.

Engineers

were faced

with

system in a constant

state of

change. Year to year

they

were

forced

to abandon

relatively

new antenna

systems, made obsolete

by dramatic

vehicle

configuration

changes and

not by poor

performance.

While few new

systems appear to

be available

in the near

future, there

has been

some serious developmental

work on

the

slot antenna

which

will be mounted as a plastic

insert

the roof

of the

vehicle. Initial performance

data

has been

excellent.

The

system also has the potential

to make the

antenna an

integral part of the

vehicle

construction

and,

once

and for all,

rid the automobile

of its added

appendage.

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