Radio Shack PLCDCS 200 - Manual (Page 12)

CAUTION
1. This unit is designed to operate on
12-volts DC, negative ground
electrical system only. Do not attempt
to install this unit in a vehicle having a
positive ground system.
2. You should not touch the
high-polished playback head with any
metallic or magnetic tools.
3. Your unit has built-in filtering to
eliminate most of the noise that might
come through the power source.
However, with some vehicles,
particularly older models, some
clicking or other unwanted noise
might be present.
IGNITION AND INTERFERENCE NOISE
Interference
Radio reception in a moving environment
(automobile) is very different from
reception in a stationary (home). It is
very important to understand the
difference.
AM reception will deteriorate when
passing through a tunnel or when
passing under high voltage lines. Also,
noise can be picked up from passing
automobiles. Although AM is subject to
environmental noise, it has the ability to
be received at great distance.
This is due to the fact that broadcasting
signals follow the curvature of the earth
and are reflected back by the upper
atmosphere.
FM reception is just the opposite of AM.
It is not subject to environmental noise
and it does not have the ability to be
received at great distances (usually 30
miles). Also, the FM signal can be
blocked by tall buildings, mountains, or
hills.
To reduce the possibility of these
problems, ALWAYS FINE TUNE a station,
and if possible, set the antenna height to
30 inches.
Ignition
The most common source of noise in
reception is the ignition system. This is
normally due to the fact that radio is
placed relatively close to the ignition
system (engine). This type of noise can
be easily detected because it will vary in
intensity of pitch with the speed of the
engine.
Usually, the ignition noise can be
suppressed considerably by using a
radio suppression type high voltage
ignition wire and suppressor resistor in
the ignition system. (Most vehicles
employ this wire and resistor but it may
be necessary to check them for correct
operation.) Another method of
suppression is the use of additional noise
suppressors. These can be obtained
from most CB/Amateur radio or
electronic supply shops.
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