Radio Operation - CG CAPTIVA 7 Owner's Manual

1B-12
Chapter 1B
AUDIO
RADIO RECEPTION
Due to varying reception locations, audio systems have performance limitations that
may on occasions create the impression that your radio is malfunctioning.
AM and FM
There are two types of radio broadcasts in Australia. Amplitude Modulation (AM)
in which the amplitude of the signal is varied to produce the sound and Frequency
Modulation (FM) in which the frequency is varied to produce the sound.
Range
AM broadcasts tend to follow the earth's curvature and also reflect from the upper
atmosphere which enables long range reception especially after sunset.
FM transmissions are basically line-of-sight (similar to TV signals) and are reflected by
buildings, mountains etc. but not by the upper atmosphere.
Interference
Interference is caused by local electrical disturbances. This can affect the amplitude of
the signal being received.
AM signals are more prone to this type of interference than FM signals. This type of
interference has little or no effect on the frequency of the received signal thus AM is
susceptible to interference from power lines, fluorescent lighting, neon signs, traffic
light control circuits, overhead tram wires and electrical storms.
With FM reception these amplitude variations are filtered out leaving a relatively clear
signal, (refer to Peculiarities of FM mobile reception below) making this one of the
major advantages of FM broadcasts.
Peculiarities of FM mobile reception
A mobile FM receiver can not be expected to continuously provide the quality of FM
reception you may have experienced on your home receiver. Contrary to popular
opinion, FM broadcasts are not static free, and although your new radio has a built-in
electronic interference absorption circuit some static will be evident from time to time
especially in areas without a direct line of sight to the transmitter.
Your radio is also equipped with a soft mute function. The purpose of this is to attenuate
the treble and audio level in weak signal areas to reduce the annoying background hiss
which is customary to weaker FM reception. There are two phenomena peculiar to FM
reception:
• Flutter – As FM signals reflect off solid objects it is possible to pass through areas
of SHADOW caused by tall buildings or hilly terrain which effectively blocks out the
signal. As the vehicle passes in and out of shadow areas the level of signal will vary
at a rapid rate, creating a flutter type of interference to the signal.
• Distortion (multipath) – Distortion may occur when the direct signal from the
transmitter and a reflected signal reach the antenna at the same time and either
cancel or aid each other, like ghosting on a TV. This results in intermittent distortion
of the signal while moving or constant distortion when stationary such as at a traffic
light or when parked.
Should this distortion occur while stationary, moving the vehicle approximately 1
or 2 meters would on most occasions correct the problem. Circuitry has also been
included in this radio to reduce this type of distortion.

RADIO OPERATION