Motorola GM Series Installatiehandleiding - Pagina 25
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1.0
Introduction
Electrical noise generated by the electrical system of a vehicle, as well as local ambient noise, can
interfere with normal operation of mobile radios. Satisfactory operation of a mobile radio may require
slight or heavy noise reduction, depending upon the relative strength of the radio signal, and upon
the ability of the radio to reject undesired noise. These requirements vary from one vehicle to
another, depending upon the vehicle type and required coverage area. When operating in a strong
signal area, a certain amount of noise interference can be tolerated. In weak signal areas, however,
noise reduction becomes very important. As a rule of thumb, noise levels create greatest
interference in the 25-50MHz band and reduce with increasing frequency.
Before attempting any noise reduction procedures, determine the noise source(s). Then, follow a
logical, systematic method of elimination until the interference is eliminated or reduced to an
acceptable level.
CAUTION: Do not add interference elimination equipment to vehicles equipped with
!
electronic ignition systems before obtaining advice from the vehicle manufacturer. Addition
of some noise suppression components may interfere with proper operation of electronic
ignition systems and could seriously damage them.
Care and patience must be exercised in locating and eliminating noise sources. There may be
several sources of noise, each slightly stronger or weaker than the other. Elimination of one source
may seem ineffective because another noise source remains active at a barely discernible
difference in level. Consult a service manual for the vehicle to determine what noise reduction
provisions the manufacturer applies when AM, AM/FM, or CB radios are installed as original
equipment. These radios are also subject to electrical noise interference, and the manufacturer may
install noise suppression components only upon those vehicles which require radio equipment at the
time of manufacture. These noise suppression components should be added in any first attempt to
suppress noise.
1.1
Noise Sources
The three major noise sources affecting mobile radio systems are: (1) radiated noise, (2) conducted
noise, and (3) induced noise. (See Figure 2-1 Noise Sources for typical vehicular noise sources.)
1.2
Radiated Noise
Radiated noise enters the radio through the antenna along with the desired signal and can block or
degrade desired communication. It can be generated by power lines, fluorescent lights, or by
electrical discharges from static build-up, ignition systems, or electrical motors. Radiated noise is the
most common cause of mobile radio interference.
REDUCING NOISE INTERFERENCE
Chapter 2