Motorola GM1200E Посібник з монтажу - Сторінка 31

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5.0

Noise Reduction Techniques

5.1

General

There are three basic ways to suppress noise. The ﬁrst is the addition of resistance in circuits

subject to ringing. This method is used for the ignition coil HV cable, spark plug wires, and spark

plugs. The second is to ﬁlter noise from low voltage wiring using coaxial bypass capacitors. The third

is to control static charge build-up using wipers for movable parts such as automobile hoods and

trunk lids, or ﬂexible bonding leads for ﬁxed members. Static in wheels may also be controlled using

collector rings. Applications of each of these techniques are discussed below.

The vehicle manufacturer's service manual also may provide noise suppression information which is

valuable in any 1st attempt at noise suppression.

5.2

Ignition System Interference

5.2.1

Engine Maintenance and Tune-Up

The most important step in reducing ignition noise is insuring that the engine is in proper tune. Pay

particular attention to the following points if the noise interference from the ignition system is severe:

Be sure the spark plugs distributor points, and condenser are in good condition.

Be sure ignition timing is properly adjusted.

Be sure the distributor cap and rotor are in good condition. They should be replaced at least

every 30,000 miles.

Be sure that spark plug wires make good, solid contact at each end and are routed as far as

possible from low voltage leads.

Many late-model automobiles are equipped with a shield over the distributor points. Check to

see that this shield is properly positioned and securely attached.

5.2.2

Available Noise Reduction Kits

Motorola offers two noise reduction kits; Model TLN8845A for alternator-equipped vehicles and

Model TLN6252A for generator-equipped vehicles. These kits are for suppression of noise in the

primary and secondary of the ignition coil and for bleeding of static charges on the hood. The

TLN6252A also is used to suppress noise from the generator and voltage regulator. Figures 2-3 and

2-4 show the contents of the kits and their usage.

Motorola also offers wheel static collectors (Motorola Part No. 1K534254-regular type and

1K563173-small type. Use of these items are described in section 5.8.

Most auto parts dealers can supply 0.05 µF bypass capacitors (condensers), resistive ignition wires,

and resistor spark plugs. The type of spark suppression used in noise reduction should always be in

accordance with the recommendations of the vehicle manufacturer, that is, if spark plugs are to be

replaced with built-in suppressor types, they should be in the proper heat ranges and thread sizes

for the particular engine. In each ignition system, there is a maximum amount of resistance that may

be connected between the distributor and a spark plug. If resistance-type ignition wire is used, the

length of each wire must be limited so that its resistance does not exceed the allowable maximum.

Reducing Noise Interference in Mobile Two-Way Radio Installations

Noise Reduction Techniques

2-7