Installation Manual

22
Chapter 10
Noise Reduction Techniques
10.1 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 may also provide noise suppression information which is
valuable in any first attempt at noise suppression.
10.2 Ignition System Interference
10.2.1 Engine Maintenance and Tune-Up
The most important step in reducing ignition noise is ensuring that the engine is in proper tune. Pay
particular attention to the following points if the noise interference from the ignition system is severe:
1. Be sure the spark plugs distributor points, and condenser are in good condition.
2. Be sure ignition timing is properly adjusted.
3. Be sure the distributor cap and rotor are in good condition. They should be replaced at least every
30,000 miles.
4. Be sure that spark plug wires make good, solid contact at each end and are routed as far as
possible from low voltage leads.
5. 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.
10.2.2 Available Noise Reduction Kits
Motorola offers one noise reduction kit: Model TLN5277 for alternator-equipped vehicles. This kit is for
suppression of noise in the primary and secondary of the ignition coil and for bleeding of static
charges on the hood. The TLN5277 also is used to suppress noise from the generator and voltage
regulator. Figure 9-1, on page 20 illustrates the kit’s usage.
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.