Noise Reduction Techniques; General; Ignition System Interference; Engine Maintenance And Tune-Up - Vertex Standard VXD series Installation Manual

Radiated noise must be attacked after conducted and induced noise has been satisfactorily sup-
pressed. The vehicle ignition system is usually the primary source of this interference. Antenna place-
ment can be critical in some installations. Remember that static discharge generates static or radiated
noise and will probably be generated only when the vehicle is in motion. Since radiated noise interfer-
ence is most noticeable in weak signal areas, it is suggested that suppression be finalized while listen-
ing to a weak "on frequency" signal. (The squelch should be "open" so that even marginal signals can
be heard.)

2.4 Noise Reduction Techniques

2.4.1 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 flex-
ible bonding leads for fixed members. Static in wheels may also be controlled using collector rings. Ap-
plications 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 first attempt at noise suppression.

2.4.2 Ignition System Interference

2.4.2.1 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:
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 ev-
ery 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.

2.4.2.2 Noise Reduction Kits

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 re-
placed 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 con-
nected 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.

2.4.2.3 Ignition Coil Interference

This type of interference is characterized by a popping sound which is most noticeable when the en-
gine is running slowly. To suppress the noise, connect a 0.1 μF coaxial capacitor from the battery side
of the ignition coil to vehicle ground (see Figure 2-3). This keeps the distributor noise from being con-
ducted through the battery lead into the electrical system of the vehicle. Note that some electronic igni-
tion systems do not route the battery lead to the ignition coil; proper operation of the ignition system
can be impaired if the"input" terminal is bypassed.
Chapter 2 Reducing Noise Interference
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