Methods of Suppressing Automotive Interference

• NCJ Number: 81055
• Author(s): H Taggart
• Date Published: 1981
• Length: 15 pages
• Sponsoring Agency: US Dept of Justice; US Dept of Justice NIJ Pub
• Corporate Author: US Dept of Commerce
• Sale Source: US Dept of Commerce; National Institute of Justice/
• Language: English
• Country: United States of America
• Note: Limited number of free copies are available from National Bureau of Standards, Law Enforcement Standards Laboratory (LESL), Technology Assessment Program.

Annotation

This report presents a review by the National Bureau of Standards on techniques for suppressing a vehicle's electromagnetic interference (EMI) to mobile radio equipment such as that used in police vehicles.

Abstract

The findings are based on a review of previous work in this field, a visit to a jurisdiction with a severe electromagnetic interference problem and a partial solution, and the laboratory testing of a typical EMI problem and possible solutions. EMI, which reduces the range of communications equipment installed in vehicles, is generated by an automobile's ignition system, motors used for blowers, windshield wipers, buzzers used for ignition and seat belt warnings, and voltage regulators which use points that open and close frequently. Automotive manufacturers currently use several techniques to reduce a vehicle's EMI, including the use of resistor spark plugs, resistor spark plug cables, silicone lubricant in the distributor, and capacitors as filters. They may include placement of grounding straps at key locations, conductive fan belt discharge, and tire static-charge reduction. The auto industry uses the Society of Automotive Engineers's Standard J551g as a voluntary standard. To reduce EMI further, several alternative techniques are available. These include using a low-pass filter system to reduce ignition EMI and modification of the distributor through applying a dielectric material to the rotor segment or placing an additional electrode near the main gap of the rotor. These techniques are effective at frequencies from approximately 30 to 1,000 megahertz, but are easier to accomplish at the lower frequencies. Using these new suppression techniques, EMI from a new automobile can be reduced as much as 10 to 15 decibels. The amount of degradation to a mobile narrow-band FM receiver, such as the type used in police cars, can be measured with the technique described. This same technique can then be used as a tool to further reduce EMI from the vehicle components. Diagrams, footnotes, one table, a list of three references, and a bibliography containing eight sources are provided. (Author summary modified)