Methods of Suppressing Automotive Interference

摘要

The purpose of this report is to (1) review the sources of electromagnetic interference (EMI) within a vehicle so that the reader will have a basic understanding of the EMI problem; (2) discuss the techniques that have been used successfully by the auto industry to suppress EMI, and (3) suggest some newer techniques for suppressing EMI within an automobile. The automotive manufacturers utilize several techniques to reduce EMI emanating from the vehicle. The techniques include resistor spark plugs, resistor spark plug cables, use of silicone lubricant in the distributor, use of capacitors as filters, placement of grounding straps at key locations, conductive fan belt discharge, and tire static-charge reduction. If even further reduction of MI is needed to obtain the maximum capability of a specific mobile communication system, there are additional suppression techniques discussed herein that can be employed to achieve this goal. These techniques are effective at frequencies from approximately 30 to 1000 MHz. Measurement results show that the EMI from a new production-line automobile, measured in accordance with SAE Standard J551g, can be reduced as much as 10 to 15 dB by employing these new suppression techniques. The amount of degradation to a mobile narrow-band FM receiver, such as the type used by law enforcement agencies, can be measured using the measurement technique described. This same technique can then be used as a tool to further reduce EMI from the vehicle components.