Ever since FM radios became popular in automobiles, the phrase “well that's one of the limitations of FM” has been heard with respect to the annoying noises and distortions associated with mobile VHF reception. This paper deals with identification of the causes of these disruptions and minimization of their effects.
FIFTEEN YEARS AGO most markets were dominated by AM radio stations. While FM stations existed nearly everwhere in the U.S. at that time, their limited acceptance did not make quality reception in a moving vehicle the highest priority.
Since that time, FM radio has grown in popularity to the point where, in most markets, FM stations hold many of the top spots in the ratings. Because of this, customers are no longer satisfied with “that's one of the limitations of FM”.
With this in mind, most radio receiver and IC manufacturers have developed circuitry to eliminate or at least minimise the effects of these conditions. This paper is intended as an aid to the FM receiver designer in identifying the causes of interference and basic techniques for combating them. A summary of the causes of interference is presented first followed by a discussion of each interference, how to identify it, and means to minimize its effect.