An FM Car Radio Receiving System that Reduces Distortion Caused by Multipath Propagation

This paper describes a diversity receiving system for car radios which effectively reduces distortion caused by multipath propagation. The system consists of two antennas connected to FM receiving units, distortion sensing logic circuits, a stereo multiplexer, and a stereo amplifier. The input of the stereo multiplexer is switched between the two FM receiving units upon command from the distortion sensing logic circuits. One advantage of this system is that the distortion sensor allows the output level to correspond to auditory perception, thus assuring accurate selection between the two antennas. The effectiveness of diversity selection in reducing multipath distortion has been confirmed in a simulation experiment which was performed using distortion sensor output data that were recorded in a field trial.

An instantaneous high-cut control function for the audio signal is also incorporated into the system to eliminate any distortion that remains after diversity selection is performed.