Simplified Baseband Diversity Combiner

In conventional FM receivers, the gain of the limiters rises during a fade to maintain constant output. The resulting sharp rise in noise complicates the problem of diversity combining, requiring the combiner to provide a very high degree of suppression of noisy signals. By suitable limiter design, the necessary AM suppression can be obtained without affecting average receiver gain, permitting the use of simple linear addition at baseband for diversity combining. Cross coupling between limiters of a set of receivers maintains constant combined output. Receivers are simply connected in parallel to provide any degree of diversity. No additional circuits or components are used for the combining function, since operation does not depend on measurement of out-of-band noise. For the same reason, the system is not disabled by loss of pilot tones or by multipath distortion products of interference appearing as excess out-of-space noise. The performance of this combiner compares favorably with other presently used combining methods.