S/N Improvement of An FM Signal At or Near Threshold Due To De-Emphasis and Noise Weighting

An extension of the theory of FM threshold characteristics [2,3] to include the effects of de-emphasis and noise weighting networks is described. It is shown that S/N improvements at threshold due to the networks are several dB less than for a FM signal 3 dB or more above threshold. At the same time, the FM threshold increases by about 2 dB due to de-emphasis and noise weighting networks. These results are useful in designing satellite communications systems for television broadcasting using FM.