Re: Noise in receivers
There is some discussion of the phenomenon at interest in Langford-Smith. See pages 1229-1234 of the Classic edition.
I have excerpted a graph that is the subject of discussion therein. One receiver configuration had a “noise hump”, the other did not.
Not the only factor, but the incidence of AGC bias does appear to be a contributor here. How it is applied to the various stages (delay and proportion) could have an effect on the shape of the noise curve. That might help explain the apparent “no noise hump” FM curves. Where RF AGC was used on FM equipment, it was usually seriously delayed, so noise increase due to the early gain reduction of an RF stage, both reducing its own SNR and allowing the following stage noise to make a greater contribution, was unlikely.
Cheers,
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