First-Hand:AM Noise Reduction System

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AM Noise Reduction System

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My story begins at Georgia Tech in 1946 with work toward a masters degree in EE.

I pursued the idea that noise reduction might be accomplished in an AM system by using two adjacent channels modulated in phase opposition. I searched all past issues of the IRE Proceedings going back to its beginning to see if the idea had been tried before and if so what problems might exist. The idea seemed to have the “all clear” but I found some mighty interesting papers in the search. Among them was early work at NRL (I think) on transmission effectiveness on system grounding by laying a conductor on the bottom of the Potomac River and multi strand antennas with hoops along them. Of greatest interest to me was work of Armstrong.

I built a transmitter and receiver of modified WWII surplus aircraft equipment to demonstrate the idea. It worked to some degree and had the advantage of a larger ratio of sideband to carrier power in one case than the conventional AM method. I thought the system might be of academic interest whether or not commercially. I did not publish a paper on the idea, but wish I had, nor consider trying for a patent.

Submitted by John L. Markwalter, Jr.