This is a very interesting thread! I thought I would share my own failed attempt at noise blanking from the early 1980s, when I spent my time on the low end of 2 meters. That way, nobody wastes their time trying to reinvent my "wheel".
My plan was to have one receiver tuned a few KHz off of the listening frequency on separate receivers with separate antennas. I would feed the two antennas through identical GaAs FET preamps into a narrowband hybrid ring combiner, in a manner where the worst of the line noise would cancel in the ring, leaving the desired signal high and dry. There was just one problem with that idea: *wideband noise is not coherent*. It's not identical when we tune up or down by even just a few Hz. Proof that the combiner actually was significantly nulling out the noise on two inputs came when I fed the amplified output of a wideband noise generator into a splitter, and fed its two outputs into separate ports on the ring. I slowly adjusted the RX frequency so that both receivers were tuned to exactly the same frequency. That indeed produced a very deep null (from S9+40 to an undetectable level!) but it was useless for reducing my line noise, as it also nulled out the desired signal! Later, I came up with a novel idea using a separate antenna, with some success. About that time, we sold our house in Toledo and bought one in a rural area, and I haven't pursued this in years. And I seriously doubt whether it would be nearly as effective on 160 as it was on VHF. (Long story.) 73, Mike W0BTU _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
