Topband: Any Linrad selective limiter noise blanker experts here?

[Mike Waters]

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