Topband: ANC-4 noise canceller

[Tom Rauch]

> This inspires me to ask a question, the answer to which I should
> probably know.  Suppose that the noise source is something like an
> arcing electric fence, where the RF is being generated at one location
> but propagates both directly to my RX and also down the fence line,
> from which it radiates as well.  Since the velocity factor of the
> fence wire is presumably different from open air, wouldn't this lead
> to some spreading in the phase of the interfering signal, limiting the
> effective cancellation that can be achieved?

A noise canceller can function two ways. 

It can make your antenna into a directional antenna that has a null 
towards the noise. Think of it as creating a phase and level 
adjustable two-element arrays. In this case you can cause a null to 
appear in any direction.

It can sample any single noise source, and feed that sample of noise 
out-of-phase in combination with signal and noise from an antenna.

The second case would work if the fence was close, the first if a 
long distance away. It would work even if the entire fence radiated, 
as long as it was one noise source (arc) in the fence. It would work 
with multiple arcs in one fence if the fence were a long distance 
away, because the antenna could null that entire direction. (But it 
would remove signals from that direction also.) 73, Tom W8JI
W8JI@contesting.com