[RFI] Sense antenna for ANC-4 power line rfi?

[Jim Brown]

On 1/13/2021 6:15 AM, Dave Cole wrote:
> 
> You may find that the phase type noise reducers don't work so well on 
> power line noise...  It can help-- but mostly it will not be very 
> effective for distributed RFI sources.
> 
> The source of transmission can be distributed, (not in all cases), along 
> several hundred, to several thousand feet of power line.  This means 
> that depending on the distance traveled down the power line, the 
> distance to your sense antenna, and the distance to your main antenna, 
> RFI will arrive at different times, and hence different phase 
> relationships to each other, from every point along the power line that 
> carries the RFI.

Yes, this is excellent advice about noise cancellation. Phase is a 
function of both time and frequency, and in the case of noise, time is 
the result of the distance the noise wavefront travels to get to the 
noise canceller (in the air and in coax from the antennas). Physically 
large sources (as a fraction of a wavelength) cause result in the 
arrival of multiple wavefronts, spread out over time, thus with 
different phase. We can tweak the canceller to kill one, but not the 
others, or the others less well.

73, Jim K9YC