Topband: Noise cancelers

[Tom Rauch]

> > I would tend
> > to think that even if the powerlines are reradiating
> > energy from a single discharge point, the vector
> > sum at your receiver should still looks like a single
> > source 
> 
> Yes, this is basically correct.  The key point is that in order to
> null the noise, there must be a stable RF phase relationship between
> the noise waveforms received in the main receive antenna feedline and
> in the noise "sense" antenna feedline.  This should be true as long as
> there is only a single noise generation source and the nulling only
> needs to be exact in a narrow bandwidth.


1.) Multiple noise sources can be nulled even if they are NOT the 
same waveform and level, as long as they come from the same 
direction and you have the sense antenna located near the main 
antenna....and both are somewhat far from the multiple noise 
sources. 

2.) Noises from a single source can be nulled fully even if the noise 
follows power lines and radiates from multiple points, if the sense 
antenna very clearly picks up the noise.

The MFJ series of noise cancelers are much better than other 
brands (assuming of course they are assembled correctly). They 
have much better phase adjustment range, and are much more 
amplitude-stable as phase is changed. It is quite easy to obtain 
50dB or deeper null on single groundwave noise sources.



73, Tom W8JI
W8JI@contesting.com