[Elecraft] RF Noise canceller ?

[Robert McGwier]

-----Original Message-----

Would this type of noise canceler not work on "white" noise also ?
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The simplest answer is no.  White noise typically arrives from random
directions, with random phases,  random polarizations, etc. etc. etc. and
are usually from thermal and uncorrelated sources.  The principle
of operation of these phasing units IS THAT THEY CAN BE PHASED to
eliminate unwanted signals since they are from a sufficiently point like
source that a null can be tuned on top of them.  How is this done?

You can arrange to add an interfering signal 180 degrees out of phase
with one from the intended antenna while not killing the signal of
interest to the point it is not heard.  In other words, you increase
the signal to (signal+interference) ratio.  To the extent that this
is automated, it is a "smart antenna".   The importance of them having
equal responses to the interferer so that simple phasing works is
a tricky business.  If amplification is required to do this, then
you have the myriad problems (IP3, IMD, DR, MDS, etc) to deal with
in this new system.  Since we are not asking for a perfect null,
but some serious suppression, these conditions can be relaxed.

If the noise source is localized or coming from a direction that is
not nearly collinear (within the 3dB beamwidth of say a directive
antenna) with the signal of interest, it can be nulled with these
phasing methods irrespective of its power spectral distribution,
white, poisson, tone, etc.


This is all reasonably complicated as you can see.

Bob
N4HY