[RFI] MFJ-1026 Sense Antenna Strategy

tom.mcdermott4 at sbcglobal.net tom.mcdermott4 at sbcglobal.net
Sun Feb 4 23:05:05 EST 2007

> Any ideas?  Would a long antenna like an on-ground wire pointed at the
> building and run up to a hundred feet away from it work?  Basically a
> BOG set to pick up the noise only?  I might be able to get away with
> that if I use small wire.
> So far I've had stellar results with the MFJ unit for noises that are
> obviously close by (like the switcher noise I can hear on a 15m dipole
> on 160m at s5 with no preamp).  I can kill these dead, but this
> particular 80m noise is the one I have the most trouble with.

Hi Dan,

I'm surprised you havn't gotten any answers so far. This would
be a good question on the topband mailing list as well (lot of experienced
people there on this type of question).

The noise cancellation technique works by effectively subtracting the
response of the noise-sense antenna from the main antenna.  If both antennas
have the same pattern, then the result of the subtraction is that nothing
is left.

Ideally, you would want the noise-sense antenna to hear the noise, but not
the European stations. Then the main antenna would hear both, and the
Subtraction (with proper phase compensation) should reduce the noise, but
Not the desired signals.

On 160 meters, it's difficult to get much of a pattern out of a small
antenna, so it's likely that both your antennas are realtively
non-directional. One
approach is to build a small rotatable loop antenna that has nulls in two
directions. If you use this as the sense antenna, and point it's null to
Europe, then it won't subtract out the desired signal from the main antenna
response. This assumes, of course, that the noise that's bothering you isn't
from the same direction as the desired signal!

	-- Tom, N5EG

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