[RFI] MFJ-1026 Sense Antenna Strategy

Dan Zimmerman N3OX n3ox at n3ox.net
Wed Jan 31 06:15:41 EST 2007

I've got a noise coming from a (somewhat) nearby apartment building on
80m that I'd like to  null with my new MFJ-1026.

It seems, though, that everything I try to null the noise also nulls
signals from EU (more or less along the same heading as the building).

Is this simply a symptom of nulling a noise that's in the far field of
the antennas?  The building is about 2 wavelengths away from my
location on 80m.

The two antennas I've tried to use as the main antenna are my flag and
my 1/4 wave transmitting vertical.  I've tried a small  inverted-L
loaded with a low Q inductor, a small magnetic loop antenna,  an
unloaded short vertical and a 15m dipole as noise sense antennas.

I can achieve a null on the noise but not without reducing the
strength of EU stations considerably.

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.

Am I just stuck with a null in that direction if I want to kill it?
If so, is there a particular antenna setup that will make the null
quite narrow when used with a phasing unit like this?


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