[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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