I have a strong source of 160 meter IX from another ham about a mile
away at a bearing 330 degrees. The key clix and pumping of the noise
floor make weak signal reception a real challenge at times. By using my
40 degree Beverage and a 3Khz roofing filter, along with turning the
pre-amps off and bringing I some attenuation seems to help for EU and
Africa. Unfortunately NA station are in the same direction as the IX
and the weaker ones are gone with the using this method toward Europe
etc. I have a MFJ 1026 noise canceller and haven't tried this yet but
would i get any benefit from put my 330 degree Beverage in the noise
port and trying to secure a null? Actually what I need is a noise
antenna that responds to ground wave, since the IX is all ground wave,
and then lets the sky wave arrivals come through from the same
direction. I don't know if such a design exists but I am even
considering a horizontal loop close to the ground for skywave arrivals
and the using something else for the null antenna. Is this even
practical to consider?
Herb Schoenbohm, KV4FZ
On 1/6/2015 7:57 PM, Tom W8JI wrote:
Finding a single RX antenna system that nulls the neighbor noise
sources at 90 and 270 degrees is proving to be a challenge.
If the noise sources are really at 90 and 270, and you have 30 feet or
more for spacing at right angles to that, it should be fairly simple.
Use a 180 degree out-of-phase array of two close spaced elements. If
you want to make it directional in the main response, it would take
two cells.
You could just use two small loops in line with the nulls oriented at
90 and 270, and phase them for a unidirectional pattern.
I could place a "noise antenna" next to each neighbor, mix the
equal-length feed lines together ( in phase ) for the noise source
null, and then place the actual receive antenna (in-line verticals,
loops, K9AY or Shared Apex ) right in the very center of my yard (
centered/equidistant from the noise antennas ).
It would not be that simple. You would have to match the levels, and
have a proper main antenna. You could do that with a "fader" at the
combiner and the correct main antenna, but it would be much more
simple to build a directive antenna with deep nulls to the sides.
Has anyone used multiple noise antennas feeding a single noise
canceling device?
I haven't. The odds of that working without independent phase shift
and level control from each noise antenna is somewhat low, because it
is unlikely the levels from sense antennas will independently have
equal phase and level relationships to the main RX antenna you are
trying to remove noise from.
You are assuming the relationship of noise at common for sense
antennas is the same phase and level relationship, allowing for some
rotation that can be compensated out, as to the main.
I don't think that is likely without some way to adjust each noise
sense antenna independently.
Far less complex would be using cells that null the sides where the
noise is (easy since they are 180 degrees apart).
If the individual cells do not hear the noise, they will not hear it
when combined.
Has anyone cascaded/combined a noise canceling device such as the
NCC-1 or MFJ-1026 with a traditional short RX vertical(s) array or
loop(s) or K9AY or Shared Apex?
I have and I'm sure many others have, also. The problem is you have
noise from two directions and two sources. The blessing is they are
180 degrees apart. If I were you, I would use a few small loops in an
array. Real small loops with deep axis nulls, not loops that are
configured to act as end fire verticals (K9AY, flag, pennant, etc),
would null 180 apart very deep.
This of course assumes the noise sources radiate from the directions
you indicated. That might not be where they really radiate from, that
just might be where the houses are. They might be radiating from
multiple places spread over a large area, like back-feeding power
lines with noise.
Are the utilities underground?
73 Tom
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