Topband: Looking for 160m narrow beam RX advice - an interesting combination of ideas

[Tom W8JI]

The issue with just combining noise antennas is, to phase antennas, there 
have to be at least two phase shift and at least two amplitude-sensitive 
paths involved. At least one path through air, and at least path one through 
the wired connections.

Since you want to null two sources, you have two cable paths and four air 
paths involved, plus the main RX antenna complexities. Equal cable lengths 
to the canceller will not solve the problems typical in systems like this.

Could you install loops in a position where the loop nulls, which are pretty 
sharp, can be oriented to simultaneously null each unwanted direction, yet 
have good response in the directions of desired signals? Small loops (real 
loops) have a very sharp axis null and a broad even response in all other 
directions, so they are excellent for removing narrow direction noise.


----- Original Message ----- 
From: "Lloyd Berg - N9LB" <lloydberg at charter.net>
To: <topband at contesting.com>
Cc: "Tom W8JI" <w8ji at w8ji.com>
Sent: Wednesday, January 07, 2015 8:11 AM
Subject: RE: Topband: Looking for 160m narrow beam RX advice - an 
interesting combination of ideas


> Thanks for the input.
>
> Yes, utilities are underground, located by the road - north side of
> property.
> This is adjacent to the proposed RX receiving area.
> I can detect no noise coming from these underground lines.
>
> South side of the property (adjacent to my backyard transmit towers) is 
> idle
> farm land - no nearby noise sources.
> I can't put antennas on the farm property because of heavy snowmobile use 
> in
> the winter.
> Residents of my rural subdivision must cross the farm to get to the
> extensive snowmobile trail system.
>
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com]On Behalf Of Tom
> W8JI
> Sent: Tuesday, January 06, 2015 5:58 PM
> To: Lloyd Berg N9LB; topband at contesting.com
> Subject: Re: Topband: Looking for 160m narrow beam RX advice -
> aninteresting combination of ideas
>
>
>> 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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