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

[Herbert Schoenbohm]

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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