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Re: Elevation-dependent Interference



Hi all,

As Richard suggests, there is an azimuth component to the
effect.  Also an Elevation component, as it turns out.
While I haven't done a complete sweep of the hemisphere, it
seems like I've got several lobes of desense and notches with
lovely silence.  The worst lobe is at the horizon in a South-
Easterly direction, but there are others.  Nothing special
about what I'm pointing at, so it seems.

So, a theory - does this make sense?  Somewhere in the area
is a non-linear element that loves to be excited by 70cm
transmitters.  As I rotate the antennas in 2 dimensions, the
noise I am picking up depends on the antenna patterns of both
the 70cm CP yagi and the 2.4 ghz grill/helix.  Where the patterns
overlap *and* line up with the non-linear element I get noise.
Where either has a null, I get silence (especially if both do).

If true, how to find it?  Presumably, it's in the direction of
the maximum, but that's a bit problematic.  See, the rotors and
antennas are on the top of our 2-story house, which is built on
a sloped lot.  It's a good 30' drop if I take one step too many
in that maximum direction.  Mostly what's out there are some
trees, and maybe a squirrel nest or two.

How far away do you think this non-linear element is?  Are we
talking somewhere on my house, or could it be across the creek
in the neighbors' yard, or farther?  Anybody have any experience?

Greg  KO6TH



>From: Richard@g3rwl.demon.co.uk (Richard W L Limebear)
>Reply-To: Richard@g3rwl.demon.co.uk
>To: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] Elevation-dependent Interference
>Date: Thu, 30 Jan 2003 18:10:09 GMT
>
>  "Greg D." writes:
>
> > I've been having trouble with desense on AO-40.  Transmit
> > on 70cm, and the 2.4 ghz noise floor rises so far I can't
> > hear anything else.
> >
> > After some experimenting, I find that as the Elevation
> > heads towards the horizon, the desense problem rises.
>
>Hmmmm. One check would be to see if its azimuth-dependent too. I'm thinking
>about non-linear junctions (aka rusty nail syndrome) producing weird 
>effects
>(e.g. corroded local metalwork, towers, gutters etc). Find the best beam
>heading then go hit the metal joints it points at.
>
>Others will doubtless add their percieved wisdom.
>
>73
>Richard W L Limebear G3RWL
>g3rwl@amsat.org
>FOC # 1188
>
>           The floggings will continue until morale improves
>----
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