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Topband: Radial radiation - one last comment

To: <shr@swtexas.net>, <Topband@contesting.com>, <w2pm@aol.com>
Subject: Topband: Radial radiation - one last comment
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Mon, 3 Dec 2007 14:09:27 -0500
List-post: <mailto:topband@contesting.com>
This is actually important to think about.

> W2PM Writes:
>
> Aside from efficiency, I've always seen far more 
> re-radiated noise from
> elevated ground planes impacting weak signals on receive. 
> With a
> balanced, symetrical ground plane that theoretically 
> shouldn't happen I
> suppose but I've seen it here and going to ground radials 
> made a
> significant difference on the receive side.

One thing overlooked by proponents of sparse ground systems, 
by that I mean a system with only a few radials, is the 
radials will ALWAYS couple heavily into everything around 
them. The only way to reduce the nearfield intensity is to 
use more and more conductors.

Think of how an open wire transmission line works. The 
conductors must be very close spaced compared to the 
distance to things around them and a very small fraction of 
a wavelength spacing. The conductors not only have to have 
equal and exactly opposite currents, they must have equal 
and opposite voltages at every point! They also have to be 
very close together compared to the distance they are from 
the point of concern.

This why, even though we imagine it doesn't happen, a 
perfect 1/2 wave of wire tapped exactly in the center used 
as a counterpoise radiates. It radiates both in the near 
field and the far field. If we connect it to a big efficient 
antenna like a vertical antenna we might miss seeing the 
effect with the other dominant field, but it is there.

While there have been articles postulating that perfect 
current balance would reduce unwanted coupling, that isn't 
really a sensible theory at all. Minimum coupling most 
likely is with some amount of current unbalance. The 
exception might be an antenna over a perfect flat 
homogeneous earth with nothing, not even a feedline or 
normal earth, near the antenna or radials.

The way we catch mistakes is to directly measure what we are 
trying to describe. It is frustrating to see dozens of 
articles occupying hundreds of pages without a single good 
measurement of what each article proposes to define. One 
would think, at least on occasion, someone would measure 
something when proposing a new theory. We used to do that in 
the 50's and earlier, but now we largely have stopped. We 
live on emotional science or computer guesses.

Why do systems have noise issues? Because the radials are 
almost as good an antenna in the nearfield as the antenna 
itself. The only way to fix that is to move them away from 
other things, including the earth, or use a very large 
number of them. We might not like the idea we have to 
actually do work or spend money and time, but it's true.

73 Tom 


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