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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