Thanks for the book reference, Hal!
On Aug 24, 2007, at 4:48 PM, Hal Kennedy wrote:
> Concentric system:
>
> The problem with radials that simple radiate out from a central
> point is that they do not cover each square meter of ground equally
> well. They are spaced far apart at the ends and tightly bunched at
> the center. To get a ?really good? radial system it is sometimes
> recommended that 120 radials be used or the ends be no more than
> 0.02 wavelength apart ? broadcasters frequently use 120. For the
> first few feet from the tower its nothing but solid copper and most
> of this is wasted.
I understood that the current is densest near the radiator, and falls
off proportionally with the (square of the) distance. So the extra
conductivity near the center is actually doing something.
Some time ago on TowerTalk, I suggested a way to save on copper is to
start off with a small number of radials (8, lets say), and then fork
the radials once they reach 0.025 wavelength apart at the ends. This
would keep all the conductors within 0.25 wavelength of one another,
but use less wire than that required to put down concentric rings.
It's an interesting idea, but it seems like all the connecting joints
would likely require more labour than is worth it for the saving in
copper (although if copper gets much more expensive)
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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