The concentric radial approach I mentioned I thought was discussed
within the 564 page book: Radio Antenna Engineering, by LaPorte. This
is a classic and good addition to anyone's antenna library -
particularly considering the price - free.
Go to www.lulu.com <http://www.lulu.com/> and type "Antenna
Engineering" into the search box. It's the first book returned in the
search. You can download all 33Meg for free.
Meanwhile, I can't find the particular radial approach I was thinking of
in the book, although many different radial schemes are discussed.
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. The
alternative is as follows:
Suppose you want a 64 radial system of 100 foot radials. Place a
concentric circular loop wire 33 feet out from the center and another 66
feet out from the tower. Connect 16 radials from the center to the fist
ring wire, 32 radial wires from the first ring wire to the second, and
64 wires outward from the outer ring wire to 100 feet. In all cases the
wires should be equally spaced around in azimuth angle. This system
will use around 55% as much copper as 64 full sized radials (I forget
the exact ratio) and yield the same performance. Soldering all the
wires to the ring loops however, is a lot of extra work. If its going
to be in or on the ground for a long time then regular solder should not
be used either - it should be silver solder.
73
Hal
N4GG
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