Guy Olinger wrote:
Careful here ... The presence of 0.4 wavelength buried radials turns the
ground underneath from the typically inferior Carolina medium into a
superior composite medium. Use of four elevated radials **over that
composite medium** is far superior to four elevated over 2-3-4 mS/m.
The NEC4.2 analysis linked below does not support the statements in the
above quote.
This analysis compares two 1/4-wave monopole systems over real earth of
conductivity 1 mS/m, d.c. 5 -- which probably is worse than the S. Carolina
antenna site under discussion..
One is driven against a set of four 1/4-wave horizontal wires at equal
spacing. The horizontal and vertical conductors are all elevated 4.9 meters
above the earth.
The other is driven against a set of 120 x 1/4-wave radial wires at 3-deg
spacing, buried 0.2 meters in the earth.
The two NEC models show no geometry or segment errors when run.
The peak gains of the two systems in these quickly-written models are within
0.5 dB of each other, and occur at the same elevation angle. Their gains
could have been made much closer to each other by trimming the monopole
heights a small amount.
A peak gain of 5.16 dBi occurred in the horizontal plane for the elevated
system over perfect earth, which is exactly as predicted for that system by
antenna theory.
Probably this illustration is sufficient to prove that elevated radials do
not need to be installed over a highly conductive ground plane in order for
the performance of the monopole using them to be the ~ equivalent of the
same monopole driven against a set of 120 x 1/4-wave buried radials.
http://s20.postimg.org/6hfsl64ml/Elevated_vs_Buried_Radials.jpg
R. Fry
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