Guy Olinger wrote:
You can model a near perfect commercial grade radial field, with a radial
system apparent series resistance of a few tenths of an ohm, and NEC4 will
still come back with an overall loss of 3 to 4 dB.
This is ~true only for a "far field" analysis (as defined by NEC software)
for a vertical monopole -- which includes the propagation losses present in
the radiated fields from that monopole, over an infinite, FLAT, real-earth
ground plane.
However that is not reality.
Such NEC2 and NEC4 analyses have led many to invalid conclusions about
the low-angle radiated fields launched by vertical monopoles of 5/8WL and
less, and their potential for producing useful skywaves
Note that AM broadcast stations using a 1/4-wave monopole driven against a
"near perfect" radial field also produce an elevation plane field close to
that radiator that is "near perfect," which means that maximum field ALWAYS
occurs in the horizontal plane regardless of the conductivity of the earth
in which those radials are buried -- and not at some Takeoff Angle.
Reality is that the peak fields radiated (launched) by a monopole driven
against 120 x 1/2-wave and even 120 x 1/4-wave buried radials are
significantly higher in the horizontal plane than could be possible for "an
overall loss of 3 to 4 dB" -- and quite independently of the conductivity of
the soil in which they are buried.
The link below further develops this...
http://www.eham.net/ehamforum/smf/index.php/topic,86663.0.html
R. Fry
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Topband reflector - topband@contesting.com
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