The geometrical derived assumption that a sloping ground lowers the
radiation peak is probably valid when the terrain is good, its slope
moderate, free of discontinuities and extends for several wavelengths from
the antenna itself. Ground effect on vertically polarized antenna is quite
different from that on horizontally polarized ones since the image antennas
are or out-of-phase or in-phase. Meanwhile an horizontal antenna benefits up
to 6db of real gain at some elevation angles (and nulls at others to keep
E=mc^2) independly by ground constants, a vertically polarized quartewave
antenna hasn't any other chance than a maximum theoretical gain of 3 dB, at
low elevation angles and if ground is perfect.
Besides reducing losses, what a good ground does with a vertical antenna is
basically lowering the pseudo brewster angle. This angle is the elevation
angle were image antenna start to be out of phase of the real one and thus
producing a detrimental effect instead of a signal enforcement.
A vertical placed on the top of a sharp hill is often more comparable to a
largely elevated monopole with his artificial groundplane than to a vertical
placed over a sloping ground.
73,
Mauri I4JMY
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|