RadioBanter - View Single Post - Horizontal Dipole

Richard Clark · June 20th 09, 06:03 PM posted to rec.radio.amateur.antenna

On Sat, 20 Jun 2009 09:44:14 -0400, wrote:

Sure enough, changing to free space instead of a real ground changed
the pattern to what I would have expected. I would have thought being
many wavelengths above ground would be just as good as free space, but
EZNEC doesn't think so. Am I missing something? Does a horizontal
dipole really have a problem seeing a broadcast TV transmitter out on
the horizon? Thanks. ...Pat

Hi Pat,

EZNEC is presenting you with lobe characteristics that are at a very
great distance (and, yet, it has no sense of skip as that would be
tested in the domain of a propagation modeler). Zero degrees up to 10
degrees are minutely examined by those interested in skip, but this is
not a TV phenomenon (not to be confused with ducting which can offer
similar DX from great distances).

The horizontally polarized transmission has its E-Field parallel to
earth. Earth is a conductor (albeit a poor one, but in comparison to
free space, it is quite a short circuit). That E-Field's two
potentials are being laid across that conductor during the wave
propagation to that far point where EZNEC then sums up all field
contributions to present you with the lobe characteristic. It stands
to reason that at that great distance, the wave will have attenuated
considerably - hence the low value.

Removing the short circuit (going to free space) removes this
attenuation.

73's
Richard Clark, KB7QHC