This is at best a qualitative result. The actual topography
drastically impacts the fresnel lensing effects of ground on
propagation. It is to be used with caution. Without knowing
the actual conductivity of the soil and this geometry or
topography, it can have a really large effect on the pattern
and predictions of the pattern. The pro version is more
realistic but is still an idealization and a compromise.
Bob
N4HY
-----Original Message-----
From: topband-bounces@contesting.com
[mailto:topband-bounces@contesting.com]On Behalf Of John Kaufmann
Sent: Wednesday, November 12, 2003 5:13 PM
To: topband@contesting.com
Subject: Topband:
The "standard" version of EZNEC does not do ground wave calculations.
However, EZNEC-PRO (the more expensive version) does have this option and
when you enable it, you can see that antennas do have ground-wave response
at essentially zero elevation angle (towards the horizon). It's also
interesting to observe that the ground wave patterns of even simple antennas
like dipoles or delta loops do not always look like the far field patterns.
The reason is that these antennas actually transmit a vertically polarized
component of radiation. Because vertical polarization propagates much
better than horizontal over ground-wave distances, the ground wave patterns
of these antennas exhibit what appears to be distortion from the enhanced
vertical component. You can get significant off-axis ground-wave response
from dipoles or delta loops which doesn't show up in a far-field plot. This
can significantly influence how local vertically-polarized noise is
rejected.
73, John W1FV
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