On Wed,7/22/2015 6:15 PM, Al Lorona wrote:
This suggests that ground loss is sort of an impedance-matching problem.
Clearly, as your ground gets really bad your antenna can still work just fine,
even better in some cases!
Hi Al,
Several observations. First, soil influences vertically polarized
antennas in two ways.
First, loss in the soil near the antenna as the field from the antenna
causes current flow in the ground. The result is simple I squared R
loss, and that power does not get radiated.
Second is the reflection from the earth in the far field where the
radiated field hits it. That reflection adds (algebraically) to the
direct signal to form the vertical pattern. The strength of the combined
direct signal plus reflected signal depends on the relative phase angle
between them, which in turn is a factor of distance, the elevation
angle, and the soil.
The second point is that conductivity is not the only soil parameter.
There is also the dielectric constant. In EZNEC, if you open the Ground
Description tab and right click on either Cond or Diel Const, you'll get
a window showing a continuum of soil types from very good to very poor.
BOTH Cond and Diel Const vary with those soil types, and both quantities
affect how the antenna behaves.
A year or two ago, I did an extensive study of the interaction of
vertically polarized antennas with soil of different types and at
different mounting heights. I presented it to the Pacificon Antenna
Forum using these slides. http://k9yc.com/VerticalHeight.pdf
73, Jim K9YC
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