[Elecraft] OT: Ground Loss (long)

[Jim Brown]

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