[TowerTalk] W7PUA Tiny Ground Probe

[Brian Beezley]

AB7E said:

"...I'd be most interested in trying to determine how deep the 
equivalent RF ground is for future modeling (because it certainly isn't 
at the surface of my dry Arizona hillside)..."

Dave, the RF ground begins at the surface, but it may extend well below. 
For a plane wave exciting uniform soil, ground current decays 
exponentially. It decays to 37% of the surface value at the skin depth, 
which is determined by ground permittivity and conductivity. By two or 
three skin depths the current has decayed to an insignificant value. You 
can see skin depth values for various kinds of soil at HF here:

https://k6sti.neocities.org/hfgc

The problem is that your soil is not necessarily uniform. The electrical 
characteristics may change gradually or suddenly. Stratified ground has 
layers of soil of different characteristics. NEC can't model that, and 
ground probes measure only the surface layer:

https://k6sti.neocities.org/sg

Using a low antenna to determine ground constants below the surface is 
an attractive idea. However, it has many problems. See the end of the 
stratified ground writeup for a brief discussion.

Brian