[TowerTalk] Topband: Ground Conductivity

[jimlux]

On 3/23/20 10:05 PM, Dan Maguire wrote:
> Grant wrote:
>>>> If you really want to know the parameters, see antennasbyn6lf.com as Rudy describes techniques for ground RF properties measuring.
> 
> Turns out that very subject was being kicked around on a recent qrz.com thread:
> 
> https://forums.qrz.com/index.php?threads/indirect-measurement-of-ground-constants-with-a-dipole.696955/
> 
> Dan, AC6LA
>

This was pretty well studied by George Hagn at SRI in the 60s/70s in the 
context of antennas for field use of HF and VHF in Vietnam and there are 
some publications out there. In fact, that's what led to the development 
of the Open Wire Line (OWL) technique.

The problem with a dipole measurement is that it measures a large area, 
and the answer you get is some unequally weighted average of the 
properties of the soil under the dipole.  I can't remember if it 
effectively weights the ends or the middle of the dipole more heavily.

The other problem is that it is affected by surrounding vegetation (i.e. 
anything within the near field potentially affects the numbers).  That's 
generally a smaller effect except in dense forest or jungle, and one can 
argue that what you're really looking for is a number to plug into a 
model for "environment"

That doesn't make it a bad technique, but one needs to understand what 
you're actually measuring and to what use you're going to put the 
numbers you've calculated.

For instance, if you're setting up a phased array, and you want to 
calculate Mutual Z (rather than measuring it) - you typically need soil 
properties on a finer grid.