There's no need to ridicule measurements of soil resistivity just
because at a deeper layer there is a strata of different resistivity.

Any information is far better than complete ignorance.

Roy, you are just displaying your knowledge of geology.

Obviously, in practice it is the resistivity of the top layer which
predominates anyway.
----
Reg.

Reg Edwards wrote:
There's no need to ridicule measurements of soil resistivity just
because at a deeper layer there is a strata of different resistivity.

Any information is far better than complete ignorance.

Roy, you are just displaying your knowledge of geology.

Obviously, in practice it is the resistivity of the top layer which
predominates anyway.


The top layer here Reg is about one to six inches thick of rich
pastorial soil. Below that is a layer of red clay with high iron
content than can be a few feet or dozens of feet deep, and mixed or
below that are various rocks. At places the rock is at the surface.

Measurements of a ground rod at various places on my farm show anything
from 50 ohms to 500 ohms for a four foot rod measured against a
reference antenna.

What value should I use Reg that would be better than a guess? In the
areas where soil is very dry on top but has wet soil below rock, should
I use the rock or the soil below it?

The fact is the method using multiple ground rods produces numbers that
might have agreed with soil characteristics at the test site, but they
produce some very wild numbers other places. I've seen that method
produce conductivities of over 40mS/m where ground wave attenuation
measurements have shown effective conductivity to be 10-15mS/m.

One fellow on 160 is particularly proud he has 45mS/m soil while his
friend 100 miles away has 5mS/m. The only problem is no one can tell
any difference in their signals, and there isn't any soil in that area
that is over 20mS/m in the AM BC band.

I tghink the best way to estimate conductivity is to measure impedance
of a dipole at low heights, and adjust the modeling program until
impedances match. That certainly seems more reasonable than using 60 Hz
AC on a short ground rod.

73 Tom