[TowerTalk] W7PUA Tiny Ground Probe

[David Gilbert]

I recently did an EZNEC analysis of a vertical antenna fed against a 
square wire mesh instead of radials.  Like all radials, the mesh is just 
a counterpoise for tuning to resonance except that the resultant 
feedpoint impedance is lower than with longer radial(s). I previously 
posted the link to a YouTube video I did of it here.

The mesh is HEAVILY influenced by height above ground because basically 
the mesh acts like top hat capacity loading does for a vertical, or "top 
hat" capacity loading does for the ends of a dipole.  The EZNEC model I 
created simply used the default ground conditions, but it seems that an 
actual test of a vertical element fed against a defined mesh various 
distances above the surface might generate a plot of resonance that good 
be curve-shaped against EZNEC plots that used different soil constants 
as a way of working backwards to the actual soil constants.

In my case, 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) but maybe the conductivity 
and permittivity tell us the same thing.  I've never known whether EZNEC 
calculates an equivalent RF depth based upon the soil conditions or not.

73,
Dave   AB7E



On 3/4/2026 9:05 AM, Jim Lux wrote:
> Yeah.. the geophysical prospecting literature is full of things like this. And as you say, tends to be low frequencies (for them, using an AM broadcast station at 1 MHz is "high frequency").
>
> I'm particularly interested in higher frequencies to do things like building a model of the subsoil structure.
>
> I might just have to take a VNA and hook it up to some coils and try it.
>   
>
>
> On Wed, 4 Mar 2026 14:58:20 +0000 (UTC), RT Clay via TowerTalk<towertalk at contesting.com> wrote:
>
> Non-contact measurement of ground conductivity is a standard method in geophysics and archaeology. What is usually used is the "Slingram method". In that method, an AC signal is sent to a small coil, and the induced voltage is measured in a second sensing coil a short distance away. The effective depth of the measurement can be controlled by how far apart the coils are (typical distance between coils is 1-2 meters). In a typical measurement, the coils are placed on or just above the ground, and the device is moved to measure conductivity along a line or grid. A contour map of conductivity can then be generated to locate buried features. A long time ago I played around with one of these devices (my father is in archaeology).
> The problem with adapting this for use with antennas is that the analysis is done assuming the DC limit. Typical measurements are done at something like 10 KHz. A quick google search did find some work at getting this to work in the few-MHz region, but the analysis there is not simple.
> Tor N4OGW
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