[TowerTalk] W7PUA Tiny Ground Probe

[Jim Lux]

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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