I think the issues is how much contribution there is from the ground path vs, the interconnecting wire laid on the surface.
?
Earth probes and amplifiers were extensively used during trench warfare in WWI, in order to eavesdrop on field telephones, that at the time used the earth as a return path for the single wire phone line. Twin wire was then introduced, and latterly the Fullerphone, with increasing development to further improve security.
?
?
The earth itself is a lossy dielectric medium, but at VLF it's mainly resistive, the ground conductivity, and underlying geology having a major effect on propagation.
?
50 or 60Hz mains "hum" and harmonics are a major issue, and extensive filtering is required to reduce their level.
?
There has been some amateur experimentation at around 8kHz, and transatlantic communications, at a very low data rate has been achieved.
?
Some interesting historical notes on underground VLF antennas, including loops, can be found here.
?
?
Regards,
?
Martin
?
?
On Wed, Feb 12, 2025 at 09:54 AM, John E. Burgar wrote:
I have been meaning to try an earth probe antenna here for over a year. I wanted to make one about 500' long with each end terminated by 8' copper coated ground rods.
