Telluric Currents (Earth Electricity) Introduction

Having gone to the trouble of driving in six 1.5m copper-coated steel rods for my Earth Current antenna (See the 8975Hz transmission experiment page), it occurred to me that it would be interesting to see if there was DC voltage difference between the two sets of rods (approx. 80m apart).   I simply connected the antenna to an R-C filter to get rid of the 50Hz mains noise and attached a Digital Volt Meter.   I was intrigued to see a residual voltage of approx. 40mV between the rods.

A quick check on the internet showed that this is a well-known phenomenon and is quite familiar to geologists using resistivity measurements to detect ore bodies beneath the surface of the earth.

The magnitude and orientation of the currents are apparently affected by changes in the Earth's magnetic field.    Telluric currents can induce significant potentials in man-made structures such as telegraph lines, intercontinental communication cables and pipelines.

I decided to use the data collection capability of my DVM (serial data out to a PC) to take some long-term measurements of this voltage difference.