Earth Antenna

[Frank Eliot]

Gentlemen -

	I had a fun time talking about one of my passions last evening. Bill Liles sent me a note pointing out that in 1902, a Mr. Nathan Stubblefield broadcast music from two stakes on the shore to a boat in the Potomac. The receiver was two metal plates on the hull of the boat at a 1/3 mile range .

	I neglected to say this explicitly last night. I think that dirt antennas (that is, where currents forced into the dirt constitute the antenna, rather than buried wires), work because the dirt has an intermediate resistance. Its resistivity is low enough that you can force current to take a looping path through it, but high enough so that the one turn loop antenna EM wave is not too badly attenuated before it exits the ground. In the case of sea water, or even the slightly-salty Potomac, I suspect that propagation is purely via currents induced in the water, and not by either magnetic induction or radiation. I suspect that with a much higher powered transmitter than was available in 1902, and using narrow-band detection techniques, that range could be substantially increased.

Frank E