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Re: Tesla Coil RF Transmitter



Original poster: "Gary Peterson" <gary@xxxxxxxxxxxx>


Original poster: stork <stork@xxxxxxxxxxxxxxxxxxx>

Does the current in the earth from the ground connection move as a conduction current . . . ?

Yes, true conduction current flows outward through the earth from a Tesla coil transmitter's ground terminal. Assuming a uniform texture and composition of the surrounding terrain, this current diminishes in strength equally in all horizontal directions as the distance from the terminal increases. This situation changes if an identically tuned Tesla receiving transformer is brought into operation at another location. In this case there is an increase in the current that flows from the transmitter's ground terminal and a conduction current passes through Earth in direction of the receiver's ground terminal.


. . . Is the earth itself a conductor or dielectric?

Earth is a heterogeneous body composed of many different elements combined together in a variety of ways. Tesla concluded that Earth is an excellent electrical conductor based upon a series of measurements he made between 1888 and 1907. He believed that electric current could propagate thousands of miles "without diminution of intention," and made observations that, he felt, supported this supposition. He also claimed that Earth's electrical charge can be made to oscillate, and that "by impressing upon it current waves [that is to say, surface waves] of certain lengths, definitely related to its diameter, the globe is thrown into resonant vibration like a wire, forming stationary waves."


Tesla felt that Earth's resistance is negligible due to its immense cross section and relative shortness as compared to its diameter. The key to good performance is a robust ground connection. Here is what he had to say:

"A [conducting] sphere of the size of a little marble offers a greater impediment to the passage of a current than the whole earth. . . . This is not merely a theory, but a truth established in numerous and carefully conducted experiments. ["The Future of the Wireless Art," Wireless Telegraphy & Telephony, Walter W. Massie & Charles R. Underhill, 1908, pp. 67-71, see http://www.tfcbooks.com/tesla/wireless03.htm]

". . . You must first understand certain things. Consider, for instance, the term "resistance." When you think of resistance you imagine, naturally, that you have a long, thin conductor; but remember that while resistance is directly proportionate to length, it is inversely proportionate to the section. It is a quality that depends on a ratio. If you take a small sphere of the same size of a pea, and compare its length with its section, you would find a certain resistance. Now you extend this pea to the size of the earth, and what is going to happen?

"While the length increases, say a thousand times or a million times, the section increases with the square of the linear dimensions, so that the bigger this thing is the less resistance it has. Indeed, if the earth were as big as the sun we would still be better off than we are; we could readily telephone from one end of the sun to the other by the system, and the larger the planet the better it would be. . . . The resistance is only at the point where you get into the earth with your current. The rest is nothing." [Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power, pp. 134-135]

While Earth is for the most part conductive, some of it's constituents are insulators. Two examples of naturally occuring dielectrics are quartz and mica. These minerals can exist as ore bodies. It is possible the position and size of such ore bodies might be deduced from changes in the waveform of the alternating electrical currents flowing around them during their passage between multiple Tesla wireless stations.

Gary