Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

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