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Re: Tesla Coil RF Transmitter

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


Original poster: Ed Phillips <evp@xxxxxxxxxxx> 

I think we can all agree that a grounded Tesla coil
without a Marconi-type antenna is a poor source of
radio waves, i.e., electromagnetic waves that have
closed back upon themselves and are no longer
associated with the antenna.

In my mind the questions to be answered are these:

1) Is a well-grounded non-sparking toploaded Tesla
coil operated in a CW mode at, say, 35 kHz capable
of producing locally a periodic disturbance in the
earth's electrical charge?


Depends on your definition of "earth's charge".  The coil
will certainly produce a local ELECTRICAL FIELD.

As noted by James Corum, et al in the paper "Concerning Cavity Q," PROCEEDINGS OF THE 1988 INTERNATIONAL TESLA SYMPOSIUM, and others, the earth possesses a naturally existing negative charge with respect to the conducting region of the atmosphere beginning at an elevation of about 50 Km. The potential difference between the earth and this region is on the order of 400,000 volts. Near the earth's surface there is a ubiquitous downward directed E-field of about 100 V/m. This is what I'm referring to when I use the phrase "earth's charge."

Tesla himself wrote about the possibility in creating disturbances in the field associated with this charge in the lecture "On Light and Other High Frequency Phenomena (http://www.tfcbooks.com/tesla/1893-02-24.htm), Franklin Institute, Philadelphia, February 1893, and National Electric Light Association, St. Louis, March 1893.

A point of great importance would be first to know what is the capacity of the earth? and what charge does it contain if electrified? Though we have no positive evidence of a charged body existing in space without other oppositely electrified bodies being near, there is a fair probability that the earth is such a body, for by whatever process it was separated from other bodies-and this is the accepted view of its origin-it must have retained a charge, as occurs in all processes of mechanical separation. If it be a charged body insulated in space its capacity should be extremely small, less than one-thousandth of a farad. But the upper strata of the air are conducting, and so, perhaps, is the medium in free space beyond the atmosphere, and these may contain an opposite charge. Then the capacity might be incomparably greater.

In any case it is of the greatest importance to get an idea of what quantity of electricity the earth contains. It is difficult to say whether we shall ever acquire this necessary knowledge, but there is hope that we may, and that is, by means of electrical resonance. If ever we can ascertain at what period the earth's charge, when disturbed, oscillates with respect to an oppositely electrified system or known circuit, we shall know a fact possibly of the greatest importance to the welfare of the human race. I propose to seek for the period by means of an electrical oscillator, or a source of alternating electric currents. One of the terminals of the source would be connected to earth as, for instance, to the city water mains, the other to an insulated body of large surface.

It is possible that the outer conducting air strata, or free space, contain an opposite charge and that, together with the earth, they form a condenser of very large capacity. In such case the period of vibration may be very low and an alternating dynamo machine might serve for the purpose of the experiment. I would then transform the current to a potential as high as it would be found possible and connect the ends of the high tension secondary to the ground and to the insulated body. By varying the frequency of the currents and carefully observing the potential of the insulated body and watching for the disturbance at various neighboring points of the earth's surface resonance might be detected. . . .

2) If so, at what distance from the TC transmitter can the
electrical disturbance be detected using a receiving
transformer of similar size?

What's the power and what's the detector sensitivity?

Let's start at 7.5 watts PEP and work up to 75 kW. We can use any LF communications receiver with a good front-end in conjuction with a precisely tuned receiving transformer with its secondary removed (see http://www.tfcbooks.com/tesla/images/wireless-08.gif).

3) If the disturbance can be detected at a multiple
wavelength distance from the launching structure,
does this distance increase with an increase in
transmitter power?

Certainly. 

I would expect so as well.

4) If the transmission-reception distance does, in fact,
increase with an increase in transmitter power, what
is the mathematical relationship between the two?

Gary 

The range should increase as the square root of the
power if no direct capacitive coupling is involved.

Ed

In other words, if the range is observed to increase at a greater rate than as the square root of the transmitter power, that would be evidence of capacitive coupling of the two elevated terminals. In the article "The True Wireless" (http://www.tfcbooks.com/tesla/wireless07.htm) Tesla indicates that the coupling between the elevated terminals of the transmitter and the distant receiver is indeed by electrostatic induction.

. . . by reference to diagram in Fig. 14 (http://www.tfcbooks.com/tesla/images/wireless-14.gif). The elevated terminal charged to a high potential induces an equal and opposite charge in the earth and there are thus Q lines giving an average current I=4Qn which circulates locally and is useless except that it adds to the momentum. A relatively small number of lines q however, go off to great distance and to these corresponds a mean current of I sub e = 4qn to which is due the action at a distance. The total average current in the antenna is thus I sub m = 4Qn + 4qn and its intensity is no criterion for the performance. The electric efficiency of the antenna is q/Q+q and this is often a very small fraction.

Gary