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TESLA ON GLOBAL WIRELESS ENERGY TRANSMISSION
FOR TELECOMMUNICATIONS AND OTHER PURPOSES

With Additional Comments by Henry Bradford and Gary Peterson

 

Atmospheric Conduction Method

Energy Transmission By Means of a Spherical Conductor Transmission Line With an Upper Half-space Return Circuit.

     Tesla's ideas about electrical conduction through the "natural media" fall into two categories: closed circuit and open circuit. [Henry Bradford]

In 1932 journalist John J. O’Neill conducted an interview with Tesla in which he talked about the difference between the wireless transmission of electric energy using what Mr. Bradford describes as either “closed circuit” or “open circuit” principles.

I also asked him if he is still at work on the project which he inaugurated in the '90's of transmitting power wirelessly anywhere on earth.  He is at work on it, he said, and it could be put into operation. . . . He at that time announced two principles which could be used in this project.  In one the ionizing of the upper air would make it as good a conductor of electricity as a metal.  In the other the power is transmitted by creating "standing waves" in the earth by charging the earth with a giant electrical oscillator that would make the earth vibrate electrically in the same way a bell vibrates mechanically when it is struck with a hammer.  "I do not use the plan involving the conductivity of the upper strata of the air," he said, "but I use the conductivity of the earth itself, and in this I need no wires to send electrical energy to any part of the globe." [“Tesla Cosmic Ray Motor May Transmit Power 'Round’ Earth,” Brooklyn Eagle, July 10, 1932.]

     The closed circuit system consists of a large Tesla coil transmitter, an ionized path connecting the transmitter to the upper atmosphere, the upper atmosphere, a second ionized path connecting the upper atmosphere back down to a receiving location, and the receiver itself.  The circuit back to the transmitter is completed through the earth.  The upper atmosphere, like any low-pressure gas, is not an ohmic conductor, but will conduct electricity if broken down; i.e., ionized.  The portion of the upper atmosphere between the transmitter and the receiver would then conduct current like a neon tube of planetary proportions.  It would require a certain amount of energy to maintain the electrical discharge through it. 

The earth is 4,000 miles radius.  Around this conducting earth is an atmosphere.  The earth is a conductor; the atmosphere above is a conductor, only there is a little stratum between the conducting atmosphere and the conducting earth which is insulating. . . . Now, you realize right away that if you set up differences of potential at one point, say, you will create in the media corresponding fluctuations of potential.  But, since the distance from the earth's surface to the conducting atmosphere is minute, as compared with the distance of the receiver at 4,000 miles, say, you can readily see that the energy cannot travel along this curve and get there, but will be immediately transformed into conduction currents, and these currents will travel like currents over a wire with a return.  The energy will be recovered in the circuit, not by a beam that passes along this curve and is reflected and absorbed, . . . but it will travel by conduction and will be recovered in this way. [Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power, Leland I. Anderson, Editor, Twenty First Century Books, 1992, pp. 129-130.]

In operation, the electrical energy flowing through the atmospheric conductor is characterized by its high voltage and low current, and through the terrestrial conductor by its high current and low voltage.  For any given power level, the loss in the atmospheric plasma transmission line is proportional to the value of the resistance (R) of the ionized path between the two stations, and inversely proportional to the amount of current (I) flowing along this path.  The voltage drop (E) across R is given by Ohm’s law, E = IR.  There is an inverse relationship between voltage and current, so for any given load, increasing the transmission line voltage reduces the current.  Looking at this relationship a different way, real power in a transmission line is dissipated as heat due to the resistive element R impeding the flow of electrons.  Decreasing the current or rate of flow of electrons through the conductor results in fewer electron 'collisions' resulting in less energy dissipation in the form of heat.  Thus, for any given load with a constant transmission-line resistance, reducing the current that flows through the transmission line also reduces the voltage drop.  This reduction in end-to-end voltage drop equates to greater transmission-line efficiency. [See I2 R, Double Proportion of Resistance to Power.]

In Tesla’s words,

. . . by such means as have been described practically any potential that is desired may be obtained, the currents through the air strata may be rendered very small, whereby the loss in the transmission may be reduced. [SYSTEM OF TRANSMISSION OF ELECTRICAL ENERGY, Sept. 2, 1897, U.S. Patent No. 645,576, Mar. 20, 1900.]

Tesla’s wireless transmitter-receiver station was designed to develop extremely high potentials on the elevated terminal in order to minimize the loss due to the atmospheric plasma transmission line resistance.  Another characteristic of the Tesla apparatus is that a high current flows in the conductor that connects the oscillator to the earth.  Looking at an entire atmospheric conduction system, each of the transmitter-receiver stations serves, in a sense, as a lever and a fulcrum that impedance matches the heavy-current power flowing through the terrestrial ground path with the high-voltage power flowing through the atmospheric path. [Kenneth L. Corum and James F. Corum]

     An independent power source is required at the receiving location to sustain the conducting path to the upper atmosphere.  Both the transmitter and the receiver have to be capable of ionizing the upper atmosphere out to some distance, in much the same way that a corona discharge ionizes the air out to a radius at which its electric field falls below the breakdown value for air, or the leader in a lightning discharge ionizes the air ahead of the bolt.

Tesla described the ionization process like this:

For example, a conductor or terminal, to which impulses such as those here considered are supplied, but which is otherwise insulated in space and is remote from any conducting-bodies, is surrounded by a luminous flame-like brush or discharge often covering many hundreds or even as much as several thousands of square feet of surface, this striking phenomenon clearly attesting the high degree of conductivity which the atmosphere attains under the influence of the immense electrical stresses to which it is subjected.  This influence is however, not confined to that portion of the atmosphere which is discernible by the eye as luminous and which, as has been the case in some instances actually observed, may fill the space within a spherical or cylindrical envelop of a diameter of sixty feet or more, but reaches out to far remote regions, the insulating qualities of the air being, as I have ascertained, still sensibly impaired at a distance many hundred times that through which the luminous discharge projects from the terminal and in all probability much farther. [SYSTEM OF TRANSMISSION OF ELECTRICAL ENERGY, Sept. 2, 1897, U.S. Patent No. 645,576, Mar. 20, 1900.]

Both wireless stations would be individually capable of ionizing the upper atmosphere in their vicinities out to distance that is based upon four physical parameters.  Tesla identified these as the “electromotive force” of the transmitted impulses, the atmospheric density, the height of the elevated terminal above the ground, “and also, apparently, in slight measure, . . . the degree of moisture contained in the air.”  By using a vertical ionizing beam of ultraviolet radiation the requirement for very tall towers is reduced.

I have also found it practicable to transmit notable amounts of energy through air strata not in direct contact with the transmitting and receiving terminals, but remote from them, the action of the impulses, in rendering conducting air of a density at which it normally behaves as an insulator, extending, as before remarked, to a considerable distance. . . . [Ibid.]

The region from the upper troposphere and upward, located between the transmitter and the receiver, would become available as a conductor by inducing the plasma state within that region. This is the “aurora” effect described by Tesla in the 1916 interview.

I have constructed and patented a form of apparatus which, with a moderate elevation of a few hundred feet, can break the air stratum down. You will then see something like an aurora borealis across the sky, and the energy will go to the distant place." [Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power, 1992, p. 110.]

Tesla also spoke about instances in which the connection between the elevated terminals is, in part, by electrostatic induction.

In some cases when small amounts of energy are required the high elevation of the terminals, and more particularly of the receiving – terminal D, may not be necessary, since, especially when the frequency of the currents is very high, a sufficient amount of energy may be collected at that terminal by electrostatic induction from the upper air strata, which are rendered conducting by the active terminal of the transmitter or through which the currents from the same are conveyed. [SYSTEM OF TRANSMISSION OF ELECTRICAL ENERGY, Sept. 2, 1897, U.S. Patent No. 645,576, Mar. 20, 1900.]

This means that a wholly conductive path between the transmitting and the receiving stations is not an absolute requirement.  A portion the transmitter’s energy can be collected at the receiver by electrostatic induction alone.  This also suggests that a flow of energy may occur between the two high-altitude ionized regions by means of electrostatic induction, that is to say, by so-called displacement current.  Once the initial station-to-upper-atmosphere connections are established by the means of displacement current and electrical conduction through the vertical ionized paths, each high-altitude ionized region grows in size in the direction of its counterparts with the passage of time,

I have likewise observed that this region of decidedly-noticeable influence continuously enlarges as time goes on, and the discharge is allowed to pass not unlike a conflagration which slowly spreads, this being possibly due to the gradual electrification or ionization of the air or to the formation of less insulating gaseous compounds. [Ibid.]

     To accomplish this would be a stupendous undertaking.  It strikes me that Tesla’s concept of transmitting electric power wirelessly via electrical conduction through a closed circuit consisting of the earth and the atmosphere is not promising from a practical viewpoint.  This is because of the enormous voltages needed to reach to useful distances from the transmitter through the atmosphere, and the power requirements for maintaining the air path in an ionized state.

Wireless power transmission by means of the atmospheric method appears to be feasible.  It can be accomplished exactly as Tesla said it could without violating the known laws of physics.  Perhaps it has not been adopted for economic reasons, and because certain basic engineering challenges that Tesla addressed while developing the system have not been revisited.  Perhaps the point-to point atmospheric conduction method is simply impractical.

I [have] contemplated the possibility of transmitting . . . high tension currents [on the order of twenty million volts] over a narrow beam of radiant energy ionizing the air and rendering it, in measure, conductive.  After preliminary laboratory experiments, I made tests on a large scale with the transmitter referred to [in Colorado Springs] and a beam of ultra-violet rays of great energy in an attempt to conduct the current to the high rarefied strata of the air and thus create an auroral such as might be utilized for illumination, especially of oceans at night.  I found that there was some virtue in the principal but the results did not justify the hope of important practical applications. [The New Art of Projecting Concentrated Non-dispersive Energy Through Natural Media.]

Tesla spoke about the commercial establishment of a wireless system in which the transmitted energy is utilized in at least three different ways—high-frequency lighting, turning electric motors, and wireless telecommunications.

     Wireless communications is not as demanding as the transmission of power.  Tesla seems to have favoured carrier frequencies in the range of tens of kilohertz or so, which would be reasonable for transmission of information at a useful rate.  He had in mind transmitters and receivers as those shown in his patent drawings, communicating through the earth via current from the ground terminal of the transmitter and the partially or wholly ionized path described above.  This raises the question of whether the current from the ground terminal of a Tesla transmitter, which definitely would exist, would have a range comparable to or greater than that of a radio wave from a radio transmitter of the same power and frequency, and the induced earth current that would accompany it.

     The principal difference between Tesla’s system, either closed or open circuit, and open circuit low frequency radio systems is that a radio transmitter is designed primarily to emit energy in the form of electromagnetic radiation from its antenna, whereas the Tesla communications transmitter is designed primarily to inject an electrical current into the earth at its ground terminal.  The mode of propagation for both systems appears to me to be the same; i.e., earth currents and surface charge coupled to a vertical electric field in the Earth-ionosphere cavity. 

Mr. Bradford describes the mode of propagation for both the Tesla system and LF radio systems as, “earth currents and surface charge coupled to a vertical electric field in the Earth-ionosphere cavity.”  While this is not a description of space wave electromagnetic radiation, it is, however, consistent with the definition of the electromagnetic field associated with an electrical current flowing through a transmission line.  Of course there is also a space wave component associated with the emissions of an LF radio transmitter in the form of electromagnetic radiation launched from its antenna.  Tesla argued the emissions from the great low frequency AM radio transmitters of the early 20th century were, predominantly, in the form of transmission line surface waves.

     The principal difference between the Tesla-produced and radio-produced disturbances appears to be the difference in the configuration of currents and fields close to the transmitter.

The basic idea is that the earth currents and charge-coupled electromagnetic field associated with Tesla coil transmissions gradually decouple from the associated charge carriers and become ordinary radio waves as a function of the distance from the transmitter.  Mr. Bradford states,

     I do not believe that the theory for it has been worked out, but in principle it is a straightforward application of electromagnetic theory.

An alternative hypothesis is one in which the configuration of the electromagnetic field associated with an ordinary radio antenna changes as it moves out of the near-field zone, as described by presently accepted antenna and propagation theory, while the configuration of the electromagnetic field associated with a Tesla coil transmitter remains essentially unchanged as it moves out beyond the near-field zone, through the far-field zone, all the way to a well grounded phase-conjugate or synchronized Tesla coil receiver.

There are two distinctly different forms of electromagnetic-wave propagation.  The first is by means of electromagnetic radiation or ordinary radio waves, such as emitted by an ordinary dipole radio antenna.  The second is by ordinary electrical conduction, such as takes place when a current flows through a transmission-line accompanied by a charge-coupled electromagnetic field.

There are two types of transmitter-antenna excited propagation modes.  The first is by means of an ordinary radio wave launched by a dipole antenna in the form of electromagnetic radiation.  The second is by means of a charge-coupled transmission-line wave launched by a high voltage, pulse-driven, top loaded helical resonator in the form of earth currents and a charge-coupled electromagnetic field.  A small radio-wave component might also be present, but this is viewed as an energy loss.  What might be called a hybrid propagation mode is a combination of the radio wave and the charge-coupled electromagnetic transmission-line wave launched by a grounded or counterpoise monopole antenna, i.e., the Marconi-type antenna, the emissions of which more or less predominate as electromagnetic radiation plus an electromagnetic transmission-line wave component.  In addition to space waves, Marconi antennas also appear to launch the type of transmission-line or surface wave described by Arnold Sommerfeld and Johann Zenneck.  This surface wave is different from the well-known Norton Surface Wave that is the result of the interaction of the ground wave part of a radio antenna’s radiated space wave with the earth’s surface.  There may be an interaction between the Zenneck and Norton surface waves which occurs along the interface between the two half-spaces resulting in the creation of an interference pattern extending outward around the launching structure.

     My guess is that at very large distances from the transmitter, the two disturbances would be indistinguishable.

If, as predicted, the disturbances produced by the two launching structures are distinctly different then the effects at a distance will be very much distinguishable.  In fact, the emissions of a refined Tesla coil transmitter in the far-field zone should be practically undetectable when using an ungrounded radio receiver with a balanced magnetic loop antenna; quo erat demonstratum.

     So it would boil down to which method of producing the disturbance is the most efficient and cost effective.  One disadvantage of very long distance radio is that VLF transmitting antennas tend to be very large and inefficient, which is one reason why long distance radio communications mostly switched from long wave to short wave in the 1930's.  One thing bothers me.  If the Tesla earth currents propagate to long distances at low frequencies, why don't the earth currents from the ground terminals of low frequency radio transmitters do likewise, or do they?

According to Tesla they do.  Some portion of the earth current associated with the excitation of a well-grounded LF radio-transmitting antenna propagates to great distances.

Counsel
 You say radio engineers put too much energy into the radiating part. What, as a matter of fact, according to your conception, is the part of the energy that is received in the receivers in the present system? . . . To illustrate my question, take for instance the energy used at Sayville [Long Island, New York] and the reception of that at Nauen [Germany]. I want to know whether it is your idea that the reception there is due to the earth currents that you have described or to the radiated energy.

Tesla
It is far more due to the earth currents than to the radiated energy.  I believe, indeed, that the radiated energy alone could not possibly produce the effect across the Atlantic.  It is simply because they are incidentally sending a current through the globe—which they think is their current—that the receiver is affected.  The current produces variations of potential at the earth's surface in Germany; these fluctuations of potential energize the circuit, and by resonance they increase the potential there and operate the receiver.  But I do not mean that it is absolutely impossible to use my apparatus and operate with electromagnetic waves across the Atlantic or Pacific.  I only say that according to calculations, for instance, which I have made of the Sayville plant, the radiated energy is very small and cannot be operative.  I have also calculated the distribution of the charge on the antenna.  I am told that the Sayville antenna is without abrupt changes of capacity.  It is impossible.  There are changes even in a cylindrical antenna; but particularly in that form at Sayville—there are very abrupt changes. [
Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power, p. 142.]

     A grounded radio transmitter generates an earth current, and observations of it might help to answer questions about the range of earth currents.  However, distinguishing current from the ground terminal from earth current induced by the radio wave (or part of the wave, depending on how you look at it) might be difficult.  The two types of earth current might be distinguishable because earth current from the ground terminal of a radio transmitter should be free from the variations in the strength of the radio wave (e.g., day-night) caused by the ionosphere.  I am not aware of such observations.  On the other hand, VLF to MF radio transmitters often use some sort of counterpoise instead of a ground connection, and do not produce an earth current directly.  The most reliable answers would come from a computer analysis.

Freely speculating for a moment, perhaps a powerful Tesla coil earth resonance transmitter operated at a non-earth-resonance frequency might result in the creation of radio waves somewhat as predicted by Mr. Bradford.  In the operation of a Tesla coil transmitter, earth resonance results from the constructive interference of outgoing Tesla waves with the reflection of preceding Tesla waves returning from the antipode.  If the transmission frequency were to be adjusted away from being purely constructive, then radio waves might result.  Going out on a limb even further, rather than a gradual transition from Tesla waves to Hertz waves with an increase in distance from the transmitter, the radio wave emissions might be global in nature and ubiquitous.

"The chief engineer shook his head slowly, "all radio stations went off the air at seven-fifty-one, and nobody can discover why.  We've called the electronic laboratory of the State Science Institute.  They said it looks like radio waves, but of a frequency never produced before, never observed anywhere, never discovered by anybody.  It looks like a wall of radio waves jamming the air, and we can't get through it, we can't touch it, we can't break it.  What's more, we can't locate its source, not by any of our usual methods.  Those waves seem to come from a transmitter that makes any known to us look like a child's toy!  That's it, Dr. Stadler, it can't be possible, it shouldn't be possible, but there it is." [Atlas Shrugged]

     Ionospheric effects like the day-night variations indicate that the radio signal received is mainly accounted for by radio waves.  Is it that low frequency radio transmitters generally use counterpoises rather than actual earth connections?  Is it that the currents from the ground terminals of the transmitters (as opposed to induced currents in the electrical disturbance in the Earth-ionosphere cavity; see the next section) do not propagate to a significant distance?  Once again, the answers to these questions, like all the other questions, could be found theoretically by straightforward computations made on a realistic model of the transmitter, receiver, and intervening medium.

Construction and operation of full-size Tesla transmitting and receiving apparatus, as described in his patents and elsewhere, will also facilitate this computer analysis.  The creation of a realistic model demands the collection of empirical data related to the performance of actual functioning Tesla coil transmitters, and active and passive Tesla coil receivers.  At the same time these data were being collected it can also be shown that radio waves are not involved with the transfer of electrical energy between the Tesla transmitting and receiving stations.  This can be done using a radio receiver with a balanced magnetic loop antenna, tunable to the Tesla coil transmitter's operating frequency.  The radio receiver's antenna can be configured in such a way so it interacts more efficiently with radio waves than with the non-radiating emissions of the Tesla coil transmitter.  Grounded monopole and low-counterpoise radio antennas cannot be used.  Even the vertical 1/2-wave dipole antenna, with or without loading coils and suspended high above the ground to minimize capacitive coupling to the earth would be compromised in its performance.

The Schumann Cavity Resonance Hypothesis

Proposed Energy Transmission By Means of a Concentric Spherical Shell Waveguide

Tesla spoke about the wireless transmission of electric energy utilizing some type of terrestrial resonance mode.  Three different forms of terrestrial resonance have been identified.  These are the “single-wire transmission line” resonances (for lack of a better term), the transverse cavity resonances, and the Schumann cavity resonances.  As their names suggest, the latter two are resonances that can be excited in the concentric spherical shell waveguide formed from the earth and the ionosphere.  Of these three, only transmission systems utilizing the transmission line resonances and the Schumann resonances are under consideration for power transmission.  Both mechanisms fall under Mr. Bradford’s so-called “open circuit" category.

     Natural lightning excites the Schumann resonances.  They are observed at the lowest few resonance frequencies (about 8 Hertz and multiples of that).  Their measured Q's of order 5 - 10 suggest that the electrical disturbances produced by lightning make a few circuits of the Earth before damping out, and create a fairly definite terrestrial standing wave of a few cycles duration.  What is wanted for wireless transmission of power is for the electrical load connected to the receiver to draw power from the transmitter via the standing wave.  I.e., when the load is switched on, the transmitter should "feel" the load, as it would in a closed circuit, and respond by providing more power via the standing wave.  According to my estimates, this would require an Earth-ionosphere cavity Q of order ~10^6 or 10^7 at the lowest Schumann resonance frequencies, whereas it appears the actual value is more like 5 or 10.  Cavity Q is defined here as the ratio of the electric field energy stored in the Earth-ionosphere cavity per cycle of the oscillation to the average power input to the cavity from the transmitter.

     This estimate of the required Q is based on the requirement that the current induced in the input impedance of the receiver should reciprocally induce power in the output impedance of the transmitter similar to the power that was transmitted initially.  This is a way of expressing the coupling between the transmitter and receiver required for the transmitter to "feel" the load on the receiver.  The Q in my estimate is the value that produces an electric field in the cavity strong enough to induce the required current in the input impedance of the receiver.  At higher frequencies, the required Q is larger, but I expect that the Q of the Earth-ionosphere cavity probably decreases because propagation losses in the Earth and ionosphere increase.  So my opinion is that Schumann electrical oscillations would not allow efficient transfer of power from the transmitter to the receiver over long distances.

Conclusions

     The concept of transferring power with small losses in this manner will not work because the standing wave would occur in the Earth-ionosphere cavity, which is too lossy (Q too small) to enable a standing wave of sufficient amplitude to be generated. This limitation is independent of the power of the transmitter.  In order for the transmitter to feed power to the receiver as efficiently as it would in a closed low-loss circuit, the power transferred to the receiver should be able to transfer power of the same order of magnitude reciprocally to the transmitter.  This is a necessary condition for the transmitter to “feel” the load connected to the receiver, and to supply power to it via the standing wave.  In order to do this, the required Q of the Earth-ionosphere cavity is of the order of 10^6 or so at the lowest Earth-ionosphere cavity Schumann resonant frequency of about 8 Hz, according to my estimates, whereas measurements based on the spectrum of natural electrical radio noise yield a Q of only about 5 to 10.  I believe that the situation only gets worse at higher frequencies because of increasing energy losses in the earth and ionosphere, as is the case in radio transmission.

     In my opinion the reason Tesla believed that he could generate very high Q whole-earth oscillations was that he did not know about the existence of the ionosphere and its damping effect.  He also dismissed the practicality of long-range radio because he was unaware of the ionosphere and its reflecting properties.

On the other hand, it has been pointed out that wireless energy transmission using the concentric spherical shell model, as discussed above, is not consistent with the Tesla type transmitter.

The conceptual difficulty with this model is that, at the very low frequencies that Tesla said that he employed (1-50 kHz), earth-ionosphere waveguide excitation, now well understood, would seem to be impossible with the either the Colorado Springs or the Long Island apparatus (at least with the apparatus that is visible in the photographs of these facilities). ["Spherical Transmission Lines and Global Propagation, An Analysis of Tesla's Experimentally Determined Propagation Model," K. L. Corum, J. F. Corum, Ph.D., and J. F. X. Daum, Ph.D. 1996, p. 10.]

The maximum recommended operating frequencies of 25 kHz as specified by Tesla is far above the highest easily observable Schumann resonance mode (the 9th overtone) that exists at approximately 66.4 Hz.  Tesla's selection of 25 kHz is wholly inconsistent with the operation of a system that is based upon the direct excitation of a Schumann resonance mode.

Another terrestrial propagation mode is far more promising.

The Earth Resonance Method

Energy Transmission By Means of a Spherical Conductor “Single-wire” Surface Wave Transmission Line

The type of transmitter used to excite this propagation mode is described and illustrated in Tesla’s patent ART OF TRANSMITTING ELECTRICAL ENERGY THROUGH THE NATURAL MEDIUMS, May 16, 1900, U.S. Patent No. 787,412, Apr. 18, 1905 and elsewhere.  It is essentially the same as the transmitter used for the atmospheric conduction method, connected to the ground and to an elevated terminal, with the elevated terminal having the modified spherical shape seen in a number of photographs and artistic renderings of the Wardenclyffe wireless station prototype.  A similar rendering of a Wardenclyffe-type structure appears in the specifications of Tesla’s APPARATUS FOR TRANSMITTING ELECTRICAL ENERGY, Jan. 18, 1902, U.S. Patent 1,119,732, Dec. 1, 1914 in which this terminal is drawn as a modified torus.

It is apparent from documents on file at the U.S. Patent Office pertaining to U.S. Patent No. 787,412 that Tesla collected actual performance data.  In response to a question from U.S. Patent Examiner G.C. Dean regarding three stated requirements that, “seem essential to the establishment of the resonating condition” Tesla’s attorneys responded, 

These three requirements, as stated are in agreement with his numerous experimental observations.  .  .  .  we would point out that the specification does not deal with theories, but with facts which applicant has experimentally observed and demonstrated again and again, and in the commercial exploitation of which he is engaged. ["Spherical Transmission Lines and Global Propagation, An Analysis of Tesla's Experimentally Determined Propagation Model," K. L. Corum, J. F. Corum, Ph.D., and J. F. X. Daum, Ph.D. 1996, p. 3n.]

Tesla determined that the time required for a transmitted pulse or wave train to travel from the transmitter to the antipode and back again is .08484 seconds.  This equates to a fundamental earth resonance frequency of 11.786892 Hz.  He believed that by incorporating a portion of the earth as part of a powerful earth-resonance Tesla coil transmitter an electrical disturbance could be impressed upon the earth and detected, “at great distance, or even all over the surface of the globe."

Tesla also made an assumption that Earth is a charged body floating in space.

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. [ON LIGHT AND OTHER HIGH FREQUENCY PHENOMENA , Nikola Tesla, Inventions, Researches and Writings of Nikola Tesla, 1894, pp. 294-373.] 

Tesla was familiar with demonstrations that involved the charging of Leiden jar capacitors and isolated metal spheres with electrostatic influence machines.  By bringing these elements into close proximity with each other, and also by making direct contact followed by their separation the charge can be manipulated.  He surely had this in mind in the creation of his mental image, not being able to know that the model of Earth’s origin was inaccurate.  The presently accepted model of planetary origin is one of accretion and collision.  

If it be a charged body insulated in space its capacity should be extremely small, less than one-thousandth of a farad. [Ibid.] 

We now know that Earth is in fact a charged body relative to the uppermost atmospheric strata, made so by processes—at least in part—related to an interaction of Earth’s magnetosphere with the continuous stream of negatively charged particles called the solar wind, flowing outward from the center of our solar system.

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. [Ibid.]

We also know one of the upper strata of Earth’s atmosphere, the ionosphere, is conducting.

In any case it is of the greatest importance to get an idea of what quantity of electricity the earth contains. [Ibid.]

Earth possesses a naturally existing negative charge with respect to the conducting region of the atmosphere beginning at an elevation of about 50 kilometers.  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.  In LIGHTNING PROTECTOR, May 6, 1916, U.S. Patent 1,266,175, May 14, 1918 Tesla referred to this charge as the “electric niveau” or electric level.

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. . . .  [Ibid.]

A Tesla coil earth resonance transmitter creates a local disturbance in the earth’s charge that manifests itself as an annular deviation in the density of the background electric field.  This disturbance propagates away from the transmitter and diminishes in intensity as the distance from the transmitter increases.  A sufficiently powerful transmitter produces a field distortion that propagates all the way to the antipode, at which point the energy is reflected back towards its point of origin.  The transmission of electrical energy across the entire globe and its reflection all the way back to its source is the basis of Tesla's earth resonance method.

While the atmospheric conduction method requires that both transmitting and receiving apparatus be placed into operation, a properly tuned and sufficiently powerful earth resonance transmitter, on the other hand, can be made to operate exactly as intended without any man-made Tesla-type receivers being activated.  The earth itself fulfills the requirement that a synchronized receiver be present.

Conclusion

Long-distance wireless transmission by means of the Atmospheric Conduction Method is feasible, defying none of the known laws of physics, but a power transmission system based upon this method may not be practicable.  The hypothesized Schumann Cavity Resonance Method, unto itself, is unworkable.  Wireless transmission by means of the Earth Resonance Method may be possible, a feasibility study using a sufficiently powerful and properly tuned Tesla coil earth-resonance transmitter being called for.

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Latest revision: 04/25/2012

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