Theory of Wireless Transmission
While working to develop an explanation for the two observed effects mentioned above, Tesla recognized that electrical energy can be projected outward into space and detected by a receiving instrument in the general vicinity of the source without the need for any interconnecting wires. He went on to develop two theories related to these observations, which are:
- By using two Tesla coil transmitter-receivers positioned at distant points on the Earth’s surface, it is possible to induce a flow of electrical current between them.
- By incorporating a portion of the Earth as part of a powerful dual-elevated-terminal Tesla coil transmitter an electrical disturbance can be impressed upon the Earth and detected “at great distance, or even all over the surface of the globe.”
Tesla also made the assumption that the 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.
Tesla was familiar with demonstrations that involved the charging of Leyden jar capacitors and isolated metal spheres with electrostatic influence machines (in modern terms, high-voltage (kV), low-current (μA) electrostatic generators). By bringing these elements into 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.
We now know that the Earth is a charged body, made so by processes—at least in part—related to the interaction between the continuous stream of charged particles called the solar wind that flows outward from the center of our solar system and Earth’s magnetosphere. We also know that Tesla's capacitance estimate was essentially correct: Earth's self-capacitance is about 710 microfarads.
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.
We also know that Earth's upper atmospheric strata are conducting, or can be made so.
In any case it is of the greatest importance to get an idea of what quantity of electricity the Earth contains.
An additional condition of which we are now aware is that 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. 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. .
Some maintain the 200 kW wireless facility would have functioned by the production and propagation of electromagnetic radiation also known as the transverse electromagnetic (TEM) radio wave, but this is not the case.
I am not producing radiation in my system; I am suppressing electromagnetic waves. But, on the other hand, my apparatus can be used effectively with electromagnetic waves. The apparatus has nothing to do with this new method except that it is the only means to practice it. So that in my system, you should free yourself of the idea that there is radiation, that energy is radiated. It is not radiated; it is conserved.
By Tesla's own account, the earth resonance system works by the creation of "powerful disturbances" in Earth's natural electric charge. The Wardenclyffe facility had a dual purpose. In addition to point-to-point telecommunications and broadcasting it was also intended to demonstrate the transmission of electrical power on a reduced scale. He stated,
It is intended to give practical demonstrations of these principles with the plant illustrated. As soon as completed, it will be possible for a business man in New York to dictate instructions, and have them instantly appear in type at his office in London or elsewhere. He will be able to call up, from his desk, and talk to any telephone subscriber on the globe, without any change whatever in the existing equipment. An inexpensive instrument, not bigger than a watch, will enable its bearer to hear anywhere, on sea or land, music or song, the speech of a political leader, the address of an eminent man of science, or the sermon of an eloquent clergyman, delivered in some other place, however distant. In the same manner any picture, character, drawing, or print can be transferred from one to another place. Millions of such instruments can be operated from but one plant of this kind. More important than all of this, however, will be the transmission of power, without wires, which will be shown on a scale large enough to carry conviction.
Wardenclyffe was the first of many installations to be constructed near major population centers around the world. If plans had moved forward without interruption the Long Island prototype would have been followed by a second plant built in the British Isles, perhaps on the west coast of Scotland near Glasgow. Each of these facilities would include a large magnifying transmitter of a design loosely based upon the apparatus assembled at the Colorado Springs Experimental Station in 1899.
- "... The plant in Colorado was merely designed in the same sense as a naval constructor designs first a small model to ascertain all the quantities before he embarks on the construction of a big vessel. I had already planned most of the details of the commercial plant, subsequently put up at Long Island, except that at that time the location was not settled upon. The Colorado plant I have used in determining the construction of the various parts, and the experiments which were carried on there were for the practical purpose of enabling me to design the transmitters and receivers which I was to employ in the large commercial plant subsequently erected..."
Using a global array of these magnifying transmitters, it was Tesla's plan to establish what he called the "World Wireless System," providing multi-channel global broadcasting, an array of secure wireless telecommunications services, and a long range aid to navigation, including means for the precise synchronization of clocks. In a more highly developed state he envisaged the 'World System' would expand to include the wireless industrial transmission of electric power.
At the time the power grid was quite limited in terms of reach and the Wardenclyffe prototype represented a way to significantly reduce the cost of "electrifying" the countryside. This wireless technique was called the "disturbed charge of ground and air method".
There is evidence that Wardenclyffe would have used extremely low frequency signals combined with higher frequency signals. In practice, the transmitter electrically influences both the Earth and the space above it.
The process is essentially the same as transmitting electricity by conduction through a wire. The earth itself is one of the conducting media involved in ground and air system technology. The other medium is the atmosphere above approximately 3 miles (4.8 km) elevation. While not an ohmic conductor, in this region of the troposphere and upwards, the density or pressure is sufficiently reduced to so that, according to theory, the atmosphere’s insulating properties can be easily impaired thus allowing an electric current to flow. Theory further states that the conducting region is developed through the process of atmospheric ionization in which the affected portions thereof are changed to plasma. The presence of the magnetic fields developed by each plant’s helical resonator suggests that an embedded magnetic field and flux linkage is also involved. Flux linkage with Earth’s natural magnetic field is also a possibility, especially in the case of an earth resonance transmission system.
The atmosphere below 3 miles (4.8 km) is also a propagating medium for a portion of the above-ground circuit. Being an insulating medium, electrostatic induction is involved rather than true electrical conduction. The practical construction limitation imposed upon the height of the elevated terminals can be overcome with a sufficiently high electrical potential. A highly energetic transmitter, as was intended at Wardenclyffe, charges the elevated terminal to the point where the atmosphere around and above the facility breaks down and becomes ionized. This leads to a flow of true conduction currents between the two terminals by a path up to and through the upper atmosphere, and back down to the other facility. The ionization of the atmosphere directly above the elevated terminals can be facilitated by the use of ionizing beams of ultraviolet radiation to form what might be called high-voltage plasma transmission lines.
In various writings, Tesla explained that the Earth itself behaves as a resonant LC circuit when it is electrically excited at certain frequencies. At Wardenclyffe he operated at frequencies ranging from 1,000 Hz to 100 kHz. Tesla found the frequency range up to 30 – 35 kHz “to be most economical.” Excitation of earth resonance at a harmonic of the 11.78 Hz fundamental frequency suggests energy transmission by means of a TM00 spherical conductor “single-wire” surface wave transmission line mode. A Schumann resonance mode (the fundamental frequency being about 7.5 to 7.9 Hz) is probably not involved. The entire Earth can be electrically resonated with a single earth-resonance transmitter, so an earth-resonance based system would require, at a minimum, that only one World Wireless System transmitter be constructed. Alternatively, two distantly spaced transmiter-receiver facilities could be constructed. Such a system would not be so dependent upon the excitation of an earth-resonance mode. In either case a surface wave, similar to the Zenneck wave would be utilized. Artificially induced earth currents would be utilized. According to Tesla, the planet's large cross-sectional area provides a low resistance path for the flow of earth currents. The greatest losses are apt to occur at the points where the transmitting / receiving plants and dedicated receiving stations are connected with the ground. This is why Tesla stated;
You see the underground work is one of the most expensive parts of the tower. In this system that I have invented it is necessary for the machine to get a grip of the Earth, otherwise it cannot shake the Earth. It has to have a grip on the Earth so that the whole of this globe can quiver, and to do that it is necessary to carry out a very expensive construction.
To close the circuit a second path is established between the two transmitter-receiver plants' elevated high-voltage terminals through the rarefied atmospheric strata above 3 miles (4.8 km). The connection is made by some combination of electrostatic induction and electrical conduction through plasma. While a number of his wireless patents, including "Apparatus for transmitting electrical energy," U.S. Patent No. 1,119,732, December 1, 1914, describe a system which uses the plasma-conduction scheme, his "Art of transmitting electrical energy through the natural mediums," U.S. Patent No. 787,412, April 18, 1905 and some of his Wardenclyffe design notes from 1901 show the overall plan also involves electrostatically induced oscillations in the potential associated with Earth's self-capacitance. The two tower earth-resonance transmitter is especially designed for this purpose. Tesla wrote,
The specific plan of producing the stationary waves, here-in described, might be departed from. For example, the circuit which impresses the powerful oscillations upon the earth might be connected to the latter at two points.
Tesla believed that a fully developed system with large high-power stations based upon the smaller Wardenclyffe prototype would permit wireless transmission and reception across large distances with negligible losses.
In the course of this work, I mastered the technique of high potentials sufficiently for enabling me to construct and operate, in 1899, a wireless transmitter developing up to twenty million volts. Some time before I contemplated the possibility of transmitting such high tension currents 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 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....
In spite of ridicule, many of Tesla's ideas have been demonstrated to be essentially correct. For example he correctly predicted the existence of the ionosphere and electrical resonance of the Earth-atmosphere system. Resonance of the earth-ionosphere cavity with a fundamental frequency in the vicinity of 7.3 Hz was demonstrated in the 1950s as the Schumann resonance. The latter phenomenon was named after Schumann, for although Tesla had detected a resonance of the Earth-atmosphere system, he was not taken seriously in his time. Furthermore, Tesla appears to have excited a different terrestrial resonance mode with a fundamental frequency of 11.78 Hz.
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