The magnifying transmitter is an alternate version of a Tesla coil. It is a high power harmonic oscillator that Nikola Tesla proposed for the wireless transmission of electrical energy. In his autobiography, Tesla stated that "...I feel certain that of all my inventions, the Magnifying Transmitter will prove most important and valuable to future generations." The magnifying transmitter is an air-core, multiple-resonant transformer that can generate very high voltages. Tesla originally termed it self-regenerative resonant transformer, a term that is no longer in general use.
The first 'Magnifier' was assembled in New York City in the precise period between 1895 - 1898. In 1899 a larger magnifier was constructed in Colorado Springs, Colorado. This machine was used to conduct fundamental experiments in wireless telecommunications and electrical power transmission. Measuring fifty-one feet (15.5 m) in diameter, it developed a working potential estimated at 3.5 million to 4 million volts and was capable of producing electrical discharges exceeding one hundred feet (30 m) in length.
In 1899, Tesla decided to move and began research in Colorado Springs. He chose this location primarily because of the frequent thunderstorms, the high altitude (where the air, being at a lower pressure, had a lower dielectric breakdown strength, making it easier to ionize), and the dryness of the air (minimizing leakage of electric charge through insulators). Tesla kept a handwritten diary of his experiments in the Colorado Springs lab where he spent nearly nine months. It consists of 500 pages of notes and nearly 200 drawings, recorded chronologically between June 1, 1899 and January 7, 1900, as the work occurred, containing explanations of his experiments.
While in Colorado, Tesla constructed many smaller resonance transformers and conducted further research on concatenated tuned electrical circuits. Tesla also designed various sensitive devices for detecting received electrical energy, including rotating coherers. These used a clockwork mechanism of gears driven by a coiled spring-drive which rotated a small glass cylinder containing metal filings. These experiments were the final stage after years of work on synchronized tuned electrical circuits. These instruments were constructed to demonstrate how a wireless receiver could be "tuned" to respond to a specific complex signal while rejecting others. Tesla logged in his diary on January 2, 1900 that a separate resonance transformer tuned to the same high frequency as a larger high-voltage resonance transformer (which acted as a transmitter) received energy from the larger coil, one of many demonstrations of the wireless transmission of electrical energy. These experiments helped to confirm Tesla's priority in the invention of radio during later disputes in the courts. These air core high-frequency resonant coils were the predecessors of systems ranging from radio to medical nuclear magnetic resonance imaging.
On July 4, 1899, Tesla discovered terrestrial stationary waves within the earth. He demonstrated that the Earth behaves as a smooth polished conductor and possesses electrical vibrations. Tesla demonstrated that the Earth could respond at predescribed frequencies of electrical vibrations. Tesla conducted experiments contributing to the understanding of electromagnetic propagation and the Earth's resonance. He transmitted signals several kilometres and lit neon tubes conducting through the ground.
Tesla researched ways to transmit energy wirelessly over long distances (via transverse waves, to a lesser extent, and, more readily, longitudinal waves). He transmitted extremely low frequencies through the ground as well as between the earth's surface and the Kennelly-Heaviside layer. He received patents on wireless transceivers that developed standing waves by this method.
The magnifying transmitter was the basis for Tesla's Wardenclyffe Tower project. Although modern Tesla coils are designed to generate disruptive discharges, this system was designed for wireless communication and power transmission via longitudinal waves and telluric currents. In 1925, John B. Flowers advanced a proposal to test Tesla's system and to implement the system. H. L. Curtis, the chief of the Bureau of Standards Radio Laboratory in Washington D.C., and J. H. Dillinger, a physicist, reviewed the proposal but declined to implement the proposed plan. Flowers's mechanical analogy test was successful, though.
The layout of the Wardenclyffe magnifying transmitter is well known, based upon Tesla's patents and various photographs in which the concept was implemented. The magnifying transmitter is not identical to the classic Tesla coil. It has the short thick primary and secondary inductor characteristic of the Tesla coil, although magnetic coupling between the two is tighter. Because of this, more aggressive measures have to be taken in terms of primary spark quenching and providing additional insulation between the primary and secondary. In addition to these two large-diameter coils that comprise the master oscillator, Tesla added a third inductor called the "extra coil."
The extra coil or helical resonator can be physically separated from the two close-coupled coils, which comprise the master oscillator or driver section. The power from the master oscillator is fed to the lower end of the extra coil resonator through a large diameter electrical conductor or pipe to minimize corona. The magnifying transmitter's base-driven extra coil behaves as a slow-wave helical resonator, the axial disturbance propagating at a velocity of less than 1% up to around 10% the speed of light in free space. The Magnifying Transmitter's axial velocity electromagnetic field is established by the coil pitch and electrical charge propagation speed through the circuit.
Using low frequency harmonic Maxwellian oscillations, Tesla attempted to develop standing waves of extremely low frequency in the Earth's electro-magnetic circuit. Based upon observations made with the device, Tesla reported that a type of Earth resonance - involving the Earth's telluric energy - could be excited with the magnifying transmitter. He discovered that the resonance frequency of the Earth was approximately 8 hertz (Hz). In the 1950s, researchers confirmed that the resonance frequency of the Earth's ionospheric cavity was in this range. See Schumann resonance
In normal operation the device is relatively silent, generating a high power electric field, but if the output voltage exceeds the design voltage of the elevated terminal, high-voltage sparks will strike out from the electrode into the air.
See also: List of Tesla patents