Nikola Tesla and His Works - On the Occassion of the Eightieth Anniversary Page 35

3.) Today’s radio technology operates exclusively with Tesla’s high-frequency currents. Various wavelengths are used for wireless telegraphy and radio broadcasting, ranging from tens of meters to several kilometers. These wavelengths correspond to frequencies ranging from tens of millions to tens of thousands of cycles. As we have seen, Tesla achieved such frequencies using various oscillators in the early nineties for high energies. When he succeeded in transmitting energy over a single wire and lighting lamps without wires in his laboratory, he contemplated how to use his currents for wireless telegraphy over great distances on Earth. Successes with the resonance of multiple electric circuits convinced him that the electromagnetic field energy from a powerful transmitting radio station, through resonance and very sensitive receiving radio apparatus, could be received even over the greatest distances on Earth to such an extent that signals could be transmitted wirelessly on a secure technical basis. Since the Earth is a good conductor of electric current, he conducted several smaller experiments in 1892 that convinced him that this property of the Earth could be utilized for transmitting electromagnetic energy. In his lecture in London, he stated the following: “If, with the help of a powerful machine, we induce rapid changes in the Earth’s potential, then a current would flow through a wire, one end of which is buried in the ground and the other end raised high, and we could amplify this current by attaching the free end of the wire to a body of larger surface area. Such an experiment can best be carried out on a ship at sea. It is entirely certain that understandable signals can be transmitted in this way.” This idea, published on February 3, 1892, before the Academy of Sciences in London, signifies nothing less than the beginning of the creation of radio technology. In it, the system of antenna-ground is described, and it is expressed that high-frequency currents, when oscillating through this system, provide a means for transmitting understandable signals. In a lecture before the Franklin Institute in Philadelphia in February 1893, Tesla elaborated further on this fundamental plan of radio technology, stating that both the transmitting and receiving radio stations should utilize open electrical circuits with an antenna-ground and that all circuits on both stations should be brought into resonance with each other. This emphasis on resonance proved not only crucial in Tesla’s radio experiments but, in general, in radio technology as the most essential factor. To create numerous radio stations that would operate without mutual interference, it was necessary to practically solve the resonance problem satisfactorily. To overcome various obstacles at great distances using radio waves, especially the curvature of the Earth, hills, and other disturbances, it was necessary to utilize the Earth and the lengths of radio waves that travel along the Earth’s surface in a curved line, unlike straight lines such as those of sunlight and short Hertz waves.