Nikola Tesla Books
The problem of resonance was already theoretically known before Tesla in the case of alternating currents with ordinary frequencies of 50-100 cycles. Tesla himself conducted certain experiments in this regard with his multiphase system, but with high-frequency currents, the issue of resonance was not just a theoretical question. It represented a practical problem that required a lot of work, time, and inventiveness to solve. Today, it seems very simple to tune a radio receiver to the wavelength of any radio station by simply turning a knob.
Forty-five years ago, when Tesla began studying this problem, no one, however, had any idea that resonance would later play such a crucial role. Only Tesla understood that solving the problem of resonance would bring a solution to the problems of wireless telegraphy, radio broadcasting, and radiotelephony. The experiments he conducted in the laboratory in 1893 and 1894 showed that it was possible to create various electrical circuits that matched precisely only a specific wavelength without mutual interference. In the radio transmitter, Tesla produced various wavelengths and managed to selectively activate the radio receiver that corresponded to a particular wavelength. This work represented a real solution to the most essential elements of radio technology on a practical basis, and all that remained was to conduct experiments over longer distances, which was not a problem for Tesla, as the distance over which wireless signals could be transmitted was a simple function of energy for the transmitting and receiving radio-station
