Nikola Tesla - The Founder of High-Frequency and Radio Engineering Page 13

electric motors on the boat, both for propulsion and for steering. The distance over which these experiments were conducted was 5–6 kilometers. In patent 613,809 of July 1898, Tesla extensively described his method and apparatus for wireless control over great distances. That patent described all the apparatus, both transmitting radio stations for emitting electromagnetic waves and receiving current circuits for performing specific movements. Tesla particularly emphasized in that patent the great sensitivity and selectivity of the receiving current circuits, so as to avoid interference, which is of crucial importance in such complicated movements. These discoveries by Tesla are of historical importance and prove that Tesla had already at that time achieved, published, and publicly demonstrated experimentally what has only in recent years begun to be applied and often advertised with considerable sensation as something new. Figure 1 shows Tesla’s model boat, with which he performed wireless control in 1898, and the following quotation from Tesla’s patent shows how perfectly he had already solved the basic problems of radio technology at that time. Among other things, Tesla states there: “When such or similar apparatus is used, sensitivity increases and, what is even more important, the security of operation, if we tune the secondary current circuit of the transmitting station to the same wavelength as the corresponding receiving circuit. I attach the greatest importance to this precisely because it would prevent the influence of waves coming from other directions on the receiving current circuits. The narrower the field of vibration of the current circuit, the more secure it is against foreign influences. To achieve the best results, it is necessary to construct the receiving current circuit or its parts, in which the oscillations mainly occur, so that they have the greatest possible self-induction and at the same time the smallest ohmic resistance. In this way I have shown that it is possible to use a very large number of such receiving current circuits — 50 or 100 or even more — each of which can be individually set in motion at will, while the others cannot influence it or interfere with it. This result makes it possible to control simultaneously the movements of an entire series of objects or apparatus on the same object, each of which is to perform a specific function. It is likewise possible, with the help of a single receiving current circuit, to set in motion many apparatus and perform a whole series of various functions at a great distance, according to the wishes of the operator of the transmitting station.”