The History of the Radio

Radio communication is the fruit of the discovery and cooperation of numerous scientists and technicians from different countries. Faraday, at the start of the 19th Century, discovered that electric fields can be induced from variable magnetic fields. A few years later the Scot James Clerk Maxwell maintained that electromagnetic waves followed the same laws as light. The term "radio", deriving from "radiation", was used in a conference held in Berlin in 1906 with reference to communication by electromagnetic waves. A young German physicist, Heinrich Rudolf Hertz, created a device (called oscillator) that produced electric discharges, which in turn generated electromagnetic waves. Together with the oscillator, Hertz demonstrated another apparatus invented by him and called “resonator”. Hertz died young, only 37 years of age, on 1 January 1894; a few months later the Englishman Oliver Joseph Lodge replaced the “Hertz resonator” with a new device that he called “coherer”. Reading a scientific magazine, Marconi came to know about the experiences of Hertz on electromagnetic waves and understood that this discovery and those devices would have made it possible to communicate by telegraph. During the summer of 1984 Marconi worked intensely to reproduce the instruments required for repeating the experiments of Hertz and Lodge. During the winter he continued with direct research to construct “coherers” that were more sensitive and in the spring of 1895 he equipped the “transmitter” with an earth antenna system. The result was a notable increase in the signal strength, which allowed Marconi to distance the receiver even more, up to several hundred metres, and in August 1895 he managed to transmit at a distance of more than one kilometre. On 2 June 1896, Marconi presented the request for the patent of a Wireless Telegraph to the London Patents Office that was released the next year. In 1901 Marconi launched the first radiotelegraph message over the Atlantic, from a transmitting station in Cornwall. One of the great limits of Marconi’s invention was that only impulses suitable for Morse code could be used, something that was unsuitable for sound transmission. In December 1900, using a spark transmitter, Fessenden managed to transmit a short phonic message. Five years later the American Dunwoody patented the use of the carborundum crystal as a detector and in the same year another engineer, Pickard, used silicon crystals. These new types of detector make it possible to spread the first receiving equipment for home use. Other metals were used for this purpose, such as the famous “galena", the mineral from which the first “radio hams” took their name: “galenists". In 1904 the British scientist Fleming created the diode and two years later, in 1906, the American engineer De Forest invented the triode. Both remained unopposed for years in the electronic sector. Radios were heavy and bulky because of their large thermionic valves up until the Second World War and only with the introduction of the transistor did the dimensions of receivers progressively become smaller.

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