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Monday, 19 June 2017

Radio

Radio is the transmission and reception of radio waves. When radio signals are sent out to many receivers at the same time, it is called a broadcast.

The first person to theorize the existence of radio waves was the Scottish physicist James Clerk Maxwell. His studies of light led him to the electromagnetic theory and in 1865 he proved that radio waves are possible.

The German scientist Heinrich Rudolf Hertz discovered the use of radio waves in transmitting information in the mid 1880s. However, with an uncharacteristic lack of foresight, while demonstrating electromagnetic waves in 1888, Hertz told his students, "I don't see any useful purpose for this mysterious, invisible electromagnetic energy."

Fortunately, others saw the potential in the technology and by 1890, French physicist Ă‰douard Branley had found a way to convert incoming signals to direct current, an important development in radio reception.



Russian scientist Alexander Stepanovich Popov demonstrated to the Russian Physical and Chemical Societyin St Petersburg in 1895 his invention, the Popov lightning detector — a primitive radio receiver. In some parts of the former Soviet Union the anniversary of this day is celebrated as Radio Day.

In 1893 the Serbian-American inventor,  Nikola Tesla gave the first public demonstration of radio in St. Louis, Missouri. Five years later, at the Electrical Exhibition held at Madison Square Garden, Nikola Tesla successfully demonstrated a radio-controlled boat. He was awarded U.S. patent No. 613,809 for a "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles."

Tesla's radio controlled boat

Italian inventor and electrical engineer. Gugielmo Marconi first began pursuing the idea of building a wireless telegraphy system based on Hertzian waves (radio) at his father's Italian country estate in 1895. Marconi gained a patent on the system the following year and in 1897 he formed in England Marconi's Wireless Telegraph Company Ltd.

British Post Office engineers inspect Marconi's radio equipment  1897. Cardiff Council Flat Holm Project. 

In 1901, Guglielmo Marconi combined the equipment of Hertz and Branley to transmit a radio signal across the Atlantic. Marconi’s pioneering development of long-distance wireless telegraphy has led to him being widely regarded as the inventor of the radio.

The term "radio" is derived from the Latin word "radius", meaning "spoke of a wheel, beam of light, ray". Although Hertz discovered the use of radio waves in transmitting information in 1886, the regular use of "radio" as a standalone word dates back to only December 30, 1904, when instructions issued by the British Post Office for transmitting telegrams specified that "The word 'Radio'... is sent in the Service Instructions." Before that, such transmissions were always referred to as “wireless telegraphy”.

Early radio messages were sent in Morse code because voice transmission required more power and better signal control than were available at the time.

The first human voice to be transmitted by radio is generally accepted to be that of Quebec physicist Reginald Aubrey Fessenden. In 1903 he built his first high-frequency alternator, drawing on the unsuccessful work of Tesla during the 1890s.

Reginald Fessenden

In 1906 Fessenden built his second alternator, which was capable of 80000 cycles. He gave the world’s first public demonstration of “true” radiotelephony broadcasting on December 21, 1906 at Brant Rock, Massachusetts. It operated in “LF” spectrum at 50 kHz with a wavelength of 6,000 meters, or 19,680 feet (about 3.75 miles). As part of the demonstration, speech was transmitted 18 kilometers (11 miles) to a listening site at Plymouth, Massachusetts. This led to the broadcasting of news, music and entertainment that we have today.

Many of today's history books and websites credit Fessenden with broadcasting music, poetry and a scripture reading to ships on the Atlantic from Brant Rock on Christmas Eve, 1906. However, validation of this event (the one solitary account was provided by Fessenden himself more than 25 years after the fact) has never been satisfactorily accomplished

In the early years of commercial broadcasting in the 1920s, Amplitude Modulation, usually shortened to AM, was the only kind of radio widely used. AM is a simple way to send a radio signal. The signal can travel long distances, and appear in faraway places, because of the earth's ionosphere. In 1933 American electrical engineer and inventor, Edwin Armstrong introduced frequency modulation (FM), a static-free version of radio.  He was granted five U.S. patents covering the basic features of the new system on December 26, 1933.

When transmitting analogue sound, the sound quality of FM signals is better than that of AM signals. However, FM signals do not travel as far as AM because they use higher frequencies that do not bounce off the Kennelly–Heaviside layer.

FM radio was demonstrated to the Federal Communications Commission for the first time in 1940. Today, many radio stations send out both kinds of signals. AM may be used for talk shows, and FM for music.

A Fisher 500 AM/FM hi-fi receiver from 1959.

Since 2012, February 13 has been celebrated by Unesco as World Radio Day. The date was chosen as United Nations Radio was launched on February 13, 1946.

Because radio waves travel faster than sound sound waves, if you stand at the base of Big Ben you can hear the chime on the radio before you hear it in real life.

Sources Daily Express, The Independent, Europress Encyclopedia

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