The Invention of Radio

موضوع: The Invention of Radio الجمعة فبراير 27, 2009 12:09 am

Radio owes its development to two other inventions, the telegraph and the telephone, all three technologies are closely related. Radio technology began as "wireless telegraphy".

Radio can refer to either the electronic appliance that we listen with
or the content listened to. However, it all started with the discovery
of "radio waves" - electromagnetic waves that have the capacity to
transmit music, speech, pictures and other data invisibly through the
air. Many devices work by using electromagnetic waves including: radio,
microwaves, cordless phones, remote controlled toys, television
broadcasts, and more.

The Roots of Radio

During the 1860s, Scottish physicist, James Clerk Maxwell predicted the existence of radio waves; and in 1886, German physicist, Heinrich Rudolph Hertz
demonstrated that rapid variations of electric current could be
projected into space in the form of radio waves similar to those of
light and heat.

In 1866, Mahlon Loomis,
an American dentist, successfully demonstrated "wireless telegraphy."
Loomis was able to make a meter connected to one kite cause another one
to move, marking the first known instance of wireless aerial
communication.

Guglielmo Marconi

Guglielmo Marconi,
an Italian inventor, proved the feasibility of radio communication. He
sent and received his first radio signal in Italy in 1895. By 1899 he
flashed the first wireless signal across the English Channel and two
years later received the letter "S", telegraphed from England to
Newfoundland. This was the first successful transatlantic
radiotelegraph message in 1902.

Nikola Tesla

In addition to Marconi, two of his
contemporaries Nikola Tesla and Nathan Stufflefield took out patents
for wireless radio transmitters. Nikola Tesla
is now credited with being the first person to patent radio technology;
the Supreme Court overturned Marconi's patent in 1943 in favor of Tesla.

Growth of Radio - Radiotelegraph and Spark-Gap Transmitters

Radio-telegraphy is the sending by radio waves the same dot-dash message (morse code) used in a telegraph.
Transmitters at that time were called spark-gap machines. It was
developed mainly for ship-to-shore and ship-to-ship communication. This
was a way of communicating between two points, however, it was not
public radio broadcasting as we know it today.

Wireless signals proved effective in communication for rescue work when
a sea disaster occurred. A number of ocean liners installed wireless
equipment. In 1899 the United States Army established wireless
communications with a lightship off Fire Island, New York. Two years
later the Navy adopted a wireless system. Up to then, the Navy had been
using visual signaling and homing pigeons for communication.

In 1901, radiotelegraph service was instituted between five Hawaiian
Islands. By 1903, a Marconi station located in Wellfleet,
Massachusetts, carried an exchange or greetings between President
Theodore Roosevelt and King Edward VII. In 1905 the naval battle of
Port Arthur in the Russo-Japanese war was reported by wireless, and in
1906 the U.S. Weather Bureau experimented with radiotelegraphy to speed
notice of weather conditions.

In 1909, Robert E. Peary, arctic explorer, radiotelegraphed: "I found
the Pole". In 1910 Marconi opened regular American-European
radiotelegraph service, which several months later, enabled an escaped
British murderer to be apprehended on the high seas. In 1912, the first
transpacific radiotelegraph service linked San Francisco with Hawaii.

Improvements to Radio Transmitters

Overseas radiotelegraph service developed slowly, primarily because the
initial radiotelegraph transmitter discharged electricity within the
circuit and between the electrodes was unstable causing a high amount
of interference. The Alexanderson high-frequency alternator and the De Forest tube resolved many of these early technical problems.

Lee DeForest - AM Radio

Lee Deforest
invented space telegraphy, the triode amplifier and the Audion. In the
early 1900s, the great requirement for further development of radio was
an efficient and delicate detector of electromagnetic radiation. Lee De
Forest provided that detector. It made it possible to amplify the radio
frequency signal picked up by the antenna before application to the
receiver detector; thus, much weaker signals could be utilized than had
previously been possible. De Forest was also the person who first used
the word "radio".

The result of Lee DeForest's work was the invention of
amplitude-modulated or AM radio that allowed for a multitude of radio
stations. The earlier spark-gap transmitters did not allow for this.

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