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telecommunications : a brief historical review
The first telecommunications system using electrical signals to carry messages started in the 1840s with machine telegraphy .
Samuel Morse first developed the telegraph in 1832 but it was not until the mid-1840s that the system was put into practical use sending coded electrical messages (Morse Code ) the wires . the telegraph became a rapid success , its speed quickly outdating the pony express for long –distance communications
The next major step forward came in 1878 with the invention of the telephone by bell . this enabled speech to be transported as electrical signals along wires and revolutionized personal communications
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In 1886 , hertz verified experimentally that electrical energy could be radiated and thus proved the existence of electromagnetic waves . this opened the way for the free-space transmission of information without wires . this provided the basis for all radio and TV broadcasting .
In 1901 , Marconi established long-distance telegraph communication by transmitting between England and Canada . although he did not realize it at the time , he achieved such long distances by reflecting radio waves in the ionosphere (layers of ionized gases and electrons existing in the earth's upper atmosphere at heights of 50-500km ) . this overcame the problem of transmitting round the earth from one side of the Atlantic to the other
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With the discoveries of the diode and thermionic valve in the early part of this century , advances were made in both receiver and transmitter design with an associated impact in telegraphy , telephony , and civil and military communications . radio broadcasting soon followed , with powerful transmitters serving to communicate over wide areas . television was first established in 1937 . radar (radio detection and ranging ) was also developed from the 1930s and played a vital role in aircraft detection and navigation in world war ll
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