Allied Radio Knight-Kit Crystal Set 83 Y 261 Handbuch - Seite 7
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Seite druckenTHE HISTORY OF RADIO .
Radio had its beginning way back in 1873, when Ulysses S. Grant was President of the United States. In
this year an Englishman by the name of James C. Maxwell made a prediction that electromagnetic waves,
or, as he called them, "ether" waves, could be sent from one p1ace to another, just as light waves were.
However, Maxwell died without ever having tested his idea
A young German scientist, Heinrich Hertz, worked on Maxwell's idea from 1885 to 1889. One day he
announced that he had succeeded in sending electromagnetic waves from one room to another in his
laboratory in Karlsruhe, Germany. Hertz, however, did not pursue his discovery .
It remained for a young Italian engineer-inventor by the name of Guglielmo Marconi to bring radio
communication to the attention of the world. In 1890 he began experiments which led to the invention of
an outfit for sending code messages from one place to another without the need of wires. Code messages
were used because no one knew how to transmit voices and music by radio. This outfit, or transmitter,
attracted the attention of Sir William Henry Preece, who encouraged Marconi to "transfer his
experiments to England. In 1899 Marconi came to the United States, where he used his method of
communication to report the Presidential election of 1900, the year that Teddy Roosevelt was elected to
his first term. In 1902 he succeeded in establishing transatlantic communication with Europe. In 1904
Marconi began a daily news service to ocean liners in the Atlantic.
HOW RADIO WORKS
The term radio is used to describe the sending and receiving of signals between two or more places
without the use of wires. The signals are sent from the sending or transmitting station in the form of
radio waves. A more technical term for radio waves is electromagnetic radiation.
Figure 4 shows a typical broadcasting and receiving system. As the announcer talks, the vibration of his
vocal cords disturbs the air molecules, causing them to bump together and create sound waves. The
microphone changes these sound waves into very weak audio frequency (AF) electrical waves. These
weak AF electrical waves are amplified many times by the speech amplifier.. After amplification, the AF
signal 18 mixed with the strong radio frequency (RF) waves In the transmitter. This