Чтение общенаучной литературы. Кытманова О.А. - 43 стр.

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troposphere about 8 kilometers (5 miles) above the Earth The ranges are around

300 to 500 kilo-meters (190 to 310 miles) suitable for communication between

mainland stations and islands or oil rigs.

The Thermionic Tube

Until the 1920s nearly all the world s radio stations sent messages in Morse code

This is known as wireless telegraphy. The transmitters generated radio waves from

sparks produced by a Poulsen arc or an Alexanderson high-frequency alternator.

None of these devices was suitable for radiotelephony, the electrical copying of

sounds, including speech.

In 1904 the British scientist, Sir Ambrose Fleming invented the thermionic diode

tube, to which the American physicist, Lee de

Forest, added an extra element, called the

grid, in 1906 . The triode, as this device came

to he known, could amplify (strengthen) weak

signals. But not until 1913 was it discovered

that the triode could also generate oscillations

of a very pure character, which were ideal for

radiotelephony.

During World War I there was great progress in the efficiency and power-

handling of the triode tube. By 1918 the armed forces were using large numbers of

low-power radio-telephony sets. When the war ended, radio manufacturers looked

around for new markets. Public radio broadcasting began in 1920 and its

development throughout the world is described in the article BROADCASTING.