Transmitter facts for kids
In electronics, a transmitter is a device which sends signals using radio waves.
The transmitter converts direct current (DC) into alternating current (AC) at the desired frequency. Most transmitters use a quartz crystal to set the frequency of the resulting carrier wave. A modulator modifies the carrier wave, by frequency modulation or amplitude modulation or some other kind, to include the information needed, such as an audio or video signal. The modified waves are sent by an antenna to another antenna at the receiver which extracts the information from the waves.
Images for kids
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A radio transmitter is usually part of a radio communication system which uses electromagnetic waves (radio waves) to transport information (in this case sound) over a distance.
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Animation of a half-wave dipole antenna transmitting radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods, with an alternating current applied at its center from a radio transmitter (not shown). The voltage charges the two sides of the antenna alternately positive (+) and negative (−). Loops of electric field (black lines) leave the antenna and travel away at the speed of light; these are the radio waves. This animation shows the action slowed enormously
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Hertz discovering radio waves in 1887 with his first primitive radio transmitter (background).
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Guglielmo Marconi's spark gap transmitter, with which he performed the first experiments in practical radio communication in 1895-1897
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High power spark gap transmitter in Australia around 1910.
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1 MW US Navy Poulsen arc transmitter which generated continuous waves using an electric arc in a magnetic field, a technology used for a brief period from 1903 until vacuum tubes took over in the 20s
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An Alexanderson alternator, a huge rotating machine used as a radio transmitter at very low frequency from about 1910 until World War 2
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One of the first vacuum tube AM radio transmitters, built by Lee De Forest in 1914. The early Audion (triode) tube is visible at right.
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One of the BBC's first broadcast transmitters, early 1920s, London. The 4 triode tubes, connected in parallel to form an oscillator, each produced around 4 kilowatts with 12 thousand volts on their anodes.
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Armstrong's first experimental FM broadcast transmitter W2XDG, in the Empire State Building, New York City, used for secret tests 1934–1935. It transmitted on 41 MHz at a power of 2 kW.
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Transmitter assembly of a 20 kW, 9.375 GHz air traffic control radar, 1947. The magnetron tube mounted between two magnets (right) produces microwaves which pass from the aperture (left) into a waveguide which conducts them to the dish antenna.
See also
In Spanish: Radiotransmisor para niños
