Radio wave

Radio waves (formerly called Hertzian waves) are a type of <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic radiation</a> with the lowest <a href="/facts/Frequencies/QUSbPaW8">frequencies</a> and the longest <a href="/facts/Wavelength/kcJU0ymz">wavelengths</a> in the <a href="/facts/Electromagnetic_spectrum/24LARvFY">electromagnetic spectrum</a>, typically with frequencies below 300 <a href="/facts/Gigahertz/6Wshj5qm">gigahertz</a> (GHz) and wavelengths greater than 1 millimeter (3⁄64 inch), about the diameter of a grain of rice. Radio waves with frequencies above about 1 GHz and wavelengths shorter than 30 centimeters are called <a href="/facts/Microwave/HmVSN31Y">microwaves</a>. Like all electromagnetic waves, radio waves in vacuum travel at the <a href="/facts/Speed_of_light/sKSQwdNx">speed of light</a>, and in the Earth's atmosphere at a slightly lower speed. Radio waves are generated by <a href="/facts/Charged_particle/2zqBJGse">charged particles</a> undergoing <a href="/facts/Acceleration/UVDmjYvR">acceleration</a>, such as time-varying <a href="/facts/Electric_current/Dc1xdnUX">electric currents</a>. Naturally occurring radio waves are emitted by <a href="/facts/Lightning/dLTuxz8n">lightning</a> and <a href="/facts/Astronomical_radio_source/FEJFMcI8">astronomical objects</a>, and are part of the <a href="/facts/Blackbody_radiation/K4YKPKXL">blackbody radiation</a> emitted by all warm objects.
Radio waves are generated artificially by an electronic device called a <a href="/facts/Transmitter/nFYghtKv">transmitter</a>, which is connected to an <a href="/facts/Antenna_(radio)/pGlcXBvc">antenna</a>, which radiates the waves. They are received by another antenna connected to a <a href="/facts/Radio_receiver/5olDTxkg">radio receiver</a>, which processes the received signal. Radio waves are very commonly used in modern technology for fixed and mobile <a href="/facts/Radio_communication/XFr909M2">radio communication</a>, <a href="/facts/Broadcasting/AV1f3dGy">broadcasting</a>, <a href="/facts/Radar/jk9BTbFA">radar</a> and <a href="/facts/Radio_navigation/sRkrEaG9">radio navigation</a> systems, <a href="/facts/Communications_satellite/y5RXPMDT">communications satellites</a>, <a href="/facts/Wireless_network/yr4SWTdl">wireless computer networks</a> and many other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can <a href="/facts/Diffract/Mk80xXHT">diffract</a> around obstacles like mountains and follow the contour of the Earth (<a href="/facts/Ground_wave/YexYxuur">ground waves</a>), shorter waves can reflect off the <a href="/facts/Ionosphere/mT9tTBE5">ionosphere</a> and return to Earth beyond the horizon (<a href="/facts/Skywave/7AaWN9Nt">skywaves</a>), while much shorter wavelengths bend or diffract very little and travel on a <a href="/facts/Line-of-sight_propagation/w4xfQd2o">line of sight</a>, so their propagation distances are limited to the visual horizon.
To prevent <a href="/facts/Electromagnetic_interference/gv3DlKNr">interference</a> between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the <a href="/facts/International_Telecommunication_Union/Yn8UKKkw">International Telecommunication Union</a> (ITU), which defines radio waves as "<a href="/facts/Electromagnetic_wave/Ynx7ujCW">electromagnetic waves</a> of <a href="/facts/Frequencies/QUSbPaW8">frequencies</a> arbitrarily lower than 3000 <a href="/facts/Gigahertz/6Wshj5qm">GHz</a>, propagated in space without artificial guide". The <a href="/facts/Radio_spectrum/AP2frA1C">radio spectrum</a> is divided into a number of radio bands on the basis of frequency, allocated to different uses. Higher-frequency, shorter-wavelength radio waves are called <a href="/facts/Microwaves/HmVSN31Y">microwaves</a>.

Radio wave open-in-new

Radio wave