Radio wave - wikipedia Radio wave This article is about the radiation. For the generic oscillation, see frequency. For the electronics, see Radio frequency engineering. For other uses, see Radio Wave ( disambiguation ). Animation of a half - wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter ( not shown ). The transmitter applies an alternating electric current to the rods, which charges them alternately positive ( + ) and negative ( − ). Loops of electric field leave the antenna and travel away at the speed of light ; these are the radio waves. In this animation the action is shown slowed down enormously. Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, or include waves of any lower frequency. At 300 GHz, the corresponding wavelength is 1 mm ( 0.039 in ), and at 3 kHz is 100 km ( 62 mi ). Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are generated by lightning, or by astronomical objects. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, communications satellites, computer networks and innumerable other applications. Radio waves are generated by radio transmitters and received by radio receivers. Different frequencies of radio waves have different propagation characteristics in the Earth 's atmosphere ; long waves can diffract around obstacles like mountains and follow the contour of the earth ( ground waves ), shorter waves can reflect off the ionosphere and return to earth beyond the horizon ( skywaves ), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon. To prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunications Union ( ITU ), which defines radio waves as `` electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide ''. The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses. Diagram of the electric fields ( E ) and magnetic fields ( H ) of radio waves emitted by a monopole radio transmitting antenna ( small dark vertical line in the center ). The E and H fields are perpendicular as implied by the phase diagram in the lower right. Contents 1 Discovery and exploitation 2 Propagation 3 Speed, wavelength, and frequency 4 Radio communication 5 Biological and environmental effects 6 See also 7 Notes 8 References Discovery and exploitation Main article : History of radio Rough plot of Earth 's atmospheric transmittance ( or opacity ) to various wavelengths of electromagnetic radiation, including radio waves. Radio waves were first predicted by mathematical work done in 1867 by Scottish mathematical physicist James Clerk Maxwell. Maxwell noticed wavelike properties of light and similarities in electrical and magnetic observations. His mathematical theory, now called Maxwell 's equations, described light waves and radio waves as waves of electromagnetism that travel in space, radiated by a charged particle as it undergoes acceleration. In 1887, Heinrich Hertz demonstrated the reality of Maxwell 's electromagnetic waves by experimentally generating radio waves in his laboratory, showing that they exhibited the same wave properties as light : standing waves, refraction, diffraction, and polarization. Radio waves, originally called `` Hertzian waves '', were first used for communication in the mid 1890s by Guglielmo Marconi, who developed the first practical radio transmitters and receivers. Propagation Main article : Radio propagation The study of electromagnetic phenomena such as reflection, refraction, polarization, diffraction, and absorption is of critical importance in the study of how radio waves move in free space and over the surface of the Earth. Different frequencies experience different combinations of these phenomena in the Earth 's atmosphere, making certain radio bands more useful for specific purposes than others. Practical radio systems use three different techniques of radio propagation to communicate : Line of sight : This refers to radio waves that travel in a straight line from the transmitting antenna to the receiving antenna. It does not necessarily require a cleared sight path ; at lower frequencies radio waves can pass through buildings, foliage and other obstructions. This is the only method of propagation possible at microwave frequencies and above. On the surface of the Earth, line of sight propagation is limited by the visual horizon to about 64 km ( 40 mi ). This is the method used by cell phones, FM and television broadcasting and radar. By using dish antennas to transmit beams of microwaves, point - to - point radio relay links transmit telephone and television signals over long distances up to the visual horizon, and ground stations can communicate with satellites and spacecraft billions of miles from Earth. Indirect propagation : Radio waves can reach points beyond the line - of - sight by diffraction and multipath propagation. Diffraction allows a radio wave to bend around obstructions such as a building edge, a vehicle, or a turn in a hall. In multipath, radio waves reflect from surfaces such as walls, floors, ceilings, vehicles and the ground. These propagation methods occur in short range radio communication systems such as cell phones, cordless phones, walkie - talkies, and wireless networks. Ground waves : At lower frequencies, in the medium wave and longwave bands, due to diffraction vertically polarized radio waves can bend over hills and mountains, and propagate beyond the horizon, traveling as surface waves which follow the contour of the Earth. This allows mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon, out to hundreds of miles. As the frequency drops, the losses decrease and the achievable range increases. Military very low frequency ( VLF ) and extremely low frequency ( ELF ) communication systems can communicate over most of the Earth, and with submarines hundreds of feet underwater. Skywaves : At medium wave and shortwave wavelengths, radio waves reflect off a conductive ionized layer in the atmosphere called the ionosphere. So radio waves directed at an angle into the sky can return to Earth beyond the horizon ; this is called `` skip '' or `` skywave '' propagation. By using multiple skips communication at intercontinental distances can be achieved. Skywave propagation is variable and dependent on atmospheric conditions ; it is most reliable at night and in the winter. Widely used during the first half of the 20th century, due to its unreliability skywave communication has mostly been abandoned. Remaining uses are by military over-the - horizon ( OTH ) radar systems, by radio amateurs, and by shortwave broadcasting stations to broadcast to other countries. Speed, wavelength, and frequency Radio waves travel at the speed of light. When passing through an object, they are slowed according to that object 's permeability and permittivity. The wavelength is the distance from one peak of the wave 's electric field ( wave 's peak / crest ) to the next, and is inversely proportional to the frequency of the wave. The distance a radio wave travels in one second, in a vacuum, is 299,792,458 meters ( 983,571,056 ft ) which is the wavelength of a 1 hertz radio signal. A 1 megahertz radio signal has a wavelength of 299.8 meters ( 984 ft ). Radio communication Main article : Radio communication In order to receive radio signals, for instance from AM / FM radio stations, a radio antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is necessary to tune in a particular signal. This is typically done via a resonator ( in its simplest form, a circuit with a capacitor, inductor, or crystal oscillator, but many modern radios use Phase Locked Loop systems ). The resonator is configured to resonate at a particular frequency, allowing the tuner to amplify sine waves at that radio frequency and ignore other sine waves. Usually, either the inductor or the capacitor of the resonator is adjustable, allowing the user to change the frequency at which it resonates. Biological and environmental effects Electromagnetic radiation has been classified by the International Agency for Research on Cancer ( IARC ) as `` Possibly carcinogenic to humans ''. The List of IARC Group 2B carcinogens classification level includes lead, DDT, and styrene substances in addition to radiofrequency electromagnetic fields. See also Look up radio wave in Wiktionary, the free dictionary. Radio portal Telecommunication portal Radio astronomy Television transmitter Notes Jump up ^ ITU Radio Regulations, Chapter I, Section I, General terms -- Article 1.5, definition : radio waves or hertzian waves Jump up ^ Harman, Peter Michael ( 1998 ). The natural philosophy of James Clerk Maxwell. Cambridge, England : Cambridge University Press. p. 6. ISBN 0 - 521 - 00585 - X. Jump up ^ `` Heinrich Hertz : The Discovery of Radio Waves ''. Juliantrubin.com. Retrieved 2011 - 11 - 08. Jump up ^ `` 22. Word Origins ''. earlyradiohistory.us. ^ Jump up to : Seybold, John S. ( 2005 ). Introduction to RF Propagation. John Wiley and Sons. pp. 3 -- 10. ISBN 0471743682. Jump up ^ http://www.1728.org/freqwave.htm Jump up ^ http://www.nrao.edu/index.php/learn/radioastronomy/radiowaves Jump up ^ Brain, Marshall ( 2000 - 12 - 07 ). `` How Radio Works ''. HowStuffWorks.com. Retrieved 2009 - 09 - 11. Jump up ^ Brain, Marshall ( 2000 - 12 - 08 ). `` How Oscillators Work ''. HowStuffWorks.com. Retrieved 2009 - 09 - 11. Jump up ^ http://www.iarc.fr/en/media-centre/pr/2011/pdfs/pr208_E.pdf and http://monographs.iarc.fr/ENG/Classification/index.php References James Clerk Maxwell, `` A Dynamical Theory of the Electromagnetic Field '', Philosophical Transactions of the Royal Society of London 155, 459 - 512 ( 1865 ). Heinrich Hertz : `` Electric waves ; being researches on the propagation of electric action with finite velocity through space '' ( 1893 ). Cornell University Library Historical Monographs Collection. Reprinted by Cornell University Library Digital Collections. Karl Rawer : `` Wave Propagation in the Ionosphere ''. Kluwer, Dordrecht 1993. ISBN 0 - 7923 - 0775 - 5 Radio spectrum ( ITU ) ELF 3 Hz / 100 Mm 30 Hz / 10 Mm SLF 30 Hz / 10 Mm 300 Hz / 1 Mm ULF 300 Hz / 1 Mm 3 kHz / 100 km VLF 3 kHz / 100 km 30 kHz / 10 km LF 30 kHz / 10 km 300 kHz / 1 km MF 300 kHz / 1 km 3 MHz / 100 m HF 3 MHz / 100 m 30 MHz / 10 m VHF 30 MHz / 10 m 300 MHz / 1 m UHF 300 MHz / 1 m 3 GHz / 100 mm SHF 3 GHz / 100 mm 30 GHz / 10 mm EHF 30 GHz / 10 mm 300 GHz / 1 mm THF 300 GHz / 1 mm 3 THz / 0.1 mm Electromagnetic spectrum ← higher frequencies longer wavelengths → Gamma rays X-rays Ultraviolet Visible Infrared Terahertz radiation Microwave Radio Visible ( optical ) Violet Blue Green Yellow Orange Red Microwaves W band V band Q band K band K band K band X band S band C band L band Radio EHF SHF UHF VHF HF MF LF VLF ULF SLF ELF Wavelength types Microwave Shortwave Medium wave Longwave Radiation ( physics and health ) Main articles Non-ionizing radiation Acoustic radiation force Infrared Light Microwave Radio waves Ultraviolet Ionizing radiation Alpha particle Background radiation Beta particle Cosmic ray Gamma ray Nuclear fission Nuclear fusion Radioactive decay Nuclear reactors Nuclear weapons Particle accelerators Radioactive materials X-ray Earth 's radiation balance Electromagnetic radiation Thermal radiation Gravitational Radiation Radiation and health Health physics Dosimetry Electromagnetic radiation and health Laser safety Lasers and aviation safety Medical radiography Mobile phone radiation and health Radiation poisoning Radiation Protection Radiation therapy Radioactivity in the life sciences Radioactive contamination Radiobiology Biological dose units and quantities Wireless electronic devices and health Radiation Heat - transfer Related articles Half - life Nuclear physics Radioactive source Radiation hardening List of civilian radiation accidents 1996 Costa Rica accident 1987 Goiânia accident 1984 Moroccan accident 1990 Zaragoza accident See also : the categories Radiation effects, Radioactivity, Radiobiology, and Radiation protection. GND : 4176841 - 3 NDL : 00561394 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Radio_wave&oldid=806020205 '' Categories : Radio technology Waves Electromagnetic spectrum Hidden categories : Wikipedia articles with GND identifiers Talk Contents About Wikipedia Alemannisch አማርኛ বাংলা Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Čeština Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Gaeilge Galego Хальмг 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Íslenska Italiano עברית Basa Jawa ქართული Қазақша Kiswahili Latina Latviešu Lëtzebuergesch Lietuvių Magyar Македонски മലയാളം मराठी မြန်မာဘာသာ Nederlands नेपाली 日本 語 Norsk Norsk nynorsk Oʻzbekcha / ўзбекча ਪੰਜਾਬੀ Polski Português Română Русский Simple English Slovenčina Slovenščina کوردی Српски / srpski Srpskohrvatski / српскохрватски Basa Sunda Suomi Svenska தமிழ் తెలుగు ไทย Türkçe Українська اردو Tiếng Việt 粵語 Žemaitėška 中文 Edit links This page was last edited on 19 October 2017, at 03 : 51. 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Question: who demonstrated that radio radiation has all the properties of waves
Answer: Heinrich Hertz