Radio is the technology of signaling and communicating using radio waves.[1][2][3] Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, and received by another antenna connected to a radio receiver. Radio is very widely used in modern technology, in radio communication, radar, radio navigation, remote control, remote sensing, and other applications.

A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US

In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking, and satellite communication, among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal (impressing an information signal on the radio wave by varying some aspect of the wave) in the transmitter. In radar, used to locate and track objects like aircraft, ships, spacecraft and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, and the reflected waves reveal the object's location. In radio navigation systems such as GPS and VOR, a mobile receiver accepts radio signals from navigational radio beacons whose position is known, and by precisely measuring the arrival time of the radio waves the receiver can calculate its position on Earth. In wireless radio remote control devices like drones, garage door openers, and keyless entry systems, radio signals transmitted from a controller device control the actions of a remote device.

Applications of radio waves that do not involve transmitting the waves significant distances, such as RF heating used in industrial processes and microwave ovens, and medical uses such as diathermy and MRI machines, are not usually called radio. The noun radio is also used to mean a broadcast radio receiver.

The existence of radio waves was first proven by German physicist Heinrich Hertz on November 11, 1886.[4] In the mid 1890s, building on techniques physicists were using to study electromagnetic waves, Guglielmo Marconi developed the first apparatus for long-distance radio communication,[5] sending a wireless Morse Code message to a source over a kilometer away in 1895,[6] and the first transatlantic signal on December 12, 1901.[7] The first commerical radio broadcast was transmitted on November 2, 1920 when the live returns of the Harding-Cox presidential election were broadcast by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA.[8]

The emission of radio waves is regulated by law, coordinated by an international body called the International Telecommunication Union (ITU), which allocates frequency bands in the radio spectrum for different uses.


Radio waves are radiated by electric charges undergoing acceleration.[9][10] They are generated artificially by time varying electric currents, consisting of electrons flowing back and forth in a metal conductor called an antenna.[11][12]

The other types of electromagnetic waves besides radio waves, infrared, visible light, ultraviolet, X-rays and gamma rays, can also carry information and be used for communication. The wide use of radio waves for telecommunication is mainly due to their desirable propagation properties stemming from their large wavelength.[12]

Radio communicationEdit

Radio communication. Information such as sound is converted by a transducer such as a microphone to an electrical signal, which modulates a radio wave produced by the transmitter. A receiver intercepts the radio wave and extracts the information-bearing modulation signal, which is converted back to a human usable form with another transducer such as a loudspeaker.
Comparison of AM and FM modulated radio waves

In radio communication systems, information is carried across space using radio waves. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal.[12][13]

At the receiver, the radio wave induces a tiny oscillating voltage in the receiving antenna which is a weaker replica of the current in the transmitting antenna.[12][13]

The radio waves from many transmitters pass through the air simultaneously without interfering with each other because each transmitter's radio waves oscillate at a different rate, in other words, each transmitter has a different frequency, measured in hertz (Hz), kilohertz (kHz), megahertz (MHz) or gigahertz (GHz). The receiving antenna typically picks up the radio signals of many transmitters. The receiver uses tuned circuits to select the radio signal desired out of all the signals picked up by the antenna and reject the others. A tuned circuit (also called resonant circuit or tank circuit) acts like a resonator, similarly to a tuning fork.[13]


Frequency spectrum of a typical modulated AM or FM radio signal. It consists of a component C at the carrier wave frequency   with the information (modulation) contained in two narrow bands of frequencies called sidebands (SB) just above and below the carrier frequency.

A modulated radio wave, carrying an information signal, occupies a range of frequencies. See diagram. The information (modulation) in a radio signal is usually concentrated in narrow frequency bands called sidebands (SB) just above and below the carrier frequency. The width in hertz of the frequency range that the radio signal occupies, the highest frequency minus the lowest frequency, is called its bandwidth (BW).[14]

The radio spectrum, the total range of radio frequencies that can be used for communication in a given area, is a limited resource.[14][3]

ITU frequency bandsEdit

The ITU arbitrarily divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10n) metres, with corresponding frequency of 3 times a power of ten, and each covering a decade of frequency or wavelength.[3][15] Each of these bands has a traditional name:

Band name Abbreviation Frequency Wavelength Band name Abbreviation Frequency Wavelength
Extremely low frequency ELF 3 – 30 Hz 100,000–10,000 km High frequency HF 3 – 30 MHz 100–10 m
Super low frequency SLF 30 – 300 Hz 10,000–1,000 km Very high frequency VHF 30 – 300 MHz 10–1 m
Ultra low frequency ULF 300 – 3000 Hz 1,000–100 km Ultra high frequency UHF 300 – 3000 MHz 100–10 cm
Very low frequency VLF 3 – 30 kHz 100–10 km Super high frequency SHF 3 – 30 GHz 10–1 cm
Low frequency LF 30 – 300 kHz 10–1 km Extremely high frequency EHF 30 – 300 GHz 10–1 mm
Medium frequency MF 300 – 3000 kHz 1000–100 m Tremendously high frequency THF 300 – 3000 GHz 1–0.1 mm


The airwaves are a resource shared by many users. Two radio transmitters in the same area that attempt to transmit on the same frequency will interfere with each other, causing garbled reception, so neither transmission may be received clearly.[14]

To prevent interference between different users, the emission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU), which allocates bands in the radio spectrum for different uses.[14][3]


Below are some of the most important uses of radio, organized by function.


AM radio station
FM radio station
Television station
Broadcasting antennas

Audio: Radio broadcastingEdit

Two-way voice communicationEdit

  • Land mobile radio system – short-range mobile or portable half-duplex radio transceivers operating in the VHF or UHF band that can be used without a license. They are often installed in vehicles, with the mobile units communicating with a dispatcher at a fixed base station. Special systems with reserved frequencies are used by first responder services; police, fire, ambulance, and emergency services, and other government services. Other systems are made for use by commercial firms such as taxi and delivery services. VHF systems use channels in the range 30–50 MHz and 150–172 MHz. UHF systems use the 450–470 MHz band and in some areas the 470–512 MHz range. In general, VHF systems have a longer range than UHF but require longer antennas. AM or FM modulation is mainly used, but digital systems such as DMR are being introduced. The radiated power is typically limited to 4 watts.[17]

Space communicationEdit

This is radio communication between a spacecraft and an Earth-based ground station, or another spacecraft. Communication with spacecraft involves the longest transmission distances of any radio links, up to billions of kilometers for interplanetary spacecraft. In order to receive the weak signals from distant spacecraft, satellite ground stations use large parabolic "dish" antennas up to 25 metres (82 ft) in diameter and extremely sensitive receivers. High frequencies in the microwave band are used, since microwaves pass through the ionosphere without refraction, and at microwave frequencies the high-gain antennas needed to focus the radio energy into a narrow beam pointed at the receiver are small and take up a minimum of space in a satellite. Portions of the UHF, L, C, S, ku and ka band are allocated for space communication. A radio link that transmits data from the Earth's surface to a spacecraft is called an uplink, while a link that transmits data from the spacecraft to the ground is called a downlink.[citation needed]

Communications satellite belonging to Azerbaijan
  • Communication satellite – an artificial satellite used as a telecommunications relay to transmit data between widely separated points on Earth. These are used because the microwaves used for telecommunications travel by line of sight and so cannot propagate around the curve of the Earth. As of 1 January 2021, there were 2,224 communications satellites in Earth orbit.[19]


Radio jamming is the deliberate radiation of radio signals designed to interfere with the reception of other radio signals. Jamming devices are called "signal suppressors" or "interference generators" or just jammers.[20]

US Federal law prohibits the nonmilitary operation or sale of any type of jamming devices, including ones that interfere with GPS, cellular, Wi-Fi and police radars.[21]


The word "radio" is derived from the Latin word "radius", meaning "spoke of a wheel, beam of light, ray". It was first applied to communications in 1881 when at the suggestion of French scientist Ernest Mercadier, Alexander Graham Bell adopted "radiophone" (meaning "radiated sound") as an alternate name for his photophone optical transmission system.[22][23]

The first use of radio- in conjunction with electromagnetic radiation appears to have been by French physicist Édouard Branly, who in 1890 developed the coherer detector, which he called in French a radio-conducteur.[24] The radio- prefix was later used to form additional descriptive compound and hyphenated words, especially in Europe. For example, in early 1898 the British publication The Practical Engineer included a reference to "the radiotelegraph" and "radiotelegraphy".[25]

The use of "radio" as a standalone word dates back to at least December 30, 1904, when instructions issued by the British Post Office for transmitting telegrams specified that "The word 'Radio'... is sent in the Service Instructions".[26]

The switch to "radio" in place of "wireless" took place slowly and unevenly in the English-speaking world. Lee de Forest helped popularize the new word in the United States—in early 1907 he founded the DeForest Radio Telephone Company, and his letter in the June 22, 1907 Electrical World about the need for legal restrictions warned that "Radio chaos will certainly be the result until such stringent regulation is enforced".[27] The United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms "wireless telegraph" and "wireless telegram", by 1912 it began to promote the use of "radio" instead. The term started to become preferred by the general public in the 1920s with the introduction of broadcasting. (the word broadcasting originated with the agricultural term meaning roughly "scattering seeds widely".)[28]


See History of radio, Invention of radio, Timeline of radio, History of broadcasting

See alsoEdit


  1. ^ "Radio". Oxford Living Dictionaries. Oxford University Press. 2019. Retrieved 26 February 2019.
  2. ^ "Definition of radio". Encyclopedia. PCMagazine website, Ziff-Davis. 2018. Retrieved 26 February 2019.
  3. ^ a b c d Ellingson, Steven W. (2016). Radio Systems Engineering. Cambridge University Press. pp. 1–4. ISBN 978-1316785164.
  4. ^ "125 Years Discovery of Electromagnetic Waves". Karlsruhe Institute of Technology. May 16, 2022. Archived from the original on July 14, 2022. Retrieved July 14, 2022.
  5. ^ Bondyopadhyay, Prebir K. (1995) "Guglielmo Marconi – The father of long distance radio communication – An engineer's tribute", 25th European Microwave Conference: Volume 2, pp. 879–85
  6. ^ "1890s – 1930s: Radio". Elon University. Archived from the original on June 8, 2022. Retrieved July 14, 2022.
  7. ^ "First radio transmission sent across the Atlantic Ocean". History. February 9, 2010. Archived from the original on February 18, 2022. Retrieved July 14, 2022.
  8. ^ "History of Commercial Radio". Federal Communications Commission. Archived from the original on January 1, 2022. Retrieved July 14, 2022.
  9. ^ Kraus, John D. (1988). Antennas, 2nd Ed. Tata-McGraw Hill. p. 50. ISBN 0074632191.
  10. ^ Serway, Raymond; Faughn, Jerry; Vuille, Chris (2008). College Physics, 8th Ed. Cengage Learning. p. 714. ISBN 978-0495386933.
  11. ^ Balanis, Constantine A. (2005). Antenna theory: Analysis and Design, 3rd Ed. John Wiley and Sons. pp. 10. ISBN 9781118585733.
  12. ^ a b c d Ellingson, Steven W. (2016). Radio Systems Engineering. Cambridge University Press. pp. 16–17. ISBN 978-1316785164.
  13. ^ a b c Brain, Marshall (2000-12-07). "How Radio Works". Retrieved 2009-09-11.
  14. ^ a b c d "Spectrum 101" (PDF). US National Aeronautics and Space Administration (NASA). February 2016. Retrieved 2 December 2019. {{cite journal}}: Cite journal requires |journal= (help), p. 6
  15. ^ "Radio Regulations, 2016 Edition" (PDF). International Telecommunication Union. 3 November 2016. Retrieved 9 November 2019. {{cite journal}}: Cite journal requires |journal= (help) Article 2, Section 1, p.27
  16. ^ Baker, William (2020). "DAB vs FM: The differences between analog and digital radio". Radio Fidelity online magazine. Retrieved 14 September 2020.
  17. ^ a b Brain, Marshall; Jeff Tyson & Julia Layton (2018). "How Cell Phones Work". How Stuff Works. InfoSpace Holdings LLC. Retrieved 31 December 2018.
  18. ^ "Ground infrastructure". Russian Satellite Communications Company.
  19. ^ "UCS Satellite Database". Union of Concerned Scientists. 1 January 2021. Retrieved 21 May 2021.
  20. ^ "What jamming of a wireless security system is and how to resist it". Ajax Systems. Retrieved 2020-01-18.
  21. ^ "Jammer Enforcement". Federal Communications Commission. 2011-03-03. Retrieved 2020-01-18.
  22. ^ "radio (n.)". Online Etymology Dictionary. Retrieved July 13, 2022.
  23. ^ "Production of Sound by Radiant Energy" by Alexander Graham Bell, Popular Science Monthly, July 1881, pages 329–330: "[W]e have named the apparatus for the production and reproduction of sound in this way the "photophone", because an ordinary beam of light contains the rays which are operative. To avoid in future any misunderstandings upon this point, we have decided to adopt the term "radiophone", proposed by M. Mercadier, as a general term signifying the production of sound by any form of radiant energy..."
  24. ^ "The Genesis of Wireless Telegraphy" by A. Frederick Collins, Electrical World and Engineer, May 10, 1902, page 811.
  25. ^ "Wireless Telegraphy", The Practical Engineer, February 25, 1898, page 174. "Dr. O. J. Lodge, who preceded Marconi in making experiments in what may be called "ray" telegraphy or radiotelegraphy by a year or two, has devised a new method of sending and receiving the messages. The reader will understand that in the radiotelegraph electric waves forming the signals of the message starting from the sending instrument and travel in all directions like rays of light from a lamp, only they are invisible."
  26. ^ "Wireless Telegraphy", The Electrical Review (London), January 20, 1905, page 108, quoting from the British Post Office's December 30, 1904 Post Office Circular.
  27. ^ "Interference with Wireless Messages", Electrical World, June 22, 1907, page 1270.
  28. ^ "broadcast (adj.)". Online Etymology Dictionary. Retrieved July 13, 2022.

External linksEdit