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{{short description|Transmission by radio waves intended to reach a wide audience}}
{{redirect|Radio station|a broader concept|Radio communication station}}
{{about|audio signals|video signals|Over-the-air television}}
[[File:Tyholt taarnet.jpg|thumb|upright|Broadcasting tower in [[Trondheim]], Norway]]
'''Radio broadcasting''' is the transmission of electromagnetic radiation (radio waves) to receivers over a wide territory. Most broadcasts are [[audio signal|audio]] (sound), sometimes with embedded [[metadata]]. Listeners need a [[Radio receiver|broadcast radio receiver]] to pick up these signals. "Terrestrial" broadcasts, including AM, FM and DAB stations, originate signals from a land-based transmitter, while "satellite radio" signals originate from a [[satellite]] in Earth orbit.
Individual own programming, or are affiliated with a [[radio network]] that provides content, either in [[broadcast syndication]] or by [[simulcast]]ing, or both. The most common transmission technologies are [[analog signal|analog]] and [[digital signal]]s. Analog radio uses one of two [[modulation]] methods: [[amplitude modulation]], used by [[AM radio]], or [[frequency modulation]], for [[FM radio]]. A newer technique, digital radio stations, transmit using one of several different [[digital audio]] standards, such as DAB ([[Digital Audio Broadcasting]]), [[HD radio]], or DRM ([[Digital Radio Mondiale]]).
==History==
{{see also|History of radio#Broadcasting|History of broadcasting}}
===Pre-radio===
Electronic distribution originated, to a limited extent, with the invention of the [[telegraph]]. The most common example, "tickers", were primarily used to distribute stock price information. An additional subscription service was time signals. The concept of audio broadcasting was first developed after the invention of telephone. In a few locations, most commonly in Europe, [[telephone newspaper]]s were established, to provide news and entertainment to subscribers. These systems had the advantage of being able to charge individual customers. However, a lack of a way to amplify signals meant that their ranges were generally limited to a single municipality.
Some early inventors foresaw wireless transmission's potential. In 1902, [[Nathan Stubblefield]], who had developed wireless transmissions using ground conduction, envisioned that: "...any one having a receiving instrument, which would consist merely of a telephone receiver and a few feet of wire, and a signaling gong, could, upon being signaled by a transmitting station in Washington, or nearer, if advisable, be informed of weather news. Eventually it will be used for the general transmission of news of every description."<ref>[https://babel.hathitrust.org/cgi/pt?id=osu.32435074857459&view=1up&seq=301 "Telephoning Without Wires"] by Trumbull White, ''Our Wonderful Progress: The World's Triumphant Knowledge and Works'', Book 2, "The World's Science and Invention", 1902, pages 297–302.</ref>
===Radio===
Although it was quickly recognized that radio transmissions were capable of being broadcast to a scattered audience without needing connecting wires, there was skepticism about its finances. In an 1898 review of early radio transmissions, then known as "Hertzian telegraphy", a reviewer opined: "As to the practical applications, there were occasions when one wanted to 'shout to the world'—as in distributing political speeches to the Press—and for such a purpose the Hertz-wave and the coherer might be of service. But did not Prof. Lodge forget that no one wants to pay for shouting to the world on a system by which it would be impossible to prevent non-subscribers from benefiting gratuitously?".<ref>"Hertzian Telegraphy at the Physical Society", ''Electrician'' (London), January 28, 1898, pages 452-453.</ref> Another limitation was that many countries required listeners to be licensed in order to operate a radio receiver.
The earliest radio broadcasting stations transmitted [[radiotelegraphy]] dots-and-dashes, for such things as time signals and weather reports, or provided news summaries intended for inclusion in shipboard newspapers. This had limited audiences, because of the need to understand [[Morse code]]. Because there was no way to collect fees from listeners, these stations were commonly operated by national governments. Beginning in 1904, the U.S. Navy broadcast daily time signals and weather reports, and a Canadian Marconi station in Camperdown, Nova Scotia began transmitting time signals in 1907.<ref>[https://babel.hathitrust.org/cgi/pt?id=nyp.33433084097686&seq=419 "The First Wireless Time Signal"] by Captain J. L. Jayne, ''The American Jeweler'', October 1912, page 411.</ref> In Europe, a station located at the [[Eiffel Tower]] in Paris, France, transmitted time signals that were audible throughout the continent.<ref>[https://www.qsl.net/vk5br/History/Eiffel_Tower.pdf "The Eiffel Tower and its Early Radio]" by LLoyd Butler, March 2013.</ref>
Although most radio stations during the first two decades of the 1900s employed radiotelegraphic transmissions, there was also experimental development of audio transmissions, mostly using "amplitude modulation" (AM) signals. The first AM technologies included high-frequency spark, alternator, and arc transmitters. However, it was not until the development of vacuum-tube (also known as "valve") transmitters that widespread audio broadcasting became practical. In addition, most early experimenters worked to create [[radiotelephone]] systems for private communication, and few were interested in broadcasting information and entertainment to general audiences.
[[File:1916 Charles Logwood at radio station 2XG.jpg|thumb|right|Charles Logwood broadcasting at 2XG in New York City in 1916.<ref name=flashed>[https://archive.org/stream/electricalexperi04gern#page/650/mode/1up "Election Returns Flashed by Radio to 7,000 Amateurs"], ''The Electrical Experimenter'', January 1917, page 650.</ref>]]
Early examples of audio broadcasts included:
*On December 21, 1906, Reginald Fessenden successfully demonstrated audio transmissions using an alternator transmitter at Brant Rock, Massachusetts, USA.<ref>"Experiments and Results in Wireless Telephony" by John Grant, ''The American Telephone Journal''. [https://babel.hathitrust.org/cgi/pt?id=mdp.39015057240221&view=1up&seq=113 Part I]: January 26, 1907, pages 49–51; [https://babel.hathitrust.org/cgi/pt?id=mdp.39015057240221&view=1up&seq=151 Part II]: February 2, 1907, pages 68–70, 79–80.</ref> An article in the December 1932 issue of ''The Proceedings of the Institute of Radio Engineers'' by former Fessenden associate Samuel M. Kintner,<ref>[https://www.worldradiohistory.com/Archive-IRE/30s/IRE-1932-12.pdf#page=31 "Pittsburgh's Contributions to Radio"] by S. M. Kintner, ''Proceedings of the Institute of Radio Engineers'', December 1932, pages 1849–1862.</ref> reviewed information from a January 29, 1932 letter from Fessenden, which reported that shortly after the initial demonstrations, Fessenden had made the first of two radio broadcasts of music and entertainment on the evening of December 24, 1906 ([[Christmas Eve]]), using the alternator transmitter. He also stated that a second program was broadcast on December 31 ([[New Year's Eve]]). Fessenden claimed that the two programs had been widely publicized in advance, and the Christmas Eve broadcast had been heard "as far down" as [[Norfolk, Virginia]], while the New Year Eve's broadcast had reached listeners in the [[West Indies]].<ref>''Fessenden, Builder of Tomorrows'' by Helen Fessenden, 1940, [https://babel.hathitrust.org/cgi/pt?id=uc1.b4540711&view=1up&seq=167 pages 153–154].</ref> However, despite Fessenden's assertion that these broadcasts were widely heard along the U.S. eastern coast, extensive research has failed to find any contemporary confirmation of these broadcasts.<ref>{{cite web |url=https://www.radioworld.com/headlines/0045/fessenden-worlds-first-broadcaster/311783 |title=Fessenden: World's First Broadcaster? |date=25 October 2006 |access-date=2017-01-17 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20170118052530/http://www.radioworld.com/headlines/0045/fessenden-worlds-first-broadcaster/311783 |archive-date=January 18, 2017 }} by James E. O'Neal, ''Radio World'', October 25, 2006. (radioworld.com)</ref><ref>{{cite web |url=https://www.radioworld.com/article/fessenden-%E2%80%94-the-next-chapter/273 |title=Fessenden – The Next Chapter |access-date=2018-03-13 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20150703180123/http://www.radioworld.com/article/fessenden-%E2%80%94-the-next-chapter/273 |archive-date=July 3, 2015 }} by James E. O'Neal, ''Radio World'', December 23, 2008. (radioworld.com)</ref>
*Far better documented are the early broadcasts of [[Lee de Forest]], using an arc transmitter. In February 1907, he transmitted electronic [[telharmonium]] music from his laboratory station in New York City.<ref>''Father of Radio'' by Lee de Forest, 1950, page 225.</ref> This was followed later that year by a series of demonstrations that included [[Eugenia Farrar]] singing "I Love You Truly".<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015020686641&view=1up&seq=60 ''I Looked and I Listened''] by Ben Gross, 1954, page 48.</ref>
*[[Charles Herrold]], who opened the Herrold College of Wireless and Engineering in San Jose, California, USA in 1909, reported that in 1910, using a high-frequency spark transmitter, he had broadcast "wireless phone concerts to local amateur wireless men".<ref>''Charles Herrold: Inventor of Radio Broadcasting''] by Gorden Greb and Mike Adams, 2003, page 6.</ref> He later switched to arc transmitters, and in 1912 reported broadcasting weekly concerts.<ref>[https://commons.wikimedia.org/wiki/File:Will_Give_Concert_by_Wireless_Telephone_-_21JUL1912.jpg "Will Give Concert by Wireless Telephone"], ''San Jose Mercury Herald'', July 21, 1912, page 27.</ref><ref>"Musical Concert by Wireless Telephone", ''San Diego Union'', July 23, 1912, page 19.</ref>
*[[Robert Goldschmidt]] inaugurated a series of weekly concerts on March 28, 1914, using a high-frequency spark transmitter located at Laeken, Belgium.<ref>[https://babel.hathitrust.org/cgi/pt?id=njp.32101051572657&view=1up&seq=605 "Radio Telephony: Article V"] by Alfred N. Goldsmith, ''The Wireless Age'', May 1917, page 565.</ref>
*Lee de Forest established experimental station [[Radio 2XG|2XG]] in the Highbridge section of New York City, which was one of the first to use a vacuum-tube transmitter. The station featured a nightly "wireless newspaper" broadcast. On November 7, 1916, the station, in conjunction with the ''New York American'', broadcast results for the U.S. presidential election.<ref>[https://archive.org/stream/electricalexperi04gern#page/650/mode/1up "Election Returns Flashed by Radio to 7,000 Amateurs"], ''The Electrical Experimenter'', January 1917, page 650.</ref>
The outbreak of World War One largely suspended the development of civilian radio. However, during this period major improvements were made in vacuum-tube technology, which went into service after the end of wartime restrictions. All of the following examples used vacuum-tube transmitters:
[[File:Soireé-Musicale.jpg|thumb|200px|November 5, 1919 ''Nieuwe Rotterdamsche Courant'' advertisement, announcing PCGG's debut broadcast scheduled for the next evening, using narrow-band frequency modulation (FM).<ref name="philips">[https://www.vintageradio.nl/Menu/philips_engels.htm "Vintage Radio Web: Philips"] {{Webarchive|url=https://web.archive.org/web/20200207125459/https://www.vintageradio.nl/Menu/philips_engels.htm |date=February 7, 2020 }} (vintageradio.nl)</ref>]]
*After the wartime restrictions were lifted, Lee de Forest relicenced 2XG, his New York City station, which resumed nightly broadcasts in November 1919. However, this station was shut down after de Forest relocated it without first getting permission. He subsequently moved its transmitter to the California Theater in San Francisco, where it was relicensed and resumed operations as [[KZY|6XC]]. In 1921, de Forest described 6XC as the "first radio-telephone station devoted solely" to broadcasting to the public.<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015080023859&view=1up&seq=994 "'Broadcasting' News by Radiotelephone"] (letter from Lee de Forest), ''Electrical World'', April 23, 1921, page 936.</ref>
* In The Hague, the Netherlands, [[Hans Idzerda]]'s station, [[PCGG]], started broadcasting on November 6, 1919, using narrow-band frequency modulation (FM), making it arguably the first commercial broadcasting station.<ref>''Nieuwe Rotterdamsche (Netherlands) Courant'', November 5, 1919, page 4.</ref>
* Radio Argentina began regularly scheduled transmissions from the [[Teatro Coliseo]] in [[Buenos Aires]] on August 27, 1920, making its own priority claim. The station got its license on November 19, 1923. The delay was due to the lack of official Argentine licensing procedures before that date. This station continued regular broadcasting of entertainment, and cultural fare for several decades.<ref>Atgelt, Carlos A. [http://www.oldradio.com/archives/international/argentin.html "Early History of Radio Broadcasting in Argentina."] {{Webarchive|url=https://web.archive.org/web/20210424214128/https://www.oldradio.com/archives/international/argentin.html |date=April 24, 2021 }} The Broadcast Archive (Oldradio.com).</ref>
*In early 1919, the Canadian Marconi facility at Montreal, Quebec, Canada received a surplus wartme transmitter, and its test transmissions, over experimental station [[CINW|XWA]], evolved into broadcasts, starting with a May 20, 1920 concert.<ref>[https://news.google.com/newspapers?id=9P8tAAAAIBAJ&sjid=cYEFAAAAIBAJ&pg=1878%2C5556437 "Wireless Concert Given for Ottawa"], ''Montreal Gazette'', May 21, 1920, page 4.</ref> This was followed by weekly broadcasts.
* Entertainment radio broadcasts in the UK began in 1920, with occasional broadcasts by the [[Marconi Research Centre]] station, [[2MT]] at [[Writtle]] near [[Chelmsford, England]]. On June 15, 1920, a widely publicized broadcast was made by soprano Dame [[Nellie Melba]] from Marconi's New Street Works factory in Chelmsford. This was the first artist of international renown to make a radio broadcast. However, later that year the broadcasts were banned by the Post Office,<ref>[https://www.worldradiohistory.com/UK/BBC/BBC-Books/Birth-of-Broadcasting-Briggs-Vol-1-1961.pdf#page=31 ''The Birth of Broadcasting''] by Asa Briggs, 1961, page 20.</ref> due to complaints that the broadcasts were interfering with military communication.
* Beginning on August 20, 1920, the ''Detroit News'' in Detroit, Michigan, USA, began daily broadcasts over what it called the [[WWJ (AM)|Detroit News Radiophone]]. This station, later licensed as station WWJ, in 1945 ran an advertisement with the claims that it was the "World's First Station" and where "commercial radio broadcasting began".<ref>[https://archive.org/details/broadcasting291unse/page/n624/mode/1up WWJ (advertisement)], ''Broadcasting'', August 20, 1945, page 31.</ref>
*After reviewing multiple post-war experimental efforts in the United States, in the words of Erik Barnouw, "There was a ferment of interest, but without sense of direction—until something happened in Pittsburgh."<ref>[https://www.worldradiohistory.com/BOOKSHELF-ARH/History/A-Tower-in-Babelon-Radio-to-1933-Barnouw-1966.pdf#page=76 ''A Tower in Babel''] by Erik Barnouw, 1966, page 64.</ref> [[Frank Conrad]] was a [[Westinghouse Electric (1886)|Westinghouse Electric Corporation]] electrical engineer. He also held a license for an experimental station, 8XK, located in his garage at his [[Wilkinsburg, Pennsylvania]] home. After seeing a local newspaper advertisement for radio receivers capable of picking up the 8XK broadcasts, Westinghouse's Harry P. Davis decided to see if there was a broad consumer market for receivers produced by the company. Westinghouse began regular broadcasts with election returns on the evening of November 2, 1920, over station 8ZZ (later [[KDKA (AM)|KDKA]]) located at its East Pittsburgh, Pennsylvania, USA headquarters. This has generally been recognized as the first commercially licensed radio station in the United States.<ref>{{Cite web |url=http://www.trft.org/TRFTpix/CDHKittross.pdf |title=Broadcasting's Oldest Stations: An Examination of Four Claimants |access-date=2 September 2016 |archive-url=https://web.archive.org/web/20170305001831/http://www.trft.org/TRFTpix/CDHKittross.pdf |archive-date=5 March 2017 |url-status=bot: unknown |df=dmy-all }}, Joseph E. Baudino and John M. Kittross, ''Journal of Broadcasting'', Winter 1977, page 62.</ref>
Effective December 1, 1921, the U.S. Department of Commerce issued regulations formally establishing a broadcasting service, and by the end of 1922, there were over 500 licensed stations.<ref>[https://babel.hathitrust.org/cgi/pt?id=osu.32435066705633&view=1up&seq=200 "Miscellaneous: Amendments to Regulations"], ''Radio Service Bulletin'', January 3, 1922, page 10.</ref> Canada soon followed, and began issuing broadcasting station licenses in April 1922.<ref>[https://digitalcollections.lib.umanitoba.ca/islandora/object/uofm%3A2937410 "Radio Department: Broadcasting Stations"], ''Winnipeg Evening Tribune'', April 25, 1922, page 5</ref> [[2MT]] in Great Britain began regular entertainment broadcasts in 1922, and that year the [[BBC|British Broadcasting Company]] was formed and given a national broadcasting monopoly. It received a [[Royal Charter]] in 1926, making it the first national broadcaster in the world,<ref>{{Cite web|url=http://www.g0mwt.org.uk/new-street/|title=CARS - Marconi Hall Street, New Street and 2MT callsign|website=www.g0mwt.org.uk}}</ref><ref>{{cite news |title=BBC History – The BBC takes to the Airwaves|url=http://news.bbc.co.uk/aboutbbcnews/spl/hi/history/html/default.stm|work=BBC News}}</ref> followed by [[Czech Radio|Czechoslovak Radio]] and other European broadcasters in 1923.
[[File:Control room and radio studio in Fabianinkatu headquarters of Yleisradio, ca 1938.jpg|thumb|Control room and radio studio of the [[Finland|Finnish]] broadcasting company [[Yle|Yleisradio]] (YLE) in the 1930s.]]
===Expansion===
Radio in education soon followed, and colleges across the U.S. began adding radio broadcasting courses to their curricula. Curry College in Milton, Massachusetts introduced one of the first broadcasting majors in when the college teamed up with WLOE in Boston to have students broadcast programs.<ref>{{cite web|url=http://www.curry.edu|title=Curry College - Home|website=www.curry.edu|access-date=July 13, 2018}}</ref> By 1931, a majority of U.S. households owned at least one [[radio receiver]].<ref>{{cite journal|last=Craig|first=Steve|year=2004|title=How America Adopted Radio: Demographic Differences in Set Ownership Reported in the 1930–1950 U.S. Censuses|journal=[[Journal of Broadcasting & Electronic Media]]|volume=48|issue=2|pages=179–195|publisher=[[Routledge]]|doi=10.1207/s15506878jobem4802_2|s2cid=145186571|url=https://www.researchgate.net/publication/233149747}}</ref>
[[File:Radio Libertaire 3.jpg|thumb|Use of a sound broadcasting station]]
In line to [[ITU Radio Regulations]] (article1.61) each ''broadcasting station'' shall be classified by the service in which it operates permanently or temporarily.
==Types==
[[Image:Radio Transmission Diagram en.svg|thumb|right|260px|Transmission diagram of sound broadcasting (AM and FM)]]
Broadcasting by radio takes several forms. These include [[AM broadcasting|AM]] and [[FM broadcasting|FM]] stations. There are several subtypes, namely [[commercial broadcasting]], [[non-commercial educational]] (NCE) [[public broadcasting]] and [[non-profit]] varieties as well as [[community radio]], student-run [[campus radio]] stations, and [[hospital radio]] stations can be found throughout the world. Many stations broadcast on [[shortwave]] bands using AM technology that can be received over thousands of miles (especially at night). For example, the [[BBC World Service|BBC]], [[Voice of America|VOA]], [[Voice of Russia|VOR]], and [[Deutsche Welle]] have transmitted via shortwave to Africa and Asia. These broadcasts are very sensitive to atmospheric conditions and solar activity.
[[Nielsen Audio]], formerly known as Arbitron, the [[United States]]–based company that reports on radio audiences, defines a "radio station" as a government-licensed AM or FM station; an HD Radio (primary or multicast) station; an internet stream of an existing government-licensed station; one of the satellite radio channels from [[XM Satellite Radio]] or [[Sirius Satellite Radio]]; or, potentially, a station that is not government licensed.<ref>{{cite news|url=http://www.nxtbook.com/nxtbooks/newbay/rw_20081008/index.php|title=What is a Radio Station?|work=[[Radio World]]|page=6}}</ref>
===AM===
{{main|AM broadcasting}}
AM stations were the earliest broadcasting stations to be developed. AM refers to [[amplitude modulation]], a mode of broadcasting radio waves by varying the amplitude of the carrier signal in response to the amplitude of the signal to be transmitted. The medium-wave band is used worldwide for AM broadcasting. Europe also uses the [[long wave]] band. In response to the growing popularity of [[FM broadcasting#Stereo FM|FM stereo]] radio stations in the late 1980s and early 1990s, some [[North America]]n stations began broadcasting in [[AM stereo]], though this never gained popularity and very few receivers were ever sold.
The signal is subject to interference from electrical storms ([[lightning]]) and other [[electromagnetic interference]] (EMI).<ref>Based on the "interference" entry of ''The Concise Oxford English Dictionary'', 11th edition, online</ref> One advantage of AM radio signal is that it can be detected (turned into sound) with simple equipment. If a signal is strong enough, not even a power source is needed; building an unpowered [[crystal radio|crystal radio receiver]] was a common childhood project in the early decades of AM broadcasting.
AM broadcasts occur on [[North America]]n airwaves in the [[medium wave]] frequency range of 525 to 1,705 [[Hertz|kHz]] (known as the "standard broadcast band"). The band was expanded in the 1990s by adding nine [[Communication channel|channels]] from 1,605 to 1,705 kHz. Channels are spaced every 10 kHz in the [[Americas]], and generally every 9 kHz everywhere else.
AM transmissions cannot be ionospheric [[radio propagation|propagated]] during the day due to strong absorption in the [[D-layer]] of the ionosphere. In a crowded channel environment, this means that the power of regional channels which share a frequency must be reduced at night or directionally beamed in order to avoid interference, which reduces the potential nighttime audience. Some stations have frequencies unshared with other stations in North America; these are called [[clear-channel station]]s. Many of them can be heard across much of the country at night. During the night, absorption largely disappears and permits signals to travel to much more distant locations via ionospheric reflections. However, fading of the signal can be severe at night.
AM radio transmitters can transmit audio frequencies up to 15 kHz (now limited to 10 kHz in the US due to FCC rules designed to reduce interference), but most receivers are only capable of reproducing frequencies up to 5 kHz or less. At the time that AM broadcasting began in the 1920s, this provided adequate fidelity for existing microphones, 78 rpm recordings, and loudspeakers. The fidelity of sound equipment subsequently improved considerably, but the receivers did not. Reducing the bandwidth of the receivers reduces the cost of manufacturing and makes them less prone to interference. AM stations are never assigned adjacent channels in the same service area. This prevents the sideband power generated by two stations from interfering with each other.<ref>{{cite web | title=Types of Technology, FM vs AM | website=kwarner.bravehost.com | date=July 13, 2012 | url=http://kwarner.bravehost.com/tech.htm | archive-url=https://web.archive.org/web/20120713084431/http://kwarner.bravehost.com/tech.htm | archive-date=July 13, 2012 | url-status=dead | access-date=August 10, 2019}}</ref> [[Bob Carver]] created an [[AM stereo]] tuner employing [[notch filter]]ing that demonstrated that an AM broadcast can meet or exceed the 15 kHz baseband bandwidth allotted to [[FM broadcasting|FM]] stations without objectionable interference. After several years, the tuner was discontinued. Bob Carver had left the company and the Carver Corporation later cut the number of models produced before discontinuing production completely.<ref>{{Cite web |title=Landing Page |url=https://www.bobcarvercorp.com/ |access-date=2025-03-25 |website=BobCarverCorp.com |language=en}}</ref>
As well as on the medium wave bands, amplitude modulation (AM) is also used on the [[shortwave]] and [[long wave]] bands. Shortwave is used largely for national broadcasters, international propaganda, or [[religious broadcasting]] organizations. Shortwave transmissions can have international or inter-continental range depending on atmospheric conditions.<ref>{{Cite book|url=https://books.google.com/books?id=HudwCgAAQBAJ|title=Beginning Shortwave Radio Listening|last=Grodkowski|first=Paul|date=August 24, 2015|publisher=Booktango|isbn=9781468964240|language=en}}</ref> Long-wave AM broadcasting occurs in Europe, Asia, and Africa. The [[ground wave]] propagation at these frequencies is little affected by daily changes in the ionosphere, so broadcasters need not reduce power at night to avoid interference with other transmitters.
===FM===
{{main|FM broadcasting}}
FM refers to [[frequency modulation]], and occurs on [[VHF]] airwaves in the frequency range of 88 to 108 [[Megahertz|MHz]] everywhere except [[Japan]] and [[Russia]]. Russia, like the former [[Soviet Union]], uses 65.9 to 74 MHz frequencies in addition to the world standard. Japan uses the 76 to 90 MHz frequency band.
[[Edwin Howard Armstrong]] invented wide-band FM radio in the early 1930s to overcome the problem of [[Electromagnetic interference|radio-frequency interference]] (RFI), which plagued AM radio reception. At the same time, greater fidelity was made possible by spacing stations further apart in the [[radio frequency]] spectrum. Instead of 10 kHz apart, as on the AM band in the US, FM channels are 200 kHz (0.2 MHz) apart. In other countries, greater spacing is sometimes mandatory, such as in New Zealand, which uses 700 kHz spacing (previously 800 kHz). The improved fidelity made available was far in advance of the audio equipment of the 1940s, but wide interchannel spacing was chosen to take advantage of the noise-suppressing feature of wideband FM.
Bandwidth of 200 [[kHz]] is not needed to accommodate an audio signal — 20 kHz to 30 kHz is all that is necessary for a narrowband FM signal. The 200 kHz bandwidth allowed room for ±75 kHz signal deviation from the assigned frequency, plus guard bands to reduce or eliminate adjacent channel interference. The larger bandwidth allows for broadcasting a 15 kHz bandwidth audio signal plus a 38 kHz [[FM broadcasting#Stereo FM|stereo "subcarrier"]]—a piggyback signal that rides on the main signal. Additional unused capacity is used by some broadcasters to transmit utility functions such as background [[music]] for public areas, [[Global Positioning System|GPS]] auxiliary signals, or financial market data.
The AM radio problem of interference at night was addressed in a different way. At the time FM was set up, the available frequencies were far higher in the spectrum than those used for AM radio - by a factor of approximately 100. Using these frequencies meant that even at far higher power, the range of a given FM signal was much shorter; thus its market was more local than for AM radio. The reception range at night is the same as in the daytime. All FM broadcast transmissions are line-of-sight, and ionospheric bounce is not viable. The much larger bandwidths, compared to AM and SSB, are more susceptible to phase dispersion. Propagation speeds are fastest in the ionosphere at the lowest sideband frequency. The celerity difference between the highest and lowest sidebands is quite apparent to the listener. Such distortion occurs up to frequencies of approximately 50 MHz. Higher frequencies do not reflect from the ionosphere, nor from storm clouds. Moon reflections have been used in some experiments, but require impractical power levels.
The original FM radio service in the U.S. was the [[Yankee Network]], located in [[New England]].<ref>Halper, Donna L. [http://www.bostonradio.org/essays/shepard-fm.html "John Shepard's FM Stations—America's first FM network."] {{Webarchive|url=https://web.archive.org/web/20060212104948/http://www.bostonradio.org/essays/shepard-fm.html |date=February 12, 2006 }} Boston Radio Archives (BostonRadio.org).</ref><ref>{{cite web | title=The Yankee Network in 1936 | website=The Archives @ BostonRadio.org | url=http://www.bostonradio.org/yankee-36.html | access-date=August 10, 2019}}</ref><ref>{{cite web | title=FM Broadcasting Chronology | website=Jeff Miller Pages | date=June 23, 2017 | url=http://jeff560.tripod.com/chronofm.html | access-date=August 10, 2019}}</ref> Regular FM broadcasting began in 1939 but did not pose a significant threat to the AM broadcasting industry. It required purchase of a special receiver. The frequencies used, 42 to 50 MHz, were not those used today. The change to the current frequencies, 88 to 108 MHz, began after the end of [[World War II]] and was to some extent imposed by AM broadcasters as an attempt to cripple what was by now realized to be a potentially serious threat.
FM radio on the new band had to begin from the ground floor. As a commercial venture, it remained a little-used audio enthusiasts' medium until the 1960s. The more prosperous AM stations, or their owners, acquired FM licenses and often broadcast the same programming on the FM station as on the AM station ("[[simulcasting]]"). The FCC limited this practice in the 1960s. By the 1980s, since almost all new radios included both AM and FM tuners, FM became the dominant medium, especially in cities. Because of its greater range, AM remained more common in rural environments.
===Pirate radio===
{{Main|Pirate radio}}
Pirate radio is illegal or non-regulated radio transmission. It is most commonly used to describe illegal broadcasting for entertainment or political purposes. Sometimes it is used for illegal two-way radio operation. Its history can be traced back to the unlicensed nature of the transmission, but historically there has been occasional use of sea vessels—fitting the most common perception of a pirate—as broadcasting bases.
Rules and regulations vary largely from country to country, but often the term pirate radio describes the unlicensed broadcast of FM radio, AM radio, or shortwave signals over a wide range. In some places, radio stations are legal where the signal is transmitted, but illegal where the signals are received—especially when the signals cross a national boundary. In other cases, a broadcast may be considered "pirate" due to the type of content, its transmission format, or the transmitting power (wattage) of the station, even if the transmission is not technically illegal (such as a webcast or an amateur radio transmission). Pirate radio stations are sometimes referred to as bootleg radio or clandestine stations.
===Terrestrial digital radio===
{{main|Digital audio broadcasting|HD radio|ISDB|Digital Radio Mondiale}}
[[Digital radio]] broadcasting has emerged, first in [[Europe]] (the [[United Kingdom|UK]] in 1995 and [[Germany]] in 1999), and later in the United States, France, the Netherlands, South Africa, and many other countries worldwide. The simplest system is named DAB Digital Radio, for [[Digital Audio Broadcasting]], and uses the [[public ___domain]] [[Digital Audio Broadcasting|EUREKA 147]] (Band III) system. DAB is used mainly in the UK and South Africa. Germany and the Netherlands use the DAB and DAB+ systems, and France uses the L-Band system of DAB Digital Radio.
The broadcasting regulators of the United States and Canada have chosen to use [[HD radio]], an [[in-band on-channel]] system that puts digital broadcasts at frequencies adjacent to the analog broadcast. HD Radio is owned by a [[consortium]] of private companies that is called [[iBiquity]]. An international [[non-profit]] consortium [[Digital Radio Mondiale]] (DRM), has introduced the [[public ___domain]] DRM system, which is used by a relatively small number of broadcasters worldwide.
==International broadcasting==
{{Unreferenced section|date=June 2021}}
{{main|International broadcasting}}
[[File:World Family of Radio Maria.png|thumb|300px|Worldwide presence of [[Radio Maria]] broadcasters]]
Broadcasters in one country have several reasons to reach out to an audience in other countries. Commercial broadcasters may simply see a business opportunity to sell advertising or subscriptions to a broader audience. This is more efficient than broadcasting to a single country, because domestic entertainment programs and information gathered by domestic news staff can be cheaply repackaged for non-domestic audiences.
Governments typically have different motivations for funding international broadcasting. One clear reason is for ideological, or [[propaganda]] reasons. Many government-owned stations portray their nation in a positive, non-threatening way. This could be to encourage business investment in or tourism to the nation. Another reason is to combat a negative image produced by other nations or internal dissidents, or insurgents. [[Radio RSA]], the broadcasting arm of the apartheid South African government, is an example of this. A third reason is to promote the ideology of the broadcaster. For example, a program on [[Voice of Russia|Radio Moscow]] from the 1960s to the 1980s was ''What is Communism?''
A second reason is to advance a nation's foreign policy interests and agenda by disseminating its views on international affairs or on the events in particular parts of the world. During the [[Cold War]] the American [[Radio Free Europe/Radio Liberty|Radio Free Europe]] and [[Radio Free Europe/Radio Liberty|Radio Liberty]] and Indian Radio [[All India Radio|AIR]] were founded to broadcast news from "behind the [[Iron Curtain]]" that was otherwise being censored and promote dissent and occasionally, to disseminate [[disinformation]]. Currently, the US operates similar services aimed at [[Cuba]] ([[Radio y Televisión Martí]]) and the [[People's Republic of China]], [[Vietnam]], [[Laos]] and [[North Korea]] ([[Radio Free Asia]]).
Besides ideological reasons, many stations are run by religious broadcasters and are used to provide religious education, religious music, or worship service programs. For example, [[Vatican Radio]], established in 1931, broadcasts such programs. Another station, such as [[HCJB]] or [[Trans World Radio]] will carry brokered programming from evangelists. In the case of the [[Broadcasting Services of the Kingdom of Saudi Arabia]], both governmental and religious programming is provided.
==Extensions==
Extensions of traditional radio-wave broadcasting for [[audio broadcasting]] in general include [[cable radio]], local wire [[television network]]s, [[DTV radio]], [[satellite radio]], and [[Internet radio]] via [[streaming media]] on the [[Internet]].
===Satellite===
{{main|Satellite radio}}
The enormous entry costs of space-based satellite transmitters and restrictions on available [[radio spectrum]] licenses has restricted growth of [[Satellite radio]] broadcasts. In the US and [[Canada]], just two services, [[XM Satellite Radio]] and [[Sirius Satellite Radio]] exist. Both XM and Sirius are owned by [[Sirius XM Satellite Radio]], which was formed by the merger of XM and Sirius on July 29, 2008, whereas in [[Canada]], [[XM Radio Canada]] and [[Sirius Canada]] remained separate companies until 2010. [[1worldspace|Worldspace]] in Africa and Asia, and [[MobaHo!|MobaHO!]] in Japan and the ROK were two unsuccessful satellite radio operators which have gone out of business.
==Program formats==
{{Main|Radio format}}
Radio program formats differ by country, regulation, and markets. For instance, the U.S. [[Federal Communications Commission]] designates the 88–92 megahertz band in the U.S. for non-profit or educational programming, with advertising prohibited.
In addition, formats change in popularity as time passes and technology improves. Early radio equipment only allowed program material to be broadcast in real time, known as ''live'' broadcasting.
==Receiver==
{{excerpt|Broadcast radio receiver}}
==See also==
{{div col|colwidth=20em}}
* [[Broadcasting construction permit]]
* [[Call sign]]
* [[Disc jockey]] (DJ)
* [[History of broadcasting]]
* [[International broadcasting]]
* [[
* [[Low power radio station]]
* [[
* [[Radio]]
* [[Radio antenna]]
* [[Radio network]]
* [[Radio personality]]
* [[RF modulation]]
* [[Sports commentator]]
* [[Television station]]
{{div col end}}
==
{{Reflist}}
==External links==
{{Wiktionary}}
{{refbegin}}
*[http://www.fcc.gov/ Federal Communications Commission website] {{Webarchive|url=https://web.archive.org/web/20110217015410/http://www.fcc.gov/ |date=February 17, 2011 }} – fcc.gov
*[http://www.dxing.info DXing.info] {{Webarchive|url=https://web.archive.org/web/20060126210901/http://www.dxing.info/ |date=January 26, 2006 }} – Information about radio stations worldwide
*[http://www.radio-locator.com/ Radio-Locator.com] {{Webarchive|url=https://web.archive.org/web/20170828091833/http://www.radio-locator.com/ |date=August 28, 2017 }} – Links to 13,000 radio stations worldwide
*[http://www.bbc.co.uk/reception/ BBC reception advice] {{Webarchive|url=https://web.archive.org/web/20060116024539/http://www.bbc.co.uk/reception/ |date=January 16, 2006 }}
*[http://dxradio.50webs.com DXradio.50webs.com] {{Webarchive|url=https://web.archive.org/web/20070621021004/http://dxradio.50webs.com/ |date=June 21, 2007 }} "The SWDXER" – with general SWL information and radio antenna tips
*[http://www.radiostationzone.com RadioStationZone.com] {{Webarchive|url=https://web.archive.org/web/20190611132759/http://radiostationzone.com/ |date=June 11, 2019 }} – 10.000+ radio stations worldwide with ratings, comments and listen live links
*{{usurped|1=[https://web.archive.org/web/20200810081053/http://www.online-radio-stations.org/ Online-Radio-Stations.org]}} – The Web Radio Tuner has a comprehensive list of over 50.000 radio stations
*[http://www.unwantedemissions.com/ UnwantedEmissions.com] {{Webarchive|url=https://web.archive.org/web/20100902131421/http://www.unwantedemissions.com/ |date=September 2, 2010 }} – A general reference to radio spectrum allocations
*[http://www.navidiku.rs/radio-stanice/ Radio stanice] {{Webarchive|url=https://web.archive.org/web/20110906061202/http://www.navidiku.rs/radio-stanice/ |date=September 6, 2011 }} – Search for radio stations throughout the Europe
*[http://www.radioemisoraslatinas.com/ Radio Emisoras Latinas] {{Webarchive|url=https://web.archive.org/web/20130407163144/http://www.radioemisoraslatinas.com/ |date=April 7, 2013 }} – has a directory with thousands of Latin America Radio Stations
{{refend}}
{{Broadcasting}}
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{{Africa in topic|List of radio stations in}}
{{Asia in topic|List of radio stations in}}
{{Europe in topic|List of radio stations in}}
{{North America in topic|List of radio stations in}}
{{South America in topic|List of radio stations in}}
* [[:Category:Lists of radio stations]] by [[:Category:Radio stations by city|city]], [[:Category:Radio stations by country|country]], [[:Category:Radio stations by format|format]], [[:Category:Radio stations by language|language]], [[:Category:Radio stations by owner|owner]], [[:Category:Radio stations by year of establishment|year of establishment]]
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{{Authority control}}
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[[Category:Radio broadcasting| ]]
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