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{{Short description|Radio broadcasting using amplitude modulation}}
{{Redirect|AM radio|the song by Everclear|AM Radio (song)|the American musical group|AM Radio (band)}}
{{Infobox technology standard
| title             = AM broadcasting
| long_name         = [[Amplitude modulation]]
| image             = Amfm3-en-de.gif
| image_size        = 
| alt               = 
| caption           = AM and FM modulated signals for radio. [[amplitude modulation]] (AM) and [[frequency modulation]] (FM) are types of [[modulation]] (coding). The electrical signal from program material, usually coming from a [[radio studio|studio]], is mixed with a [[carrier wave]] of a specific frequency, then broadcast. In the case of AM, this mixing (modulation) is done by altering the [[amplitude]] (strength) of the carrier wave, proportional to the original signal. In contrast, in the case of FM, it is the carrier wave's [[frequency]] that is varied. A radio receiver contains a demodulator that [[Demodulation|extracts]] the original program material from the broadcast wave.
| abbreviation      = AM
| native_name       = <!-- Name in local language. If more than one, separate using {{plain list}} -->
| native_name_lang  = <!-- ISO 639-1 code e.g. "fr" for French. If more than one, use {{lang}} inside native_name items instead -->
| status            = Active
| year_started      = {{Start date and age|1901|df=y}}
| first_published   = <!-- {{Start date|YYYY|MM|DD|df=y}} -->
| version           = 
| version_date      = 
| preview           = 
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| organization      = 
| committee         = 
| series            = 
| editors           = 
| authors           = [[Reginald Fessenden]]
| base_standards    = 
| related_standards = 
| predecessor       = 
| successor         = 
| domain            = 
| license           = Public
| copyright         = 
| website           = {{URL| https://www.fcc.gov/general/am-radio}}
}}

'''AM broadcasting''' is [[radio broadcasting]] using [[amplitude modulation]] (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for [[medium wave]] (also known as "AM band") transmissions, but also on the longwave and [[shortwave radio]] bands.
 
The earliest experimental AM transmissions began in the early 1900s. However, widespread AM broadcasting was not established until the 1920s, following the development of [[vacuum tube]] receivers and transmitters. AM radio remained the dominant method of broadcasting for the next 30 years, a period called the "[[Golden Age of Radio]]", until [[television broadcasting]] became widespread in the 1950s and received much of the programming previously carried by radio. Later, AM radio's audiences declined greatly due to competition from FM ([[FM broadcasting|frequency modulation]]) radio, [[Digital Audio Broadcasting]] (DAB), [[satellite radio]], [[HD Radio|HD (digital) radio]], [[Internet radio]], [[music streaming service]]s, and [[podcast]]ing.

Compared to FM or [[Digital transmission|digital transmissions]], AM transmissions are more expensive to transmit due to the necessity of having to transmit a high power carrier wave to overcome ground losses, and the large antenna radiators required at the low broadcast frequencies, but can be sent over long distances via the ionosphere at night; however, they are much more susceptible to interference, and often have lower audio fidelity.<ref>{{Cite web |date=<!-- 9:40 AM EST --> November 6, 2017 |title=VERIFY: Why Does AM Radio Sound Worse Than FM? |url=https://www.wfmynews2.com/article/news/verify/verify-why-does-am-radio-sound-worse-than-fm/83-489480515 |access-date=2022-12-29 |website=wfmynews2.com |language=en-US}}</ref><ref>{{Cite web |title=A Science Odyssey: Radio Transmission: FM vs AM |url=https://www.pbs.org/wgbh/aso/tryit/radio/radiorelayer.html |access-date=December 29, 2022 |website=pbs.org}}</ref> Thus, AM broadcasters tend to specialize in spoken-word formats, such as [[talk radio]], [[all-news radio]] and [[sports radio]], with music formats primarily for FM and digital stations.

[[File:DRM-Frequenzbereiche.png|thumb|Main radio bands]]

==History==
{{broader|History of radio|History of broadcasting}}
{{see also|FM broadcasting#History}}

{{Pull quote|text=People who weren't around in the Twenties when radio exploded can't know what it meant, this milestone for mankind. Suddenly, with radio, there was instant human communication. No longer were our homes isolated and lonely and silent. The world came into our homes for the first time. Music came pouring in. Laughter came in. News came in. The world shrank, with radio.|author=[[Red Barber]], sportscaster|source=<ref name="Nahin">{{cite book
 | last1  = Nahin
 | first1 = Paul J.
 | title  = The Science of Radio: With Matlab and Electronics Workbench Demonstration, 2nd Ed.
 | publisher = Springer Science & Business Media 
 | date   = 2001
 | pages  = xxxix
 | url    = https://books.google.com/books?id=V1GBW6UD4CcC&pg=PR39
 | isbn   = 0387951504
 }}</ref>}}

===Early broadcasting development===
[[File:Mariette Mazarin 1908 radio broadcast.png|thumb|One of the earliest radio broadcasts, French soprano Mariette Mazarin singing into Lee de Forest's arc transmitter in New York City on February 24, 1910.<ref>[https://books.google.com/books?id=cSfOAAAAMAAJ&pg=PA333 "A Review of Radio"], by Lee de Forest, ''Radio Broadcast'', Vol. 1, No. 4, August 1922, p. 333.</ref>]]
[[File:De Forest xmtr broadcasting presidential election Nov 1916.jpg|thumb|Lee de Forest used an early vacuum-tube transmitter to broadcast returns for the Hughes-Wilson presidential election returns on November 7, 1916, over [[Radio 2XG|2XG]] in New York City. Pictured is engineer Charles Logwood.<ref>[https://www.worldradiohistory.com/Archive-Electrical-Experimenter/EE-1917-01.pdf#page=30 "Election Returns Flashed by Radio to 7,000 Amateurs"], ''Electrical Experimenter'', Vol. 4, No. 9, January 1917, p. 650.</ref>]]
The idea of broadcasting — the unrestricted transmission of signals to a widespread audience — dates back to the founding period of radio development, even though the earliest radio transmissions, originally known as "Hertzian radiation" and "wireless telegraphy", used [[spark-gap transmitter]]s that could only transmit the dots-and-dashes of [[Morse code]]. In October 1898, a London publication, ''The Electrician'', noted that "there are rare cases where, as Dr. [[Oliver Lodge|[Oliver] Lodge]] once expressed it, it might be advantageous to 'shout' the message, spreading it broadcast to receivers in all directions".<ref>[https://babel.hathitrust.org/cgi/pt?id=njp.32101050973286&view=1up&seq=842 "Wireless Telegraphy"], ''The Electrician (London)'', October 14, 1898, pp. 814–815.</ref> However, it was recognized that this would involve significant financial issues, as that same year ''The Electrician'' also commented "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>[https://babel.hathitrust.org/cgi/pt?id=uc1.c2602954&view=1up&seq=476 "Hertzian Telegraphy at the Physical Society], ''The Electrician (London)'', January 28, 1898, pp. 452–453.</ref>

On January 1, 1902, [[Nathan Stubblefield]] gave a short-range "wireless telephone" demonstration, that included simultaneously broadcasting speech and music to seven locations throughout Murray, Kentucky. However, this was transmitted using [[electromagnetic induction|induction]] rather than radio signals, and although Stubblefield predicted that his system would be perfected so that "it will be possible to communicate with hundreds of homes at the same time", and "a single message can be sent from a central station to all parts of the United States", he was unable to overcome the inherent distance limitations of this technology.<ref>[https://gahistoricnewspapers.galileo.usg.edu/lccn/sn87090456/1902-03-08/ed-1/seq-6/ "Kentucky Inventor Solves Problem of Wireless Telephony"], ''The Sunny South'', March 8, 1902, p. 6.</ref>

The earliest public radiotelegraph broadcasts were provided as government services, beginning with daily time signals inaugurated on January 1, 1905, by a number of U.S. Navy stations.<ref>[https://books.google.com/books?id=WsYSAAAAYAAJ&pg=PA52 "The First Wireless Time Signal"] (letter from Captain J. L. Jayne), ''Electrician and Mechanic'', January 1913, page 52. (Reprinted from ''The American Jeweler'', October 1912, p. 411).</ref> In Europe, signals transmitted from a station located on the [[Eiffel Tower]] were received throughout much of Europe. In both the United States and France this led to a small market of receiver lines geared for jewelers who needed accurate time to set their clocks, including the Ondophone in France,<ref>[https://babel.hathitrust.org/cgi/pt?id=njp.32101042848000&view=1up&seq=903 "Vest-Pocket Wireless Receiving Instrument"], ''Electrical Review and Western Electrician'', April 11, 1914, p. 745.</ref> and the De Forest RS-100 Jewelers Time Receiver in the United States<ref>[https://books.google.com/books?id=-MI7AQAAMAAJ&pg=PA200 "Radio Apparatus"] (advertisement), ''Radio Amateur News'', October 1919, p. 200.</ref>
The ability to pick up time signal broadcasts, in addition to Morse code weather reports and news summaries, also attracted the interest of [[amateur radio]] enthusiasts.

===Early amplitude modulation (AM) transmitter technologies===
It was immediately recognized that, much like the telegraph had preceded the invention of the telephone, the ability to make audio radio transmissions would be a significant technical advance. Despite this knowledge, it still took two decades to perfect the technology needed to make quality audio transmissions. In addition, the telephone had rarely been used for distributing entertainment, outside of a few "[[telephone newspaper]]" systems, most of which were established in Europe, beginning with the Paris [[Théâtrophone]]. With this in mind, most early [[radiotelephone]] development envisioned that the device would be more profitably developed as a "wireless telephone" for personal communication, or for providing links where regular telephone lines could not be run, rather than for the uncertain finances of broadcasting.
[[File:15JUN1920 Melba radio broadcast.jpg|thumb|[[Nellie Melba]] making a broadcast over the Marconi Chelmsford Works radio station in England on June 15, 1920.<ref>[https://babel.hathitrust.org/cgi/pt?id=hvd.32044102952173&seq=70 "A Newspaper's Use of the Radio Phone"], ''The Wireless Age'', November 1920,  page 10.</ref>]]
[[File:20111110-OC-AMW-0038 - Flickr - USDAgov (1).jpg|thumb|upright=1.2|Farmer listening to U.S. government weather and crop reports using a crystal radio in 1923. Public service government time, weather, and farm broadcasts were the first radio "broadcasts".]] 
[[File:Crystal radio advertisement.png|thumb|upright=1.3|A family listening to an early broadcast using a [[crystal radio]] receiver in 1922. Crystal sets, used before the advent of vacuum tube radios in the 1920s, could not drive [[loudspeaker]]s, so the family had to listen on earphones.]]

The person generally credited as the primary early developer of AM technology is Canadian-born inventor [[Reginald Fessenden]]. The original spark-gap radio transmitters were impractical for transmitting audio, since they produced discontinuous pulses known as "[[damped wave]]s". Fessenden realized that what was needed was a new type of radio transmitter that produced steady "undamped" (better known as "[[continuous wave]]") signals, which could then be "modulated" to reflect the sounds being transmitted.

Fessenden's basic approach was disclosed in U.S. Patent 706,737, which he applied for on May 29, 1901, and was issued the next year. It called for the use of a high-speed [[alternator]] (referred to as "an alternating-current dynamo") that generated "pure sine waves" and produced "a continuous train of radiant waves of substantially uniform strength", or, in modern terminology, a continuous-wave (CW) transmitter.<ref>[https://patentimages.storage.googleapis.com/pdfs/US706737.pdf U.S. Patent 706,737], submitted May 29, 1901, and issued August 12, 1902, to Reginald Fessenden.</ref> Fessenden began his research on audio transmissions while doing developmental work for the United States Weather Service on Cobb Island, Maryland. Because he did not yet have a continuous-wave transmitter, initially he worked with an experimental "high-frequency spark" transmitter, taking advantage of the fact that the higher the spark rate, the closer a spark-gap transmission comes to producing continuous waves. He later reported that, in the fall of 1900, he successfully transmitted speech over a distance of about 1.6 kilometers (one mile),<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015057240221&view=1up&seq=113 "Experiments and Results in Wireless Telephony"], by John Grant, ''The American Telephone Journal'', January 26, 1907, pp. 49–51.</ref> which appears to have been the first successful audio transmission using radio signals. However, at this time the sound was far too distorted to be commercially practical.<ref>''The Continuous Wave'' by Hugh G. J. Aitken, 1985, p. 61.</ref> For a time he continued working with more sophisticated high-frequency spark transmitters, including versions that used compressed air, which began to take on some of the characteristics of [[arc converter|arc-transmitters]].<ref>Aitken (1985), p. 62.</ref> Fessenden attempted to sell this form of radiotelephone for point-to-point communication, but was unsuccessful.<ref name=FESS>{{cite web|url=https://ewh.ieee.org/reg/7/millennium/radio/radio_wireless.html |title=Fessenden, Reginald A. ''Inventing the Wireless Telephone and the Future'' |publisher=[[IEEE]] |access-date=2017-07-22}}</ref>

====Alternator transmitter====

Fessenden's work with high-frequency spark transmissions was only a temporary measure. His ultimate plan for creating an audio-capable transmitter was to redesign an electrical [[alternator]], which normally produced alternating current of at most a few hundred ([[hertz|Hz]]), to increase its rotational speed and so generate currents of tens-of-thousands Hz, thus producing a steady continuous-wave transmission when connected to an aerial. The next step, adopted from standard wire-telephone practice, was to insert a simple [[carbon microphone]] into the transmission line, to modulate the [[carrier wave]] signal to produce AM audio transmissions. However, it would take many years of expensive development before even a prototype alternator-transmitter would be ready, and a few years beyond that for high-power versions to become available.<ref>Aitken (1985), p. 69.</ref>

Fessenden worked with [[General Electric]]'s (GE) [[Ernst Alexanderson|Ernst F. W. Alexanderson]], who in August 1906, delivered an improved model which operated at a transmitting frequency of approximately 50&nbsp;kHz, although at low power. The alternator-transmitter achieved the goal of transmitting quality audio signals, but the lack of any way to amplify the signals meant they were somewhat weak. On December 21, 1906, Fessenden made an extensive demonstration of the new alternator-transmitter at Brant Rock, Massachusetts, showing its utility for point-to-point wireless telephony, including interconnecting his stations to the wire telephone network. As part of the demonstration, speech was transmitted 18 kilometers (11 miles) to a listening site at Plymouth, Massachusetts.<ref name="experiments">"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=111 Part I]: January 26, 1907, pp. 49–51; [https://babel.hathitrust.org/cgi/pt?id=mdp.39015057240221&view=1up&seq=151 Part II]: February 2, 1907, pp. 68–70, 79–80.</ref>

An ''American Telephone Journal'' account of the December 21 alternator-transmitter demonstration included the statement that "It is admirably adapted to the transmission of news, music, etc. as, owing to the fact that no wires are needed, simultaneous transmission to many subscribers can be effected as easily as to a few",<ref name="experiments"/> echoing the words of a handout distributed to the demonstration witnesses, which stated "[Radio] Telephony is admirably adapted for transmitting news, stock quotations, music, race reports, etc. simultaneously over a city, on account of the fact that no wires are needed and a single apparatus can distribute to 10,000 subscribers as easily as to a few. It is proposed to erect stations for this purpose in the large cities here and abroad."<ref>[https://www.radioworld.com/columns-and-views/dec-21-1906-a-very-significant-date-in-radio/338869 "Dec. 21, 1906: A Very Significant Date in Radio"] by James E. O'Neal, December 22, 2016 (radioworld.com).</ref> However, other than two holiday transmissions reportedly made shortly after these demonstrations, Fessenden does not appear to have conducted any radio broadcasts for the general public, or to have even given additional thought about the potential of a regular broadcast service, and in a 1908 article providing a comprehensive review of the potential uses for his radiotelephone invention, he made no references to broadcasting.<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015068171985&view=1up&seq=638 "Wireless Telephony: G. Possibilities"] by Reginald A. Fessenden, ''Transactions of the American Institute of Electrical Engineers'', Vol. XXVII (1908), Part I, pp. 606–608.</ref>

Because there was no way to amplify electrical currents at this time, modulation was usually accomplished by a carbon [[microphone]] inserted directly in the antenna wire. This meant that the full transmitter power flowed through the microphone, and even using water cooling, the power handling ability of the microphones severely limited the power of the transmissions. Ultimately only a small number of large and powerful [[Alexanderson alternator]]s would be developed. However, they would be almost exclusively used for long-range radiotelegraph communication, and occasionally for radiotelephone experimentation, but were never used for general broadcasting.

====Arc transmitters====
Almost all of the continuous wave AM transmissions made prior to 1915 were made by versions of the [[arc converter]] transmitter, which had been initially developed by [[Valdemar Poulsen]] in 1903.<ref>[https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=789449A&KC=A&FT=D&ND=1&date=19050509&DB=&locale=en_EP# "Method of Producing Alternating Currents With a High Number of Vibrations"] U.S. patent 789,449, filed June 10, 1903, and granted May 9, 1905, to Valdemar Poulsen.</ref> Arc transmitters worked by producing a pulsating electrical arc in an enclosed hydrogen atmosphere. They were much more compact than alternator transmitters, and could operate on somewhat higher transmitting frequencies. However, they suffered from some of the same deficiencies. The lack of any means to amplify electrical currents meant that, like the alternator transmitters, modulation was usually accomplished by a microphone inserted directly in the antenna wire, which again resulted in overheating issues, even with the use of water-cooled microphones. Thus, transmitter powers tended to be limited. The arc was also somewhat unstable, which reduced audio quality. Experimenters who used arc transmitters for their radiotelephone research included [[Ernst Ruhmer]], [[Quirino Majorana]], [[Charles Herrold|Charles "Doc" Herrold]], and [[Lee de Forest]].

====Vacuum tube transmitters====
Advances in [[vacuum tube]] technology (called "valves" in British usage), especially after around 1915, revolutionized radio technology. Vacuum tube devices could be used to amplify electrical currents, which overcame the overheating issues of needing to insert microphones directly in the transmission antenna circuit. Vacuum tube transmitters also provided high-quality AM signals, and could operate on higher transmitting frequencies than alternator and arc transmitters.<ref>[https://archive.org/stream/electricalexperi07gern#page/1000/mode/1up "The Versatile Audion"] by H. Winfield Secor, ''Electrical Experimenter'', February 1920, pages 1000–1001, 1080-1083.</ref> Non-governmental radio transmissions were prohibited in many countries during World War I, but AM radiotelephony technology advanced greatly due to wartime research, and after the war the availability of tubes sparked a great increase in the number of amateur radio stations experimenting with AM transmission of news or music. Vacuum tubes remained the central technology of radio for 40 years, until [[transistor]]s began to dominate in the late 1950s, and are still used in the highest power broadcast transmitters.

===Receivers===
[[File:Vintage Zenith Console Radio, Model 12S-568, With the Zenith Robot (or Shutter) Dial, Circa 1941 (8655513293).jpg|thumb|1938 Zenith Model 12-S vacuum-tube console radio, capable of picking up mediumwave and shortwave AM transmissions. "All Wave" receivers could also pick up the third AM band: longwave (LW).]]
Unlike telegraph and telephone systems, which used completely different types of equipment, most radio receivers were equally suitable for both radiotelegraph and radiotelephone reception. In 1903 and 1904, the [[electrolytic detector]] and [[thermionic diode]] ([[Fleming valve]]) were invented by [[Reginald Fessenden]] and [[John Ambrose Fleming]], respectively. Most important, in 1904–1906, the [[crystal detector]], the simplest and cheapest AM detector, was developed by [[Greenleaf Whittier Pickard|G. W. Pickard]]. Homemade [[crystal radio]]s spread rapidly during the next 15 years, providing ready audiences for the first radio broadcasts. One limitation of crystals sets was the lack of amplifying the signals, so listeners had to use [[earphone]]s, and it required the development of vacuum-tube receivers before [[loudspeaker]]s could be used. The [[Loudspeaker|dynamic cone loudspeaker]], invented in 1924, greatly improved audio [[frequency response]] over the previous horn speakers, allowing music to be reproduced with good fidelity.<ref name="McNicol13">{{Cite web|url=http://archive.org/details/radiosconquestof00mcnirich|title=Radio's conquest of space|first=Donald Monroe|last=McNicol|date=August 11, 1946|publisher=New York : Murry Hill|via=Internet Archive}}</ref> AM radio offered the highest sound quality available in a home audio device prior to the introduction of the [[high-fidelity]], [[long-playing]] record in the late 1940s.

Listening habits changed in the 1960s due to the introduction of the revolutionary [[transistor radio]] (Regency TR-1, the first transistor radio released December 1954), which was made possible by the invention of the [[transistor]] in 1948. (The transistor was invented at Bell labs and released in June 1948.) Their compact size — small enough to fit in a shirt pocket — and lower power requirements, compared to vacuum tubes, meant that for the first time radio receivers were readily portable. The transistor radio became the most widely used communication device in history, with billions manufactured by the 1970s. Radio became a ubiquitous "companion medium" which people could take with them anywhere they went.

===Early experimental broadcasts===

The demarcation between what is considered "experimental" and "organized" broadcasting is largely arbitrary. Listed below are some of the early AM radio broadcasts, which, due to their irregular schedules and limited purposes, can be classified as "experimental":

* <u>Christmas Eve 1906.</u> Until the early 1930s, it was generally accepted that [[Lee de Forest]]'s series of demonstration broadcasts begun in 1907 were the first transmissions of music and entertainment by radio. However, in 1932, an article prepared by Samuel M. Kintner, a former associate of Reginald Fessenden, asserted that Fessenden had actually conducted two earlier broadcasts.<ref>"Pittsburgh's Contributions to Radio" by S. M. Kintner, ''Proceedings of the Institute of Radio Engineers'', December 1932, pp. 1849–1862.</ref> This claim was based solely on information included in a January 29, 1932, letter that Fessenden had sent to Kintner. (Fessenden subsequently died 5 months before Kintner's article appeared.) In his letter, Fessenden reported that, on the evening of December 24, 1906 ([[Christmas Eve]]), he had made the first of two broadcasts of music and entertainment to a general audience, using the alternator-transmitter at Brant Rock, Massachusetts. Fessenden remembered producing a short program that included playing a phonograph record, followed by his playing the violin and singing, and closing with a Bible reading. He also stated that a second short program was broadcast on December 31 ([[New Year's Eve]]). The intended audience for both transmissions was primarily shipboard radio operators along the Atlantic seaboard. Fessenden claimed these two programs had been widely publicized in advance, with the Christmas Eve broadcast heard "as far down" as Norfolk, Virginia, while the New Year's Eve broadcast had been received in the West Indies.<ref>[https://babel.hathitrust.org/cgi/pt?id=uc1.b4540711&view=1up&seq=167 ''Fessenden: Builder of Tomorrows''] by Helen Fessenden, 1940, pp. 153–154.</ref> However, extensive efforts to verify Fessenden's claim during both the 50th<ref>[https://www.radioworld.com/columns-and-views/fessenden-the-next-chapter/300426 "Fessenden — The Next Chapter"] by James E. O'Neal, ''Radio World'', December 23, 2008 (radioworld.com).</ref> and 100th<ref>[https://www.radioworld.com/news-and-business/fessenden-worlds-first-broadcaster/311783 "Fessenden, World's First Broadcaster?"] by James E. O'Neal, ''Radio World'', October 25, 2006 (radioworld.com).</ref> anniversaries of the claimed broadcasts, which included reviewing ships' radio log accounts and other contemporary sources, have so far failed to confirm that these reported holiday broadcasts actually took place.
* <u>1907-1912.</u> Lee de Forest conducted multiple test broadcasts beginning in 1907, and was widely quoted promoting the potential of organized radio broadcasting. Using a series of arc transmitters, he made his first entertainment broadcast in February 1907, transmitting electronic [[telharmonium]] music from his Parker Building laboratory station in New York City.<ref>''Father of Radio'' by Lee de Forest, 1950, pages 225.</ref> This was followed by tests that included, in the fall, [[Eugenia Farrar]] singing "[[I Love You Truly]]" and "[[Just Awearyin' for You]]".<ref>"I Was First to Sing Over the Radio" by Eugenia H. Farrar, ''The American Swedish Monthly'', January 1955, pp. 10, 26.</ref> Additional promotional events in New York included live performances by famous Metropolitan Opera stars such as Mariette Mazarin and [[Enrico Caruso]]. He also broadcast phonograph music from the [[Eiffel Tower]] in Paris. His company equipped the U.S. Navy's [[Great White Fleet]] with experimental arc radiotelephones for their 1908 around-the-world cruise, and the operators broadcast phonograph music as the ships entered ports like San Francisco and Honolulu.<ref>[https://chroniclingamerica.loc.gov/lccn/sn82015415/1908-11-25/ed-1/seq-1/ "Mysterious Voices Startled Him: Wizard Isbell Thought He Heard Angels Talking"], ''Hawaiian Star'', November 25, 1908, p. 1.</ref>
* <u>June 1910.</u> In a June 23, 1910, notarized letter that was published in a catalog produced by the Electro Importing Company of New York, Charles "Doc" Herrold reported that, using one of that company's spark coils to create a "high frequency spark" transmitter, he had successfully broadcast "wireless phone concerts to local amateur wireless men". Herrold lived in San Jose, California.<ref>Electro Importing Company catalog page, reproduced in ''Charles Herrold, Inventor of Radio Broadcasting'' by Gordon Greb and Mike Adams, 2003, p. 6.</ref>
* <u>1913.</u> Robert Goldschmidt began experimental radiotelephone transmissions from the [[Robert Goldschmidt#First European scheduled broadcasts|Laeken station]], near Brussels, Belgium, and by March 13, 1914, the tests had been heard as far away as the Eiffel Tower in Paris.<ref name="cahiers">''"De la T.S.F. au Congo-Belge et de l'école pratique de Laeken aux concerts radiophoniques"'' (Wireless in the Belgian Congo and from the Laeken Training School to Radio Concerts) by Bruno Brasseur, ''Cahiers d'Histoire de la Radiodiffusion'', Number 118, October–December 2013.</ref>
* <u>1914–1919.</u> "University of Wisconsin electrical engineering Professor Edward Bennett sets up a personal radio transmitter on campus and in June 1915 is issued an Experimental radio station license with the call sign 9XM.<ref name="wprs">[https://www.wpr.org/wprs-tradition-innovation Wisconsin Public Radio's Tradition Of Innovation] (wpr.org)</ref> Activities included regular Morse Code broadcasts of weather forecasts and  sending game reports for a Wisconsin-Ohio State basketball game on February 17, 1917.
* <u>January 15, 1920.</u> Broadcasting in the United Kingdom began with impromptu news and phonograph music over 2MT, the 15&nbsp;kW experimental tube transmitter at Marconi's factory in [[Chelmsford]], Essex, at a frequency of 120&nbsp;kHz. On June 15, 1920, the ''[[Daily Mail]]'' newspaper sponsored the first scheduled British radio concert, by the famed Australian opera diva [[Nellie Melba]].<ref>[https://books.google.com/books?id=R88-AQAAMAAJ&pg=RA1-PA10 "A Newspaper's Use of the Radio Phone"], ''The Wireless Age'', November 1920, p. 10.</ref> This transmission was heard throughout much of Europe, including in Berlin, Paris, The Hague, Madrid, Spain, and Sweden. Chelmsford continued broadcasting concerts with noted performers. A few months later, in spite of burgeoning popularity, the government ended the broadcasts, due to complaints that the station's longwave signal was interfering with more important communication, in particular military aircraft radio.<ref>''The History of Broadcasting in the United Kingdom: Vol. I: The Birth of Broadcasting'' by Asa Briggs, 1961, pp. 49–50.</ref>
* <u>August 27, 1920.</u> Argentina made the first mass radio transmission as a communication medium. Medicine students of the UBA made the first radio program by transmitting Wagner's Parsifal on radio and picked up by about 100 amateurs in the city, emitting from the roof of the Teatro Colón. They kept transmitting over the nights different operas being the first in offering a radio program. There were known as the "Locos de la azotea" (the crazies of the roof).<ref>{{Cite web|url=https://www.radionacional.com.ar/la-verdadera-historia-de-los-locos-de-la-azotea/|title=La Verdadera Historia de los Locos de la Azotea – Radio Nacional}}</ref>

===Organized broadcasting===
{{Pull quote|text=People who weren't around in the 20s when radio exploded can't know what it meant, this milestone for mankind. Suddenly, with radio, there was instant human communication. No longer were our homes isolated and lonely and silent. The world came into our homes for the first time. Music came pouring in. Laughter came in. News came in. The world shrank, with radio.|author=[[Red Barber]], sportscaster|source=<ref>''The Broadcasters'' by Red Barber, 1970, pp. 11–12.</ref>}}
[[File:Musical Concert by Wireless Telephone (scan) - 23JUL1912.jpg|thumb|In July 1912, Charles "Doc" Herrold began weekly broadcasts in San Jose, California, using an arc transmitter.]]
[[File:German Post Office subscription radio receiver 1923.jpg|thumb|upright=1.2|Broadcasting in Germany began 1922 as a Post Office monopoly on a subscription basis, using sealed receivers which could only receive one station.]]

Following World War I, the number of stations providing a regular broadcasting service greatly increased, primarily due to advances in vacuum-tube technology. In response to ongoing activities, government regulators eventually codified standards for which stations could make broadcasts intended for the general public, for example, in the United States formal recognition of a "broadcasting service" came with the establishment of regulations effective December 1, 1921,<ref>[https://babel.hathitrust.org/cgi/pt?id=osu.32435066705633&view=1up&seq=200 "Miscellaneous: Amendments to Regulations"], ''Radio Service Bulletin'', January 3, 1922, p. 10.</ref> and Canadian authorities created a separate category of "radio-telephone broadcasting stations" in April 1922.<ref>"Radio Department: Broadcasting Stations", ''Winnipeg Evening Tribune'', April 25, 1922, p. 5.</ref> However, there were numerous cases of entertainment broadcasts being presented on a regular schedule before their formal recognition by government regulators. Some early examples include:

* <u>July 21, 1912.</u> The first person to transmit entertainment broadcasts on a regular schedule appears to have been Charles "Doc" Herrold, who inaugurated weekly programs, using an arc transmitter, from his Wireless School station in San Jose, California.<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> The broadcasts continued until the station was shut down due to the entrance of the United States into World War I in April 1917.
* <u>March 28, 1914.</u> The [[Robert Goldschmidt#First European scheduled broadcasts|Laeken station]] in Belgium, under the oversight of Robert Goldschmidt, inaugurated a weekly series of concerts,<ref>[https://chroniclingamerica.loc.gov/lccn/sn83045462/1914-03-29/ed-1/seq-2/ "Hear Tenor Through Wireless"], ''Washington Evening Star'', 29 March 1914, Part one, p. 2.</ref> transmitted at 5:00&nbsp;p.m. on Saturdays. These continued for about 4 months until July, and were ended by the start of World War I.<ref>[https://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19340425-1.2.100 "20th Anniversary of First Broadcast"] by Raymond Braillard, ''The (Singapore) Straits Times'', 25 April 1934, p. 17 (reprinted from the British Broadcasting Corporation's ''World-Radio'', 30 March 1934, p. 446) (nlb.gov.sg).</ref> In August 1914 the Laeken facilities were destroyed, to keep them from falling into the hands of invading German troops.
* <u>November 1916.</u> De Forest perfected "Oscillion" power vacuum tubes, capable of use in radio transmitters, and inaugurated daily broadcasts of entertainment and news from his New York "Highbridge" station, [[Radio 2XG|2XG]]. This station also suspended operations in April 1917 due to the prohibition of civilian radio transmissions following the United States' entry into World War I.<ref name="Telephony1916">{{cite journal
  | title = Wireless Transmission of News
  | journal = Telephony
  | volume = 71
  | issue = 27
  | pages = 32–33
  | publisher = Telephony Publishing Co.
  | location = Chicago
  | date = December 30, 1916
  | url = https://books.google.com/books?id=_NQ7AQAAMAAJ&pg=RA20-PT20
  | access-date = December 23, 2015}}</ref> Its most publicized program was the broadcasting of election results for the [[1916 United States presidential election|Hughes-Wilson presidential election]] on November 7, 1916, with updates provided by wire from the ''[[New York American]]'' offices. An estimated 7,000 radio listeners as far as 200 miles (320 kilometers) from New York heard election returns interspersed with patriotic music.<ref name="Experimenter1917">[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. (archive.org)</ref>
* <u>April 17, 1919.</u> Shortly after the end of World War I, F.&nbsp;S. McCullough at the Glenn L. Martin aviation plant in Cleveland, Ohio, began a weekly series of phonograph concerts.<ref>"Hear Caruso Sing by Wireless Thursday!", ''Cleveland Plain Dealer'', April 17, 1919, page 1.</ref> However, the broadcasts were soon suspended, due to interference complaints by the U.S. Navy.<ref>"Stop Wireless Concerts Here", ''Cleveland Plain Dealer'', May 29, 1919, p. 9.</ref> 
* <u>November 6, 1919.</u> The first scheduled (pre-announced in the press) Dutch radio broadcast was made by Nederlandsche Radio Industrie station [[PCGG]] at The Hague, which began regular concerts broadcasts. It found it had a large audience outside the Netherlands, mostly in the UK. (Rather than true AM signals, at least initially this station used a form of narrowband FM, which required receivers to be slightly detuned to receive the signals using [[Detector (radio)#Frequency and phase modulation detectors|slope detection]].)<ref>[https://www.americanradiohistory.com/hd2/IDX-Site-Early-Radio/Archive-Wireless-World-IDX/80s/Wireless-World-1986-02-OCR-Page-0028.pdf "Communications Commentary: PCGG"], ''Electronics & Wireless World'', February 1986, p. 26.</ref>
* <u>Late 1919.</u> De Forest's New York station, 2XG, returned to the airwaves in late 1919 after having to suspend operations during World War I.<ref>[https://books.google.com/books?id=-MI7AQAAMAAJ&pg=PA295 "Foot Ball Score—Via Wireless Telephone"] by Morris Press, ''Radio Amateur News'', December 1919, pp. 295, 321.</ref> The station continued to operate until early 1920, when it was shut down because the transmitter had been moved to a new location without permission.
* <u>May 20, 1920.</u> Experimental Canadian Marconi station [[CINW|XWA]] (later CFCF, deleted in 2010 as CINW) in Montreal began regular broadcasts,<ref>[https://news.google.com/newspapers?id=9P8tAAAAIBAJ&sjid=cYEFAAAAIBAJ&pg=1878%2C5556437 "Wireless Concert Given for Ottawa"], ''Montreal Gazette'', May 21, 1920, p. 4.</ref> and claims status as the first commercial broadcaster in the world.
* <u>June 1920.</u> De Forest transferred 2XG's former transmitter to San Francisco, California, where it was relicensed as [[KZY|6XC]], the "California Theater station".<ref>"Ninth California Theatre Concert", ''Pacific Coast Musical Review'', May 29, 1920, page 9.</ref> By June 1920 the station began transmitting daily concerts.<ref>"Electrical Home Visitors to Hear Wireless Concert", ''San Francisco Chronicle'', June 20, 1920, p. 8.</ref> De Forest later stated that this was the "first radio-telephone station devoted solely" to broadcasting to the public.<ref>[https://books.google.com/books?id=hSEVAQAAMAAJ&pg=PA936 News by Radiotelephone"] (letter from Lee de Forest), ''Electrical World'', April 23, 1921, p. 936.</ref>
* <u>August 20, 1920.</u> On this date the ''[[Detroit News]]'' began daily transmissions over station [[WWJ (AM)|8MK]] (later WWJ), located in the newspaper's headquarters building. The newspaper began extensively publicizing station operations beginning on August 31, 1920, with a special program featuring primary election returns.<ref>[https://commons.wikimedia.org/wiki/File:The_News_Radiophone_to_Give_Vote_Results_-_31AUG1920.jpg "The News Radiophone To Give Vote Results"], ''Detroit News'', August 31, 1920, pp. 1–2.</ref> Station management later claimed the title of being where "commercial radio broadcasting began".<ref>[https://www.americanradiohistory.com/hd2/IDX-Business/Magazines/Archive-BC-IDX/45-OCR/1945-08-20-BC-OCR-Page-0031.pdf WWJ (advertisement)], ''Broadcasting Magazine'', August 20, 1945, p. 31. (americanradiohistory.com)</ref>
* <u>November 2, 1920.</u> Beginning on October 17, 1919,<ref>[https://news.google.com/newspapers?id=731RAAAAIBAJ&sjid=VWgDAAAAIBAJ&pg=1821%2C536271 "The Radio Amateur: Wireless Telephone Here"] by C. E. Urban, ''Pittsburgh Gazette Times'', Sixth section, p. 13.</ref> Westinghouse engineer [[Frank Conrad]] began broadcasting recorded and live music on a semi-regular schedule from his home station, 8XK in Wilkinsburg, Pennsylvania. This inspired his employer to begin its own ambitious service at the company's headquarters in East Pittsburgh, Pennsylvania. Operations began, initially with the call sign 8ZZ, with an election night program featuring election returns on November 2, 1920.<ref>[https://commons.wikimedia.org/wiki/File:To_Give_Election_Results_by_Radio_-_28OCT1920.jpg "To Give Election Results by Radio"], ''Cleveland Plain Dealer'', October 28, 1920, p. 10.</ref> As [[KDKA (AM)|KDKA]], the station adopted a daily schedule beginning on December 21, 1920.<ref>[https://babel.hathitrust.org/cgi/pt?id=njp.32101051572632&view=1up&seq=558 "KDKA"], ''The Wireless Age'', August 1922, p. 40.</ref> This station is another contender for the title of "first commercial station".
* <u>January 3, 1921.</u> University of Wisconsin - Regular schedule of voice broadcasts begin; 9XM is the first radio station in the United States to provide the weather forecast by voice (January 3). In September, farm market broadcasts are added. On November 1, 9XM carries the first live broadcast of a symphony orchestra—the Cincinnati Symphony Orchestra from the UW Armory using a single microphone.<ref name="wprs" />

===Radio networks===
{{main|Radio network}}
[[File:Broadcasting a radio play at NBC studio.jpg|thumb|upright=1.5|A live radio play being broadcast at NBC studios in New York. Most 1920s through 1940s network programs were broadcast live.]]

Because most longwave radio frequencies were used for international radiotelegraph communication, a majority of early broadcasting stations operated on mediumwave frequencies, whose limited range generally restricted them to local audiences. One method for overcoming this limitation, as well as a method for sharing program costs, was to create radio [[Radio network|networks]], linking stations together with telephone lines to provide a nationwide audience.

====United States====
In the U.S., the [[AT&T|American Telephone and Telegraph Company]] (AT&T) was the first organization to create a radio network, and also to promote commercial advertising, which it called "toll" broadcasting. Its flagship station, [[WFAN (AM)|WEAF]] (now WFAN) in New York City, sold blocks of airtime to commercial sponsors that developed entertainment shows containing [[radio commercial|commercial messages]]. AT&T held a monopoly on quality telephone lines, and by 1924 had linked 12 stations in Eastern cities into a "chain". The [[RCA Corporation|Radio Corporation of America]] (RCA), [[General Electric]], and [[Westinghouse Electric Corporation|Westinghouse]] organized a competing network around its own flagship station, RCA's [[WABC (AM)|WJZ]] (now WABC) in New York City, but were hampered by AT&T's refusal to lease connecting lines or allow them to sell airtime. In 1926, AT&T sold its radio operations to RCA, which used them to form the nucleus of the new [[National Broadcasting Company|NBC]] network.<ref>[https://news.google.com/newspapers?id=iI8tAAAAIBAJ&sjid=yZwFAAAAIBAJ&pg=5492%2C2424619 "Announcing the National Broadcasting Company, Inc."] (advertisement), ''Reading (Pennsylvania) Eagle'', September 13, 1926, p. 10.</ref> By the 1930s, most of the major radio stations in the country were affiliated with networks owned by two companies, NBC and [[Columbia Broadcasting System|CBS]]. In 1934, a third national network, the [[Mutual Radio Network]], was formed as a cooperative owned by its stations.

====United Kingdom====
[[File:BBC receiver license 1923.jpg|325px|thumb|A BBC receiver licence from 1922. The British government required listeners to purchase yearly licences, which financed the stations.]]

A second country which quickly adopted network programming was the United Kingdom, and its national network quickly became a prototype for a state-managed monopoly of broadcasting.<ref name="Hilmes">{{cite book
  | last = Hilmes
  | first = Michele 
  | title = Network Nations: A Transnational History of British and American Broadcasting
  | publisher = Routledge
  | year = 2011
  | pages = 6
  | url = https://books.google.com/books?id=qimGXa2MwHEC&pg=PA6
  | isbn = 978-0415883856}}</ref> A rising interest in radio broadcasting by the British public pressured the government to reintroduce the service, following its suspension in 1920. However, the government also wanted to avoid what it termed the "chaotic" U.S. experience of allowing large numbers of stations to operate with few restrictions. There were also concerns about broadcasting becoming dominated by the Marconi company.<ref>[https://babel.hathitrust.org/cgi/pt?id=nyp.33433090816954&view=1up&seq=524 "Radio Fans to Pay Tribute to John Bull"], ''Popular Radio'', November 1922, p. 222.</ref>  Arrangements were made for six large radio manufacturers to form a consortium, the [[British Broadcasting Company]] (BBC), established on October 18, 1922, which was given a monopoly on broadcasting. This enterprise was supported by a tax on radio sets sales, plus an annual license fee on receivers, collected by the Post Office.<ref name="Street2">{{cite book|url=https://books.google.com/books?id=y7jo0IcUZeoC&pg=PA27|title=A Concise History of British Radio, 1922-2002|isbn=9781903053140|last1=Street|first1=Sean|year=2002|publisher=Kelly Publications }}</ref> Initially the eight stations were allowed regional autonomy. In 1927, the original broadcasting organization was replaced by a government chartered [[British Broadcasting Corporation]].<ref name="Street3">{{cite book|url=https://books.google.com/books?id=y7jo0IcUZeoC&pg=PA34|title=A Concise History of British Radio, 1922-2002|isbn=9781903053140|last1=Street|first1=Sean|year=2002|publisher=Kelly Publications }}</ref> an independent nonprofit supported solely by a 10 shilling [[receiver license]] fee.<ref name="Street3" /> Both highbrow and mass-appeal programs were carried by the [[BBC National Programme|National]] and [[BBC Regional Programme|Regional]] networks.

==="Golden Age of Radio"===
{{main|Golden Age of Radio}}
[[File:Radio copyright problem cartoon - Radio News May 1925.png|thumb|upright=1.5|When broadcasting began in 1920, music was played on air without regard to its copyright status. Music publishers challenged this practice as being copyright infringement, which for a time kept many popular tunes off the air, and this 1925 U.S. editorial cartoon shows a rich publisher muzzling two radio performers. The radio industry eventually agreed to make royalty payments.]]
The period from the early 1920s through the 1940s is often called the "Golden Age of Radio". During this period AM radio was the main source of home entertainment, until it was replaced by television. For the first time entertainment was provided from outside the home, replacing traditional forms of entertainment such as oral storytelling and music from family members. New forms were created, including [[radio play]]s, mystery serials, [[soap opera]]s, [[quiz show]]s, [[variety show|variety hours]], [[situation comedy|situation comedies]] and [[children's show]]s. Radio news, including remote reporting, allowed listeners to be vicariously present at notable events.

Radio greatly eased the isolation of rural life. Political officials could now speak directly to millions of citizens. One of the first to take advantage of this was American president [[Franklin Roosevelt]], who became famous for his [[fireside chats]] during the [[Great Depression]]. However, broadcasting also provided the means to use [[propaganda]] as a powerful government tool, and contributed to the rise of [[fascist]] and [[communist]] ideologies.

===Decline in popularity===

In the 1940s, two new broadcast media, [[FM broadcasting|FM radio]] and [[television]], began to provide extensive competition with the established broadcasting services. The AM radio industry suffered a serious loss of audience and advertising revenue, and coped by developing new strategies. Network broadcasting gave way to [[radio format|format]] broadcasting: instead of broadcasting the same programs all over the country, stations individually adopted specialized formats which appealed to different audiences, such as regional and local news, sports, "talk" programs, and programs targeted at minorities. Instead of live music, most stations began playing less expensive recorded music.

In the late 1960s and 1970s, top 40 rock and roll stations in the U.S. and Canada such as [[WABC (AM)|WABC]] and [[CHUM (AM)|CHUM]] transmitted highly processed and extended audio to 11 kHz, successfully attracting huge audiences.  For young people, listening to AM broadcasts and participating in their music surveys and contests was the social media of the time.

In the late 1970s, spurred by the exodus of musical programming to FM stations, the AM radio industry in the United States developed technology for broadcasting in [[stereophonic sound|stereo]]. Other nations adopted AM stereo, most commonly choosing Motorola's C-QUAM, and in 1993, the United States also made the C-QUAM system its standard, after a period allowing four different standards to compete. The selection of a single standard improved acceptance of [[AM stereo]],<ref name="stereo">[https://www.fcc.gov/media/radio/am-stereo-broadcasting "AM Stereo Broadcasting"]{{Dead link|date=July 2025 |bot=InternetArchiveBot |fix-attempted=yes }} (fcc.gov)</ref> however overall there was limited adoption of AM stereo worldwide, and interest declined after 1990. With the continued migration of AM stations away from music to news, sports, and talk formats, receiver manufacturers saw little reason to adopt the more expensive stereo tuners, and thus radio stations have little incentive to upgrade to stereo transmission.

In countries where the use of directional antennas is common, such as the United States, transmitter sites consisting of multiple towers often occupy large tracts of land that have significantly increased in value over the decades, to the point that the value of land exceeds that of the station itself. This sometimes results in the sale of the transmitter site, with the station relocating to a more distant shared site using significantly less power,<ref>[https://www.post-gazette.com/ae/tv-radio/2019/12/24/KQV-Pittsburgh-back-on-air-easy-listening-format/stories/201912240090 "Radio fans' holiday joy: KQV is back on the air"] by Maria Sciullo, ''Pittsburgh Post-Gazette'', December 24, 2019.</ref> or completely shutting down operations.<ref>[https://radioinsight.com/headlines/204891/1560-wfme-new-york-to-suspend-operations-friday/ "1560 WFME New York To Suspend Operations Friday"] by Lance Venta, February 11, 2021 (radioinsight.com).</ref>

The ongoing development of alternative transmission systems, including Digital Audio Broadcasting (DAB), satellite radio, and HD (digital) radio, continued the decline of the popularity of the traditional broadcast technologies. These new options, including the introduction of Internet streaming, particularly resulted in the reduction of shortwave transmissions, as international broadcasters found ways to reach their audiences more easily.<ref>[https://www.radioworld.com/news-and-business/whatever-happened-to-shortwave-radio/302129 "Whatever Happened to Shortwave Radio?"] by James Careless, March 8, 2010 (radioworld.com).</ref>

In 2022, it was reported that AM radio was being removed from a number of [[electric vehicle]] (EV) models, including from cars manufactured by Tesla, Audi, Porsche, BMW and Volvo, reportedly due to automakers concerns that an EV's higher electromagnetic interference can disrupt the reception of AM transmissions and hurt the listening experience, among other reasons.<ref>{{Cite news |last=Levenson |first=Michael |date=2022-12-10 |title=In a Future Filled With Electric Cars, AM Radio May Be Left Behind |language=en-US |work=The New York Times |url=https://www.nytimes.com/2022/12/10/business/media/am-radio-cars.html |access-date=2022-12-29 |issn=0362-4331}}</ref><ref>{{Cite web |last=Gilboy |first=James |date=2022-07-06 |title=Automakers Are Starting to Drop AM Radio in New Cars. Here's Why |url=https://www.thedrive.com/news/heres-why-some-automakers-tune-out-am-radios-in-new-cars |access-date=2022-12-29 |website=The Drive |language=en}}</ref> However the United States Congress has introduced a bill to require all vehicles sold in the US to have an AM receiver to receive emergency broadcasts.<ref>{{cite news |last1=Gitlin |first1=Jonathan M. |title=Congress wants AM radio in all new cars—trade groups say that's a mistake |url=https://arstechnica.com/cars/2023/05/ev-advocates-join-tech-groups-and-automakers-to-oppose-am-radio-mandate/ |access-date=23 May 2023 |work=Ars Technica |date=23 May 2023 |language=en-us}}</ref>

==AM band revitalization efforts in the United States==
The FM broadcast band was established in 1941 in the United States, and at the time some suggested that the AM band would soon be eliminated. In 1948, wide-band FM's inventor, [[Edwin Howard Armstrong|Edwin H. Armstrong]], predicted that "The broadcasters will set up FM stations which will parallel, carry the same program, as over their AM stations... eventually the day will come, of course, when we will no longer have to build receivers capable of receiving both types of transmission, and then the AM transmitters will disappear."<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015035872822&view=1up&seq=478 "Statement of Major Edwin H. Armstrong"] (January 15, 1948), "Restrictive union practices of the American Federation of Musicians", ''United States Congress, House Committee on Education and Labor'' (1948 hearings), pages 144-145.</ref> However, FM stations actually struggled for many decades, and it was not until 1978 that FM listenership surpassed that of AM stations. Since then the AM band's share of the audience has continued to decline.

===Fairness Doctrine repeal===
{{Also|Fairness Doctrine#Revocation}}

In 1987, the elimination of the [[Fairness Doctrine]] requirement meant that talk shows, which were commonly carried by AM stations, could adopt a more focused presentation on controversial topics, without the distraction of having to provide airtime for any contrasting opinions. In addition, satellite distribution made it possible for programs to be economically carried on a national scale. The introduction of nationwide talk shows, most prominently [[Rush Limbaugh]]'s beginning in 1988, was sometimes credited with "saving" AM radio.<ref>Scott Fybush. [https://www.fybush.com/nerw-20210217/ "Limbaugh Dead; What Next for Talk Radio?"] Fybush.com. February 17, 2021. Retrieved July 10, 2024.</ref> However, these stations tended to attract older listeners who were of lesser interest to advertisers, and AM radio's audience share continued to erode.

===AM stereo and AMAX standards===
{{Main|AM stereo#Adoption in the United States|AMAX}}
[[File:AMAX radio receiver certification logo.gif|thumb|200px|right|Radios meeting the AMAX standards could display a certification logo, with the "stereo" notation reserved for those capable of AM stereo reception]]

In 1961, the FCC adopted a single standard for FM stereo transmissions, which was widely credited with enhancing FM's popularity. Developing the technology for AM broadcasting in stereo was challenging due to the need to limit the transmissions to a 20&nbsp;kHz bandwidth, while also making the transmissions backward compatible with existing non-stereo receivers.

In 1990, the FCC authorized an AM stereo standard developed by Magnavox, but two years later revised its decision to instead approve four competing implementations, saying it would "let the marketplace decide" which was best.<ref name="stereo"/> The lack of a common standard resulted in consumer confusion and increased the complexity and cost of producing AM stereo receivers.

In 1993, the FCC again revised its policy, by selecting [[C-QUAM]] as the sole AM stereo implementation. In 1993, the FCC also endorsed, although it did not make mandatory, [[AMAX]] broadcasting standards that were developed by the [[Electronic Industries Alliance|Electronic Industries Association]] (EIA) and the [[National Association of Broadcasters]] (NAB) with the intention of helping AM stations, especially ones with musical formats, become more competitive with FM broadcasters by promoting better quality receivers. However, the stereo AM and AMAX initiatives had little impact, and a 2015 review of these events concluded that

<blockquote>Initially the consumer manufacturers made a concerted attempt to specify performance of AM receivers through the 1993 AMAX standard, a joint effort of the EIA and the NAB, with FCC backing...  The FCC rapidly followed up on this with codification of the CQUAM AM stereo standard, also in 1993. At this point, the stage appeared to be set for rejuvenation of the AM band. Nevertheless, with the legacy of confusion and disappointment in the rollout of the multiple incompatible AM stereo systems, and failure of the manufacturers (including the auto makers) to effectively promote AMAX radios, coupled with the ever-increasing background of noise in the band, the general public soon lost interest and moved on to other media.<ref>[https://www.kintronic.com/wp-content/uploads/2016/01/NAB-AM-Receiver-Paper.pdf "Smart AM Receivers for the 21st Century"] by Stephen F. Smith and Thomas F. King, ''Proceedings of the National Association of Broadcasters Engineering Conference, Las Vegas, Nevada'', April 12, 2015, pages 1-2.</ref></blockquote>

===Expanded band===
{{Main|AM expanded band#United States}}

On June 8, 1988, an [[International Telecommunication Union]] (ITU)-sponsored conference held at Rio de Janeiro, Brazil adopted provisions, effective July 1, 1990, to extend the upper end of the Region 2 AM broadcast band, by adding ten frequencies which spanned from 1610&nbsp;kHz to 1700&nbsp;kHz.<ref>[http://handle.itu.int/11.1004/020.1000/4.118.43.en.100 ''Final Acts of the Regional Radio Conference to Establish a Plan for the Broadcasting Service in the Band 1605-1705 in Region 2''] (PDF) (Rio de Janeiro, 1988, ITU.int)</ref> At this time it was suggested that as many as 500 U.S. stations could be assigned to the new frequencies.<ref>[https://www.worldradiohistory.com/Archive-BC/BC-1988/BC-1988-05-23.pdf#page=55 "RIO is stage for AM spectrum conference"], ''Broadcasting'', May 23, 1988, pp. 55–56.</ref>

On April 12, 1990, the FCC voted to begin the process of populating the expanded band, with the main priority being the reduction of interference on the existing AM band, by transferring selected stations to the new frequencies. It was now estimated that the expanded band could accommodate around 300 U.S. stations.<ref>[https://www.worldradiohistory.com/Archive-Billboard/90s/1990/BB-1990-04-28.pdf#page=10 "FCC Votes To Proceed With AM-Band Improvement Plans"] by Bill Holland, ''Billboard'', April 28, 1990, page 10.</ref> However, it turned out that the number of possible station reassignments was much lower, with a 2006 accounting reporting that, out of 4,758 licensed U.S. AM stations, only 56 were now operating on the expanded band.<ref>[https://www.radioworld.com/news-and-business/life-on-expanded-band-is-pretty-good "Life on Expanded Band Is (Pretty) Good"] by Randy J. Stine, February 28, 2006 (radioworld.com)</ref> Moreover, despite an initial requirement that by the end of 5 years, either the original station or its expanded band counterpart had to cease broadcasting,<ref>[https://babel.hathitrust.org/cgi/pt?id=uva.x004848309;view=1up;seq=268 "Mass Media Bureau Announces Revised AM Expanded Band Allotment Plan and Filing Window for Eligible Stations"] (FCC DA 97-537), March 17, 1997.</ref> as of 2015, there were 25 cases where the original standard band station was still on the air, despite also operating as an expanded band station.

===HD radio===
{{Main|HD Radio}}
[[File:Hdradio-logo.svg|right|200px|thumb|alt=]]

HD Radio is a digital audio broadcasting method developed by [[iBiquity]]. In 2002 its "hybrid mode", which simultaneously transmits a standard analog signal as well as a digital one, was approved by the FCC for use by AM stations, initially only during daytime hours, due to concerns that during the night its wider bandwidth would cause unacceptable interference to stations on adjacent frequencies.<ref>{{cite news |first=TaNoah |last=Morgan |date=11 October 2002 |title=Digital radio approved by FCC |newspaper=[[Baltimore Sun]] |url=https://www.baltimoresun.com/news/bs-xpm-2002-10-11-0210110010-story.html}}</ref> In 2007 nighttime operation was also authorized.<ref>{{cite news |first=Peter |last=Gutmann |date=23 August 2007 |title=HD Radio rules take effect |website=Radio+Television Business Report (RBR.com) |url=https://www.rbr.com/hd-radio-rules-take-effect-by-peter-gutmann/}}</ref>

The number of hybrid mode AM stations is not exactly known, because the FCC does not keep track of the stations employing the system, and some authorized stations have later turned it off. But as of 2020 the commission estimated that fewer than 250&nbsp;AM stations were transmitting hybrid mode signals.<ref>{{cite news |title=Proposed rule: All-digital AM broadcasting, revitalization of the AM radio service |date=25 November 2019 |periodical=[[The Federal Register]] |url=https://www.federalregister.gov/documents/2020/01/07/2019-27609/all-digital-am-broadcasting-revitalization-of-the-am-radio-service}}</ref> On October 27, 2020, the FCC voted to allow AM stations to eliminate their analog transmissions and convert to all-digital operation, with the requirement that stations making the change had to continue to make programming available over "at least one free over-the-air digital programming stream that is comparable to or better in audio quality than a standard analog broadcast".<ref>{{cite news |title=Final rule: All-digital AM broadcasting, revitalization of the AM radio service |date=3 December 2020 |periodical=[[The Federal Register]] |url=https://www.federalregister.gov/documents/2020/12/03/2020-25252/all-digital-am-broadcasting-revitalization-of-the-am-radio-service}}</ref>

===FM translator stations===
{{Main|Broadcast relay station#United States}}
[[File:WCHL 2017.png|thumb|200px|alt=right|Many U.S. AM stations no longer publicize their AM signals, instead promoting simulcasts by FM band translators and Internet streams.<ref>Logo for [[WCHL (AM)|WCHL]], 1360 AM in Chapel Hill, North Carolina, whose publicized signal is over FM translator W250BP at 97.9 MHz.</ref>]]

Despite the various actions, AM band audiences continued to contract, and the number of stations began to slowly decline. A 2009 FCC review reported that "The story of AM radio over the last 50 years has been a transition from being the dominant form of audio entertainment for all age groups to being almost non-existent to the youngest demographic groups. Among persons aged 12–24, AM accounts for only 4% of listening, while FM accounts for 96%. Among persons aged 25–34, AM accounts for only 9% of listening, while FM accounts for 91%. The median age of listeners to the AM band is 57 years old, a full generation older than the median age of FM listeners."<ref name="FCC auth">[https://babel.hathitrust.org/cgi/pt?id=osu.32435081039638&view=1up&seq=874 "Report and Order: In the Matter of Amendment of Service and Eligibility Rules for FM Broadcast Translator Stations"] (MB Docket Mo. 07-172, RM-11338), June 29, 2009, pages 9642–9660.</ref>

In 2009, the FCC made a major regulatory change, when it adopted a policy allowing AM stations to simulcast over FM translator stations. Translators had previously been available only to FM broadcasters, in order to increase coverage in fringe areas. Their assignment for use by AM stations was intended to approximate the station's daytime coverage, which in cases where the stations reduced power at night, often resulted in expanded nighttime coverage. Although the translator stations are not permitted to originate programming when the "primary" AM station is broadcasting, they are permitted to do so during nighttime hours for AM stations licensed for daytime-only operation.<ref name="OK">[https://www.commlawblog.com/2009/06/articles/broadcast/fcc-oks-am-on-fm-translators/ "FCC OK's AM on FM Translators"] by FHH Law, June 30, 2009 (commlawblog.com).</ref>

Prior to the adoption of the new policy, as of March 18, 2009, the FCC had issued 215 Special Temporary Authority grants for FM translators relaying AM stations.<ref name="OK"/> After creation of the new policy, by 2011 there were approximately 500 in operation,<ref>[https://www.radioworld.com/news-and-business/uses-of-fm-translators-morph-quickly "Uses of FM Translators Morph Quickly"] by Randy J. Stine, August 3, 2011 (radioworld.com)</ref> and as of 2020 approximately 2,800 of the 4,570 licensed AM stations were rebroadcasting on one or more FM translators.<ref name="worry">[https://www.radioworld.com/news-and-business/headlines/special-report-am-advocates-watch-and-worry "Special Report: AM Advocates Watch and Worry"] by Randy J. Stine, October 5, 2020 (radioworld.com)</ref> In 2009, the FCC stated that "We do not intend to allow these cross-service translators to be used as surrogates for FM stations".<ref name="FCC auth"/> However, based on station slogans, especially in the case of recently adopted musical formats, in most cases the expectation is that listeners will primarily be tuning into the FM signal rather than the nominally "primary" AM station. A 2020 review noted that "for many owners, keeping their AM stations on the air now is pretty much just about retaining their FM translator footprint rather than keeping the AM on the air on its own merits".<ref name="worry"/>

===Additional activities===
In 2018 the FCC, led by then-Commission Chairman [[Ajit Pai]], proposed greatly reducing signal protection for 50&nbsp;kW Class A "[[Clear-channel station|clear channel]]" stations. This would allow co-channel secondary stations to operate with higher powers, especially at night. However, the [[Federal Emergency Management Agency]] (FEMA) expressed concerns that this would reduce the effectiveness of emergency communications.<ref>[https://www.federalregister.gov/documents/2018/11/20/2018-25101/revitalization-of-the-am-radio-service "Proposed Rule: Revitalization of the AM Radio Service"], ''Federal Register'', November 20, 2018.</ref>

===Electric vehicles===
In May 2023, a bipartisan group of lawmakers in the United States introduced legislation making it illegal for automakers to eliminate AM radio from their cars. The lawmakers argue that AM radio is an important tool for public safety due to being a component of the [[Emergency Alert System]] (EAS). Some automakers have been eliminating AM radio from their [[electric vehicles]] (EVs) due to interference from the [[Traction motor|electric motors]], but the lawmakers argue that this is a safety risk and that car owners should have access to AM radio regardless of the type of vehicle they drive. The proposed legislation would require all new vehicles to include AM radio at no additional charge, and it would also require automakers that have already eliminated AM radio to inform customers of alternatives.<ref>{{cite web |last1=Muller
|first1=Joann |title=Scoop: Congress moves to preserve AM radio in cars |url=https://www.axios.com/2023/05/17/am-radio-congress-cars |publisher=Axios |date=17 May 2023 |access-date=18 May 2023}}</ref>

==Other digital standards==
[[Digital Radio Mondiale|DRM30]] is another standard to broadcast on the AM bands,<ref>{{Cite web |title=TECHNICAL BASES FOR DRM SERVICES COVERAGE PLANNING |url=https://tech.ebu.ch/docs/tech/tech3330.pdf |website=tech.ebu.ch}}</ref> with implementation in India<ref>{{Cite web|url=http://digitalradioinsider.blogspot.com/2024/11/drm-advantage-for-terrestrial-digital.html|title=Digital Radio FM Insider: DRM Advantage for Terrestrial Digital Radio in Italy and India|date=November 23, 2024}}</ref><ref>{{Cite web|url=http://digitalradioinsider.blogspot.com/2025/01/radio-industry-urges-indian-government.html|title=Digital Radio FM Insider: Radio Industry Urges Indian Government to Opt for DRM For Digital Radio|date=2025-01-11}}</ref><ref>{{Cite web|url=https://www.drm.org/drm-only-logical-cost-effective-solution-for-indian-fm-digitisation/|title=DRM – Only Logical, Cost-Effective Solution for Indian FM Digitisation|date=2025-01-14}}</ref> and China,<ref>{{Cite web|url=https://www.redtech.pro/china-accelerates-drm-adoption-in-automotive-industry/|title=China accelerates DRM adoption in automotive industry|first=RedTech|last=Staff|date=2024-12-04}}</ref> among other countries.<ref>{{Cite web|url=https://www.drm.org/other-countries/|title=Other Countries}}</ref>

==Technical information==

AM radio technology is simpler than later transmission systems. An AM receiver detects amplitude variations in the [[electromagnetic radiation|radio wave]]s at a particular frequency, then amplifies changes in the signal [[voltage]] to operate a [[loudspeaker]] or [[earphone]]. However, the simplicity of AM transmission also makes it vulnerable to "static" ([[radio noise]], [[radio frequency interference]]) created by both natural atmospheric electrical activity such as lightning, and electrical and electronic equipment, including fluorescent lights, motors and vehicle ignition systems. In large urban centers, AM radio signals can be severely disrupted by metal structures and tall buildings. As a result, AM radio tends to do best in areas where [[FM broadcast band|FM frequencies]] are in short supply, or in thinly populated or mountainous areas where FM coverage is poor. Great care must be taken to avoid mutual interference between stations operating on the same frequency. In general, an AM transmission needs to be about 20 times stronger than an interfering signal to avoid a reduction in quality, in contrast to FM signals, where the "[[capture effect]]" means that the dominant signal needs to only be about twice as strong as the interfering one.

To allow room for more stations on the mediumwave broadcast band in the United States, in June 1989 the FCC adopted a [[National Radio Systems Committee]] (NRSC) standard that limited maximum transmitted audio [[Bandwidth (signal processing)|bandwidth]] to 10.2&nbsp;kHz, limiting occupied bandwidth to 20.4&nbsp;kHz. The former audio limitation was 15&nbsp;kHz resulting in [[Bandwidth (signal processing)|bandwidth]] of 30&nbsp;kHz. Another common limitation on AM fidelity is the result of receiver design, although some efforts have been made to improve this, notably through the [[AMAX]] standards adopted in the United States.

===Broadcast band frequencies===
AM broadcasts are used on several frequency bands. The allocation of these bands is governed by the [[International Telecommunication Union|ITU]]'s [[Radio Regulations]] and, on the national level, by each country's telecommunications administration (the FCC in the U.S., for example) subject to international agreements.

The frequency ranges given here are those that are allocated to stations. Because of the bandwidth taken up by the [[sideband]]s, the range allocated for the band as a whole is usually about 5&nbsp;kHz wider on either side.

{{anchor|AM_longwave_band}}

====Longwave broadcasting====
''[[Longwave]]'' (also known as [[Low frequency]] (LF)) (148.5&nbsp;[[Kilohertz|kHz]] – 283.5&nbsp;kHz) Broadcasting stations in this band are assigned transmitting frequencies in the range 153&nbsp;kHz – 279&nbsp;kHz, and generally maintain 9&nbsp;kHz spacing. 
Longwave assignments for broadcasting only exist in [[ITU region|ITU Region&nbsp;1]] (Europe, Africa, and northern and central Asia) and are not allocated elsewhere. Individual stations have coverage measured in the hundreds of kilometers; however, there is only a very limited number of available broadcasting slots.

Most of the earliest broadcasting experiments took place on [[longwave]] frequencies; however, complaints about interference from existing services, particularly the military, led to most broadcasting moving to higher frequencies.

====Medium-wave broadcasting{{anchor|commercial_AM_bands}}====
''[[Medium wave]]'' (also known as [[Medium frequency]] (MF)), is by far the most commonly used AM broadcasting band. In ITU Regions&nbsp;1 and 3, transmitting frequencies run from 531&nbsp;kHz – 1602&nbsp;kHz, with 9&nbsp;kHz spacing (526.5&nbsp;kHz – 1606.5&nbsp;kHz), and in ITU Region&nbsp;2 (the Americas), transmitting frequencies are 530&nbsp;kHz – 1700&nbsp;kHz, using 10&nbsp;kHz spacing (525&nbsp;kHz – 1705&nbsp;kHz), including the ITU [[AM expanded band|Extended AM broadcast band]], authorized in Region&nbsp;2, between 1605&nbsp;kHz and 1705&nbsp;kHz, previously used for police radio.<ref>{{cite report |title=Federal Communications Commission rules |at=47 CFR §2.106}}</ref>

====Shortwave broadcasting====
''[[Shortwave]]'' (also known as [[High frequency]] (HF)) transmissions range from approximately 2.3 to 26.1&nbsp;MHz, divided into 14&nbsp;broadcast bands. Shortwave broadcasts generally use a narrow 5&nbsp;kHz channel spacing. Shortwave is used by audio services intended to be heard at great distances from the transmitting station. The long range of shortwave broadcasts comes at the expense of lower [[High fidelity|audio fidelity]].

Most broadcast services use AM transmissions, although some use a modified version of AM such as [[Single-sideband modulation]] (SSB) or an AM-compatible version of SSB such as "SSB with carrier reinserted".

====VHF AM broadcasting====
Beginning in the mid-1930s, the United States evaluated options for the establishment of broadcasting stations using much higher transmitting frequencies. In October&nbsp;1937, the FCC announced a second band of AM stations, consisting of 75&nbsp;channels spanning from 41.02 to 43.98&nbsp;MHz, which were informally called ''[[Apex (radio band)|Apex]]''.

The 40&nbsp;kHz spacing between adjacent frequencies was four times that of the 10&nbsp;kHz spacing used on the standard AM broadcast band, which reduced adjacent-frequency interference, and provided more bandwidth for high-fidelity programming. However, this band was eliminated effective 1&nbsp;January 1941, after the FCC determined that establishing a band of FM stations was preferable.<ref>[http://www.theradiohistorian.org/Apex/Apex1.htm "America's Apex Broadcasting Stations of the 1930s"] by John Schneider, ''Monitoring Times Magazine'', December 2010. (theradiohistorian.com)</ref>

===Other distribution methods===
{{Main|Carrier current}}
Beginning in the mid-1930s, starting with "[[WBRU#Beginnings|The Brown Network]]" at Brown University in Providence, Rhode Island, a very low power broadcasting method known as [[carrier current]] was developed, and mostly adopted on U.S. college campuses. In this approach AM broadcast signals are distributed over electric power lines, which radiate a signal receivable at a short distance from the lines.<ref>''The Gas Pipe Networks'' by Louis M. Bloch, Jr, 1980.</ref> In Switzerland a system known as "wire broadcasting" (''Telefonrundspruch'' in German) transmitted AM signals over telephone lines in the [[longwave]] band until 1998, when it was shut down.<ref>{{cite web|url=http://www.biennophone.ch/telefonrundspruch.htm|title=Sammlung alter Biennophone-Radios|publisher=Biennophone.ch|access-date=23 July 2017}}</ref> In the UK, [[Rediffusion]] was an early pioneer of AM radio cable distribution.

Hybrid digital broadcast systems, which combine (mono analog) AM transmission with digital sidebands, have started to be used around the world. In the United States, [[iBiquity]]'s proprietary [[HD Radio]] has been adopted and approved by the FCC for medium wave transmissions,<ref>[https://www.fcc.gov/media/radio/digital-radio "Digital Radio"] (fcc.gov)</ref> while [[Digital Radio Mondiale]] is a more open effort often used on the [[shortwave bands]], and can be used alongside many AM broadcasts. Both of these standards are capable of broadcasting audio of significantly greater fidelity than that of standard AM with current bandwidth limitations, and a theoretical frequency response of 0–16&nbsp;kHz, in addition to stereo sound and text data.

===Microbroadcasting===
{{see also|Low-power broadcasting}}
Some [[microbroadcasting|microbroadcasters]], especially those in the United States operating under the FCC's [[Part 15]] rules,<ref>{{cite book   | title = Localist Movements in a Global Economy Sustainability, Justice, and Urban Development in the United StatesStates | author1= David J. Hess | author2 = Professor David J Hess | author3 = Robert Gottlieb |publisher = MIT Press | location=   |url = https://books.google.com/books?id=BS7rsOQv5MUC | date = 2009  | page =  199 | isbn = 9780262012645  | access-date = 7 February 2021}}</ref> and [[pirate radio]] operators on mediumwave and shortwave, achieve greater range than possible on the [[FM broadcast band|FM band]]. On mediumwave these stations often transmit on 1610&nbsp;kHz to 1710&nbsp;kHz. Hobbyists also use low-power AM (LPAM) transmitters to provide programming for vintage radio equipment in areas where AM programming is not widely available or does not carry programming the listener desires; in such cases the transmitter, which is designed to cover only the immediate property and perhaps nearby areas, is connected to a computer, an FM radio or an MP3 player. Microbroadcasting and pirate radio have generally been supplanted by streaming audio on the Internet, but some schools and hobbyists still use LPAM transmissions.

==See also==
* [[Digital Radio Mondiale]] (DRM), a digital radio method using the bands LW, MW, SW, and the VHF bands
* [[Amplitude Modulation Signalling System]], a digital system for adding low bitrate information to an AM broadcast signal
* [[CAM-D]], a hybrid digital radio format for AM broadcasting
* [[Effective radiated power]] (ERP), standardised definition of radio frequency power
* [[AM expanded band|Extended AM broadcast band]]
* [[History of radio]]
* [[List of 50 kW AM radio stations in the United States]]
* [[Lists of radio stations in North America]]
* [[List of oldest radio stations|Oldest radio stations]]
* [[MW DX]]ing, the hobby of receiving distant AM radio stations on the mediumwave band.

==References==
{{Reflist}}

{{Audio broadcasting}}
{{Telecommunications}}

{{DEFAULTSORT:Am Broadcasting}}
[[Category:Broadcast engineering]]
[[Category:Radio communications]]