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FM broadcasting in the United States began in the 1930s at engineer and inventor
Edwin Howard Armstrong Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American electrical engineer and inventor, who developed FM (frequency modulation) radio and the superheterodyne receiver system. He held 42 patents and received numerous aw ...
's experimental station,
W2XMN W2XMN was an experimental FM radio station located in Alpine, New Jersey. It was constructed beginning in 1936 by Edwin Howard Armstrong in order to promote his invention of wide-band FM broadcasting. W2XMN was the first FM station to begin regula ...
. The use of
FM radio FM broadcasting is a method of radio broadcasting using frequency modulation (FM). Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high fidelity sound over broadcast radio. FM broadcasting is cap ...
has been associated with higher sound quality in music radio.


History of FM radio in the U.S.

In the United States, FM broadcasting stations currently are assigned to 101 channels, designated 87.9 to 107.9 MHz, within a 20.2 MHz-wide frequency band, spanning 87.8–108.0 MHz. In the 1930s investigations were begun into establishing radio stations transmitting on "Very High Frequency" (VHF) assignments above 30 MHz. In October 1937, the
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...
(FCC) announced new frequency allocations, which included a band of experimental and educational "
Apex The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics), a teenaged super villainess in the Marvel Universe * Ape-X, a super-intelligent ape in the Squadron Supreme universe *Apex ...
" stations, that consisted of 75 channels spanning from 41.02 to 43.98 MHz."Upper Bands Set Aside for Television"
''Broadcasting'', November 1, 1937, pages 60-61.
Like the existing AM band these stations employed amplitude modulation, however the 40 kHz spacing between adjacent frequencies was four times as much as the 10 kHz spacing on the standard AM broadcast band, which reduced adjacent-frequency interference, and provided more bandwidth for high-fidelity programming. Also during the 1930s a competing transmission technology, "wide-band frequency modulation", was developed in the United States by
Edwin Howard Armstrong Edwin Howard Armstrong (December 18, 1890 – February 1, 1954) was an American electrical engineer and inventor, who developed FM (frequency modulation) radio and the superheterodyne receiver system. He held 42 patents and received numerous aw ...
, which was promoted as being superior to AM transmissions, in particular due to its high-fidelity and near immunity to static interference. On June 17, 1936 Armstrong formally demonstrated his FM system to the FCC. That year he also set up the first FM radio station,
W2XMN W2XMN was an experimental FM radio station located in Alpine, New Jersey. It was constructed beginning in 1936 by Edwin Howard Armstrong in order to promote his invention of wide-band FM broadcasting. W2XMN was the first FM station to begin regula ...
in Alpine, New Jersey, to function as a demonstration station. In 1937 the
Yankee Network The Yankee Network was an American radio network, based in Boston, Massachusetts, with affiliate radio stations throughout New England. At the height of its influence, the Yankee Network had as many as twenty-four affiliated radio stations. The ...
, looking to eventually establish commercial FM operations, was granted a construction permit for an experimental station, W1XOJ, in Paxton, Massachusetts. The first publicized W2XMN broadcast took place on July 18, 1939, which used a high-quality phone line link to rebroadcast a program from WQXR in New York City. On July 24, 1939, W1XOJ inaugurated a regular schedule of 16 hours a day (8 a.m. to midnight). On January 5, 1940, Armstrong, working with the Yankee Network, demonstrated FM broadcasting in a long-distance relay network, via five stations in five states. In May 1940, largely as the result of Armstrong's efforts, the FCC decided to eliminate the Apex band, and authorized an FM band effective January 1, 1941, operating on 40 channels spanning 42–50 MHz. On October 31, 1940, the first 15 commercial station Construction Permit authorizations were issued. On March 1, 1941 W47NV began broadcasting in
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,
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, becoming the first fully licensed commercial FM station. There was significant interest in the new FM band by station owners, however, construction restrictions that went into place during World War II limited the growth of the new service. Following the end of the war, the FCC moved to standardize its frequency allocations. One area of concern was the effects of
tropospheric The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
and
Sporadic E propagation Sporadic E (usually abbreviated E) is an unusual form of radio propagation using a low level of the Earth's ionosphere that normally does not refract radio waves. Sporadic E propagation reflects signals off relatively small "clouds" in ...
, which at times reflected station signals over great distances, causing mutual interference. A particularly controversial proposal, spearheaded by the
Radio Corporation of America The RCA Corporation was a major American electronics company, which was founded as the Radio Corporation of America in 1919. It was initially a patent trust owned by General Electric (GE), Westinghouse, AT&T Corporation and United Fruit Comp ...
(RCA), which was headed by
David Sarnoff David Sarnoff (February 27, 1891 – December 12, 1971) was an American businessman and pioneer of American radio and television. Throughout most of his career, he led the Radio Corporation of America (RCA) in various capacities from shortly afte ...
, was that the FM band needed to be shifted to higher frequencies in order to avoid this potential problem. Armstrong charged that this reassignment had the covert goal of disrupting FM radio development, however RCA's proposal prevailed, and on June 27, 1945 the FCC announced the reassignment of the FM band to 80 channels from 88–106 MHz (which was soon expanded to 100 channels from 88–108 MHz), while allocating the former FM band frequencies to "non-government fixed and mobile" (42–44 MHz), and television channel 1 (44–50 MHz), controversially ignoring the effect of tropospheric and Sporadic E propagation on those services. A period of allowing existing FM stations to broadcast on both the original "low" and new "high" FM bands followed, though as late as 1947, in Detroit, there were only 3,000 FM receivers in use for the new band, and 21,000 for the old band. The dual band transition period ended at midnight on January 8, 1949, at which time all low band transmissions had to end, making obsolete 395,000 receivers already purchased by the public for the original band. Although converters were manufactured allowing low band FM sets to receive high band transmissions, they were complicated to install and often as (or more) expensive than buying a new high band set. The greater expense was the cost for the radio stations converting to the new FM radio band. The FM radio industry did not recover significantly from the setback until the upsurge in high fidelity equipment in the late 1950s. In the early 1960s, FM began to benefit from increased investment, as broadcasters looked to it to expand their markets; television had been built out by this point, and the shift to music as the dominant format of AM in the wake of television and the rise of
rock 'n' roll Rock and roll (often written as rock & roll, rock 'n' roll, or rock 'n roll) is a genre of popular music that evolved in the United States during the late 1940s and early 1950s. It originated from African-American music such as jazz, rhythm an ...
had led to an AM band so crowded that the FCC was limiting many stations to daytime-only operation, a restriction to which FM was not subject. The FCC gave FM two boosts in the early 1960s: first by setting a technical standard for stereo broadcasts, and second by adopting the
FM Non-Duplication Rule The FM Non-Duplication Rule was adopted by the U.S. Federal Communications Commission (FCC) on July 1, 1964, after a year's consideration. It limited holders of FM broadcasting in the United States, FM licenses in City of license, cities of more t ...
in 1964, prohibiting broadcasters with an AM and FM license in cities of more than 100,000 from transmitting more than 50% of the same programming on both stations. By the end of the 1970s, 50.1% of radio listeners were listening to FM stations, ending AM's historical lead. By 1982, FM commanded 70% of the general audience, and 84% among the 12- to 24-year-old demographic. The shift in popularity of FM radio over AM in United States during the 1970s has been called by record producer Steve Greenberg "a seismic technological shift that had torn apart the very idea of the mass audience upon which pop hits depended". (AM radio would adapt by shifting its focus to
talk radio Talk radio is a radio format containing discussion about topical issues and consisting entirely or almost entirely of original spoken word content rather than outside music. Most shows are regularly hosted by a single individual, and often featur ...
, which would be deregulated in the late 1980s after the repeal of the
Fairness Doctrine The fairness doctrine of the United States Federal Communications Commission (FCC), introduced in 1949, was a policy that required the holders of broadcast licenses both to present controversial issues of public importance and to do so in a mann ...
.)


FM radio channel assignments in the U.S.

In the United States, FM broadcasting stations operate on a 20.2 MHz-wide frequency band, spanning from 87.8 MHz to 108 MHz. This is divided into 101 0.2 MHz-wide channels, which are designated as channels 200 through 300. In actual practice, few except the FCC use these channel numbers; the frequencies are used instead. (Stations that broadcast on 87.7 MHz are in actuality licensed as television stations.) To receive a station, an FM receiver is tuned to the center frequency of the station's channel. The lowest and almost-unused channel, channel 200, extends from 87.8 MHz to 88.0 MHz; thus its center frequency is 87.9 MHz. Channel 201 has a center frequency of 88.1 MHz, and so on, up to channel 300, which extends from 107.8 to 108.0 MHz and has a center frequency of 107.9 MHz. Because each channel is 0.2 MHz wide, the center frequencies of adjacent channels differ by 0.2 MHz. Because the lowest channel is centered on 87.9 MHz, the tenths digit (in MHz) of the center frequency of any FM station in the United States is always an odd number. FM audio for analog television channel 6 is broadcast at a carrier frequency of 87.75 MHz, and many radios can tune this low; full-power stations ceased analog operations in 2009 under FCC orders, but a few low-power stations are still operated solely for their right to use this frequency and broadcast only nominal video programming, if any (these, too, will reportedly eventually be forced to shut down). For the same reason, assignment restrictions between TV stations on channel 6 and nearby FM stations are stringent: there is only one station in the United States (
CSN International Christian Satellite Network (CSN) International is a Christian radio network based in Twin Falls, Idaho. KAWZ, 89.9 MHz, in Twin Falls is the uplink station, feeding 337 broadcast translators nationwide and 42 full-power radio stations across ...
translator Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The ...
K200AA in
Sun Valley, Nevada Sun Valley is a census-designated place (CDP) in Washoe County, Nevada, United States. The population was 19,299 at the 2010 census. It is north of Reno and is part of the Reno– Sparks Metropolitan Statistical Area. Geography The community ...
) licensed to operate on 87.9 MHz, because it was forced off of another channel. Therefore, in effect, the FM broadcast band comprises only FM channels 201 (88.1 MHz) through 300 (107.9 MHz). Originally, FM stations in a market were generally spaced four channels (800 kHz) apart. This spacing was developed in response to problems perceived on the original FM band, mostly due to deficiencies in receiver technology of the time. With modern equipment, this is widely understood to be unnecessary, and in many countries shorter spacings are used. (See
FM broadcast band The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations. The range of frequencies used differs between different parts of the world. In Europe and Africa (defined as International Telecommunication Union (I ...
.) Other spacing restrictions relate to mixing products with nearby television, air-traffic control, and two-way radio systems as well as other FM broadcast stations. The most significant such taboo restricts the allocation of stations 10.6 and 10.8 MHz apart, to protect against mixing products which will interfere with an FM receiver's standard 10.7 MHz
intermediate frequency In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier sign ...
stage.
Commercial broadcasting Commercial broadcasting (also called private broadcasting) is the broadcasting of television programs and radio programming by privately owned corporate media, as opposed to state sponsorship. It was the United States′ first model of radio (an ...
is licensed only on channels 221 through 300 (the upper 80 channels, frequencies between 92.1 and 107.9 MHz), with 200 through 220 (the lower 21 channels, frequencies between 87.9 and 91.9 MHz) reserved for
non-commercial educational A non-commercial educational station (NCE station) is a radio station or television station that does not accept on-air advertisements (TV ads or radio ads), as defined in the United States by the Federal Communications Commission (FCC) and was or ...
(NCE) broadcasting. In some " Twin city" markets close to the Canada–United States or Mexico–United States border, such as
Detroit, Michigan Detroit ( , ; , ) is the largest city in the U.S. state of Michigan. It is also the largest U.S. city on the United States–Canada border, and the seat of government of Wayne County. The City of Detroit had a population of 639,111 at ...
, and
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, or
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, and
Tijuana Tijuana ( ,"Tijuana"
(US) and
< ...
,
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, commercial stations operating from those countries target U.S. audiences on "reserved band" channels, as neither Canada nor Mexico has such a reservation. Because of this necessary sharing, the FCC reserves a few other channels for such NCE stations. FM stations in the U.S. are now assigned based on a table of separation distance values from currently licensed stations, based on station "class" (power output, antenna height, and geographical location). These regulations (see Docket 80-90) have resulted in approximately double the number of possible stations, and increases in allowable power levels, over the original
bandplan A frequency plan, bandplan, band plan or wavelength plan is a plan for using a particular band of radio frequencies, that are a portion of the electromagnetic spectrum. Each frequency plan defines the frequency range to be included, how channels ...
scheme described above. All powers are specified as
effective radiated power Effective radiated power (ERP), synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency (RF) power, such as that emitted by a radio transmitter. It is the total power in watts that would hav ...
(ERP), which takes into account the magnifying effect (
gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in de ...
) of multiple antenna elements. The U.S. is divided into Zone I (roughly the northeastern quarter of the U.S. mainland, excluding the far northern areas), Zone I-A (
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south of 40 degrees
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, U.S. Virgin Islands,
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), and Zone II (all other locations). The highest-power stations are class C in zone II, and class B in the others. There are no B stations in zone II, nor any C stations in the others. (See the
list of broadcast station classes This is a list of broadcast station classes applicable in much of North America under international agreements between the United States, Canada and Mexico. Effective radiated power (ERP) and height above average terrain (HAAT) are listed unless ot ...
.) Canada is also divided in this manner, based on the most highly populated regions. High power is useful in penetrating buildings, diffracting around hills, and refracting for some distance beyond the horizon. 100,000-watt FM stations can regularly be heard up to 100 miles (160 km) away, and farther (e.g., 150 miles, 240 km) if there are no competing signals. A few old "grandfathered" stations do not conform to these power rules.
WBCT WBCT (93.7 MHz, "B-93") is a commercial FM radio station licensed to Grand Rapids, Michigan and owned by iHeartMedia. The studios and offices are located at 77 Monroe Center in Downtown Grand Rapids. The station has had a country music radio ...
(93.7) in
Grand Rapids Grand Rapids is a city and county seat of Kent County in the U.S. state of Michigan. At the 2020 census, the city had a population of 198,917 which ranks it as the second most-populated city in the state after Detroit. Grand Rapids is the ...
,
Michigan Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...
, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. This huge power level does not usually help to increase range as much as one might expect, because VHF frequencies travel in nearly straight lines over the horizon and off into space. Nevertheless, when there were fewer FM stations competing, this station could be heard near Bloomington, Illinois, almost distant.


See also

*
FM broadcasting FM broadcasting is a method of radio broadcasting using frequency modulation (FM). Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high fidelity sound over broadcast radio. FM broadcasting is cap ...
*
FM broadcast band The FM broadcast band is a range of radio frequencies used for FM broadcasting by radio stations. The range of frequencies used differs between different parts of the world. In Europe and Africa (defined as International Telecommunication Union (I ...
*
AM broadcasting 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") transmis ...
* AM stereo *
List of broadcast station classes This is a list of broadcast station classes applicable in much of North America under international agreements between the United States, Canada and Mexico. Effective radiated power (ERP) and height above average terrain (HAAT) are listed unless ot ...
*
History of radio The early history of radio is the history of technology that produces and uses radio equipment, radio instruments that use radio waves. Within the timeline of radio, many people contributed theory and inventions in what became radio. Radio deve ...
* RDS (Radio Data System) *
Oldest radio station It is generally recognised that the first radio transmission was made from a temporary station set up by Guglielmo Marconi in 1895. This followed on from pioneering work in the field by a number of people including Alessandro Volta, André-M ...


References


External links

Related websites
An Introduction to FM MPX
* ttp://transmitters.tripod.com/stereo.htm Stereo for DummiesMany graphs that show waveforms at different points in the FM Multiplex process
FM Transmitters
{{DEFAULTSORT:Fm Broadcasting In The United States Radio in the United States