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A clear-channel station is an AM
radio station Radio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based radio ...
in North America that has the highest protection from
interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extr ...
from other stations, particularly concerning night-time
skywave In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of ...
propagation. The system exists to ensure the viability of cross-country or cross-continent radio service enforced through a series of treaties and statutory laws. Known as Class A stations since 1982, they are occasionally still referred to by their former classifications of Class I-A (the highest classification), Class I-B (the next highest class), or Class I-N (for stations in Alaska too far away to cause interference to the primary clear-channel stations in the lower 48 states). The term "clear-channel" is used most often in the context of North America and the Caribbean, where the concept originated. Since 1941, these stations have been required to maintain an
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 ...
of at least 10,000
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s to retain their status. Nearly all such stations in the United States, Canada and The Bahamas broadcast at 50,000 watts, with several clear-channel stations in Mexico going as high as 150,000 watts and XEW in
Mexico City Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...
having operated at 250,000 watts for over 80 years. Cuba was originally included in the plan and had several stations given clear-channel status, but stopped participating after the
Cuban Revolution The Cuban Revolution ( es, Revolución Cubana) was carried out after the 1952 Cuban coup d'état which placed Fulgencio Batista as head of state and the failed mass strike in opposition that followed. After failing to contest Batista in cou ...
of 1959.


Description

Sixty
medium wave Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band. During the daytime ...
frequencies were set aside in 1941 under the
North American Regional Broadcasting Agreement The North American Regional Broadcasting Agreement (NARBA, es, Convenio Regional Norteamericano de Radiodifusión) refers to a series of international treaties that defined technical standards for AM band (mediumwave) radio stations. These agreem ...
(NARBA) for nighttime use by only one, two or three specific AM stations, covering a wide area via
skywave In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of ...
propagation Propagation can refer to: * Chain propagation in a chemical reaction mechanism *Crack propagation, the growth of a crack during the fracture of materials * Propaganda, non-objective information used to further an agenda * Reproduction, and other fo ...
. These frequencies were known as the "clear channels", and the stations on them are thus clear-channel stations. NARBA set aside 37 Class I-A frequencies and 27 Class I-B frequencies. The Class I-N stations in Alaska shared those same frequencies. Where only one station was assigned to a clear channel, the treaty provides that it must operate with a
nominal power Nominal power is a power capacity in engineering. Radio broadcasting Nominal power is a measurement of a mediumwave radio station's output used in the United States. Photovoltaic devices Nominal power is the nameplate capacity of photovoltaic ( ...
of 50
kilowatts The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
or more. These were for the most part Class I-A. Stations on the other clear channels, with two or more stations, must use between 10 kW and 50 kW, and most often use a
directional antenna A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance ...
so as not to interfere with each other. In addition to the frequencies, the treaty also specified the specific locations where stations on Class I-B channels could be built. Some of the original NARBA signatories, including the United States, Canada and Mexico, have implemented bilateral agreements that supersede NARBA's terms, eliminating among other things the distinction between the two kinds of clear channel: the original "I-A" and "I-B" classes, and the newer, U.S.-only "I-N" class, which are now all included in class A. Classes "I-A" and "I-B" still mandate a minimum efficiency of 362.10 mV/m/kW at 1 km, whereas Class "I-N" is permitted to use the lower Class B minimum efficiency of 281.63 mV/m/kW at 1 km. There exist exceptions, where a former Class B station was elevated to Class A, yet it maintained its previous antenna system, or made only minor changes thereto. Clear-channel stations, unlike all other AM stations in North America, have a ''secondary service area''; that is, they are entitled to protection from interference with their nighttime skywave signals. Other stations are entitled, at most, to protection from nighttime interference in their ''primary service area''—that which is covered by their
groundwave In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within liquids, at t ...
signal. Many stations beyond those listed in the treaty have been assigned to operate on a clear channel (and some had been long before NARBA came into effect in 1941). In most cases, those stations operate during the daytime only, so as not to interfere with the primary stations on those channels. Since the early 1980s, many such stations have been permitted to operate at night with such low power as to be deemed not to interfere; these stations are still considered "daytimers" and are not entitled to any protection from interference with their nighttime signals. Another group of stations, formerly known as ''class II'' stations, were licensed to operate on the former "I-B" clear channels with significant power at night, provided that they use directional antenna systems to minimize radiation towards the primary stations.


History

For the U.S., a form of clear channels first appeared in 1922 when the
Commerce Department The United States Department of Commerce is an executive department of the U.S. federal government concerned with creating the conditions for economic growth and opportunity. Among its tasks are gathering economic and demographic data for busin ...
moved stations which had all used three (initially two) frequencies (two for entertainment stations, one for "weather and crop reports") onto 52 frequencies. Two were set aside for low-power local and regional stations, while the large stations in major cities each got their own frequency. A few frequencies were used on both the East and West coasts, which were considered far enough apart to limit interference. At that time, large stations were limited to 1000 watts and some licences were revoked. On November 11, 1928, the United States implemented
General Order 40 The Federal Radio Commission's (FRC) General Order 40, dated August 30, 1928, described the standards for a sweeping reorganization of radio broadcasting in the United States. This order grouped the AM radio band transmitting frequencies into thre ...
, which classified each allocation in the
AM band Medium wave (MW) is the part of the medium frequency (MF) radio band used mainly for AM radio broadcasting. The spectrum provides about 120 channels with more limited sound quality than FM stations on the FM broadcast band. During the daytim ...
as either Local, Regional or Clear. The classification system considered stations in Canada as well. Gradually maximum power was increased to 50,000 watts: additionally there were some short-lived experiments with 250–500 kilowatt "super-power" operations. This system was continued in the 1941 NARBA system, although almost all stations shifted broadcast frequencies. The FCC's intent behind licensing 50,000 watt ''clear-channel'' stations was to provide reliable radio service to the thousands of Americans who lived in the vast rural areas of the United States. As a result, these stations usually reached large portions of North America at night. Radio fans (and staff at those stations) often affectionately call such stations "flamethrowers" or "blowtorches" because of their high power, and boast about their reach by a combined state and provincial count of their coverage area. As early as the 1930s, debate raged in
Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...
, and in the U.S. broadcasting industry over whether continuation of the clear-channel system was justifiable. The licensees of clear-channel stations argued that, without their special status, many rural areas would receive no radio service at all. Rural broadcasters pointed out that most of the clear-channel stations were licensed to serve large cities on the two coasts, which made little sense for a service that was meant to provide radio to the vast rural areas in the middle of the country. The clear-channel licensees requested that the power limit on the "I-A" channels in the U.S., set at 50 kW by the FCC, be lifted entirely. They pointed to successful experiments made by
WLW WLW (700 AM) is a commercial news/talk radio station licensed to Cincinnati, Ohio. Owned by iHeartMedia, WLW is a clear-channel station, often identifying itself as The Big One. WLW operates with around the clock. Its daytime signal provides ...
in
Cincinnati Cincinnati ( ) is a city in the U.S. state of Ohio and the county seat of Hamilton County. Settled in 1788, the city is located at the northern side of the confluence of the Licking and Ohio rivers, the latter of which marks the state line wit ...
before
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, and in later years successful implementation by state broadcasters in Europe and the Middle East, as evidence that this would work and improve the service received by most Americans. Other broadcasters, particularly in the western states, argued to the contrary; that if the special status of the clear-channel stations was eliminated, ''they'' would be able to build facilities to provide local service to those rural "dark areas". One of the most outspoken of the small-town broadcasters,
Ed Craney Edmund Blodgette Craney (February 19, 1905 – April 6, 1991
of KGIR in
Butte, Montana Butte ( ) is a consolidated city-county and the county seat of Silver Bow County, Montana, United States. In 1977, the city and county governments consolidated to form the sole entity of Butte-Silver Bow. The city covers , and, according to the ...
, went so far as to apply to move his station, then on the 1370 kHz regional channel, to a class I-A signal on 660 kHz, asking the FCC to downgrade the
NBC The National Broadcasting Company (NBC) is an Television in the United States, American English-language Commercial broadcasting, commercial television network, broadcast television and radio network. The flagship property of the NBC Enterta ...
New York
flagship A flagship is a vessel used by the commanding officer of a group of naval ships, characteristically a flag officer entitled by custom to fly a distinguishing flag. Used more loosely, it is the lead ship in a fleet of vessels, typically the fi ...
, WEAF, to make way for the Butte station. The FCC denied Craney's petition. In 1941 several existing clear-channel stations applied for power increases to between 500 and 750 kW; dissemination of national defense information is cited as one reason this would be in the public interest. In October 1941 the FCC's engineering department presented a report on a complete reorganization of the clear-channel service; the report considered the possibility of "some 25 superpower stations of 500,000 watts or more, strategically located to provide maximum service" (as ''Broadcasting'' described it), and suggested that stations would have to be relocated away from the east and west coasts in such a scenario, as coastal stations waste energy over the oceans. One complication the FCC considered was the "
Wheeler resolution Senate Resolution 294, Limitation of Power of Radio Broadcast Stations, commonly known as the Wheeler resolution, is a United States Senate The United States Senate is the upper chamber of the United States Congress, with the House of Repr ...
", passed by the
United States Senate The United States Senate is the upper chamber of the United States Congress, with the House of Representatives being the lower chamber. Together they compose the national bicameral legislature of the United States. The composition and pow ...
in 1938, expressing the view of the Senate that radio stations should be limited to a maximum power of 50 kW. One station,
KOB The kob (''Kobus kob'') is an antelope found across Central Africa and parts of West Africa and East Africa. Together with the closely related reedbucks, waterbucks, lechwe, Nile lechwe, and puku, it forms the Reduncinae tribe. Found along ...
in
Albuquerque, New Mexico Albuquerque ( ; ), ; kee, Arawageeki; tow, Vakêêke; zun, Alo:ke:k'ya; apj, Gołgéeki'yé. abbreviated ABQ, is the most populous city in the U.S. state of New Mexico. Its nicknames, The Duke City and Burque, both reference its founding in ...
, fought a long legal battle against 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) and New York's WABC for the right to move from a regional channel to a clear channel, 770 kHz, arguing that the New York signal was so weak in the mountain west that it served no one. KOB eventually won the argument in the late 1960s; it and several other western stations were allowed to move to eastern clear channels. (Western clear channels, such as 680 in San Francisco, had been "duplicated" in the eastern states for many years.) These new ''class II-A'' assignments (in places like
Boise, Idaho Boise (, , ) is the capital and most populous city of the U.S. state of Idaho and is the county seat of Ada County. On the Boise River in southwestern Idaho, it is east of the Oregon border and north of the Nevada border. The downtown are ...
;
Las Vegas Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the Las Vegas ...
and
Reno, Nevada Reno ( ) is a city in the northwest section of the U.S. state of Nevada, along the Nevada-California border, about north from Lake Tahoe, known as "The Biggest Little City in the World". Known for its casino and tourism industry, Reno is the ...
;
Lexington, Nebraska Lexington is a city in Dawson County, Nebraska, United States. The population was 10,348 at the 2020 census. It is the county seat of Dawson County. Lexington is located in southern Nebraska, on the Platte River, southeast of North Platte. It si ...
;
Casper, Wyoming Casper is a city in, and the county seat of, Natrona County, Wyoming, United States. Casper is the second-largest city in the state, with the population at 59,038 as of the 2020 census. Only Cheyenne, the state capital, is larger. Casper is nic ...
;
Kalispell, Montana Kalispell (, Montana Salish: Ql̓ispé, Kutenai language: kqayaqawakⱡuʔnam) is a city in, and the county seat of, Flathead County, Montana, United States. The 2020 census put Kalispell's population at 24,558. In Montana's northwest region, ...
; and others) began what would later be called "the breakdown of the clear channels". The class I-A station owners' proposal to increase power fifteenfold was not immediately quashed, but the new II-A stations would make it effectively impossible for stations on the duplicated channels to do so, and the owners eventually lost interest. That proposal was finally taken off the FCC's docket in the late 1970s. On May 29, 1980, the FCC voted to limit the protection for all clear-channel stations to a 750-mile (1 207 km) radius around the
transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna (radio), antenna. The transmitter itself generates a radio frequency alternating current, which i ...
. Stations on those frequencies outside the area of protection were no longer required to sign off or power down after sundown. In 1987 the FCC changed its rules to prohibit applications for new "class-D" stations. (Class-D stations have night power between zero and 250 watts, and frequently operate on clear channels.) However, any existing station could voluntarily relinquish nighttime authority, thereby becoming a class-D, and several have done so since the rule change.


Daytimers

Daytimers (also known as daytime-only stations) are
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") transm ...
stations that are limited to broadcasting during the daytime only, as their signals would interfere with clear-channel and other radio stations at night, when solar radiation is reduced, and medium wave radio signals can propagate much farther. Such stations are allowed three manners of operation after sunset; to sign off the air completely until sunrise, reduce power (sometimes dramatically, to only a few watts), or switch to a nighttime-only frequency (such as the Detroit area's WNZK, which broadcasts on 690 during the day, and on 680 at night). Their broadcast class is Class D. A great number of these stations use FM translators to continue their broadcasts overnight, and some also broadcast on the internet and have separate streams that air when the station's over-the-air signal has signed off. Daytime-only stations first originated in the late 1920s shortly after General Order 40 was imposed. One of the first to do so was WKEN in
Kenmore, New York Kenmore is a village in Erie County, New York, United States. The population was 15,423 at the 2010 census. It is part of the Buffalo–Niagara Falls metropolitan area. Kenmore is in the south part of the town of Tonawanda, and together with th ...
(now
WUFO WUFO (1080 kHz) is a commercial AM radio station licensed to Amherst, New York, and serving the Buffalo metropolitan area. It is owned by the Visions Multi Media Group headed by Sheila. L. Brown and it broadcasts a hybrid Urban AC and Classic Hi ...
). WKEN proposed the concept to avoid the then-common practice of having to share one frequency between multiple stations; under General Order 40, WKEN would have had to share its frequency with WKBW, and the daytime-only proposal allowed both stations their own frequency. WUFO remains a daytime-only station to the present day, albeit with a 24/7 FM translator introduced in mid-2017. As of 2013, daytimers only exist in the United States and Mexico. The last Canadian daytime station, CKOT, signed off on February 17 of that year after converting to the FM band. There were 61 daytimers in Mexico in 2015.


List of all clear-channel stations

The following two tables show all of the class-A stations in North America. First is the Canada, Mexico, and contiguous United States table, for the former class I-A and class I-B stations.
General Order 40 The Federal Radio Commission's (FRC) General Order 40, dated August 30, 1928, described the standards for a sweeping reorganization of radio broadcasting in the United States. This order grouped the AM radio band transmitting frequencies into thre ...
allocations are in bold. Second is the Alaska table, for the former class I-N stations. Under the most recent treaty, Mexican Class A stations that previously operated with 50 kW or less (but a minimum of 10 kW nights) may increase power to 100 kW days while retaining their 10 kW night operation. This created some anomalies where stations licensed for 10 kW during all hours could increase power to 100 kW days and 10 kW nights, unless a directional antenna system was installed for nights, in which case the maximum night power was 50 kW. Additionally, one Class B station that had been operating non-directionally with 100 kW days and 50 kW nights was required to reduce power to 50 kW during all hours.


Notes


List of former clear-channel stations


See also

*
Regulation of radio broadcast in the United States Radio regulation in the United States was enforced to eliminate different stations from broadcasting on each other's airwaves. Regulated by the Federal Communications Commission, standardization was encouraged by the chronological and economic ad ...
*
Clear Channel Communications iHeartMedia, Inc., formerly CC Media Holdings, Inc., is an American mass media corporation headquartered in San Antonio, Texas. It is the holding company of iHeartCommunications, Inc. (formerly Clear Channel Communications, Inc.), a company fou ...
*
MW DX MW DX, short for mediumwave DXing, is the hobby of receiving distant mediumwave (also known as '' AM'') radio stations. MW DX is similar to TV and FM DX in that broadcast band (BCB) stations are the reception targets. However, the nature of the lo ...


References


External links


AM Station Classes - Clear, Regional, and Local Channels
(FCC Website)

{{Telecommunications United States communications regulation Mass media regulation in Canada