The term is also used in the context of T1

A clear channel, in its general sense, is a communications channel, such as a radio frequency, on which only one transmitter operates at a time. In North America, it's also a regulatory category for mediumwave radio stations.

Clear-channel stations

Certain mediumwave frequencies were set aside under the North American Radio Broadcasting Agreement (NARBA for short) for nighttime use by only one or two specific AM stations, covering a wide area via skywave propagation; these frequencies were known as the clear channels, and the stations on them are thus clear-channel stations. Where only one station was assigned to a clear channel, the treaty provides that it must operate with a nominal power of 50 kilowatts or more; stations on the other clear channels, with two or more stations, must use between 10 and 50 kW, and most often use a directional antenna so as not to interfere with each other. In addition to the frequencies, the treaty also specified the specific locations where stations on this second kind of channel (known as class I-B) could be built.

Some of the original NARBA signatories, including the United States, Canada, and Mexico, have implemented bilateral agreements that supersede its terms, eliminating among other things the distinction between the two kinds of clear channel: the original "I-A", "I-B", and "I-N" station classes are now all included in class A.

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 to 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 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 to 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.

Clear Channel Communications, a San Antonio, Texas-based company which owns over 900 U.S. radio stations, was originally formed to purchase one clear-channel station, WOAI. The company now owns more than a dozen such stations.

History

For the U.S., clear channels first appeared in 1922 when the Commerce Department 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 used for all low-power stations and the large stations 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 this time large stations were limited to 1000 watts and some licences were revoked. Later in 1928, the AM band was reorganized with local, regional and clear channels (and a few reserved for Canada) by the new Federal Radio Commission's General Order 40. Gradually maximum power was increased to 50,000 watts (with some short lived experiments with 250–500 kilowatt "super-power" operation). This system was continued in the 1941 NARBA system although almost all stations shifted broadcast frequencies.

As early as the 1950s, debate raged in Washington, D.C., 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. They requested that the power limit on the "I-A" channels in the U.S. be increased from 50 kW to 750 kW, pointing to WLW's successful experiments before the war, 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 were eliminated, they would be able to build new stations to provide local service to those rural "dark areas".

One station, KOB in Albuquerque, New Mexico, fought a long legal battle against the 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, like 680 in San Francisco, California, had been "duplicated" in the eastern states for many years.) These new class II-A assignments (in places like Window Rock, Arizona; Boise, Idaho; Las Vegas and Reno, Nevada; Lexington, Nebraska; Casper, Wyoming; Kalispell, Montana; and others) began what would later be called "the breakdown of the clear channels". The class I-A station owners' proposal to increase power fifteen-fold 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 the twenty-five clear channel stations to a 750 mile radius around the transmitter. Those stations 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.

List of all clear-channel stations

The following two tables show all of the class-A stations in North America. Stations in Alaska (the former class I-Ns) are shown separately.

Class A stations (except Alaska) Freq. Callsign Community 540 CBK Regina, Saskatchewan 540 CBT Grand Falls, Newfoundland and Labrador 540 XEWA San Luis Potosí, San Luis Potosí 640 CBN St. John's, Newfoundland and Labrador 640 KFI Los Angeles, California 650 WSM Nashville, Tennessee 660 WFAN New York, New York 670 WSCR Chicago, Illinois 680 KNBR San Francisco, California 690 CINF Montreal, Quebec 690 XETRA Tijuana, Baja California 700 WLW Cincinnati, Ohio 710 KIRO Seattle, Washington 710 WOR New York, New York 720 WGN Chicago, Illinois 730 CKAC Montreal, Quebec 730 XEX Mexico City, D.F. 740 CFZM Toronto, Ontario 750 WSB Atlanta, Georgia 760 WJR Detroit, Michigan 770 WABC New York, New York 780 WBBM Chicago, Illinois 800 XEROK Ciudad Juárez, Chihuahua 810 KGO San Francisco, California 810 WGY Schenectady, New York 820 WBAP Fort Worth, Texas 830 WCCO Minneapolis, Minnesota 840 WHAS Louisville, Kentucky 850 KOA Denver, Colorado 860 CJBC Toronto, Ontario 870 WWL New Orleans, Louisiana 880 WCBS New York, New York 890 WLS Chicago, Illinois 900 XEW Mexico City, D.F. 940 CINW Montreal, Quebec 940 XEQ Mexico City, D.F. 990 CBW Winnipeg, Manitoba 990 CBY Corner Brook, Newfoundland and Labrador 1000 KOMO Seattle, Washington 1000 WMVP Chicago, Illinois 1010 CBR Calgary, Alberta 1010 CFRB Toronto, Ontario 1020 KDKA Pittsburgh, Pennsylvania 1030 WBZ Boston, Massachusetts 1040 WHO Des Moines, Iowa 1050 XEG Monterrey, Nuevo León 1060 KYW Philadelphia, Pennsylvania 1060 XEEP Mexico City, D.F. 1070 defunct Moncton, New Brunswick 1070 KNX Los Angeles, California 1080 WTIC Hartford, Connecticut 1080 KRLD Dallas, Texas 1090 KAAY Little Rock, Arkansas 1090 WBAL Baltimore, Maryland 1100 WTAM Cleveland, Ohio 1110 KFAB Omaha, Nebraska 1110 WBT Charlotte, North Carolina 1120 KMOX St. Louis, Missouri 1130 CKWX Vancouver, British Columbia 1130 KWKH Shreveport, Louisiana 1130 WBBR New York, New York 1140 WRVA Richmond, Virginia 1140 XEMR Monterrey, Nuevo León 1160 KSL Salt Lake City, Utah 1170 KFAQ Tulsa, Oklahoma 1170 WWVA Wheeling, West Virginia 1180 WHAM Rochester, New York 1190 KEX Portland, Oregon 1190 WOWO Fort Wayne, Indiana 1190 XEWK Guadalajara, Jalisco 1200 WOAI San Antonio, Texas 1210 WPHT Philadelphia, Pennsylvania 1220 XEB Mexico City, D.F. 1500 KSTP Saint Paul, Minnesota 1500 WWWT Washington, D.C. 1510 KGA Spokane, Washington 1510 WLAC Nashville, Tennessee 1520 KOKC Oklahoma City, Oklahoma 1520 WWKB Buffalo, New York 1530 KFBK Sacramento, California 1530 WCKY Cincinnati, Ohio 1540 KXEL Waterloo, Iowa 1540 ZNS-1 Nassau, Bahamas 1550 CBE Windsor, Ontario 1550 XERUV Xalapa, Veracruz 1560 KNZR Bakersfield, California 1560 WQEW New York, New York 1570 XERF Ciudad Acuña, Coahuila 1580 CKDO Oshawa, Ontario

Class A (former class I-N) stations in Alaska Freq. Callsign Community 640 KYUK Bethel 650 KENI Anchorage 660 KFAR Fairbanks 670 KDLG Dillingham 680 KBRW Barrow 700 KBYR Anchorage 720 KOTZ Kotzebue 750 KFQD Anchorage 770 KCHU Valdez 780 KNOM Nome 820 KCBF Fairbanks 850 KICY Nome 890 KBBI Homer 1020 KAXX Eagle River 1080 KUDO Anchorage 1170 KJNP North Pole

Notes

See also

• Canadian allocations changes under NARBA

External links

• AM Station Classes - Clear, Regional, and Local Channels (FCC Website)
• Big USA, Mexico, and Canadian AM radio stations