Call signs in North America
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Call signs are frequently still used by North American broadcast stations, in addition to amateur radio and other international radio stations that continue to identify by call signs around the world. Each country has a different set of patterns for its own call signs. Call signs are allocated to ham radio stations in Barbados, Canada, Mexico and across the United States.
Many countries have specific conventions for classifying call signs by transmitter characteristics and location. The call sign format for radio and television call signs follows a number of conventions. All call signs begin with a prefix assigned by the International Telecommunications Union. For example, the United States has been assigned the following prefixes: "AAA"–"ALZ", "K", "N", "W". For a complete list, see international call sign allocations.
Bermuda, Bahamas, and the Caribbean
Pertaining to their status as former or current colonies, all of the British West Indies islands shared the VS, ZB–ZJ, ZN–ZO, and ZQ prefixes. The current, largely post-independence, allocation list is as follows:
- Anguilla (in amateur radio "VP2E" prefix)
- Antigua and Barbuda (uses "V2" prefix)
- Bahamas (has the "C6" prefix)
- Barbados (uses "8P")
- Bermuda (also uses "VS", in amateur radio normally "VP9")
- British Virgin Islands (for amateur radio uses "VP2V")
- Cayman Islands ("ZF" for amateur operation, "ZF1" for Grand Cayman, "ZF8" for Little Cayman and "ZF9" for Cayman Brac islands. Visiting reciprocal for all islands is "ZF2")
- Dominica (Commonwealth of Dominica, uses "J7")
- Grenada (uses "J3")
- Jamaica (uses "6Y")
- Montserrat (for amateur operation "VP2M" prefix)
- St. Kitts and Nevis (uses "V4")
- St. Lucia (uses "J6")
- St. Vincent and the Grenadines (uses "J8")
- Turks and Caicos Islands (typically uses "VP5")
Cuba uses the prefixes "CL"–"CM", "CO", and "T4", with district numbers from 0 to 9 to amateur operations.
The Dominican Republic uses the prefixes "HI"–"HJ".
French West Indies
All of the French possessions share the prefix "F". Further divisions that are used by amateur stations are:
Haiti has been assigned the callsign prefixes "HH" and "4V".
Trinidad and Tobago
The island nation of Trinidad and Tobago use the "9Y"–"9Z" prefixes.
Canadian broadcast stations are assigned a three-, four-, or five-letter base call sign (not including the "–FM", "TV" or "–DT" suffix) beginning with "CB", "CF", "CH", "CI", "CJ", "CK", "VA"–"VG", "VO", "VX", "VY", or "XJ"–"XO". The "CB" series calls are assigned to Chile by the ITU, but Canada makes de facto use of this series anyway for stations belonging to, but not exclusively broadcasting programs from, the Canadian Broadcasting Corporation (CBC).
Several other prefixes, including "CG", "CY", "CZ" and the "XJ" to "XO" range, are available. Conventional radio and television stations almost exclusively use "C" call signs; with a few exceptions noted below, the "V" codes are restricted to specialized uses such as amateur radio.
Mexican broadcast stations are assigned a three-, four-, five-, or six-letter call signs beginning with "XE" (for mediumwave and shortwave stations) or "XH" (for FM radio and television stations). Some FM and television stations (like XETV) are grandfathered with "XE" call signs and a "–FM", "-TDT" or "–TV" suffix. Mexican stations are required to identify twice an hour and to play the Mexican national anthem every day at 6am and midnight local time. Television rebroadcasters are assigned the callsigns of the station they are licensed to retransmit; for instance, XEZ-TV, located on Cerro El Zamorano in Querétaro, has a repeater on Cerro Culiacán serving Celaya, Guanajuato, which is also XEZ-TV.
Amateur radio stations in Mexico use "XE1" for the central region, "XE2" for the northern region, and "XE3" for the southern region. "XF" prefixes indicate islands. "XF4" is usually used for the Revillagigedo Islands and nearby islets. Special call signs for contests or celebrations are occasionally issued, often in the 4A and 6D series, although these will follow the usual district numbering system (4A3 for the south, etc.).
The earliest identification, used in the 1910s and into the early 1920s, was arbitrary. The U.S. government began requiring stations to use three-letter call signs around 1912, but they could be chosen at random. This system was replaced by the basic form of the current system in the early 1920s. Examples of pre-1920 stations include 8XK in Pittsburgh, Pennsylvania, which became KDKA in November 1920, and Charles Herrold's series of identifiers from 1909 in San Jose, California: first "This is the Herrold Station" or "San Jose calling", then the call signs FN, SJN, 6XF, and 6XE, then, with the advent of modern call signs, KQW in December 1921, and eventually KCBS from 1949 onward.
All broadcast call signs in the United States begin with either "K" or "W", with "K" usually west of the Mississippi River and "W" usually east of it (except in Louisiana and Minnesota, which do not strictly follow the dividing line between the two groups). Initial letters "AA" through "AL", as well as "N", are internationally allocated to the United States but are not used for broadcast stations.
In the United States, broadcast stations have call signs of three to seven characters in length, including suffixes for certain types of service, but the minimum length for new stations is four characters, and seven-character call signs result only from rare combinations of suffixes.
Call signs are also used in other parts of the world, particularly those which have had significant U.S. influence at some point. This includes the Philippines (which is assigned "DZ", "DY", "DX" or "DW" followed by two letters), Japan (which is assigned "JO" followed by two letters), South Korea (which is assigned "HL" followed by two letters), Argentina (which uses "AY", "L2", and "LO" to "LZ") and formerly Australia. Another well-known call sign outside of the region is HCJB in Ecuador, and several radio time sources used to set radio clocks or for audible listening, such as CHU in Ottawa, Ontario, Canada.
- City of license – another element of station licensing
- Facility ID – used by the FCC in the United States to distinguish broadcast stations without regard to call sign changes
The rules governing call signs for stations in the United States are set out in the FCC rules, 47 C.F.R. chapter I. Specific rules for each particular service are set out in the part of the rules dealing with that service. A general overview of call sign formats is found at 47 C.F.R. 2.302. Rules for broadcast stations' call sign are principally defined in 47 C.F.R. 73.3550.
- Tophour.com - Top-of-the-hour station identifications with call signs from American AM and FM radio stations
- Military Callsign List
- K/W Call Letters in the United States - A comprehensive historical review of K and W call letter assignments for AM band (mediumwave) radio stations in the United States
-  - United States Callsign Policies