In radio (including television), a callsign or call sign (also call letters) is a unique designation for amateur, broadcast, and sometimes military radio use, as well as for broadcast television. Such callsigns are formal, semi-permanent, and issued by a nation's telecommunications agency.
Each country has a set of alphabetic or numeric International Telecommunication Union-designated prefixes with which their callsigns must begin. For example:
- The U.S.A. uses the prefixes: W, K, N, and AAA to ALZ (only W and K are used for broadcast stations).
- Canada uses the prefixes: CF-CK, CY-CZ, VA-VG, VO, VX-VY, XJ-XO
- Mexico uses X
- The United Kingdom uses the prefixes: G, M, and 2
- France uses the prefixes: F, TM
- Germany uses the prefixes: DA-DR
- Chad uses the prefix: TT
- Italy uses the prefix: I
Amateur radio callsigns normally consist of a one- or two-character prefix, a number (which sometimes corresponds to a geographic area within the country) and a 1, 2, or 3 character suffix. The number following the prefix is normally a single number (0 to 9). Some prefixes, such as Djibouti's (J2), consist of a letter followed by a number. Hence, in the hypothetical Djibouti callsign, J29DBA, the prefix is J2, the number is 9, and the suffix is DBA. In the Italian callsign, IK1TZO, IK is the prefix, the number component is 1 and corresponds to the Piemonte region, and TZO is the suffix. Another example is WB3EBO. WB is the prefix, the number 3 most often indicates that the station is located in Delaware, Maryland, Pennsylvania, or the District of Columbia. The suffix is EBO. For the district numbers within the United States, see ARRL map (http://www.arrl.org/awards/was/map.gif).
There are some common conventions followed for callsigns in North America.
Canadian broadcast stations are assigned a three-, four- or five-letter callsign beginning with CF, CH, CI, CJ, CK, VE, VF, or VO. (Several other codes are available, but are not currently in use.) Most stations operated by the Canadian Broadcasting Corporation use callsigns beginning with CB by arrangement between the Canadian and Chilean authorities. Callsigns beginning with VE and VF are only assigned to very-low-power local rebroadcasters; VO callsigns may only be used by four stations in Newfoundland which were licensed before that province joined Canadian Confederation in 1949. All Canadian FM stations have a "-FM" suffix, and likewise TV stations and "-TV", except for low-power rebroadcasters which have seminumeric callsigns. Higher-power rebroadcasters are generally licensed under the callsign of the originating station, followed by a numeric suffix and, for FM rebroadcasters of an AM station, a "-FM" suffix; for example, CJBC-1-FM rebroadcasts CJBC (860 Toronto), whereas CJBC-FM-1 rebroadcasts CJBC-FM (90.3 Toronto).
Canadian stations are required to identify by callsign hourly, but not at any specific time, and this rule is even more rarely enforced than the U.S. rule (see below).
Mexican broadcast stations are assigned a three-, four-, five-, or six-letter callsign beginning with XE (mediumwave) or XH (all others). Some FM and TV stations are grandfathered with XE callsigns and a "-FM" or "-TV" suffix. Mexican stations are required to identify twice an hour, at both the top and the bottom. Mexican stations broadcasting English-language programming are in addition required to play the Mexican national anthem every day at midnight local time.
In the United States, broadcast stations have callsigns between three and six characters in length, though the minimum length for new stations is four letters. Full-power stations receive four-letter callsigns, while broadcast translators and low-power stations usually receive callsigns with five or six characters, including two or three numbers. Stations with three letters were granted those names in the 1920s and have been grandfathered into the current system, even though many such stations have changed owners. These stations include KOA in Denver, Colorado, WGN in Chicago, Illinois, and WJZ-TV in Baltimore, Maryland. The Federal Communications Commission for many years maintained a policy of "drop it and lose it forever" with respect to three-letter callsigns, but recently allowed KKHJ (930 Los Angeles) to regain its historic three-letter call, KHJ.
New stations are assigned a code beginning with K, if they are west of the Mississippi River, and beginning with W if they are east of the river. Again, some early stations have been grandfathered in, so there are some broadcasters with a K prefix east of the Mississippi, and some with a W on the west side. Some examples would be KDKA in Pittsburgh, Pennsylvania and WDAY in Fargo, North Dakota. Stations located near the Mississippi River may have either letter, depending on the precise location of their community of license and on historical contingencies. Communities with mixed W- and K- stations because of locality to the river include Minneapolis-St. Paul, Minnesota, and St. Louis, Missouri.
FM and TV translators, and many (but not all) low-power TV stations are assigned sequential callsigns. They use an appropriate initial letter followed by a two- or three-digit channel number, and then a two-letter sequential suffix. For example, a TV translator on channel 4 might have the call sign K04AX. The FM band also has channel numbers starting at the number 200 (or 201 for practical purposes), although they are less well-known to regular listeners who usually tune in to a station based on its frequency. W201BE could be used for an FM translator at 88.1 MHz. Such callsigns are never reused.
New full-power stations are assigned sequential callsigns if the permittee does not choose one of their own; these are always four letters, of which the third is the least-significant digit and the second is the most-significant digit of the sequence number. (Callsigns which were already assigned are skipped in the sequence.) Hence, many very early stations, like WMAQ Chicago (now WSCR) and WMAF South Dartmouth (now defunct) were assigned W-A- (or K-A-) callsigns.
Radio and television callsigns are followed by a dash and the two-letter class of station: "-FM", "-LP", "-TV", or "-CA". (There is no such thing as "-AM", although it is commonly used in the industry press; likewise "-DT" for digital television, although the latter has at least some FCC recognition.)
Many stations prefer not to use callsigns at all, since a slogan is more easily remembered by listeners (and those filling in diaries for the Arbitron Company's radio ratings). However, in the U.S., the Federal Communications Commission does require periodic identification using the formal callsign, as close to the top of each hour as possible, at a "natural break in programming"; this rule is rarely enforced. Radio stations are also required to identify their community of license. There are some unusual cases, though, such as the low-frequency WWVB time station. That station broadcasts a one bit per second signal that cannot be understood by humans, so the station is identified by shifting the broadcast carrier wave's phase by 45°.
It is fairly common for stations to choose a callsign that can be transformed into a name, such as Boston's WXKS-FM (107.9 Medford), one of many Clear Channel Communications-owned stations that call themselves "KISS". Much more commonly, the letters stand for something. Some of the most famous of these include WGN, owned by the Chicago Tribune, which stands for "World's Greatest Newspaper," and WLS, then owned by Sears, Roebuck, the "World's Largest Store".
Extremely early callsigns used in the 1910s and into the early 1920s were arbitrary. The U.S. government began requiring stations to use three-letter callsigns around 1912, but they could be chosen at random. KDKA initially broadcast as 8XK before gaining its well-known letters in 1920. The Rosicrucian Order, AMORC of San Jose, California used the callsign 6KZ.
Experimental broadcast stations (indeed, all experimental stations, broadcast or not) use callsigns out of the amateur radio sequence, with the letter following the region digit required to be an X. (All VHF stations before World War II were licensed as experimental stations.) Notable experimental stations included Major Armstrong's FM station W2XMN in Alpine, New Jersey, Powell Crosley's 500-kW superpower AM W8XO, operating nights only with WLW's programming and frequency from Mason, Ohio), and Don Lee's pioneering television station, W6XAO in Los Angeles. (Synchronous "booster" transmitters for AM stations are still considered experimental in the US, despite fifty years of experience in Europe, and new experimental callsigns are being assigned for new licenses even now, by inserting a region digit and the letter X into the parent station's callsign.)
Somewhat confusingly, the National Weather Service also uses similar call signs for weather reporting stations, as does the ICAO airport code system.
In Australia, broadcast callsigns begin with a single-digit number indicating the state or territory, followed by two letters for AM stations and three for FM. Some AM stations retain their old callsigns when moving to FM, or just add an extra letter to the end. Australian broadcast stations originally used the prefix VL-, but since Australia has no nearby neighbors, this practice was soon discarded in use.
Television station callsigns begin with two letters usually denoting the station itself, followed by a third letter denoting the state. For example, NBN's callsign stands for Newcastle Broadcasting, New South Wales. There are some exceptions:
- ABC television stations outside of state capitals add a fourth letter between AB and the state. This is used to denote the area e.g. the Newcastle station is known as ABHN, standing for Australian Broadcasting Corporation, Hunter Valley, New South Wales. State capital stations follow the same rule as commerical stations.
- SBS television stations all use SBS in their callsigns, regardless of the state.
- Commercial station Imparja Television uses IMP, even though they are based in Alice Springs in the Northern Territory.
Letters and numbers used by Australian stations:
- N - New South Wales
- Q - Queensland
- V - Victoria
- S - South Australia
- C - Canberra and the Australian Capital Territory
- W - Western Australia
- D - Darwin and the Northern Territory
- T - Tasmania
In Europe and much of Asia, callsigns are normally not used for broadcast stations. Japan, South Korea and Taiwan are exceptions to this general rule. Other countries have yet other formats for assigning callsigns to domestic services.
The United States Army uses fixed callsigns for Army stations which begin with W, such as WAR, used by U.S. Army Headquarters.
US Air Force
The United States Air Force uses semi-fixed identifiers consisting of a name followed by a two or three digit number. The name is assigned to a unit on a semi-permanent basis; they change only when the U.S. Department of Defense goes to DEFCON 3. For example, JAMBO 51 would be assigned to a particular B-52 aircrew of the 5th Bomb Wing, while NODAK 1 would be an F-16 fighter with the North Dakota Air National Guard. The most recognizable callsign of this type is Air Force One, used when any plane is carrying the U.S. President, or Marine One, used to identify any helicopter doing the same thing.
Fixed callsigns for USAF stations begin with A, such as AIR, used by USAF Headquarters.
US Navy/Coast Guard
The United States Navy and United States Coast Guard use a mixture of tactical callsigns and formal callsigns beginning with the letter N. For example, the carrier USS John F. Kennedy has the callsign NJFK.
- United States Callsign Policies (http://earlyradiohistory.us/recap.htm)
- Amateur Call Prefixes (http://www.ac6v.com/prefixes.htm)