In broadcasting and radio communications, a call sign (also known as a callsign or call letters, or abbreviated as a call) is a unique designation for a transmitting station. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise a station's identity.
International series
International call signs are formal, semi-permanent, and issued by a nation's telecommunications agency. They are used for amateur, broadcast, commercial, maritime and sometimes military radio use (including television in some countries).
Each country has a set of alphabetic or numeric International Telecommunication Union-designated prefixes with which their call signs must begin. For example:
- The United States uses the prefixes: W, K, N, and AAA to ALZ. Only W and K are used by broadcast stations. There are zones which come after the first letter, denoted by a number.
- Canada uses the prefixes: CF-CK, CY-CZ, VA-VG, VO, VX-VY, XJ-XO (Canadian Broadcasting Corporation (CBC), uses CB). (Stations beginning with VO were allocated to Newfoundland, before it joined confederation with Canada in 1949 and grandfathered into Canada's prefixes.)
- Mexico uses XA-XI. Broadcast stations use the prefix XE on the mediumwave AM band and XH for television.
- The United Kingdom uses the prefixes: G, M, ZB-ZJ, ZN-ZO, ZQ, and 2
- The Bahamas and Bermuda use part of the Z allocations given to the United Kingdom, from when they were still colonies of England. (In the case of Bermuda, they still are a crown dependency).
- Chile uses CA-CE, but gives the CBC's stations the CB allocation via a special agreement with the Canadian federal government.
- Cuba uses CL-CM, and CO.
- France uses the prefixes: F, TM
- Germany uses the prefixes: DA-DR
- Chad uses the prefix: TT
- Italy uses the prefix: I
- The Philippines uses the prefixes DW and DZ for broadcast stations in Luzon, DY for stations in Visayas and DX for Mindanao radio stations.
- Israel uses the prefixes: 4X and recently 4Z
Aviation
Call signs in aviation are derived from several different policies, depending on the type of flight operation being conducted, and depending on whether the caller is in an aircraft or at a ground facility. In most countries, unscheduled general aviation flights identify themselves using the call sign correseponding to the aircraft's registration number (also called N-number in the U.S., or tail number). In this case, the call sign is spoken using the ICAO phonetic alphabet. Aircraft registration numbers internationally follow the pattern of a country prefix (N in the U.S.), followed by a unique identifier made up of letters and numbers. For example, an aircraft registred as N9876Q conducting a general aviation flight would be use the call sign november niner eight seven six quebec. Alternatively, pilots may use the aircraft type in lieu of the N in the registration number, i.e. Cessna niner eight seven six quebec. After making initial contact to a ground facility, air traffic controllers may choose to use an abbreviated call sign (omitting all but the last two or three digits) for an aircraft under his or her control, so long as it is unambiguous.
In the United States, a registration number begins with the letter N, followed by up to five digits and/or letters in one of these schemes: one to five numbers (N12345), one to four numbers and one suffix letter (N1234Z), or one to three numbers and two suffix letters (N123AZ). The numeric part of the registration never starts with zero. To avoid confusion with the digits 1 (one) and 0 (zero), the alphabetic letters I (india) and O (oscar) are not used in registration numbers.
Commercial operators, including airlines, air cargo and air taxi operators, will usually use an ICAO or FAA-registered call sign for their company, which is used together with the flight number. For example, British Airways flight 75 would use the call sign Speedbird seven-five, since Speedbird is the registered call sign for British Airways. Air taxi operators in the United States sometimes do not have a registered call sign, in which case the prefix T is used followed by the aircraft registration number (i.e. tango november niner eight seven six quebec).
Some variations of call signs exist to express safety concerns to all operators and controllers monitoring the transmissions. Aircraft call signs will use the suffix "heavy" to indicate a large aircraft, i.e. United Two-Five Heavy. For air ambulance flights, the callsign prefix Lifeguard is used before the normal callsign, i.e.Lifeguard three three alfa.
Glider pilots often use a supplementary number (the competition number) in their call signs.
Military flights use a variety of registered call signs with flight numbers, just like commercial operators. i.e. Navy Golf Alfa Kilo 21, REACH 31792.
Ground facilities identify themselves by the name and function of the facility: i.e. Seattle Tower for the tower controller's position, or Boston Center for a en-route air traffic control facility.
Ships and Boats
Merchant vessels are assigned a call sign by their national licensing authority. In the case of states such as Liberia or Panama, which are flags of convenience for ship registration, call signs for larger vessels consist of the national prefix plus three letters (for example, 3LXYZ). United States vessels are given call signs beginning with the letter W. Originally both ships and broadcast stations were given call signs in this series consiting of three or four letters, but gradually American-flagged vessels were given callsigns with mixed letters and numbers.
Amateur radio
Amateur radio call signs are in the international series and 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 call sign, J29DBA, the prefix is J2, the number is 9, and the suffix is DBA. Others may start with a number followed by a letter, for example, Jamaican call signs begin with 6Y.
The numbers are sometimes assigned geographically. In the Italian call sign, IK1TZO, IK is the prefix, the number component is 1 and corresponds to the Piedmont 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, and the suffix is EBO. For district numbers within the United States, see ARRL map.
Broadcast call signs
North America
Broadcast stations in North America generally use call letters in the international series. There are some common conventions followed in each country. In Canada, call signs begin with the letter C, except for four stations in St. John's which begin with VO. Mexican call signs begin with an XE for medium-wave (AM) radio stations and XH in other cases. In the United States, the first letter generally is K for stations west of the Mississippi River and W for those east of the Mississippi. There are a number of exceptions, most of which are located in the states immediately to either side of the river.
Government-operated international broadcasters, such as Radio Canada International and Voice of America, are not assigned call signs; however, privately-operated shortwave stations, like WWCR and CFRX, are.
Australia
In Australia, broadcast call signs 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 call signs 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, although the VL prefix can still be implied in an international context. (Certain ABC radio stations, particularly outside of metropolitan areas, may use five-letter callsigns for FM stations: xABCFM for ABC Classic FM, xABCRN for Radio National, and xABCRR for ABC Local Radio.)
Television station call signs begin with two letters usually denoting the station itself, followed by a third letter denoting the state. For example, NBN's call sign stands for Newcastle Broadcasting, New South Wales. There are some exceptions:
- ABC television stations outside of state capitals add a fourth letter (and in rare cases a fifth) 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 commercial stations, also using AB as the first two letters; for example, ABN is Sydney's ABC television station.
- SBS television stations all use SBS in their call signs, 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:
- Radio
- 1 - Australian Capital Territory (new designation)
- 2 - New South Wales, the Australian Capital Territory and some external territories
- 3 - Victoria
- 4 - Queensland
- 5 - South Australia
- 6 - Western Australia
- 7 - Tasmania
- 8 - Northern Territory
- Television
Europe/Asia
In Europe and much of Asia, call signs are normally not used for broadcast stations. Japan, South Korea, the Philippines and Taiwan are exceptions to this general rule. Other countries have yet other formats for assigning call signs to domestic services.
Military call signs
In wartime, monitoring an adversary's communications can be a valuable form of intelligence. Consistent call signs can aid in this monitoring, so in wartime, military units often employ tactical call signs and sometimes change them at regular intervals. In peacetime, some military stations will use fixed call signs in the international series.
U.S. Army
The United States Army uses fixed call signs which begin with W, such as WAR, used by U.S. Army Headquarters.
U.S. Air Force
Fixed call signs for the United States Air Force stations begin with A, such as AIR, used by USAF Headquarters. The USAF also 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 call sign of this type is Air Force One, used when any Air Force aircraft is transporting the U.S. President. Individual military pilots or other flight officers usually adopt a personal aviator call sign.
U.S. Navy/Coast Guard
The United States Navy and United States Coast Guard use a mixture of tactical call signs and international call signs beginning with the letter N. For example, the carrier USS John F. Kennedy has the call sign NJFK.
Transmitters requiring no call signs
No call signs are issued to transmitters of long-range navigation systems (LORAN-C, Decca, Alpha, Omega) or transmitters on frequencies below 10 kHz, because frequencies below 10 kHz are not subject to international regulations. In addition, in some countries low-power personal and broadcast radio (Citizen's Band, Part 15, and the like) is allowed; a call sign is not always required for such stations, though especially on personal radio services it is considered a matter of etiquette to create one's own.
See also
References
- United States Federal Aviation Administration, Aeronautical Information Manual, Official Guide to Basic Flight Information and ATC Procedures, 2004. Chapter 4, Section 2