- Call sign
broadcastingand radiocommunications, a call sign (also known as a callsign or call letters, or abbreviated as a call, or otherwise known as a handle) is a unique designation for a transmitting station. In some countries they are used as names for broadcasting stations, but in many other countries they are not. 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 call signs are formal, semi-permanent, and issued by a nation's
telecommunicationsagency. They are used for amateur, broadcast, commercial, maritime and sometimes militaryradio use (including televisionin 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:
Australiauses "AX", "VH"–"VN","VK" and "VZ".
Canadauses "CF-CK", "CY"-"CZ", "VA-VG", "VE", "VO", "VX"-"VY", and "XJ"-"XO".
Chinauses "BAA"-"BZZ", "XSA"-"XSZ", "3HA"-"3UZ", "VR", "XX".
Japanuses "JA"–"JS", "7J"–"7N", and "8J"–"8N".
Russiauses "R" and "UA"–"UI".
United Kingdomuses "G", "M", "VS", "ZB"–"ZJ", "ZN"–"ZO", "ZQ", and "2".
United Statesuses "K", "W", "N", and "AA"–"AL".
The earliest allotment of call letters was made at the 1912
London International Radiotelegraphic Convention, [ [http://earlyradiohistory.us/recap.htm United States Call Sign Policies] ] which provided that the call letters of stations in the international system must each be formed of a group of three letters, which shall be distinguishable from one another. The Convention made a partial allotment of call letters among nations that signed the Convention, and the International Bureau at Berne, with the consent of such nations, modified and added to this assignment of call letters by circular of 23 April 1913.
Because these assignments were originally made in the second decade of the 20th century, they often reflect a former political structure that has long since ceased to exist. For example, the "V" series (as in Victoria) originally was reserved for the
British Empire, though Great Britainitself was assigned all of "B", "G", and "M"; individual subseries of "V" were carved out and assigned to individual dominions and territories.
The modern successor nations often (but not always) retain these series, in some cases supplemented by additional assignments. In 1927, the
Soviet Unionwas assigned the entire "U" series; when the USSRbroke up, several former Soviet republics received blocks of "U" call signs. (However, Russia was not a signatory to the 1912 convention, so, in 1912, "UAA"–"UMZ" were assigned to Franceand its colonies, and "UNA"–"UZZ" were assigned to Austria-Hungaryand Bosnia and Herzegovina.)
The United States was represented by the military at the 1927 conference, which is why it received (or, in some cases, retained) "A" (for Army) and "N" (for Navy). The "W" and "K" for civilian stations followed as the simple addition of a dash to the
Morse codeletters "A" and "N". (However, in 1912, "KDA–KZZ", all of "N", and all of "W" were assigned to the United States, but all of "A" was assigned to Germany and its protectorates.)
Call signs in
aviationare derived from several different policies, depending upon the type of flight operation and whether or not the caller is in an aircraft or at a ground facility. In most countries, unscheduled general aviationflights identify themselves using the call sign corresponding 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 International Civil Aviation Organization (ICAO) phonetic alphabet. Aircraft registration numbers internationally follow the pattern of a country prefix, followed by a unique identifier made up of letters and numbers. For example, an aircraft registered as "N9876Q" conducting a general aviationflight would use the call sign "November-niner-eight-seven-six-Quebec." (In radio transmissioners "niner" is often used instead of nine so that there is less chance of confusion with the numeral "five", which sounds similar.)
In most countries, the aircraft call sign or "tail number" or registration marks are linked to the international radio call sign allocation table and follow a convention that aircraft radio stations (and, by extension, the aircraft itself) receive call signs consisting of five letters. For example, all British civil aircraft have a five-letter call sign beginning with G. Canadian aircraft have a call sign beginning with C-F or C-G, such as C-FABC. Wing In Ground-effect vehicles (hovercraft) in Canada are eligible to receive C-Hxxx call signs, and ultralight aircraft receive C-Ixxx call signs. In days gone by, even American aircraft used five letter call signs, such as KH-ABC, but they were replaced prior to
World War IIby the current American system of aircraft call signs (see below).
The - (dash) in the registration is only included on the
fuselageof the airplane for readability. In air traffic managementsystems (ATC radar screen, flow management systems, etc.) and on flight planforms, the dash is not used (e.g. "PHVHA", "FABCD", "CFABC").
Once an aircraft has made contact with a particular
air traffic controlfacility the call sign may be abbreviated. Sometimes the aircraft make or model is used in front of the full or abbreviated call sign, for instance, the American aircraft mentioned above might then use "Cessna Seven-Six-Quebec". Alternatively, the initial letter of the call sign can be concatenated with the final two or three characters, for instance a British aircraft registered GBFRM may identify as "Golf-Romeo-Mike" while the American aircraft might use "November-Seven-Six-Quebec". The use of abbreviated call signs has its dangers, in the case when aircraft with similar call signs are in the same vicinity. Therefore abbreviated signs are used only so long as it is unambiguous. [United Kingdom Civil Aviation Authority, [http://www.caa.co.uk/application.aspx?categoryid=33&pagetype=65&applicationid=11&mode=detail&id=247 CAP 413: "Radiotelephony Manual"] , Edition 16, paragraph 1.8.2 and table 9. CAA, 2006.]
The United States does not follow the five-letter call sign convention, and in that country the 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 scheduled airline, air cargo and
air taxioperators, will usually use an ICAOor FAA-registered call sign for their company. By ICAO Annex 10 Chapter 126.96.36.199.2.1 - Full call signs type c, a call sign consists out of the telephonydesignator of the aircraft operating agency, followed by the flight identification. The flight identification is very often the same as the flight number, but could be different due to call sign confusion, if two or more flight close to each other have similar flight numbers (i.e. KL649 and KL645). For example, British Airwaysflight 75 would use the call sign " SpeedbirdSeven-Five" (with the last word properly pronounced "fife"), since "Speedbird" is the telephony designator for British Airways and 75 would be the flight identification. (The telephony designator is not the same as the call sign, although the two are sometimes conflated). Pan Amhad the telephony designator of "Clipper".
For these call signs, proper usage varies by country. In some countries, such as the United States, numbers are spoken normally (for the example above, "Speedbird Seventy-five") instead of being spelled out digit by digit, leading to the possibility of confusion. In most other countries, including the United Kingdom, they are spelled out. [Ibid, paragraph 1.4.2(a).] 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 (e.g. "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" for large aircraft, to indicate an aircraft that is going to cause significant
wake turbulence, e.g. "United Two-Five Heavy"; All aircraft capable of operating with a gross take-off weight of more than 255,000 lbs. must use this suffix whether or not they are operating at this weight during a particular phase of flight. These are typically Boeing747, some models of the 757, 777, or 767, AirbusA340, A330 and A300, McDonnell DouglasDC-10 or MD-11, or Lockheed L-1011 aircraft. The suffix "super" is used for the Airbus A380.cite web | title = Airbus A380 vortex-revised guidance material | publisher = ICAO | date = 16 January 2007| url = http://www.icao.int/icao/en/ro/apac/2007/FIT_SEA5/ip05.pdf | accessdate = 2007-11-09 ] For air ambulanceservices or other flights involving the safety of life (such as aircraft carrying a person who has suffered a heart attack), "lifeguard" is added to the call sign. For flights in which life is not in direct danger (such as transporting organs for transplant), the call sign prefix "Pan-Pan-Medical" is used before the normal call sign, e.g. "Pan-Pan-Medical Three-Three-Alpha", "Pan-Pan-Medical Northwest Four-Five-Eight", or "Pan-Pan-Medical Singapore Niner-Two-Three". Pan Pan is the voice radio signal for "urgent", while Mayday is the voice radio signal for "distress". The word may be omitted for air ambulance services with assigned call signs, especially when they have notified air traffic control operators that they are on an air ambulance mission at the beginning of their flight and do not change from one controller to another. The Life Flightair ambulance service, for example, might simply identify as "Life-Flight Three". An aircraft that has declared an in-flight emergency will sometimes prefix the word "Mayday" to its call sign. [http://www.youtube.com/watch?v=9KhZwsYtNDE]
Formerly one of the rarest call signs, "Concorde", was once used to identify British Airways
Concordeaircraft. The intent of this call sign was to raise the air traffic control operators' awareness of the unique performance of the aircraft and the special attention it required. The call sign was appended to British Airways' normal radio call sign, e.g. "Speedbird-Concorde One" [cite video
title = [http://video.google.com/videoplay?docid=7422409257931235094&q=Concorde+Tribute&total=86&start=0&num=10&so=0&type=search&plindex=3 Concorde - 27 Supersonic Years]
publisher = British Airways
date = 2003] . In normal service,
Air Francedid not use it at all; its Concorde flights simply used the standard "Airfrans" call sign.Fact|date=August 2007 Gliderpilots often can use any of three different call signs. Since most (not all) gliders now show standard CAA general aviation registrations e.g. G-xxxx they can call using the same call sign and abbreviation rules as other light aircraft. Before these registrations came in (between 2004 - 2008) they used to use and normally still do use either a three letter code issued to all gliders by the British Gliding Association know as the aircraft's Trigraph e.g. XYZ normally calling ATC as "Glider X-ray, Yankee, Zulu" or if they paid extra could get from the BGA a numeric or mixed numeric and letter code known as a competition number for marking their aircraft and as a call sign. For Example R4 "Romeo Four", or 26 "Two Six" or F1 "Foxtrot One". Optionally gliders will normally tag on the "Glider" in front of their call sign when calling ATC units so that the controller knows for example that the glider will be unable to maintain a particular height as Gliders are normally either descending in a straight glide or circling to climb.Some gliders are still not required to carry a CAA General Aviation type registration as they are older designs or prototypes and can therefore only continue to just use their Trigraph or Competition number as a call sign. These are known as Annex II aircraft as they are listed in EASA Annex II. Militaryflights use a variety of registered call signs with flight numbers, similar to those of commercial operators. e.g. "Navy Golf-Alpha-Kilo-Twenty-One", "Reach-Three-One-Seven-Niner Two".
Tactical call signs Canadian Air Force rescue squadrons: for example, 442 Squadron based at Comox, British Columbia (on Vancouver Island) use the call sign "Snake 90x" depending on the tail of the Cormorant CH-149 (EH-101)helicopter: 901, 902, 903, etc. When tasked on a search and rescue (SAR) mission, however, the aircraft call sign becomes "Rescue 90x". Snake refers to the squadron's emblem (unit patch) which features a "sisiutil", a mythical two-headed sea serpent from northwest coast aboriginal folklore, or sea snake.
Ground facilities identify themselves by the name and function of the facility: e.g. "Seattle Tower" for the tower air traffic control operators' position, "SoCal Approach" for a
TRACON, or "Boston Center" for an Area Control Center. All other ICAO countries around the world, for example the European Joint Aviation Authorities (JAA), use "'Control" or "Radar" instead of "Center" in their airspace. ("Langen Radar", "Brussels Control", "Paris Control", ...).
ICAO24-bit transpondercode is intended for non-human usage in the Mode-S and ADS-B protocols.
hips and boats
Merchant vessels are assigned call signs by their national licensing authorities. In the case of states such as
Liberiaor Panama, which are flags of conveniencefor ship registration, call signs for larger vessels consist of the national prefix plus three letters (for example, 3LXY, and sometimes followed by a number, i.e. 3Lxy2). United States civilian vessels are given call signs beginning with the letters "W" or "K". Originally both ships and broadcast stations were given call signs in this series consisting of three or four letters, but gradually American-flagged vessels were given call signs with mixed letters and numbers.Some 4-letter call signs are again assigned to broadcast stations after the ships to which those call signs were assigned are removed from U.S. registry, an example is WEZU which was the international radio call sign of the ship SS "Lash Atlantico" but is now assigned to a broadcast station.
Leisure craft with VHF radios may not be assigned call signs, in which case the name of the vessel is used instead. Ships wishing to have a radio license anyway are under F.C.C. class SA: "Ship recreational or voluntarily equipped." Those calls follow the land mobile format of the initial letter K or W followed by 1 or 2 letters followed by 3 or 4 numbers (such as KX0983 or WXX0029).
US Coast Guard small boats have a number that is shown on both bows (i.e. port and starboard) in which the first two digits indicate the nomin al length of the boat in feet. For example, Coast Guard 47021 refers to the 21st in the series of 47 foot motor lifeboats. The call sign might be abbreviated to the final two or three numbers during operations, for example Coast Guard zero two one.
IMOassigns a unique identity signature for all ships to be used in the Automatic Identification System(AIS), this is however not intended for human usage.
Amateur radiocall signs are in the international series and normally consist of a one, two or three character prefix, a number (which may be used to denote a geographical area, identify the callsign as belonging to the amateur service, or identify a licensee as a visitor or temporary resident), and a 1, 2, or 3 character suffix. In Australia callsigns are structed with a two letter prefix, a number (which identifies geographical area), and a 2, 3 or 4 letter suffix. This suffix may be followed by a further suffix, or personal identifier, such as /P (portable), /M (mobile), /AM (aeronautical mobile) or /MM (maritime mobile). 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.When operating with reciprocal agreements under the jurisdiction of a foreign government, an identifying station prepends the call sign with the country prefix and number of the country/territory from which the operation is occurring. For example, W4/G3ABC would denote an licensed amateur from the United Kingdom who is operating in the fourth district of the United States. There are exceptions; in the case of U.S./Canadian reciprocal operations, the country/territory identifier is, instead, appended to the call sign; e.g., W1AW/VE4, or VE3XYZ/W1.
When identifying a station by voice, the call sign may be given by simply stating the letters and numbers, or using a phonetic alphabet. Some countries such as Germany mandate the use of the phonetic alphabet for identification.
Broadcast call signs
Broadcast stations in
North Americagenerally use call letters in the international series. There are some common conventions followed in each country. 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, such as KDKA in Pittsburgh and WFAAin Dallas, but these are historical artifacts from a rule change in the 1930s, and most of the exceptions are located in the states immediately to either side of the river. The westernmost station in the continental United States beginning with W is WOAI in San Antonio. WVUV-LPin Pago Pago, American Samoa, is the westernmost station with a W call-sign. KYW in Philadelphia is the easternmost station with a K call sign.
An exception to this is that all time broadcasting stations have a three or four letter call sign beginning with WWV. The three current government-operated time stations, WWV (and longwave sister station
WWVB), and WWVH, are located in Fort Collins, Coloradoand Kekaha, Hawaii, respectively, both of which would normally use call signs beginning with "K".
The US government-operated international broadcaster the
Voice of Americano longer has call signs assigned to it; however Radio Canada International's transmitter in Sackville is still assigned CKCX. Privately-operated shortwave stations, like WWCRand CFRX, also have call signs.
Australia, broadcast call signs begin with a single-digit number indicating the state or territory, followed by two or three letters for AM stations and usually three letters 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 call signs for FM stations: "xABCFM" for ABC Classic FM, "xABCRN" for Radio National, and "xABCRR" for ABC Local Radio- the "x" being the state number.)
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. Also, SBS FM radio stations use a five-letter call sign, "xSBSFM". (Sydney and Melbourne's AM stations use xEA, short for "Ethnic Australia".)
Imparja Televisionuses IMP, even though they are based in Alice Springsin the Northern Territory.
Letters and numbers used by Australian stations:
*New designation. **Stands for Canberra.
† Also applies to stations in the ACT and some external territories.
‡ Stands for Darwin.
The use of broadcast call signs in New Zealand historically consisted of a digit, and two letters for AM or three for FM. The usage was:
**1 - Northern half of the North Island
**2 - Southern half of the North Island, and Marlborough and Nelson regions of the South Island
**3 - South Island, north of the Waitaki River, excluding Marlborough & Nelson
**4 - South Island, south of the Waitaki River
**X - private commercial station
**Y - Radio NZ, non-commercial (National Programme, Concert Programme) and Access Radio Wellington (2YB)
**Z - Radio NZ, commercial (now mostly
The Radio Network)
For example - 1ZB was a Radio NZ commercial station in Auckland; 4XF was Foveaux Radio in Invercargill (now More FM); 4YC was the Concert Programme in Dunedin.
FM stations appeared to have no standard format for the letters, just picking three that 'fit' the station. To make matters more confusing, some stations such as 4ZA-FM (now Classic Hits Southland 98.8FM) and 4XO Gold (now More FM Dunedin) retained their AM call signs.
Auckland, Wellington, Christchurch and Dunedin as major centres for the four regions had specific Radio NZ call signs used:
* xYA - National Programme
* xYC - Concert Programme
* xZB - Community Network commercial
* xZM - Music commercial (except Dunedin)
During the early 1990s the use of call signs became less common, to the point that most broadcasters do not use them at all. Some are retained in some form for branding - for example, 4XO Dunedin (until it was rebranded More FM Dunedin in 2004), Newstalk ZB (using the old 1ZB, 2ZB, 3ZB, 4ZB and various other Radio NZ commercial frequencies) and ZM (originally ZMFM, replacing the old 1ZM, 2ZM and 3ZM, now nationwide). Stations licensed since 1990 have not had call signs allocated.
With consolidation in the commercial radio market, the only stations now using a call sign in New Zealand are the long.established 1XX in the Bay of Plenty, and the recently-arrived (2005) LPFM Primetime 1ZZ [http://www.primetimeradio.co.nz] in the Bay of Islands, whose "call sign" is self-assignedFact|date=February 2007.
In Brazil, some radio stations still broadcast their call signs few times a day, but this practice is becoming very rare. For TV stations and radio stations it's used letters ZY, plus one letter (ZYA and ZYB for TV stations, ZYI, ZYL and ZYK for AM radios, ZYG for
short waveradios, ZYC, ZYD and ZYM for FM radios) and three numbers, for example: ZYB883 (analog ch. 18) is TV Tribuna in Santos.
Europe and Asia
In Europe and much of Asia, call signs are normally not used for broadcast stations.
Japan, South Korea, the Philippinesand Taiwan are exceptions to this general rule. Other countries have other formats for assigning call signs to domestic services.
Traditionally, broadcast stations are assigned one of three predominant prefixes depending on the location of their license:
* DZ for
* DY for the
* DX for
DW is now also used for stations in Luzon. DZ is mostly AM band, while DW is FM band. Other call sign prefixes assigned to the Philippines are DU and DV.
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.
United States Armyuses fixed station call signs which begin with "W", such as WAR, used by U.S. Army Headquarters.
Tactical call signs are often assigned to a company sized unit or higher. For example the collective "Checkmate" might be assigned to an entire company and thus "Checkmate 1" would be the first
platoonleader , "Checkmate 2" to the second platoon leader, etc. As there are usually only 4 platoons, "Checkmate 5" becomes the Company XO and "Checkmate 6" is the Company Commander. This system can be extended to squad or fireteam level by adding another number, for example the squad leader of the second squad of the third platoon in Checkmate company would have the call sign "Checkmate 32", pronounced "three two".
A humorous reference to a person in the household, usually the wife, is "Household 6" or HH6. This is because the number six denotes the element leader on the radio when using unit call signs. (i.e. If you heard "warrior six" on the radio, you would know you were speaking to the leader of the unit known to those on that radio net as "warrior".)
U.S. Air Force
Fixed call signs for the
United States Air Forcestations 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 DEFCON3. 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. Similarly, when the President is flown in a U.S. Marine Corps helicopter, the call sign is Marine One. When President George W. Bush, a former Air National Guardfighter pilot, was flown to the aircraft carrier Abraham Lincoln in a Navy S-3B Viking, it was the first use of the "Navy One" call sign.
Individual military pilots or other flight officers usually adopt a personal
aviator call sign.
U.S. Navy/Coast Guard
United States Navyand United States Coast Guarduse 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 for unclassified and navigation communications with other vessels, but uses varying tactical call signs that vary with its mission.
Tactical voice communications ("combat net radio") use a system of call signs of the form "letter-digit-digit". Within a standard infantry battalion these characters represent companies, platoons and sections respectively, so that 3 Section, 1 Platoon of B Company might be F13. In addition, F13A might be the
second-in-commandof that section, in charge of its Delta fire team.
Note that the letter part of the call sign is "not" the company's own letter (B vs F in the above example) - indeed, the letter designations are randomly assigned using
BATCOsheets, or appear on CEI's (communication electronic instruction), and change along with the BATCO codes every 24 hours. This, together with frequency changes and voice procedure aimed at making every unit sound the same, introduces a degree of protection against simple traffic analysis and eavesdropping.
Not all radio users fit into the standard battalion model, but in order to continue the obfuscation they will be assigned a call sign that appears to be part of such a system. Presumably, the well-known B20 falls into this category.
Finally, the controller of each net has the call sign 0 ("zero"). There may also be a second controller - either a backup station or a commander who has delegated communication tasks to a signaller but may occasionally wish to speak in person - with the call sign 0A ("zero alpha").
Earlier systems used a series of appointment titles to identify users and individuals, "
Sunray", for instance, referring to the appropriate leader.
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.
International regulations no longer require a call sign for broadcast stations; however, they are still required for broadcasters in many countries, including the United States.
Mobile phoneservices do not use call signs on-air for obvious reasons; however, the U.S. still assigns a call sign to each mobile-phone spectrum license.
Airline call sign
Aviator call sign
Cosmonaut call sign
Maritime Mobile Service Identity
NATO phonetic alphabet
*United States Federal Aviation Administration, "Aeronautical Information Manual, Official Guide to Basic Flight Information and ATC Procedures," 2004. [http://www.faa.gov/ATpubs/AIM/Chap4/aim0402.html Chapter 4, Section 2]
* [http://earlyradiohistory.us/recap.htm United States Call Sign Policies]
* [http://gullfoss2.fcc.gov/prod/callsign/prod/main.html United States "FCC" call sign search]
* [http://www.ac6v.com/prefixes.htm Amateur Call Prefixes]
* [http://www.milaircomms.com/mil_callsigns.html Military Callsigns]
* [http://www.ominous-valve.com/callsign.txt More Military Callsigns]
* [http://www.radio-locator.com Radio-Locator] a search engine of all of the radio stations in the world with websites, searchable by location and call sign
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