In broadcasting and radio communications, a call sign (also known as a call name or call letters—and historically as a call signal—or abbreviated as a call) is a unique designation for a transmitting station. In North America they are used as names for broadcasting stations. 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.
The use of call signs as unique identifiers dates to the landline railroad telegraph system. Because there was only one telegraph line linking all railroad stations, there needed to be a way to address each one when sending a telegram. In order to save time, two letter identifiers were adopted for this purpose. This pattern continued in radiotelegraph operation; radio companies initially assigned two-letter identifiers to coastal stations and stations aboard ships at sea. These were not globally unique, so a one-letter company identifier (for instance, 'M' and two letters as a Marconi Station) was later added. By 1912, the need to quickly identify stations operated by multiple companies in multiple nations required an international standard; an ITU prefix would be used to identify a country, and the rest of the call sign an individual station in that country.
Call signs are also used for air traffic control communication with airplanes and manned spacecraft.
Famous quotes containing the words call and/or sign:
“So that if you would form a just judgment of what is of infinite importance to you not to be misled in,namely, in what degree of real merit you stand ... call in religion and morality.Look,What is written in the law of God?How readest thou?Consult calm reason and the unchangeable obligations of justice and truth;Mwhat say they?”
—Laurence Sterne (17131768)
“Every sign by itself seems dead. What gives it life?In use it is alive. Is life breathed into it there?Or is the use its life?”
—Ludwig Wittgenstein (18891951)