Call Signs
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 identifier for a transmitter 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. 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 onboard ships at sea. These were not globally unique, so a one-letter company identifier (for instance, 'M' and two letters as a Marconi st ...
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Broadcasting
Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a one-to-many model. Broadcasting began with AM radio, which came into popular use around 1920 with the spread of vacuum tube radio transmitters and receivers. Before this, all forms of electronic communication (early radio, telephone, and telegraph)