In broadcasting and radio communications, a call sign 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.
Russian nuclear icebreaker Arktika with call sign UKTY
All U.S. states issue call sign license plates upon request for motor vehicles owned by amateur radio operators. This road vehicle is from California.
Department of Commerce callbook, 1919
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves. They are received by another antenna connected to a radio receiver. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.
An antenna farm hosting various radio antennas on Sandia Peak near Albuquerque, New Mexico, US
1100 W AM broadcasting transmitter
Mast radiator antenna of AM radio station
Panasonic AM radio from 1964