The history of broadcasting began with early radio transmissions which only carried the dots and dashes of wireless telegraphy. The history of radio broadcasting (experimentally around 1906, commercially around 1920) starts with audio (sound) broadcasting services which are broadcast through the air as radio waves from a transmitter to an antenna and, thus, to a receiving device. Stations can be linked in radio networks to broadcast common programming, either in syndication or simulcast or both.