The National Broadcasting Company (NBC) is an American broadcast television network that originated as a radio network in November 1926, and expanded into television in April 1939. Throughout its history, the network has had many owned-and-operated and affiliated stations. The station's advertised channel number follows the call letters. In most cases, this is their virtual channel (PSIP) number, which may match the channel allocation that the station originally broadcast on during its prior affiliation with the network.