North American Regional Broadcasting Agreement

The North American Regional Broadcasting Agreement (NARBA, French: Accord régional sur la radiodiffusion en Amérique du Nord; Spanish: Convenio Regional Norteamericano de Radiodifusión) refers to a series of international treaties that defined technical standards for AM band (mediumwave) radio stations. These agreements also addressed how frequency assignments were distributed among the signatories, with a special emphasis on high-powered clear channel allocations.

Source: Wikipedia — North American Regional Broadcasting Agreement (CC BY-SA 4.0)