Radio broadcasting in Phoenix began in October 1921 when a local businessman named Earl Nielsen began making experimental broadcasts over his amateur radio station. The call letters were 6BBH. The first station to receive a broadcast license was KDYW, which only lasted a couple of years (1922-1924).

Originally, all stations used 360 meters (833 kHz), while a few used 400 meters (750 kHz) for weather reports and the like as well. The AM band as we know it today didn't open until 1924 (550-1350 kHz), with expansion in 1928 (to 1500 kHz), 1941 (to 1600 kHz), and 1990 (to 1700 kHz).