I remember listening to WWVA in the early 60s and hearing them describe themselves as "clear channel, 50,000 watts." No written source but this is my recollection. Clear channel= no other station in the US or Canada on that frequency. I know that 50,000 was the maximum that any AM radio station was allowed to use; the Mexican radio stations used more (get Jannete Carter to tell stories about living with her mother when the Carter Family was broadcasting of "border radio" XERA and they used 500,000 watts power and sometimes the toaster picked up XERA. . . sorry for the digression