Quote:
Originally posted by agger_rob
If I remember correctly, clear channel originally referred to an AM station that could be heard across the country, or at least in many states, especially at nighttime. Such stations are WSM in Nashville that reached over 30 states and KMOX in St. Louis that can be heard in Canada on a clear night.
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Very Good -- you're pretty close.
In the very early days of radio, there was no regulation, and all stations basically operated on the same frequency with whatever power they could manage. The result was huge amounts of interference.
When the Communications Act of 1934 was passed, it assigned frequencies and allowed power for each US AM radio station.
There were a number of them designated "clear channel" stations, with a maximum of 50,000 watts of power, 24/7. In the beginning, there were no other stations anywhere else in the country on those frequencies. Later, some lower powered stations were allowed to share the frequency, but at a much lower power. Some of those other stations had to reduce power even further at night, or sign off all together at sundown because the AM signal travels much farther at night.
As of the 70's or 80's, only WLW in Cincinnati was a TRUE clear channel station (700 KHz). Other 50KW stations included the ones you mentioned, plus stations like WABC, NY; WLS, Chicago; WBZ, Boston; KDKA, Pittsburgh; KOA, Denver; WOWO, Ft. Wayne; WKYC (Now WWWE, I think), Cleveland, KOMA, Oklahoma City; KABC and KRLA, Los Angeles; WJBK, Detroit; CKLW, Windsor/Detroit.
There were quite a few others, as well.
Speaking of CKLW, there were a number of "Canadian Clear Channels" which tended to be toward the top of the AM band, and that's the reason that a lot of higher frequency US AM stations still have to sign off at night.
More than you wanted to know, I'm sure.