By Ken Foote | Director of Programming KTVT, KTXA

I have written about AM Radio before on this blog as I am a child of AM’s golden years. Yet even today in 2015, I am still in awe of its capability and here’s one reason why!

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On Tuesday, I was driving back home from Oklahoma City after a business trip. About 4:15pm, I changed my car radio to the AM dial to see what I could pick up. What I heard were stations operating with 50,000 watts day and night and that are non-directional (meaning they broadcast a perfect circle signal pattern). And at an unusual time too.

The first one was WOAI/San Antonio, known as NewsRadio 1200 . As the crow flies, I was about 420 miles from their tower yet the signal quality was like a local station.  The second one was WHO/Des Moines, NewsTalk 1040. Same power and signal pattern as WOAI, but 475 miles as the crow flies. Perfect reception. Last but not least, KMOX/St. Louis, NewsTalk 1120 (a CBS Radio owned station). Again, identical power and signal pattern as WOAI and WHO but 460 miles as the crow flies.

These three stations are also referred to as “clear channel” AM stations as they are the only ones that are authorized by the FCC to operate with 50,000 watts of power at night with a non-directional pattern within a 750 mile radius of their tower.

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AM radio waves are generated either as “ground wave” or “sky wave”.  Most AM radio operators focus on ground wave because there is more control over the propagation of that signal. With a sky wave, there is not as much control. I was hearing the sky wave signal of these stations that are not bound by the curve of the Earth as ground wave is, that bounce off of the Earth’s ionosphere (which is electrically charged), and expand past the horizon, hence the additional coverage. This is similar to what shortwave broadcasters do.

When I got back in I reported this to one of our engineers. His reply was, “well, there was cold front moving in too.”  AM sky waves love cold weather!

In the DFW area, the clear channel AM station that technically operates similar to WOAI, WHO, and KMOX is WBAP NewsTalk 820. Its signal blankets close to 40 states. Our AM radio station, KRLD NewsRadio 1080, is also 50,000 watts too but at night it changes its pattern to more north and west in order to protect another station on the 1080 frequency.

The miracles of AM radio waves never cease to amaze me! See you next time.

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