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Tropospheric Ducting – What Happened to My Station?

What Happened to My Station?

Steve Callahan for Radio-Guide Magazine

It’s been good season for tropospheric ducting along the New England shore. You might not be familiar with the term “tropospheric ducting,” but you just might have experienced it and not known why.

We’re all familiar with the way that AM signals bounce at night and come down far from their point of origin. Anyone who has listened to the big 50,000 Watt clear channel AMs knows the thrill of hearing a distant AM on a regular radio. I was once surprised to hear WBZ from Boston while in a traffic jam one night in Atlanta, Georgia. An AM station’s “skywave” component reflects off the ionosphere as it cools down at night and the usually transparent-to-AM layer turns reflective and the AM signal comes back to earth far from it’s transmitter. Frequency and tower height influence the degree of skywave along with seasonal differences and weather conditions.

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