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Communication - Why Do Am Stations Have A Wider Broadcast Range At Night?
Why do AM stations have a wider broadcast range at night?
The variation in the broadcasting capability of AM stations is caused by the nature of the Earth's ionosphere. The ionosphere is a region of the upper atmosphere composed of several layers of gases. The gases become electrically charged, or ionized, by X-rays and ultraviolet rays that exist in solar radiation.
AM radio signals reflect off the ionosphere. This is what enables radio waves to curve around the Earth and AM broadcasts to be transmitted over great distances. At night, when the layers of ionosphere partially dissipate, the ionosphere is best able to reflect AM radio waves. As a result, distant AM stations come in more clearly at night.
Sources: Asimov, Isaac. Understanding Physics, p. 45; Churchman, Lee W. Survey of Electronics, pp. 64-66; World Book Encyclopedia, vol. 16, p. 85.
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