short waves


short waves,

radio waves whose frequencies range from about 3 to 25 megahertz (Mhz), corresponding roughly to the high-frequency band (see radio frequencyradio frequency,
range of electromagnetic waves with a frequency or wavelength suitable for communication uses. Some of these waves serve as carriers of the lower-frequency audio waves; others are modulated by video or digital information.
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). When they impinge on certain layers of the ionosphere, short waves are largely reflected back toward the earth. By one or more reflections between the earth and the ionosphere, a short-wave radio signal can be received at long distances from the transmitter.