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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.
..... Click the link for more information. ). 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.