Shortwaves

radio waves of the wavelength range from 10 to 100 m. They are reflected from the ionosphere and undergo very little absorption in the process. Through multiple reflection from the ionosphere and the earth’s surface, shortwaves may propagate over great distances; therefore, they are used in radio communications under terrestrial conditions. Shortwave radio reception depends on both regular and irregular processes in the ionosphere, which are related to solar activity, the season, and the time of day. Shortwaves cannot be used for space communications, since they cannot penetrate the ionosphere.