Shortwave radio is a name for radio waves in the range of 3-30 megahertz. Shortwave is often used for broadcasting, and radio receivers made to tune in those broadcasts are sometimes called shortwave radios. The earth's ionosphere carries radio waves in this range over great distances, and signals can travel around the globe under certain conditions. This makes it possible for radio stations all over the world to broadcast to listeners in faraway countries. Sunspot activity and solar flares can interfere with shortwave reception, and different frequencies work better at different times during the day or year.