Radio transmission in the 1.7-30 MHz frequency range worldwide. Like AM radio, shortwave signals reflect back from the ionosphere and follow the curvature of the earth. As a result, shortwave (SW) signals can span hundreds and even thousands of miles.
The shortwave term was coined in the early 1900s when radio emerged, and the spectrum was divided into short, medium and long wavelengths. Ham radio operators continue to use the shortwave bands (see amateur radio
). See AM radio
and FM radio