Shortwave radio is radio transmission using shortwave frequencies, generally 1.6–30 MHz (187.4–10.0 m), just above the medium wave AM broadcast band. Shortwave radio has an ability to enter a state of skywave or skip propagation, in which the radio waves are reflected or refracted back to Earth from the ionosphere, as opposed to being absorbed. This is a particularly important characteristic: it allows the transmitted signal to be reflected around the curve of the Earth, thus shortwave is not line-of-sight. This allows for very long distance communications. Shortwave radio is used for broadcasting of voice and music to shortwave listeners over very large areas; sometimes entire continents or beyond. Additionally, it is used for two-way international communication by amateur radio enthusiasts for hobby, educational and emergency purposes.

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