Radio waves can be used to carry messages and simple television pictures at very large distances. Radio-waves are grouped into bands; each band has particular nature and special set of uses: http://en.wikipedia.org/wiki/Radio_spectrum
In order to reach greater distances than line of sight, some radio waves can be made to travel towards the sky. (sky waves) The waves are then refracted by the ionosphere (layers of air stretching from 80 – 550 km above the Earth) and returned later to Earth. These wave signals are subsequently intercepted by receiving ground stations.