The properties of radio waves are frequency dependent. At low frequencies, radio waves are able to pass through obstacles, but the power falls off sharply if the distance from the source increases: in the air the power falls roughly by the cube of the distance. At high frequencies, radio waves tend to travel in straight lines and bounce off obstacles. They are also absorbed by rain. At all frequencies, radio waves are subject to interference from motors and other electrical equipments.



In the VLF, LF and MF bands, radio waves follow the ground and can be detected for 1000 km at the lower frequencies, less at the higher ones.

In the HF and VHF bands, the ground waves tend to be absorbed by the earth. However, the waves that reach the ionosphere are refracted by it and sent back to earth. Under certain atmospheric conditions, the signal may bounce several times. Amateur radio operators use these bands to talk long distances. The military also communicates in the HF and VHF bands.