electromagnetic spectrum at lower frequencies than microwave s.
The wavelengths of radio waves range from thousands of metres to around 30 cm. These correspond to frequencies as low as 3 Hz and as high as 1 gigahertz (10 9 Hz). Radio-wave communications signals travel through the air in a straight line, reflect off of clouds or layers of the ionosphere, or are relayed by satellites in space. They are used in standard broadcast radio and television, short-wave radio, navigation and air-traffic control, cellular telephony, and even remote-controlled toys.