The radio system uses propagation of electromagnetic waves through space, to send information. The r.f. wave is, however, of a much lower frequency and so longer wavelength. The shorter waves in the electromagnetic spectrum have the highest frequency and the longer waves the lowest.
Radio waves range from a few kilohertz to several gigahertz.
Radio waves are used in many other applications such as television, telephone transmission, radar, navigational systems and space communications. The table below shows various radio wavelenths in the electromagnetic spectrum. The wave operates at v.l.f., l.f. and m.f. frequencies The sky wave is deflected back to the earth by the ionospere, which allows the signal field to carry over much larger distances than the ground wave. At particular frequencies the sky wave can be reflected completely around the planet by reflecting between the ionospere and the ground. The wave can penetrate the ionospere and so is lost to space.