Above is a diagram of a wave. Any such wave can be described by either its wavelength, or
its frequency. Its wavelength is the distance between identical points on two adjacent waves.
Its frequency describes the number of waves that occur each second - the units of frequency
are Hertz (Hz).
In free space, radio waves travel at the speed of light which is approximately 3 * 108
metres per second. The relationship between the frequency and wavelength of a radio wave is
given by the following formula:
Wavelength = (3 * 108 / Frequency)
Radio waves are electromagnetic - they contain both electric and magnetic fields. The
electric and magnetic fields are at right angles to each other and also at right angles to the
direction of propagation as shown in the diagram below.
The electromagnetic spectrum refers to the entire range of possible frequencies. Different
parts of the spectrum have different names, as shown in the diagram below.
image obtained from http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html
The part of the spectrum useable for radio communications ranges from below
10kHz (104Hz) to over 100GHz (1011Hz).
The radio spectrum is divided into bands. Waves of different frequencies
behave differently. This along with the amount of spectrum available in the band governs the
use of that band.
Satellite communications from space to ground, and vice versa, are focused in
the 3 - 30GHz band. Above 30GHz is used for inter satellite links.