An electromagnetic wave is defined by its wavelength, which represents the spatial periodicity of oscillations (distance between two maximum oscillations for example). It may be characterised by its frequency, i.e. the number of waves made per second. A frequency is expressed in hertz (Hz). Wavelength, which is also the distance covered by the wave during a period of oscillation, is inversely proportional to frequency: the greater the frequency, the shorter the wavelength.

1 kHz = 10³ Hz soit 1000 Hz

1 MHz = 10 ⁶ Hz soit 1000 kHz

 1 GHz= 10 ⁹ Hz, soit 1000 MHz