Electromagnetic waves can transmit data wirelessly in the radio-frequency range (from100 kHz to 300 GHz), whereby the electrical and the magnetic fields combine and become electromagnetic waves.
Frequency is defined as how often the electromagnetic wave oscillates per second. The measurement unit is Hz (Hertz, named after the German physicist Heinrich Hertz 1857-1894)
One thousand oscillations per second are abbreviated as kHz (kilohertz), one million oscillations as MHz (megahertz) and one billion as GHz (gigahertz).
Due to its large transmission range and the fast propagation of its electromagnetic waves, radio-frequency radiation (RF radiation) is used especially by wireless
communications technologies*, by broadcasting and TV stations, radar and microwave radio relays, but also by cordless phones, baby monitors, and microwave ovens.
At the beginning of the 90s, wireless technologies advanced to incorporating pulse-modulated frequencies that made the cell phone boom possible.
It is possible now that a single frequency can service eight handsets at the same time, whereas before eight different frequencies were needed. In the case of cell phone networks, for example,
the phone conversation transmitted between a given handset and cell tower is re-established 217 times per second**.