What is the radio spectrum?
The radio frequency spectrum is used to support a large number of electronic communications services and applications. Access to radio frequencies is an essential requirement for telecommunications, particularly for aviation, shipping, defence services, public safety, broadcasting, broadband access and mobile radio.
The Electromagnetic Spectrum (not to scale)
Radio technologies use electromagnetic waves to send information in free space. Many different radio applications can be used at the same time by employing waves of different “frequency” (the number of times an electromagnetic wave vibrates in a second, in “Hertz” (Hz)). The radio spectrum is defined as that part of the electromagnetic spectrum at frequencies between 3,000 Hz (3 kHz) and 300 x109 Hz (300 GHz).
Signals transmitted at various frequencies behave in different ways. Broadly speaking, the lower the frequency, the greater the distance but the smaller the amount of information that can be carried. Furthermore, different frequencies are affected differently by the Earth’s atmosphere, rainfall, buildings, etc., so radio applications are always seeking to use frequencies that are optimal for their purpose. For instance, mobile phone users expect to be able to communicate without hindrance inside buildings, and this requirement needs to be reflected in the selection of frequencies.
The radio spectrum is divided into "bands", i.e. ranges of frequencies. Different applications use different bands. Terrestrial TV broadcasting typically takes place within the frequency range between 400 and 800 MHz, mobile phones around 900, 1,800 and 2,000 MHz, cordless phones just below 1900 MHz, WiFi “hot-spots” above 2400 MHz or 5000 MHz and satellite communications tend to use even higher frequencies.
Wireless communications are also increasingly being used to provide broadband access to the Internet, e-mail and other on-line services.