Mobile phones – communications on the go
Glossary
Advanced Mobile Phone System (AMPS). Analogue systems of mobile phones send information over radio waves as an electrical copy of the sounds picked up by the phone's microphone (in this case the human voice). The information is sent as a continuous flow of energy, so that only one conversation at a time is possible on any one frequency. More information on analogue and digital systems can be found at Sound into pulses: The benefits of digital transmission (Telstra Learning Centre, Australia) and What is the difference between analog and digital cell phones? (How Stuff Works, USA).
channel. A band of radio frequencies assigned for a particular purpose.
Code Division Multiple Access (CDMA). This technology converts analogue signals into digital which are then transmitted over a network. CDMA enables multiple phone calls to be carried on the same frequency by using a voice-coding system. For more information see How cell phones work – cellular access technologies (How Stuff Works, USA).
electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).
frequency. A measure of how frequently an electromagnetic wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA).
Global System for Mobile Telecommunications (GSM). Digital systems of mobile phones convert voices into a series of on-or-off electrical pulses which are then relayed in short bursts as packages of data. GSM is efficient because in the intervals between bursts, other phones can also send packets of data: in this way, this digital technology enables up to eight conversations to be held on the same channel virtually simultaneously. More information on analogue and digital systems can be found at Sound into pulses: The benefits of digital transmission (Telstra Learning Centre, Australia) and What is the difference between analog and digital cell phones? (How Stuff Works, USA).
radio waves. Low frequency electromagnetic radiation. Radio waves have wavelengths ranging from less than a centimetre to as long as 100 kilometres. The hertz (Hz) is the unit of frequency and means one complete oscillation per second. Many frequencies are much higher than this so other units are used (eg, 1 megahertz (1MHz) = 1,000,000Hz).
We divide the radio wave part of the electromagnetic spectrum into bands that are allocated to different uses. These include AM radio (amplitude modulation), FM radio (frequency modulation) and CB radio (citizens' band), television, aircraft communications, satellites, mobile phones and pagers. Within each band, no two transmissions can use the same part of the spectrum – or frequency – at the same time. For this reason, each band within the radio wave spectrum, itself a part of the broader electromagnetic spectrum, must be managed carefully to ensure the best use of this limited resource.
The frequency of radio waves used in magnetic resonance imaging range from 1-100 megahertz, depending on the strength of the magnetic field in the scanner. This is close to the range of frequencies used for FM radio (88-108 megahertz). For more information see How the radio spectrum works (How Stuff Works, USA).
Page updated August 2006.