(Troy Maben/Associated Press)
In Depth
Technology
How it works: Cellphones
The basics behind mobile phone technology
November 20, 2007
By Nicole Tomlinson
Cellphones and other mobile devices send and receive information using low-powered radiofrequency (RF) transmitters, which emit radiation in the form of electromagnetic fields (EMFs).
When a call is placed from a modern mobile handset, a transmission (usually at frequencies between 800 megahertz and 2,200 MHz) is sent from the device to the nearest mobile base station antenna. These antennae are usually mounted on a tower or tall building in the area to maximize the strength and coverage of the signal.
The base station routes the call through a switching centre, where it’s transferred to another cellphone, another base station, or to the local landline system in order to connect with the cellphone or regular phone of the person you're trying to contact.
A geographic area serviced by a base station is often referred to as a cell — hence the term cellphone.
Electromagnetic radiation
Handsets generally operate at low power levels, ranging between 0.2 to 0.6 watts. Base stations transmit anywhere from a few watts to 100 watts or more, depending on the number of cellphone transmissions being processed and the size of the region the base station services.
Electromagnetic radiation emitted by cellphone technology is non-ionizing, meaning the frequency is too low and the wavelength is too long to produce the energy needed to break chemical bonds between cells. This distinction is important because, unlike radiation emitted by ultraviolet light, X-rays, and Gamma rays, EMFs produced by handsets and mobile base stations don’t cause ionization or radioactivity in the body.
A mobile phone user’s level of exposure to RF energy depends on several factors, including the number and duration of calls, the amount of cellphone traffic at a given time, the user’s distance from the nearest base station, the size and power of the handset, and how close the device is to the person’s body.
Handsets act as antennas – so the closer the device is to a user’s head, the greater their exposure to RF energy is generally expected to be. The amount of RF energy absorbed decreases rapidly and significantly the further away the mobile phone is from the body.
The intensity of RF energy emitted by cellular telephones depends on the level of signal sent to or from the nearest base station. The further a handset is from the base station antenna, the more power it needs to use to maintain a connection between the two locations.
SOURCES: Health Canada, National Cancer Institute, WHO
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