Cell Phone Health Risks
Cellular technology provides a two-way radio communications system between a portable handset and the nearest base station. A given geographical region is divided into zones, or cells, each of which is equipped with a base station. The base station receives radio frequency signals from cell phones and sends radio frequency signals to neighboring stations and other cell phones. The base station is also connected to the conventional landline telephone network. When a call is placed from a cellular phone, a signal is sent from the antenna of the phone to the base station antenna. The base station routes the voice signal through a switching center, where the call can be transferred to another cellular telephone, another base station, or to the local land-line telephone system.
The intensity of radio frequency exposure depends on the power level of the signal, which depends, in part, on the distance of the telephone from the base station. The farther the telephone is from the base station antenna, the higher the power level needed to maintain the connection. In a rural area, the cell may extend over many miles, and in urban areas may cover only a fraction of a mile.
The closer the transmitter of the wireless telephone is to the body, the greater the exposure. With handheld cellular phones, the radio transmitter is in the handset, which is typically held against the side of the head while the phone is in use. With car cellular phones, the antenna is mounted on the outside of the car some distance from the user. With transportable cellular phones or bag phones, the transmitter is with the battery pack in a portable unit separate from the handset. Cordless phones are not cellular phones; they have a base unit wired to the landline telephone service and typically operate at a lower frequency and much lower power than other wireless phones. Lower power is typical of cordless phones, because the radio signal from the handset only needs to reach the base unit in the home or office versus a distant base station.
During the 1980s and early to middle 1990s, most cell phones in the United States operated in the microwave frequency range between 800 and 900 MHz (megahertz: a million hertz; a hertz has a frequency of one cycle per second). There has been a trend lately toward use of higher frequencies, and it is unknown whether cancer risk depends on the level of frequency. There has also been a change from phones based on analog signal transmission to those based on digital signal transmission, and increased use of devices that keep the radio transmitter farther from the head while the phone is in use (hands-free accessories).