There are four types of wireless telephones:
cordless,
transportable,
mobile or Car Phones, and
portable or Wireless Cell Phones.
Cordless telephones, commonly used in homes, have base units that are plugged into telephone jacks and wired to local telephone service; these are not considered Wireless Cell Phones. The question of health risks associated with cordless phones, which operate at 1/600th the power of Wireless Cell Phones, has not been raised. The radio frequencies are 900 Mhz, 2.4 GHz and 5.8 GHz.
Transportable, mobile, and portable phones are all considered Wireless Cell Phones.
Transportable phones are also known as "bag phones." These operate with equipment stored in a small carrying case; the antenna of the bag phone usually extends from the carrying case. Because they are most commonly stored inside the car with the phone user, or carried by the phone user, bag phones can be a greater source of RF exposure than Car Phones. Transportable telephone use is declining as portable Wireless Cell Phones become more popular. For rural areas where more power is needed the transpoartable phones are being replaced by satellite phones.
Mobile Cell phones, also called "Car Phones," usually have an antenna mounted on the outside of a car—on the window, fender, roof, or trunk. The antenna of a Wireless Cellular Phone is the phone's primary source of radio frequency. The metal surface of a car provides a shield between the Mobile Cell phone user and the energy associated with the antenna. The physical distance between the Mobile Cell phone user and the antenna also serves as protection against RF energy. Because of these two obstacles—the metal car surface and the physical separation—users of Mobile Cell phones are thought to have little exposure to RF energy.
The antenna of a portable Wireless Cellular Phone is integrated into the body of the phone. Because the antenna of a portable Wireless Cellualar Phone is close to the phone user's head, portable Wireless Cell Phones pose greater RF exposure than the other types of cordless phones.
Wireless Cell Phones are an important source of RF exposure for those who use them. The amount of RF to which a person is exposed depends on a number of factors. The number of "cells" or Base Stations in a geographical area depends upon the Wireless Cellular Phone traffic in that area. For example, large cities may have many cells or Base Stations per square mile, whereas a less-populated, rural area may have a single cell stretching over several square miles. The farther away a Cell Phone Antenna is from its Base Station, the higher the power level needed to maintain the connection. Very small nework cells or Base Stations are therefore associated with much lower exposures.
Each geographical network cell has a different number of available channels. Wireless Cell Phones operate ideally with the least amount of interference from neighboring channels. To help achieve optimal operation, Wireless Cell Phones automatically step down to the lowest power level available that still maintains a connection with the base station. On the other hand, any physical obstacle, such as buildings or trees, interfering with the connection between Base Station and Wireless Cellular Phone forces the Base Station to increase the power sent to that phone. Therefore the amount of power sent from a Base Station to a particular Wireless Cellualr Phone can vary, even within a single call.
Manufacturers are required to report the specific absorption rate (SAR) of their product to the FCC. The SAR is the amount of RF energy absorbed from the phone into the local tissues. The upper limit of SAR allowed is 1.6 watts per kilogram of body weight. Exposure to RF also depends on the duration and frequency of Wireless Cellular Phone use, with more use implying more exposure. Finally, older Wireless Cell Phones (analog models) involve higher exposure than newer, digital equipment. SAR values are more important to the people working on Base Stations.