palmOne Vision Smart Device Treo 650 User Manual page 292

risks. Some products that claim to shield the user from RF absorption use special phone cases,
while others involve nothing more than a metallic accessory attached to the phone. Studies have
shown that these products generally do not work as advertised. Unlike "hand-free" kits, these so-
called "shields" may interfere with proper operation of the phone. The phone may be forced to
boost its power to compensate, leading to an increase in RF absorption. In February 2002, the
Federal trade Commission (FTC) charged two companies that sold devices that claimed to
protect wireless phone users from radiation with making false and unsubstantiated claims.
According to FTC, these defendants lacked a reasonable basis to substantiate their claim.
What are wireless telephone base stations?
Fixed antennas used for wireless telecommunications are referred to as cellular base stations,
cell stations, PCS ("Personal Communications Service") stations or telephone transmission
towers. These base stations consist of antennas and electronic equipment. Because the antennas
need to be high in the air, they are often located on towers, poles, water tanks, or rooftops.
Typical heights for freestanding base station towers are 50-200 feet.
Some base stations use antennas that look like poles, 10 to 15 feet in length, that are referred to
as "omni-directional" antennas. These types of antennas are usually found in rural areas. In urban
and suburban areas, wireless providers now more commonly use panel or sector antennas for
their base stations. These antennas consist of rectangular panels, about 1 by 4 feet in dimension.
The antennas are usually arranged in three groups of three antennas each. One antenna in each
group is used to transmit signals to wireless phones, and the other two antennas in each group
are used to receive signals from wireless phones.
At any base station site, the amount of RF energy produced depends on the number of radio
channels (transmitters) per antenna and the power of each transmitter. Typically, 21 channels
per antenna sector are available. For a typical cell site using sector antennas, each of the three
transmitting antennas could be connected to up to 21 transmitters for a total of 63 transmitters.
However, it is unlikely that all of the transmitters would be transmitting at the same time. When
omni-directional antennas are used, a cellular base station could theoretically use up to 96
transmitters, but this would be very unusual, and, once again, it is unlikely that all transmitters
would be in operation simultaneously. Base stations used for PCS communications generally
require fewer transmitters than those used for cellular radio transmissions, since PCS carriers
usually have a higher density of base station antenna sites.
280 Safety