Palm 650 User Manual page 323

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.
Are wireless telephone base stations safe?
The electromagnetic RF signals transmitted from base station antennas stations travel
toward the horizon in relatively narrow paths. For example, the radiation pattern for an
antenna array mounted on a tower can be likened to a thin pancake centered around the
antenna system. The individual pattern for a single array of sector antennas is wedge-
Section 5A: Safety 311