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11. 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-
shaped, like a piece of pie. As with all forms of electromagnetic energy,
the power decreases rapidly as one moves away from the antenna.
Therefore, RF exposure on the ground is much less than exposure very
close to the antenna and in the path of the transmitted radio signal. In
fact, ground-level exposure from such antennas is typically thousands of
times less than the exposure levels recommended as safe by expert
organizations. So exposure to nearby residents would be well within
safety margins.
Cellular and PCS base stations in the United States are required to
comply with limits for exposure recommended by expert organizations
and endorsed by government agencies responsible for health and safety.
Measurements made near cellular and PCS base station antennas
mounted on towers have confirmed that ground-level exposures are
typically thousands of times less than the exposure limits adopted by the
FCC. In fact, in order to be exposed to levels at or near the FCC limits for
cellular or PCS frequencies an individual would essentially have to
remain in the main transmitted radio signal (at the height of the
antenna) and within a few feet from the antenna. This is, of course, very
unlikely to occur.
When cellular and PCS antennas are mounted on rooftops, RF levels on
that roof or on others near by would probably be greater than those
typically encountered on the ground. However, exposure levels
approaching or exceeding safety guidelines should be encountered only
very close to or directly in front of the antennas. In addition, for sector-
type antennas, typically used for such rooftop base stations, RF levels to
the side and in back of these antennas are insignificant. General
guidelines on antenna installations and circumstances that might give
rise to a concern about an facility's conformance with FCC regulations
can be found in A Local Government Official's Guide to Transmitting
Section 4: Safety Guidelines and Warranty Information
4A: Safety
233
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