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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-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 Antenna RF
Emission Safety: Rules, Procedures, and Practical Guidance. This Guide
can be accessed at:
http://www.fcc.gov/oet/rfsafety
.
Who regulates exposure to radiation from microwave ovens, television
sets and computer monitors?
The Food and Drug Administration is responsible for protecting the public
from harmful radiation emissions from these consumer products.
Does the FCC routinely monitor radiofrequency radiation from
antennas?
The FCC does not have the resources or the personnel to routinely
monitor the emissions for all the thousands of transmitters that are subject
to FCC jurisdiction. However, the FCC does have measurement
instrumentation for evaluating RF levels in areas that may be accessible to
the public or to workers. If there is evidence for potential non-compliance
with FCC exposure guidelines for a FCC-regulated facility, staff from the
FCC's Office of Engineering and Technology or the FCC Enforcement
Bureau can conduct and investigation, and, if appropriate, perform actual
measurements. Circumstances that could 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 Antenna RF Emission Safety:
Rules, Procedures, and Practical Guidance. This Guide can be accessed
at: http://www.fcc.gov/oet/rfsafety
. Potential exposure problems should be
brought to the FCC's attention by contacting the FCC RF Safety Program
at: 202-418-2464 or by email: rfsafety@fcc.gov
.
Does the FCC maintain a database that includes information on the
location and technical parameters of all the transmitting towers it
regulates?
Each of the FCC Bureaus maintains its own licensing database system for
the service(s) it regulates (e.g., television, cellular service, satellite earth
stations.) The FCC issues two types of licenses: site specific and market
based. In the case of site specific licensed facilities, technical operating
information is collected from the licensee as part of the licensing process.
RushUG.book Page 199 Monday, June 13, 2005 1:33 PM