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Background
Primary antennas for transmitting wireless
telephone service, including cellular and Personal Communications
Service (PCS), are usually located outdoors on towers, water
tanks, and other elevated structures like rooftops and sides of
buildings. The combination of antenna towers and associated
electronic equipment is referred to as a "cellular or PCS
cell site" or "base station." Cellular or PCS cell
site towers are typically 50-200 feet high. Antennas are usually
arranged in groups of three, with one antenna in each group used
to transmit signals to mobile units, and the other two antennas
used to receive signals from mobile units.
At a cell site, the total radio frequency (RF)
power that can be transmitted from each transmitting antenna
depends on the number of radio channels (transmitters) that have
been authorized by the Federal Communications Commission (FCC) and
the power of each transmitter. Although the FCC permits an
effective radiated power (ERP) of up to 500 watts per channel
(depending on the tower height), the majority of cellular or PCS
cell sites in urban and suburban areas operate at an ERP of 100
watts per channel or less.
An ERP of 100 watts corresponds to an actual
radiated power of 5-10 watts, depending on the type of antenna
used. In urban areas, cell sites commonly emit an ERP of 10 watts
per channel or less. For PCS cell sites, even lower ERPs are
typical. As with all forms of electromagnetic energy, the power
density from a cellular or PCS transmitter rapidly decreases as
distance from the antenna increases.
Consequently, normal ground-level exposure is
much less than the exposure that might be encountered if one were
very close to the antenna and in its main transmitted beam.
Measurements made near typical cellular and PCS cell sites have
shown that ground-level power densities are well below the
exposure limits recommended by RF/microwave safety standards used
by the FCC.
Guidelines
In 1996, the FCC adopted updated guidelines
for evaluating human exposure to RF fields from fixed transmitting
antennas such as those used for cellular and PCS cell sites. The
FCC's guidelines are identical to those recommended by the
National Council on Radiation Protection and Measurements (NCRP),
a non-profit corporation chartered by Congress to develop
information and recommendations concerning radiation protection.
The FCC's guidelines also resemble the 1992 guidelines recommended
by the Institute of Electrical and Electronics Engineers (IEEE), a
non-profit technical and professional engineering society, and
endorsed by the American National Standards Institute (ANSI), a
non-profit, privately-funded, membership organization that
coordinates development of voluntary national standards in the
United States.
In the case of cellular and PCS cell site
transmitters, the FCC’s RF exposure guidelines recommend a
maximum permissible exposure level to the general public of
approximately 580 microwatts per square centimeter. This limit is
many times greater than RF levels typically found near the base of
cellular or PCS cell site towers or in the vicinity of other,
lower-powered cell site transmitters.
Calculations corresponding to a “worst-case”
situation (all transmitters operating simultaneously and
continuously at the maximum licensed power) show that, in order to
be exposed to RF levels near the FCC’s guidelines, an individual
would essentially have to remain in the main transmitting beam and
within a few feet of the antenna for several minutes or longer.
Thus, the possibility that a member of the general public could be
exposed to RF levels in excess of the FCC guidelines is extremely
remote.
When cellular and PCS antennas are mounted on
rooftops, RF emissions could exceed higher than desirable
guideline levels on the rooftop itself, even though rooftop
antennas usually operate at lower power levels than free-standing
power antennas. Such levels might become an issue for maintenance
or other personnel working on the rooftop. Exposures exceeding the
guidelines levels, however, are only likely to be encountered very
close to, and directly in front of, the antennas. In such cases,
precautions such as time limits can avoid exposure in excess of
the guidelines. Individuals living or working within the building
are not at risk.
For More Information
For more information on this issue, visit the
FCC’s RF Safety Web site at
www.fcc.gov/oet/rfsafety. For further information about any
other telecommunications-related issues, visit the FCC’s
Consumer & Governmental Affairs Bureau Web site at
www.fcc.gov/cgb, or contact the FCC’s
Consumer Center by e-mailing
fccinfo@fcc.gov; calling 1-888-CALL-FCC (1-888-225-5322)
voice or 1-888-TELL-FCC (1-888-835-5322) TTY; faxing
1-866-418-0232; or writing to:
Federal
Communications Commission
Consumer and Governmental Affairs Bureau
Consumer Information and Complaints Division
445 12 St. SW
Washington, DC 20554.
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Federal Communications Commission
