Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
FCC Maximum Permissible RF Exposure Regulations
The Federal Communications Commission (FCC) is the United States' governing body for the electromagnetic spectrum.
They are the Big Brother of radio waves. As with most (hopefully) government functions, the intentions are good,
and the people working in them are sincere in the execution of their duties, but they are not always right. If
that were not the case, then there would never be a need to challenge policies. One of the biggest challenges
for the average citizen these days is keeping frequency band allocations that are dedicated to hobbyists from
being re-delegated to commercial applications.
One area where the FCC has excelled is in the consumer safety realm, regarding safe exposure limits to electromagnetic
fields. Even that is somewhat subject to political concerns - for instance, the
SAR (specific absorbed radiation) limits for cell phone
radiation in the human body. Phone manufacturers say no harm is done with 2 W of 1-2 GHz radiation blasting an
inch from your brain, or from 1 W of 2.4 GHz energy sitting on your crotch (notebook computer). Time will tell,
but a recent study found that the normal 10-year development period for cancer is beginning to reveal high incidences
brain cancer on long-time, high-use mobile phone addicts.
Here are the most current Maximum Permissible Exposure number form the FCC (2007).
Limits for Maximum Permissible Exposure (MPE) - from §1.1310
Limits for General Population/Uncontrolled Exposure
f = frequency in MHz
† = plane-wave equivalent power density (see note)
far field strength that would have the E-field or H-field components calculated or measured.
Equivalent far field density for near and far fields can be calculated using
Power Density = |Etotal|2/3770 mW/cm2 or Power Density = |Htotal|2/37.7
Here are some excerpts from the FCC website that address some commonly asked questions
about RF radiation:
- WHAT IS "RADIOFREQUENCY" AND MICROWAVE RADIATION?
Electromagnetic radiation consists of waves of electric and magnetic energy moving together (i.e., radiating)
through space at the speed of light. Taken together, all forms of electromagnetic energy are referred to as
the electromagnetic "spectrum." Radio waves and microwaves emitted by transmitting antennas are one form of
electromagnetic energy. They are collectively referred to as "radiofrequency" or "RF" energy or radiation. Often
the term "electromagnetic field" or "radiofrequency field" may be used to indicate the presence of electromagnetic
or RF energy.
The RF waves emanating from an antenna are generated by the movement of electrical charges
in the antenna. Electromagnetic waves can be characterized by a wavelength and a frequency. The wavelength is
the distance covered by one complete cycle of the electromagnetic wave, while the frequency is the number of
electromagnetic waves passing a given point in one second. The frequency of an RF signal is usually expressed
in terms of a unit called the "hertz" (abbreviated "Hz"). One Hz equals one cycle per second. One megahertz
("MHz") equals one million cycles per second.
Different forms of electromagnetic energy are categorized
by their wavelengths and frequencies. The RF part of the electromagnetic spectrum is generally defined as that
part of the spectrum where electromagnetic waves have frequencies in the range of about 3 kilohertz (3 kHz)
to 300 gigahertz (300 GHz). Microwaves are a specific category of radio waves that can be defined as radiofrequency
energy where frequencies range from several hundred MHz to several GHz.
- WHAT IS NON-IONIZING RADIATION?
"Ionization" is a process by which electrons are stripped from atoms and molecules. This process can produce
molecular changes that can lead to damage in biological tissue, including effects on DNA, the genetic material.
This process requires interaction with high levels of electromagnetic energy. Those types of electromagnetic
radiation with enough energy to ionize biological material include X-radiation and gamma radiation. Therefore,
X-rays and gamma rays are examples of ionizing radiation.
The energy levels associated with RF and microwave
radiation, on the other hand, are not great enough to cause the ionization of atoms and molecules and RF energy
is, therefore, is a type of non-ionizing radiation. Other types of non-ionizing radiation include visible light,
infrared radiation and other forms of electromagnetic radiation with relatively low frequencies. Often the term
"radiation" is used to apply to ionizing radiation such as that associated with nuclear power plants. Ionizing
radiation should not be confused with the lower-energy, non-ionizing, radiation with respect to possible biological
effects, since the mechanisms of action are quite different.
- HOW IS RADIOFREQUENCY ENERGY USED?
Probably the most important use for RF energy is in providing telecommunications services. Radio and television
broadcasting, cellular telephones, personal communications services (PCS), pagers, cordless telephones, business
radio, radio communications for police and fire departments, amateur radio, microwave point-to-point links and
satellite communications are just a few of the many telecommunications applications of RF energy. Microwave
ovens are a good example of a non-communication use of RF energy. Radiofrequency radiation, especially at microwave
frequencies, can transfer energy to water molecules. High levels of microwaves will generate heat in water-rich
materials such as most foods. This efficient absorption of microwave energy via water molecules results in rapid
heating throughout an object, thus allowing food to be cooked more quickly in a microwave oven than in a conventional
oven. Other important non-communication uses of RF energy are for radar and for industrial heating and sealing.
Radar is a valuable tool used in many applications from traffic enforcement to air traffic control and military
applications. Industrial heaters and sealers generate RF radiation that rapidly heats the material being processed
in the same way that a microwave oven cooks food. These devices have many uses in industry, including molding
plastic materials, gluing wood products, sealing items such as shoes and pocketbooks, and processing food products.
There are also a number of medical applications of RF energy.
- HOW IS RADIOFREQUENCY RADIATION MEASURED?
An RF electromagnetic wave or RF "field" has both an electric and a magnetic component (electric field and magnetic
field), and it is often convenient to express the intensity of the RF environment at a given location in terms
of units specific for each component. For example, the unit "volts per meter" (V/m) is used to measure the strength
of the electric field (electric "field strength"), and the unit "amperes per meter" (A/m) is used to express
the strength of the magnetic field (magnetic "field strength"). Another commonly used unit for characterizing
an RF electromagnetic field is "power density." Power density is most accurately used when the point of measurement
is far enough away from an antenna to be located in what is commonly referred to as the "far-field" zone of
Power density is defined as power per unit area. For example, power density can be expressed
in terms of milliwatts per square centimeter (mW/cm2) or microwatts per square centimeter (µW/cm2). One mW equals
0.001 watt of power, and one µW equals 0.000001 watt. With respect to frequencies in the microwave range and
higher, power density is usually used to express intensity.
The quantity used to measure how much RF
energy is actually absorbed in a body is called the "Specific
Absorption Rate" or "SAR." It is usually expressed in units of watts per kilogram (W/kg) or milliwatts per
gram (mW/g). In the case of exposure of the whole body, a standing human adult can absorb RF energy at a maximum
rate when the frequency of the RF radiation is in the range of about 80 and 100 MHz. This means that the "whole-body"
SAR is at a maximum under these conditions. Because of this "resonance" phenomenon, RF safety standards are
generally most restrictive for these frequencies. For exposure of parts of the body, such as the exposure from
hand-held mobile phones, SAR is also used to measure absorption or RF energy (see later questions on mobile
- WHAT BIOLOGICAL EFFECTS CAN BE CAUSED BY RF ENERGY?
Biological effects can result from animal or human exposure to RF energy. Biological effects that result from
heating of tissue by RF energy are often referred to as "thermal" effects. It has been known for many years
that exposure to very high levels of RF radiation can be harmful due to the ability of RF energy to heat biological
tissue rapidly. This is the principle by which microwave ovens cook food. Exposure to very high RF intensities
can result in heating of biological tissue and an increase in body temperature. Tissue damage in humans could
occur during exposure to high RF levels because of the body's inability to cope with or dissipate the excessive
heat that could be generated. Two areas of the body, the eyes and the testes, are particularly vulnerable to
RF heating because of the relative lack of available blood flow to dissipate the excessive heat load.
At relatively low levels of exposure to RF radiation, i.e., levels lower than those that would produce significant
heating, the evidence for production of harmful biological effects is ambiguous and unproven. Such effects have
sometimes been referred to as "non-thermal" effects. Several years ago research reports began appearing in the
scientific literature describing the observation of a range of low-level biological effects. However, in many
cases further experimental research has been unable to reproduce these effects. Furthermore, there has been
no determination that such effects constitute a human health hazard. It is generally agreed that further research
is needed to determine the generality of such effects and their possible relevance, if any, to human health.
In the meantime, standards-setting organizations and government agencies continue to monitor the latest experimental
findings to confirm their validity and determine whether changes in safety limits are needed to protect human
- CAN PEOPLE BE EXPOSED TO LEVELS OF RADIOFREQUENCY RADIATION AND MICROWAVES THAT COULD BE HARMFUL?
Studies have shown that environmental levels of RF energy routinely encountered by the general public are typically
far below levels necessary to produce significant heating and increased body temperature. However, there may
be situations, particularly workplace environments near high- powered RF sources, where recommended limits for
safe exposure of human beings to RF energy could be exceeded. In such cases, restrictive measures or actions
may be necessary to ensure the safe use of RF energy.
- CAN RADIOFREQUENCY RADIATION CAUSE CANCER?
Some studies have also examined the possibility of a link between RF and microwave exposure and cancer. Results
to date have been inconclusive. While some experimental data have suggested a possible link between exposure
and tumor formation in animals exposed under certain specific conditions, the results have not been independently
replicated. In fact, other studies have failed to find evidence for a causal link to cancer or any related condition.
Further research is underway in several laboratories to help resolve this question. The Food and Drug Administration
has further information on this topic with respect to RF exposure from mobile phones at the following Web site:
- WHAT LEVELS ARE SAFE FOR EXPOSURE TO RF ENERGY?
Exposure standards for radiofrequency energy have been developed by various organizations and countries. These
standards recommend safe levels of exposure for both the general public and for workers. In the United States,
the FCC has adopted and used recognized safety guidelines for evaluating RF environmental exposure since 1985.
Federal health and safety agencies, such as the EPA, FDA, the National Institute for Occupational Safety and
Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) have also been involved in monitoring
and investigating issues related to RF exposure.
The FCC guidelines for human exposure to RF electromagnetic
fields were derived from the recommendations of two expert organizations, the National Council on Radiation
Protection and Measurements (NCRP) and the Institute of Electrical and Electronics Engineers (IEEE). Both the
NCRP exposure criteria and the IEEE standard were developed by expert scientists and engineers after extensive
reviews of the scientific literature related to RF biological effects. The exposure guidelines are based on
thresholds for known adverse effects, and they incorporate appropriate margins of safety. In adopting the most
recent RF exposure guidelines, the FCC consulted with the EPA, FDA, OSHA and NIOSH, and obtained their support
for the guidelines that the FCC is now using.
Many countries in Europe and elsewhere use exposure guidelines
developed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The ICNIRP safety limits
are generally similar to those of the NCRP and IEEE, with a few exceptions. For example, ICNIRP recommends somewhat
different exposure levels in the lower and upper frequency ranges and for localized exposure due to such devices
as hand-held cellular telephones. One of the goals of the WHO EMF Project (see above) is to provide a framework
for international harmonization of RF safety standards.
The NCRP, IEEE and ICNIRP exposure guidelines
identify the same threshold level at which harmful biological effects may occur, and the values for Maximum
Permissible Exposure (MPE) recommended for electric and magnetic field strength and power density in both documents
are based on this threshold level. The threshold level is a Specific Absorption Rate (SAR) value for the whole
body of 4 watts per kilogram (4 W/kg). In addition, the NCRP, IEEE and ICNIRP guidelines are different for different
transmitting frequencies. This is due to the findings (discussed above) that whole-body human absorption of
RF energy varies with the frequency of the RF signal. The most restrictive limits on whole-body exposure are
in the frequency range of 30-300 MHz where the human body absorbs RF energy most efficiently when the whole
body is exposed. For devices that only expose part of the body, such as mobile phones, different exposure limits
are specified (see below).
The exposure limits used by the FCC are expressed in terms of SAR, electric
and magnetic field strength and power density for transmitters operating at frequencies from 300 kHz to 100
GHz. The actual values can be found in either of two informational bulletins available at this Web site (OET
Bulletin 56 or OET Bulletin 65), see listing for "OET Safety Bulletins."
- WHY HAS THE FCC ADOPTED GUIDELINES FOR RF EXPOSURE?
The FCC authorizes and licenses devices, transmitters and facilities that generate RF and microwave radiation.
It has jurisdiction over all transmitting services in the U.S. except those specifically operated by the Federal
Government. However, the FCC's primary jurisdiction does not lie in the health and safety area, and it must
rely on other agencies and organizations for guidance in these matters.
Under the National Environmental
Policy Act of 1969 (NEPA), the FCC has certain responsibilities to consider whether its actions will "significantly
affect the quality of the human environment." Therefore, FCC approval and licensing of transmitters and facilities
must be evaluated for significant impact on the environment. Human exposure to RF radiation emitted by FCC-regulated
transmitters is one of several factors that must be considered in such environmental evaluations. In 1996, the
FCC revised its guidelines for RF exposure as a result of a multi-year proceeding and as required by the Telecommunications
Act of 1996.
Major RF transmitting facilities under the jurisdiction of the FCC, such as radio and television
broadcast stations, satellite-earth stations, experimental radio stations and certain cellular, PCS and paging
facilities are required to undergo routine evaluation for RF compliance whenever an application is submitted
to the FCC for construction or modification of a transmitting facility or renewal of a license. Failure to comply
with the FCC's RF exposure guidelines could lead to the preparation of a formal Environmental Assessment, possible
Environmental Impact Statement and eventual rejection of an application. Technical guidelines for evaluating
compliance with the FCC RF safety requirements can be found in the FCC's OET Bulletin 65 (see "OET Safety Bulletins"
listing elsewhere at this Web site).
Low-powered, intermittent, or inaccessible RF transmitters and
facilities are normally "categorically excluded" from the requirement for routine evaluation for RF exposure.
These exclusions are based on calculations and measurement data indicating that such transmitting stations or
devices are unlikely to cause exposures in excess of the guidelines under normal conditions of use. The FCC's
policies on RF exposure and categorical exclusion can be found in Section 1.1307(b) of the FCC's Rules and Regulations
[(47 CFR 1.1307(b)]. It should be emphasized, however, that these exclusions are not exclusions from compliance,
but, rather, only exclusions from routine evaluation. Transmitters or facilities that are otherwise categorically
excluded from evaluation may be required, on a case-by-case basis, to demonstrate compliance when evidence of
potential non-compliance of the transmitter or facility is brought to the Commission's attention [see 47 CFR
1.1307(c) and (d)].
- HOW SAFE ARE MOBILE PHONES? CAN THEY CAUSE CANCER?
In recent years, publicity, speculation, and concern over claims of possible health effects due to RF emissions
from hand-held wireless telephones prompted industry-sponsored groups to initiate research programs to investigate
whether there is any risk to users of these devices. Research organizations funded by the cellular industry
and wireless equipment manufacturers, have been investigating potential health effects from the use of hand-held
cellular telephones and other wireless devices, especially with respect to concerns that mobile phones might
There is no scientific evidence to date that proves that wireless phone usage can lead
to cancer or a variety of other health effects, including headaches, dizziness or memory loss. However, studies
are ongoing and key government agencies, such as the Food and Drug Administration (FDA) continue to monitor
the results of the latest scientific research on this topic. Also, as noted above, the World Health Organization
has established an ongoing program to monitor research in this area and make recommendations related to the
safety of mobile phones.
In 1993," the FDA, which has primary jurisdiction for investigating mobile
phone safety, stated that it did not have enough information at that time to rule out the possibility of risk,
but if such a risk exists, "it is probably small." The FDA concluded that there is no proof that cellular telephones
can be harmful, but if individuals remain concerned several precautionary actions could be taken, including
limiting conversations on hand-held cellular telephones and making greater use of telephones with vehicle-mounted
antennas where there is a greater separation distance between the user and the radiating antennas. The Web site
for the FDA's Center for Devices and Radiological Health provides further information on mobile phone safety:
The Government Accounting Office (GAO) recently completed a draft report of an investigation into safety
concerns related to mobile phones. The report concludes that further research is needed to confirm whether mobile
phones are completely safe for the user, and the report recommends that the FDA take the lead in monitoring
the latest research results.
The FCC's exposure guidelines specify limits for human exposure to RF emissions
from hand- held mobile phones in terms of Specific Absorption Rate (SAR), a measure of the rate of absorption
of RF energy by the body. The safe limit for a mobile phone user is an SAR of 1.6 watts per kg (1.6 W/kg), averaged
over one gram of tissue, and compliance with this limit must be demonstrated before FCC approval is granted
for marketing of a phone in the United States. Somewhat less restrictive limits, e.g., 2 W/kg averaged over
10 grams of tissue, are specified by the ICNIRP guidelines used in Europe and some other countries.
Measurements and analysis of SAR in models of the human head have shown that the 1.6 W/kg limit is unlikely
to be exceeded under normal conditions of use of cellular and PCS hand-held phones. The same can be said for
cordless telephones used in the home. Testing of hand-held phones is normally done under conditions of maximum
power usage, thus providing an additional margin of safety, since most phone usage is not at maximum power.
Information on SAR levels for many phones is available electronically through the FCC's Web site and database.
- ARE CELLULAR AND PCS TOWERS AND ANTENNAS SAFE?
Cellular radio services transmit using frequencies between 800 and 900 megahertz (MHz). Transmitters in the
Personal Communications Service (PCS) use frequencies in the range of 1850-1990 MHz. Antennas used for cellular
and PCS transmissions are typically located on towers, water tanks or other elevated structures including rooftops
and the sides of buildings. The combination of antennas and associated electronic equipment is referred to as
a cellular or PCS "base station" or "cell site." Typical heights for free-standing base station towers or structures
are 50-200 feet. A cellular base station may utilize several "omni-directional" antennas that look like poles,
10 to 15 feet in length, although these types of antennas are becoming less common in urban areas.
urban and suburban areas, cellular and PCS service providers now more commonly use "sector" antennas for their
base stations. These antennas are rectangular panels, e.g., about 1 by 4 feet in dimension, typically mounted
on a rooftop or other structure, but they are also mounted on towers or poles. The antennas are usually arranged
in three groups of three each. One antenna in each group is used to transmit signals to mobile units (car phones
or hand-held phones), and the other two antennas in each group are used to receive signals from mobile units.
At a given cell or PCS site, the total RF power that could be transmitted from each transmitting antenna
at a cell site depends on the number of radio channels (transmitters) that have been authorized and the power
of each transmitter. Typically, for a cellular base station, a maximum of 21 channels per sector (depending
on the system) could be used. Thus, for a typical cell site utilizing sector antennas, each of the three transmitting
antennas could be connected to up to 21 transmitters for a total of 63 transmitters per site. When omni-directional
antennas are used, up to 96 transmitters could be implemented at a cell site, but this would be very unusual.
Furthermore, while a typical base station could have as many as 63 transmitters, not all of the transmitters
would be expected to operate simultaneously thus reducing overall emission levels. For the case of PCS base
stations, fewer transmitters are normally required due to the relatively greater number of base stations.
The signals from a cellular or PCS base station antenna are essentially directed toward the horizon
in a relatively narrow pattern in the vertical plane. The radiation pattern for an omni- directional antenna
might be compared to a thin doughnut or pancake centered around the antenna while the pattern for a sector antenna
is fan-shaped, like a wedge cut from a pie. As with all forms of electromagnetic energy, the power density from
a cellular or PCS transmitter decreases rapidly as one moves away from the antenna. Consequently, normal ground-level
exposure is much less than exposures 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 installations, especially
those with tower- mounted antennas, have shown that ground-level power densities are thousands of times less
than the FCC's limits for safe exposure. 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 transmitting beam
(at the height of the antenna) and within a few feet from the antenna. This makes it extremely unlikely that
a member of the general public could be exposed to RF levels in excess of these guidelines due to cellular or
PCS base station transmitters.
When cellular and PCS antennas are mounted at rooftop locations it is
possible that ambient RF levels could be greater than those typically encountered on the ground. However, once
again, exposures approaching or exceeding the safety guidelines are only likely to be encountered very close
to or directly in front of the antennas. For sector-type antennas RF levels to the side and in back of these
antennas are insignificant.
For further information on celluar radio systems go to www.fcc.gov/wtb/cellular/cellfaq.html
- ARE CELLULAR AND OTHER RADIO TOWERS LOCATED NEAR HOMES OR SCHOOLS SAFE FOR RESIDENTS AND STUDENTS?
As discussed above, radiofrequency emissions from antennas used for wireless transmissions such as cellular
and PCS signals result in exposure levels on the ground that are typically thousands of times less than safety
limits. These safety limits were adopted by the FCC based on the recommendations of expert organizations and
endorsed by agencies of the Federal Government responsible for health and safety. Therefore, there is no reason
to believe that such towers could constitute a potential health hazard to nearby residents or students.
Other antennas, such as those used for radio and television broadcast transmissions, use power levels that
are generally higher than those used for cellular and PCS antennas. Therefore, in some cases there could be
a potential for higher levels of exposure on the ground. However, all broadcast stations are required to demonstrate
compliance with FCC safety guidelines, and ambient exposures to nearby persons from such stations are typically
well below FCC safety limits.
- ARE EMISSIONS FROM RADIO AND TELEVISION ANTENNAS SAFE?
Radio and television broadcast stations transmit their signals via RF electromagnetic waves. There are thousands
of radio and TV stations on the air in the United States. Broadcast stations transmit at various RF frequencies,
depending on the channel, ranging from about 550 kHz for AM radio up to about 800 MHz for some UHF television
stations. Frequencies for FM radio and VHF television lie in between these two extremes. Operating powers ("effective
radiated power") can be as little as a few hundred watts for some radio stations or up to millions of watts
for certain television stations. Some of these signals can be a significant source of RF energy in the local
environment, and the FCC requires that broadcast stations submit evidence of compliance with FCC RF guidelines.
The amount of RF energy to which the public or workers might be exposed as a result of broadcast antennas
depends on several factors, including the type of station, design characteristics of the antenna being used,
power transmitted to the antenna, height of the antenna and distance from the antenna. Since energy at some
frequencies is absorbed by the human body more readily than energy at other frequencies, the frequency of the
transmitted signal as well as its intensity is important. Calculations can be performed to predict what field
intensity levels would exist at various distances from an antenna.
Public access to broadcasting antennas
is normally restricted so that individuals cannot be exposed to high-level fields that might exist near antennas.
Measurements made by the FCC, EPA and others have shown that ambient RF radiation levels in inhabited areas
near broadcasting facilities are typically well below the exposure levels recommended by current standards and
guidelines. There have been a few situations around the country where RF levels in publicly accessible areas
have been found to be higher than those recommended by applicable safety standards. But, in spite of the relatively
high operating powers of many stations, such cases are unusual, and members of the general public are unlikely
to be exposed to RF levels from broadcast towers that exceed FCC limits. Furthermore, wherever such situations
have arisen corrective measures have been undertaken to ensure that areas promptly come into compliance with
the applicable guidelines.
Antenna maintenance workers are occasionally required to climb antenna structures
for such purposes as painting, repairs, or beacon replacement. Both the EPA and OSHA have reported that in these
cases it is possible for a worker to be exposed to high levels of RF energy if work is performed on an active
tower or in areas immediately surrounding a radiating antenna. Therefore, precautions should be taken to ensure
that maintenance personnel are not exposed to unsafe RF fields.
- HOW SAFE ARE MICROWAVE AND SATELLITE ANTENNAS?
Point-to-point microwave antennas transmit and receive microwave signals across relatively short distances (from
a few tenths of a mile to 30 miles or more). These antennas are usually rectangular or circular in shape and
are normally found mounted on a supporting tower, on rooftops, sides of buildings or on similar structures that
provide clear and unobstructed line-of- sight paths between both ends of a transmission path or link. These
antennas have a variety of uses such as transmitting voice and data messages and serving as links between broadcast
or cable-TV studios and transmitting antennas.
The RF signals from these antennas travel in a directed
beam from a transmitting antenna to a receiving antenna, and dispersion of microwave energy outside of the relatively
narrow beam is minimal or insignificant. In addition, these antennas transmit using very low power levels, usually
on the order of a few watts or less. Measurements have shown that ground-level power densities due to microwave
directional antennas are normally a thousand times or more below recommended safety limits. Moreover, as an
added margin of safety, microwave tower sites are normally inaccessible to the general public. Significant exposures
from these antennas could only occur in the unlikely event that an individual were to stand directly in front
of and very close to an antenna for a period of time.
Ground-based antennas used for satellite-earth
communications typically are parabolic "dish" antennas, some as large as 10 to 30 meters in diameter, that are
used to transmit ("uplinks") or receive ("downlinks") microwave signals to or from satellites in orbit around
the earth. The satellites receive the signals beamed up to them and, in turn, retransmit the signals back down
to an earthbound receiving station. These signals allow delivery of a variety of communications services, including
long distance telephone service. Some satellite-earth station antennas are used only to receive RF signals (i.e.,
just like a rooftop television antenna used at a residence), and, since they do not transmit, RF exposure is
not an issue.
Since satellite-earth station antennas are directed toward satellites above the earth,
transmitted beams point skyward at various angles of inclination, depending on the particular satellite being
used. Because of the longer distances involved, power levels used to transmit these signals are relatively large
when compared, for example, to those used by the microwave point-to-point antennas discussed above. However,
as with microwave antennas, the beams used for transmitting earth-to-satellite signals are concentrated and
highly directional, similar to the beam from a flashlight. In addition, public access would normally be restricted
at station sites where exposure levels could approach or exceed safe limits.
Although many satellite-earth
stations are "fixed" sites, portable uplink antennas are also used, e.g., for electronic news gathering. These
antennas can be deployed in various locations. Therefore, precautions may be necessary, such as temporarily
restricting access in the vicinity of the antenna, to avoid exposure to the main transmitted beam. In general,
however, it is unlikely that a transmitting earth station antenna would routinely expose members of the public
to potentially harmful levels of microwaves.
- WHAT IS THE FCC'S POLICY ON RADIOFREQUENCY WARNING SIGNS? FOR EXAMPLE, WHEN SHOULD SIGNS BE POSTED, WHERE
SHOULD THEY BE LOCATED AND WHAT SHOULD THEY SAY?
Radiofrequency warning or "alerting" signs should be used to provide information on the presence of RF radiation
or to control exposure to RF radiation within a given area. Standard radiofrequency hazard warning signs are
commercially available from several vendors. Appropriate signs should incorporate the format recommended by
the Institute for Electrical and Electronics Engineers (IEEE) and as specified in the IEEE standard: IEEE C95.2-1999
(Web address: www.ieee.org ). When signs are used, meaningful information should be placed on the sign advising
of the potential for high RF fields. In some cases, it may be appropriate to also provide instructions to direct
individuals as to how to work safely in the RF environment of concern. Signs should be located prominently in
areas that will be readily seen by those persons who may potentially have access to an area where RF fields
- CAN IMPLANTED ELECTRONIC CARDIAC PACEMAKERS BE AFFECTED BY NEARBY RF DEVICES SUCH AS MICROWAVE OVENS OR
Over the past several years there has been concern that signals from some RF devices could interfere with the
operation of implanted electronic pacemakers and other medical devices. Because pacemakers are electronic devices,
they could be susceptible to electromagnetic signals that could cause them to malfunction. Some claims of such
effects in the past involved emissions from microwave ovens. However, it has never been shown that signals from
a microwave oven are strong enough to cause such interference.
Some studies have shown that mobile phones
can interfere with implanted cardiac pacemakers if a phone is used in close proximity (within about 8 inches)
of a pacemaker. To avoid this potential problem, pacemaker patients can avoid placing a phone in a pocket close
to the location of their pacemaker or otherwise place the phone near the pacemaker location during phone use.
Patients with pacemakers should consult their physician or the FDA if they believe that they may have a problem
related to RF interference. Further information on this is available from the FDA: www.fda.gov/cdrh .
- DOES THE FCC REGULATE EXPOSURE TO RADIATION FROM MICROWAVE OVENS, TELEVISION SETS AND COMPUTER MONITORS?
The Commission does not regulate exposure to radiation emissions from these devices. Protecting the public from
harmful radiation emissions from these consumer products are the responsibility of the U.S. Food and Drug Administration
(FDA). Inquries should be directed to the FDA's Center for Devices and Radiological Health (CDRH), and, specifically,
to the CDRH Office of Compliance at (301) 594-4654.
- DOES THE FCC ROUTINELY MONITOR RADIOFREQUENCY RADIATION FROM ANTENNAS?
The FCC does not have the resources nor 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 an FCC-regulated facility, staff from the FCC's Office
of Engineering and Technology or the Enforcement Bureau can conduct and investigation, and, if appropriate,
perform actual measurements. Potential exposure problems should be brought to the FCC's attention by contacting
the FCC RF Safety Program at: 1-888-225-5322 or by e-mail: firstname.lastname@example.org.
- DOES THE FCC MAINTAIN A DATABASE THAT INCLUDES INFORMATION ON THE LOCATION AND TECHNICAL PARAMETERS OF ALL
THE TOWERS AND ANTENNAS IT REGULATES?
The Commission does not have a transmitter-specific database for all the services it regulates. The Commission
has limited information for some services such as radio and television broadcast stations, and many larger antenna
towers are required to register with the FCC if they meet certain criteria. In those cases, location is generally
specified in terms of degrees, minutes, and seconds. However, this is not sufficient to distinguish between
collocated transmitters. In some services, licenses are allowed to use additional transmitters or to increase
power without filing with the Commission. Other services are licensed by geographic area, such that the Commission
has no knowledge concerning the actual number or location of transmitters within a given geographic area.
The FCC General Menu Reports (GENMen) search engine unites most of the Commission's licensing databases
under a single umbrella. Databases included are the Wireless Telecommunication Bureau's ULS, the Media Bureau's
CDBS, COALS (cable data) and BLS, the International Bureau's IBFS and. Entry points into the various databases
include frequency, state/county, latitude/longitude, callsign and licensee name.
The FCC also publishes
on at least a weekly basis, bulk extracts of the various Commission licensing databases. Each licensing database
has it own unique file structure. These extracts consisted of multiple, very large files. OET maintains an index
to these databases.
OET has developed has developed a Spectrum Utilization Study Software tool-set that
can be used to create a MS ACCESS version of the individual exported licensing databases and then create MapInfo
"mid" and "mif" files so that radio assignments can be plotted. This experimental software is used to conduct
internal spectrum utilization studies needed in the rulemaking process. No technical support is proved.
For further information on the Commission's existing databases, please contact Donald Campbell at email@example.com
- WHICH OTHER FEDERAL AGENCIES HAVE RESPONSIBILITIES RELATED TO POTENTIAL RF HEALTH EFFECTS?
Certain agencies in the Federal Government have been involved in monitoring, researching or regulating issues
related to human exposure to RF radiation. These agencies include the Food and Drug Administration (FDA), the
Environmental Protection Agency (EPA), the Occupational Safety and Health Administration (OSHA), the National
Institute for Occupational Safety and Health (NIOSH), the National Telecommunications and Information Administration
(NTIA) and the Department of Defense (DOD).
By authority of the Radiation Control for Health and Safety
Act of 1968, the Center for Devices and Radiological Health (CDRH) of the FDA develops performance standards
for the emission of radiation from electronic products including X-ray equipment, other medical devices, television
sets, microwave ovens, laser products and sunlamps. The CDRH established a product performance standard for
microwave ovens in 1971 limiting the amount of RF leakage from ovens. However, the CDRH has not adopted performance
standards for other RF-emitting products. The FDA is, however, the lead federal health agency in monitoring
the latest research developments and advising other agencies with respect to the safety of RF-emitting products
used by the public, such as cellular and PCS phones.
The FDA's microwave oven standard is an emission
standard (as opposed to an exposure standard) that allows specific levels of microwave leakage (measured at
five centimeters from the oven surface). The standard also requires ovens to have two independent interlock
systems that prevent the oven from generating microwaves the moment that the latch is released or the door of
the oven is opened. The FDA has stated that ovens that meet its standards and are used according to the manufacturer's
recommendations are safe for consumer and industrial use. More information is available from:
The EPA has, in the past, considered
developing federal guidelines for public exposure to RF radiation. However, EPA activities related to RF safety
and health are presently limited to advisory functions. For example, the EPA now chairs an Inter-agency Radiofrequency
Working Group, which coordinates RF health-related activities among the various federal agencies with health
or regulatory responsibilities in this area.
OSHA is responsible for protecting workers from exposure
to hazardous chemical and physical agents. In 1971, OSHA issued a protection guide for exposure of workers to
RF radiation [29 CFR 1910.97]. However, this guide was later ruled to be only advisory and not mandatory. Moreover,
it was based on an earlier RF exposure standard that has now been revised. At the present time, OSHA uses the
IEEE and/or FCC exposure guidelines for enforcement purposes under OSHA's "general duty clause" (for more information
see: www.osha- slc.gov/SLTC/radiofrequencyradiation/index.html ).
NIOSH is part of the U.S. Department
of Health and Human Services. It conducts research and investigations into issues related to occupational exposure
to chemical and physical agents. NIOSH has, in the past, undertaken to develop RF exposure guidelines for workers,
but final guidelines were never adopted by the agency. NIOSH conducts safety-related RF studies through its
Physical Agents Effects Branch in Cincinnati,Ohio.
The NTIA is an agency of the U.S. Department of Commerce
and is responsible for authorizing Federal Government use of the RF electromagnetic spectrum. Like the FCC,
the NTIA also has NEPA responsibilities and has considered adopting guidelines for evaluating RF exposure from
U.S. Government transmitters such as radar and military facilities.
The Department of Defense (DOD)
has conducted research on the biological effects of RF energy for a number of years. This research is now conducted
primarily at the U.S. Air Force Research Laboratory located at Brooks Air Force Base, Texas.
- CAN LOCAL AND STATE GOVERNMENTAL BODIES ESTABLISH LIMITS FOR RF EXPOSURE?
In the United States some local and state jurisdictions have also enacted rules and regulations pertaining to
human exposure to RF energy. However, the Telecommunications Act of 1996 contained provisions relating to federal
jurisdiction to regulate human exposure to RF emissions from certain transmitting devices.. In particular, Section
704 of the Act states that, "No State or local government or instrumentality thereof may regulate the placement,
construction, and modification of personal wireless service facilities on the basis of the environmental effects
of radio frequency emissions to the extent that such facilities comply with the Commission's regulations concerning
such emissions." Further information on FCC policy with respect to facilities siting is available in a factsheet
from the FCC's Wireless Telecommunications Bureau (see www.fcc.gov/wtb).
- WHERE CAN I OBTAIN MORE INFORMATION ON POTENTIAL HEALTH EFFECTS OF RADIOFREQUENCY ENERGY?
Although relatively few offices or agencies within the Federal Government routinely deal with the issue of human
exposure to RF fields, it is possible to obtain information and assistance on certain topics from the following
federal agencies. Most of these agencies also have Internet Web sites.
FDA: For information about radiation
from microwave ovens and other consumer and industrial products contact: Center for Devices and Radiological
Health (CDRH), Food and Drug Administration, Radiation Biology Branch, Rockville, MD 20857, (301) 443-7118.
EPA: The Environmental Protection Agency's Office of Radiation Programs is responsible for monitoring
potential health effects due to public exposure to RF fields. Contact: Environmental Protection Agency, Office
of Radiation and Indoor Air, 401 M Street, S.W., Washington, D.C. 20460, (202) 564-9235.
OSHA: The Occupational
Safety and Health Administration's (OSHA) Health Response Team (1781 South 300 West, Salt Lake City, Utah 84165)
has been involved in studies related to occupational exposure to RF radiation. Phone: (801) 524-7906.
NIOSH: The National Institute for Occupational Safety and Health (NIOSH) monitors RF- related safety issues
as they pertain to the workplace. Contact: NIOSH, Physical Agents Effects Branch, Mail Stop C-27, 4676 Columbia
Parkway, Cincinnati, Ohio 45226. Toll-free number: 1-800-35-NIOSH (1-800-356-4674) or (513) 533-8153.
DOD: Questions regarding Department of Defense activities related to RF safety and its biological research
program can be directed to the Radio Frequency Radiation Branch, Air Force Research Laboratory, Brooks Air Force
Base, TX 78235, (210) 536-4833.
FCC: Questions regarding potential RF hazards from FCC-regulated transmitters
can be directed to the RF Safety Program, Office of Engineering and Technology, Technical Analysis Branch, Federal
Communications Commission, 445 Twelfth Street, S.W., Washington, D.C. 20554. Phone: 1-888-225-5322. E-mail:
firstname.lastname@example.org. Web site: www.fcc.gov/oet/rfsafety.
In addition to government agencies, there are other sources of information regarding RF energy and health
effects. Some states maintain non-ionizing radiation programs or, at least, some expertise in this field, usually
in a department of public health or environmental control. The following table lists some representative Internet
Web sites that provide information on this topic. However, the FCC neither endorses or verifies the accuracy
of any information provided at these sites. They are being provided for information only.