RF safety and
(Most recent revision of this document: Sept. 5, 2021)
Could amateur radio be hazardous to your
What about cellphones and other wireless devices? Those became
controversial questions in the late 20th and early 21st centuries. In 2020, suddenly Covid-19 came to dominate
health news coverage in the media. Now the headlines are all about Covid-19
and its impact on society. Every day we learn about overcrowded
hospitals, horrible deaths experienced by people on ventilators, and
about lockdowns and the effectiveness of vaccines--combined with
stories about those who choose not to take the vaccines. Underlying
it all is the big question: when will this global pandemic
When Covid-19 is finally off the front pages,
the media will surely resume publishing news of research about the
health effects of RF fields and about the key underlying
question: do radio, television and wireless signals cause cancer?
Amateur radio, broadcast radio and TV, cellphones
and many other wireless devices all transmit what are called "non-ionizing
electromagnetic radiation" (EMR)--radio signals. Often the term "electromagnetic
fields" (EMFs) is used to describe both radio signals and the lower frequency
energy radiated by power lines and electric devices. Cellphones are
a particular concern now because at least five billion of them are in use around
the world at last count. As evidence grows that they may pose long-term health
risks, this is becoming a serious problem. Amateur radio operators
can benefit from what is being learned in studies of EMF exposure from
cellphones because some amateur radio transmissions may also pose risks to
amateurs, their families and others nearby.
The Federal Communications Commission has
exposure standards for devices that generate EMFs, including amateur
equipment and cellphones. Most amateur radio operators are required to
determine if their transmissions comply with those standards, as are
providers, among many others. But questions are being raised
the standards. Are they adequate to protect public health?
The FCC and other regulatory bodies all over the world have been
whether additional regulations were needed to protect the public from
effects of EMFs.
By 2021 more than 250 EMF scientists from
44 countries signed an appeal to the United Nations, the World Health
and U.N. member states calling for much stricter standards for EMF
in light of the growing evidence of health hazards posed by even
Their statement read in part, "Numerous
recent scientific publications have shown that EMF affects living organisms at
levels well below most international and national guidelines. Effects include
increased cancer risk, cellular stress, increase in harmful free radicals, genetic
damages, structural and functional changes of the reproductive system, learning
and memory deficits, neurological disorders, and negative impacts on general
well-being in humans.” For more information about this appeal, go to emfscientist.org
These scientists can back up their claims by citing
peer-reviewed research published in some of the leading academic
journals worldwide. But there is a major debate underway between
these scientists and others who dispute their conclusions and the
methodology of their research. The scientists who signed the U.N. appeal generally
do not accept grants, honoraria or consultancies from groups that may
have a vested interest in the outcome of their research--and some of
them openly criticize other scientists who do accept such money.
This website is probably not the place to
resolve these controversial issues of public health. About all we
can do is acknowledge the controversy and summarize a little of the
most notable research.
No one would deny that radio frequency energy can
be a health hazard. It has been known since World War II that RF
energy has thermal effects (i.e., it can cause excessive body heating)
if the power density is high enough. The thermal effects of RF energy
can include blindness and sterility, among other health problems. But more
recently concern has shifted to athermal biological effects of EMFs
that are too weak to cause whole-body heating. The
FCC's RF safety standards are designed only to prevent thermal effects.
Much more stringent standards would be needed to address athermal effects--and
implementing such standards would be so expensive that governments and
corporations worldwide are refusing to adopt stricter standards.
A SAMPLING OF RECENT RESEARCH
Research showing biological effects of athermal
(low-level) EMFs has been reported for many years. Lately, however,
the evidence has become even more compelling. Every year about 200
new peer-reviewed scholarly papers are presented at the annual conference
of the Bioelectromagnetics Society, an international organization of scientists
and medical researchers. The Bioelectromagnetics Society and its
European counterpart, the European BioElectromagnetics Association, hold
joint meetings that showcase some of the latest research on the biological
effects of EMFs. For example, the 2015 conference
program was more than 100 pages long and included a short summary of each
research project reported at the conference. The new research explored
many aspects of the biological effects of EMFs on living organisms.
In addition to the presentations and papers at these conferences, many
other research reports about this topic are published every year in scholarly
Two earlier studies, including one published
in 2015 in a peer-reviewed academic journal, documented high rates of several
cancers, including lymphoma and lung cancer, among laboratory animals
(mice) exposed for a lifetime to low-level GSM cellphone-type signals at
2 GHz, compared to a control group not exposed to RF.(3) Surprisingly,
some weaker RF fields produced higher tumor rates than stronger fields,
raising still more concerns. The 2015 study concluded, "our findings
may help to understand the repeatedly reported increased incidences of
brain tumors in heavy users of mobile phones."
A definitive summary of recent research has
been published and is regularly updated in Bioinitiative 2012, a detailed online report.(2) Anyone concerned about EMFs and health,
including the hazards of amateur radio transmissions, should read at least
the 2014 Supplement of this document's Summary for the Public. It
may be read or downloaded at bioinitiative.org.
It would not be possible to summarize all
of this research briefly, but here are a few examples. Probably
the most anticipated such study was conducted by the U.S. National
Toxicology Program, which spent about $30 million over almost 20 years
design and carry out a large-scale study of cancer in laboratory
animals exposed to cellphone-like (GSM and CDMA) RF fields for their
entire lifetime, starting in the uterus. These animals were
to a control group that was not similarly exposed. When the
results were published in 2018, scientists on all sides lined up to
praise or criticize the NTP's research, methodology and
conclusions. In essence, the study found that male rats had a
statistically significant excess of glioma (a particularly aggreessive
form of brain cancer) and also schwannoma of the heart, a tumor that is
normally rare. The NTP
responded to questions about what mechanism could have caused
this result by launching additional research into gene expression,
oxidative stress and DNA damage plus the role of heat, behavior and
stress affecting the animals. At about the same time, another
large study at the Ramazzini Institute in Italy reached similar
conclusions, including the development of heart schwannomas in male
rats. The scientific director at Ramazzini said it is unlikely to
be coincidence when the same unusual form of cancer is observed in the
same type of rats in two studies of RF exposure conducted thousands of
This 2015 study, by Dr. Alexander Lerchl and eight other researchers in
Germany, replicated and corroborated an earlier study by a different group
of German scientists who did similar research using the same methods--and
got similar results.(4) When a study has been fully replicated like
this, it carries far more weight than a study that has not been replicated.
It is also notable because the lead researcher had often publicly questioned
the idea that low-level EMFs could cause serious health problems.
His group may have set out to disprove the earlier study--but they ended
up confirming it.
Both studies used standard procedures for
animal experiments and left little room for denial that low-level EMF exposure
promoted the growth of tumors in mice in these circumstances. Both
studies concluded that EMF is a cancer promoter--it causes tumors
to develop once something else such as a chemical agent initiates the process
by causing a cell to become defective. RF energy with certain waveforms
may interfere with the work of the immune system to detect and destroy
defective cells, allowing a tumor to form. That concept is by no
means new--there are two QST articles cited at the end of this web
page that discussed the same concept more than 20 years ago. Even
ARRL Handbook by 1992 had a discussion of the health hazards of low-level
RF fields, but that material has since been removed from the
Another factor in these studies is that
exposed animals for a lifetime (from in the uterus before birth until
end of their normal life expectancy). Cellphones are too new to
any kind of study that tracks humans' cellphone EMF exposure versus
for a lifetime. Nor could such research be done with human
subjects: it is not ethical to expose humans to a possible
carcinogen for a lifetime.
These recent animal experiments raise
questions about the long-term safety of cellphone use because many
cellphones expose users to EMFs at much higher specific absorption rates
than some used in these studies. However, amateur radio operators
can take some comfort in the fact that their hand-held radios (which can
expose users to even stronger fields than most cellphones) have push-to-talk
buttons--they don't transmit full time. Many cellphones now have
multiple transmitters that do operate full time (although the average power
increases when you're making a call, exchanging data or running a built-in
wi-fi hot spot, especially if the cell site you're accessing is distant).
If your phone is close to your body (maybe in a pocket) and it's turned
on, it is exposing you to the type of EMFs that may have caused laboratory mice
to develop cancerous tumors. The Lerchl study and many others have
not included tests of non-digital waveforms. Nor have intermittent,
low-duty-cycle signals (like most amateur radio transmissions) been included
in most tests. But these studies did demonstrate that EMFs at levels
below recognized safety standards can be carcinogenic under some circumstances.
The idea that pulsed RF (which is what cellphone
signals really are) is associated with lung cancer is not new, either.
A 1994 study of electric utility workers in Quebec and France found abnormally
high rates of lung cancer. A large group of workers wore meters that
measured their exposure to pulsed RF. It found a statistically significant
link to lung cancer.(5) That study, initially supported by a power
company, raised questions that could not be answered because the company
denied later researchers access to the data.
The Lerchl study's reference to previous work that
observed "increased incidences of brain tumors in heavy users of mobile
phones" was footnoted with citations of two studies. One was a large-scale
study in 13 countries that attempted to measure cellphone usage by persons
who developed brain tumors. In addition to checking cellphone usage
records, it sent interviewers out with the delicate task of asking cancer
victims (or their families if they were incapacitated or had died) how
much they used cellphones. Despite the obvious imprecision of assessing
EMF exposure under those circumstances, the study did show that heavy users
had higher than normal rates of two types of cancer.(6)
Much previous research also found evidence
that EMF exposure is associated with elevated rates of various cancers.
Way back in the 1980s, Dr. Samuel Milham shocked amateur radio operators
when he published a journal article reporting that radio amateurs had higher
than normal rates of certain cancers.(7) Milham suggested that
this might have resulted from workplace exposure rather than amateur radio
because disproportionate numbers of amateurs work in occupations that involve
heavy exposure to EMFs. Milham and several of the others cited here
were doing epidemiological research, the type that looks at the
health patterns of groups of people to identify health hazards. That
kind of research has helped identify many carcinogens, including
lead, asbestos and tobacco. It doesn't prove causation, just correlation.
But it does identify topics for further study.
THE EMF CONTROVERSY
In 2011 a body of the World Health Organization
declared low-level cellphone-type EMFs to be a "possible" carcinogen.(8)
Some health advocates contended that the agency's next-higher classification
("probable carcinogen") would have been more appropriate. Those who
deny that low-level EMFs have any health effects were not pleased with
the "possible" designation. The entire topic of EMFs and health remains
controversial enough that meetings of researchers have been known to deteriorate
into name-calling sessions, often between independent scientists and those
who have accepted money from corporations or groups with a strong financial
interest in the outcome.
As suggested earlier, one especially troubling aspect of the EMF-versus-health
debate is the role of people who are paid or de facto spokespersons for
organizations with vast sums of money at stake. Many (but by no means
all) of the people who deny that low-level EMFs pose any health hazard
are affiliated with or bankrolled by such entities. Many researchers
accept lucrative grants, consultancies, speakers' fees or salaries from
deep-pocketed bio-effects deniers. Some of them try to discredit
research that doesn't support their organization's position by attacking
the researchers or their methodology. If they don't like the result,
it's flawed research. Probably the best example of that kind of thing--ever--was
the way the tobacco industry forestalled anti-smoking safeguards for decades
(thus causing many needless deaths) by citing questionable research calculated
to create doubts about the validity of other, more reputable research and
thereby reassure smokers who wanted to believe smoking was harmless.
Similar denials came from the beef industry
in 2015 when the same World Health Organization body that declared EMFs
to be a possible carcinogen voted to place red meat and processed meat
on its list of carcinogens. A spokesperson for the U.S. beef industry
issued a statement saying, "Cancer is a complex disease that even the best
and brightest minds don't fully understand... Billions of dollars
have been spent on studies all over the world and no single food has ever
been proven to cause or cure cancer."(9) Representatives of industries
that generate EMFs continue to issue similar denials that there are biological
effects of low-level RF radiation and power frequency EMFs, despite the
flood of peer-reviewed research showing such effects year after year.
As in the case of red meats, the carcinogenic effects of EMFs appear to
be small compared to the carcinogenic effects of cigarette smoking, but
there is strong evidence that EMFs do have carcinogenic effects
at certain low signal strengths and with certain waveforms, especially
some digital waveforms. Nevertheless, the controversy continues,
with research supported by affected industries often contradicting resarch
by independent researchers, leading to accusations of bias in the research.
A relevant example of possible bias in the
EMF debate could be the often-cited Danish Cohort Studies.(10) Denmark
was one of the pioneers in introducing cellphones. The government
had a record of both early cellphone users and cancer diagnoses.
The cohort study reviewed the health records of 420,000 early cellphone
users (from 1987 to 1995) and concluded that they did not have a higher
rate of cancer than a control group of non-users. That would be persuasive
except for a few problems. First, it turned out that 200,000 early
business users of cellphones (probably the heaviest users at a time when
cellphone service had hefty usage charges) were not counted among cellphone
users but were instead placed in the control group of non-users because
the researchers couldn't obtain their names. Also, cellphone use
increased rapidly in 1996 and thereafter, but the many new users were in
the control group and not counted among cellphone users. And early
cellphone users who later ended their cellphone service were still counted
as cellphone users. On top of that, Danish authorities later reported
that brain cancer rates among Danish males had actually increased 41 percent
between about 2000 and 2010. If you allow for a time lag between
cellphone use and a tumor being diagnosed, that tracks cellphone usage
To those who believe cellphone EMFs pose no
health hazard, the Danish Cohort Studies are persuasive evidence:
the 420,000 identified early cellphone users didn't have an abnormally
high brain cancer rate. To those who believe cellphone EMFs do pose
health hazards, the same research is Exhibit A for untrustworthy research
yielding questionable results.
At the end of this article there's a link to a portion
of chapter 36 of the 1992 ARRL Handbook devoted to RF safety.
(ARRL is the national association for amateur radio in the U.S.)
It had extensive documentation, including many footnotes to research
that showed biological effects of low-level EMFs even back then.
However, in recent editions of the Handbook the RF safety section
has been rewritten to give the discussion a very different spin, eliminating
virtually all of the research summarized in the 1992 edition. The
current section has no references to research showing athermal health hazards
and seems to rule out the possibility of any such research being valid.
Laboratory animal studies are dismissed as, in essence, not applicable
to humans and epidemiological research like Dr. Milham's study of cancer
rates among radio amateurs is dismissed as preliminary and not really proving
anything. Milham found a statistically significant excess of some
cancers among hams, but recent Handbooks
dismiss that by pointing
out that cigarette smoking is linked to even higher cancer rates. The
only way a reader of the current Handbook might learn of the research
on the hazards of athermal EMF exposure would be by looking up a 1989 QST
article that the RF safety section does cite. That article by Ivan
Shulman, MD, WC2S, had extensive documentation and offered an excellent
discussion of athermal EMF hazards. (See below for links to Dr. Shulman's
article, the chapter 36 excerpt from the 1992 Handbook and other
RF safety articles.)
I first worked on the EMF safety issue
as an employee of an association with an undeniable vested interest.
I served on the legal staff of the National Association of Broadcasters
in the early 1980s. The FCC was then considering Docket 79-144, which
proposed to adopt a new RF safety standard and require broadcasters to
meet it. From the broadcast industry's viewpoint, that had pros and
cons. On one hand, complying with federal standards might be costly
for some broadcasters. Some questioned whether there was enough scientific
evidence to justify having FCC-mandated standards at that point.
But on the other hand, the potential for much stricter local standards
(standards that were not necessarily scientifically-based) prompted broadcasters
to conclude that having uniform national standards was best. Clearly,
the issue could not be ignored. By the early 1980s several localities
had adopted what appeared to be unrealistic RF exposure standards.
The broadcast industry, to its credit, did not send out p.r. persons to
obfuscate the issue like the tobacco industry did
When Docket 79-144 was adopted, amateur radio operators were given a categorical
exemption from the routine evaluations of RF exposure around their stations
that were required of most other licensees. Amateurs were not exempt
from complying with the standards; they were merely exempt from finding
out if they complied with the standards. In 1990 the FCC and
the Environmental Protection Agency conducted measurements of the RF fields
at a number of amateur radio stations in Southern California. The photo
at left shows the EPA's Ed Mantiply (left) and the FCC's Dr. Robert Cleveland
conducting measurements on the deck of an amateur's home near Los Angeles.
They were measuring EMFs from a Yagi HF antenna on a tower about 70 feet
above the deck. I accompanied the FCC/EPA field researchers and helped
to line up volunteers willing to have the RF fields at their stations evaluated.
The researchers measured a variety of antennas, including hidden antennas
in trees and attics as well as antennas on high and low towers, verticals,
mobile antennas and rover installations.
The FCC/EPA team's conclusion was that
most amateur radio stations produced only very weak RF fields in inhabited
areas, although they did note higher power densities near certain installations,
especially a vehicle-mounted rover-type station that was using relatively
high power. They also measured fields exceeding the soon-to-be-adopted
FCC standard near a 100-watt mobile installation on two meters.(11)
By the early 1990s, there was still
more research pointing to possible health effects of RF energy at athermal
levels. Professional bodies were adopting stricter standards for
RF exposure, and in 1992 the American National Standards Institute (ANSI)
revised its own guidelines to recommend much greater protection from RF
exposure for the general public (although that standard was still intended
only to protect from body heating, not athermal effects). The FCC
responded with Docket 93-62, proposing to adopt most of the revised ANSI
standard for its licensees.
When the new rules were adopted in 1996, amateurs
were no longer categorically exempt from doing routine evaluations of the
RF fields around their stations unless they were running low power (defined
as less than 500 watts PEP on 160, 80, and 40 meters, with a sliding scale
down to 50 watts on 30-300 MHz and back up to 250 watts PEP on 13
cm. and higher bands).(12)
Docket 93-62 allowed amateurs to assess the RF power density on their own
property under the ANSI "controlled environments" standard, intended for
occupational and workplace exposure. It required use of the stricter
"uncontrolled environments" standard (intended for places accessible to
the public) for evaluating RF field exposure beyond an amateur's own property.
The graph at right shows the maximum permissible exposure in mw/cm2
by frequency. Exposures can be averaged over a six-minute period
in controlled environments and over 30 minutes in uncontrolled environments,
thereby rewarding those who make short transmissions and listen most of
the time. Averaging is also allowed for non-key-down modes such as
SSB. Even with speech compression, the duty cycle for SSB is assumed
to be no more than 50 percent of peak power.
The required evaluation can be done with a
simple computer program or even by consulting a chart such as the one prepared
by the FCC (see below). It turned out that virtually all amateur
stations could comply with the RF safety standards without major changes
in their antennas or station configurations. The rules also required
educational efforts such as including questions about RF safety on amateur
radio exams for the first time.
In addition to participating in the 1990 FCC/EPA field survey, I was involved
in this process in several other ways. ARRL had a Committee on the
Biological Effects of RF energy. I served on it from 1989 until 1994,
alongside several medical researchers, including Dr. W. Ross Adey (K6UI),
who had authored or co-authored several hundred journal articles and papers
on EMFs and related topics, including many that noted biological effects
of low-level exposures. In the aftermath of the Milham study, which
found elevated levels of certain cancers among radio amateurs, our committee
was able to get two articles on RF safety into QST and an entire
section into the ARRL Handbook for a few editions. But what
we did was controversial. In 1994 all members of this committee were
either asked to resign or resigned voluntarily in protest. A new
Committee on RF Safety was established to replace the Bio-Effects Committee.
I continued to speak and work on RF safety
issues after 1994. I filed comments at the FCC in favor of the RF
safety rules that the commission eventually adopted in Docket 93-62.
(ARRL opposed those rules but cooperated in their implementation after
they were enacted.)
The FCC again considered the difficult questions
of EMFs and health in the 2000s. In Docket 13-84, the commission
in 2013 adopted some rule revisions, proposed others and announced a new
of Inquiry, asking whether the existing exposure standards should be
revised in light of new research. The FCC had always taken the position
that it is not a public health agency and should therefore defer to other
federal agencies as well as outside groups that have established RF safety
standards. By then standard-setting bodies worldwide were reconsidering
their exposure standards. While generally supporting the adequacy
of its existing standards, the FCC solicited public input on the advisability
of making them more or less strict.
In view of the growing use of mobile phones,
the FCC made some changes in the way they are evaluated for safety in its
2013 proceeding. In one controversial move, the FCC announced that
it would judge the specific absorption rate (SAR) of RF energy from
cellphones at the ear under a more relaxed standard. Like many countries,
the U.S. has a stricter standard for cellphone exposure to the human head
and body than for "extremities" like hands and feet. The FCC decided
that in the future the ear lobe (the "ear pinna") would be evaluated as
an "extremity," not under the tougher standard for the head. That
triggered an appeal by some health advocates. The change was strongly
supported by groups such as CTIA - The Wireless Association, the entity
that represents the cellphone industry in Washington.
The FCC also acted to base more evaluations
of RF safety on SARs, which take into account the effect on specific parts
of the body, instead of the maximum permissible exposure (MPE) system,
which considers the effect of RF energy on the entire body. The MPE
system uses power density calculations based only on whole-body heating.
Some low power transmitters had escaped evaluations because they were not
capable of whole-body heating.
The FCC announced its final results of the
2013 proceeding in a 159-page report and order in 2019. In that
document, the FCC declined to change the RF safety standards affecting
amateur radio. But the FCC also acted to require more amateurs to
conduct routine evaluations of the RF fields near their stations.
The old power-based exemption was replaced by a mathematical formula to
determine if a given station was exempt from doing a routine
evaluation, considering the frequency, power output and the distance
from the antenna to any populated area. The FCC also deleted the
former exemption for mobile and portable (hand-held) stations. In
the end, most hams were in a situation where
doing a routine evaluation was less trouble than doing the calculations
to prove they were exempt from doing an evaluation. To
perhaps oversimplify a little, the new rules went into effect in May of
2021, with all amateurs required to comply by 2023.
CALCULATIONS FOR HIGH GAIN ANTENNAS
As noted earlier, the FCC and EPA researchers
conducted a field survey of RF fields at amateur radio stations in 1990
and found that most amateur installations did not produce fields exceeding
the ANSI standard. However, they measured fields exceeding the standard
30 to 40 feet in front of a 5-element Yagi on a rover van with a 500-watt
amplifier and also near a two meter mobile with 100 watts and a quarter-wave
whip antenna, among others. In general, the only amateur installations
that appeared to produce fields exceeding the standard were those with
relatively high average effective radiated power and antennas close to
places where people might be present.
More recently, other types of installations that were not available to
be measured by the FCC/EPA team in 1990 have come into widespread use.
One is a special case: very high-gain dish antennas used by amateurs,
often in groups all operating side by side on one hilltop, on 10 GHz and
higher bands. The photo at left shows a group of amateur radio microwave
enthusiasts with six dish antennas on a hilltop near Los Angeles.
What they are doing has become very popular during the ARRL 10 GHz and
Up Contest. Such groups gather at the best available radio locations,
often sites that also have other amateur or non-amateur transmitters on
the air simultaneously. The FCC's rules for evaluating RF exposures
at sites with two or more co-located transmitters require calculating (or
measuring) the total exposure from all transmitters that may be running
at the same time. However, it may be difficult for visiting hams
to comply with that requirement. They may not have a suitable 10
GHz power density meter and also may not know about all of the other transmitters
that may be operating at a mountaintop communications site.
RF fields at such sites fall under the standard
for controlled environments only if the site is inaccessible to members
of the public. If there is no gate or if the gate is left open, the
site should be evaluated under the more stringent standard for uncontrolled
environments. A site like Frazier Mountain (near Frazier Park, California)
would be a classic example of an uncontrolled environment when the U.S.
Forest Service gate is open, as it usually is during the summer and early
fall. That site is particularly attractive to VHF-oriented hams,
but it also attracts other visitors, especially on summer weekends.
It's not unusual for amateurs to use very
high effective radiated power to maximize the distances they can communicate
during microwave contests. For example, many stations employ 10 to
20 watts of 10 GHz transmitter power and 2-foot to 3-foot diameter dish
antennas. A typical 2-foot dish antenna may have 30 dBd (32.2 dBi)
gain at 10 GHz. With 20 watts of transmitter power, that would produce
about 35,000 watts EIRP. One amateur recently announced that during
an upcoming contest he would be running 40 watts to a 4-foot dish mounted
on a tripod. Assuming the dish is reasonably efficient, it could
deliver 40 dBi gain and turn 40 watts into 400,000 watts of EIRP--at eye
level for nearby people.
Under the formulas in FCC Bulletin 65 (linked
below--see page 29), such an installation would need to be 270 feet
from any member of the general public in its main beam to satisfy the uncontrolled
environment standard and 120 feet from others who are aware of the exposure
(the controlled environment standard) if using the EPA-recommended ground
reflection factor. The required separation distance could be reduced
by making very short transmissions and using SSB instead of a key-down
mode (to reduce the average EIRP).
This all assumes that the dish is highly directional and has well-suppressed
sidelobes--and that there are no reflective objects in the near field to
cause dangerous hot spots. The plot at right shows the pattern of
a typical high-gain dish antenna. The very narrow main beam is about
20 dB. stronger than any of the numerous sidelobes. However, the
sidelobes contain enough energy to be hazardous at substantial distances,
especially if the dish is tripod-mounted instead of being high on a tower.
Bulletin 65 uses the same formula to estimate
far field main beam exposures for dish antennas as for other antennas (see
Bulletin 65, pages 19 and 29, and Bulletin 65, Supplement B, page 17).
For both, the FCC suggests using this formula: Far field exposure
at a given distance in mw/cm2 = EIRP (in mw) / 4 x 3.14159
x distance2 (in cm). The same units of measurement must
be used for all parts of the equation: be careful not to mix watts
and kilowatts or centimeters and meters.
To estimate where the far field begins for a dish
antenna, the FCC suggests this formula: Distance to far field = 0.6
x diameter2 / wavelength (again, use the same units of measurement
for everything including the distance, dish diameter and wavelength).
In the example just given of the 4-foot dish, the far field would begin
approximately 99.6 feet from the dish at 10 GHz.
Even with a much smaller dish, the required
separation from members of the public is substantial. Another page
on this website describes my 2015 microwave expedition to Hawaii.
I used a 48 cm. (about 19 inch) dish for 5.7 and 10 GHz, with 18 watts
of transmitter power on 10 GHz. The dish and feed manufacturer rates
the unit at 29.2 dBi gain on 10 GHz. That works out to more than
15,000 watts EIRP and a required separation from the general public of
57.3 feet. The far field for that antenna begins at 15.7 feet on
10 GHz. Even a dish antenna as small as that should be used with
caution if other people are nearby.
Because of the very high gain of microwave dish
antennas, portable operating on a band like 10 GHz has more potential for
creating high RF exposures than most other amateur radio activities.
One other activity with a similar potential is earth-moon-earth communications
when the antenna is pointed at the horizon for work at moonrise or moonset.
Even a modest four-bay two-meter EME array may deliver 20 or even 23 DBi
gain, and it's not unusual for hams to use the maximum legal power (1500
watts) with such an installation to overcome the high path loss to the
moon and back. That works out to as much as 300,000 watts of EIRP,
and it's at the frequency where the FCC standard is most strict.
Such an installation could expose members of the public to RF fields exceeding
the standard at a worst-case distance of up to 572.8 feet and even exceed
the "controlled environment" standard up to 256.2 feet from the antenna.
Fortunately, EME stations rarely transmit key-down for even half of the
time (because of the typical 48-seconds-on, 72-seconds-off sequencing of
digital modes), thus greatly reducing the average power. They also tend
not to point their antennas at the horizon often, but when they do, the
hazard zone can encompass a city block.
A third amateur activity that sometimes has the potential to create high
public exposures to RF fields is ordinary HF operating with high power
and a low antenna, especially a directional one. The photo at left
shows the field strength on a public sidewalk from a 500-watt transmitter
on 10 meters feeding a popular triband Yagi 25 feet above the ground on
a tower behind the amateur's house. The tower is about 60 feet from
the sidewalk. The measured RF field is almost 1.0 mw/cm2,
nearly five times the standard for public exposure at that frequency, which
is .22 mw/cm2. This photo was taken in 1990, shortly before
the FCC/EPA research team visited this site. Ground reflections probably
contributed to the high meter reading. When the tower was raised
to its full height (70 feet), the measured RF field was well below the
When using a computer program or the FCC's
tables to do a routine RF safety evaluation, it's okay to use power averaging
to reduce the required separation distances. In fact, the FCC's Bulletin
65 Supplement B encourages the use of average power, not maximum power.
However, crunching the numbers in a way that
shows compliance with the FCC's standards will give a false sense of security
to anyone who forgets that the standard itself is believed to be far too
lenient by many EMF scientists. Remember that the FCC-mandated RF
safety calculations are only intended to protect from body heating--not
from the hazards of athermal EMFs that have now been documented.
Long ago EMF scientists began talking about "prudent avoidance"--minimizing
human exposure to EMFs whenever it's feasible to do so.
LINKS TO PREVIOUS ARTICLES
This web page has several links. One
is a follow-up article on the effect of the FCC's
1996 rules (Docket 93-62) that I wrote in 1998 for the Proceedings
of the Central States VHF Conference. Another is a BASIC
computer program that I published in CQ VHF
magazine in January,
1997. This public domain BASIC program was reviewed for accuracy
by the staff of the Office of Engineering and Technology at the FCC; it
can be used with confidence to do routine evaluations.
if you download it, save it as an ASCII text file (not as an HTML
With some browsers it is necessary not only to select "plain text" as
type of file but also to have ".txt" in the name to get a clean
Once it's on your hard drive, rename it as "RFSAFETY.BAS" so it will
under most versions of BASIC that are available for free on the
internet. There's now also a compiled version called
"RFSAFETY.EXE" that may be downloaded and run directly on most Windows
Both the FCC and the ARRL have material
available online concerning RF safety issues. The FCC's site includes
the official and very comprehensive OET Bulletin 65, Supplement B (see
note 11, below). It specifically addresses amateur radio RF safety
compliance issues with charts and tables that may be used in routine evaluations.
The ARRL has RF safety information in several publications and on its website.
A good introduction might be the RF safety section
of Chapter 36 of the 1992 ARRL Handbook, which was prepared
by the ARRL Bio-Effects Committee serving at that time. In addition,
Dr. Ivan Shulman (WC2S), the Bio-Effects Committee chairman, published
summarizing previous research about the hazards of low-level EMFs and offering
many suggestions for RF safety. Five years later, I published a QST
article summarizing some later research and offering practical examples
of safe and unsafe operation of an amateur radio station.
-Wayne Overbeck, Ph.D., J.D., N6NB
1. For information about the Bioelectromagnetics Society, go to
2. BioInitiative Working Group, Cindy Sage and David 0. Carpenter,
Editors. BioInitiative Report: A Rationale for a Biologically-based
Public Exposure Standard for Electromagnetic Radiation at www.bioinitiative.org,
December 31, 2012.
3. A. Lerchl et al., Tumor promotion by exposure to radiofrequency
electromagnetic fields below exposure limits for humans. Biochemical
and Biophysical Research Communications(2015), http://dx.dol.org/10.1016/j.bbrc.2015.02.151
4. T. Tillmann, H. Ernst, J. Streckert, et al., Indication of
cocarcinogenic potential of chronic UMTS-modulated radiofrequency exposure
in an ethylnitrosourea mouse model, Int. J. Radiat. Biol. 86(2010) 529-541.
5. B. Armstrong et al., Association between exposure to pulsed
electromagnetic fields and cancer in electric utility workers in Quebec,
Canada and France, Am. J. Epidemiol. (1994) 140(9): 805-820.
6. Interphone Study Group, Brain tumour risk in relation to mobile
telephone use: Results of the INTERPHONE International case-control
study, Int. J. Epidemiol. 39(2010) 675-694
7. S. Milham, Increased mortality in amateur radio operators due
to lymphatic and hematopoetic malignancies, Am. J. Epidemiol. (1988) 127(1):50-54.
8. International Agency for Research on Cancer (IARC) of the World
9. Quoted by Reuters on Oct. 23, 2015 in an article appearing
in the New York Times online edition.
10. P. Frei et al., Use of mobile phones and risk of brain tumours:
Update of Danish Cohort Study, BMJ 2011;343:d6387
11. Federal Communications Commission (FCC), "Measurements of
Environmental Electromagnetic Fields at Amateur Radio Stations," FCC Report
No. FCC/OET ASD-9601, February 1996. FCC, Office of Engineering and Technology
(OET), Washington, D.C. 20554. (To view this report, Google
12. For the FCC's guidelines for evaluating RF exposure, see FCC
Office of Engineering Technology Bulletin 65 for general applications
and Bulletin 65 Supplement B for evaluations specific to amateur
radio. To view them, Google "OET65.PDF" or "OET65B.PDF". While
the FCC is upgrading its website, the existing links to FCC documents are
subject to change.
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