RF Safety and Amateur Radio
(Most recent revision of this document:  Jan. 22, 2022)




     Could amateur radio be hazardous to your health?  What about cellphones and other wireless devices?  Those became controversial questions in the late 20th and early 21st centuries. The media sometimes publish news of research about the health effects of RF fields and about the key underlying question:  does exposure to radio, television and wireless signals lead to any kind of 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 radio equipment and cellphones.  Most amateur radio operators are required to determine if their transmissions comply with those standards, as are cellphone providers, among many others.  But questions are being raised about the standards.  Are they adequate to protect public health?  The FCC and other regulatory bodies all over the world have been considering whether additional regulations were needed to protect the public from harmful effects of EMFs. 
     By 2021 more than 250 EMF scientists from 44 countries signed an appeal to the United Nations, the World Health Organization and U.N. member states calling for much stricter standards for EMF exposure in light of the growing evidence of health hazards posed by even low-level EMFs. 

    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 journals worldwide.
     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 to 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 compared 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 miles apart

     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."
     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 the 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 Handbook.
     Another factor in these studies is that they exposed animals for a lifetime (from in the uterus before birth until the end of their normal life expectancy).  Cellphones are too new to permit any kind of study that tracks humans' cellphone EMF exposure versus health 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 pretty well.
     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 QST article, the chapter 36 excerpt from the 1992 Handbook and other RF safety articles.)
 

REGULATING EXPOSURES

      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.)
 

DOCKET 13-84

     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 Notice 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 FCC standard.
     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.  Suggestion:  if you download it, save it as an ASCII text file (not as an HTML file).  With some browsers it is necessary not only to select "plain text" as the type of file but also to have ".txt" in the name to get a clean copy.  Once it's on your hard drive, rename it as "RFSAFETY.BAS" so it will run 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 computers.
      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 a definitive 1989 QST article 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 

Endnotes:

1.  For information about the Bioelectromagnetics Society, go to www.bems.org.

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 Health Organization.

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 "ASD-9601".)

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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