(This article appeared in the 1998 Proceedings of the Central States VHF Conference and was presented at the conference in Kansas City, Mo. in July, 1998.) 
A Retrospective View
By Wayne Overbeck, N6NB

Barely a week after I discussed the proposed RF safety rules at the 1996 Central States VHF Conference, the Federal Communications Commission adopted these long-awaited and controversial rules. Now, two years later, we need to take another look at the new rules themselves, and at the health concerns and public fears that these rules were intended to address. Where do we stand on these troublesome issues today? 

In general, the rules themselves have created far fewer problems for radio amateurs than some initially predicted--if they have caused any problems at all. And the new rules have given amateurs new leverage in dealing with neighbors and local public officials. But at the same time, research on RF safety issues has continued, leading to some troubling new (and well publicized) findings. These findings, in turn, have helped to galvanize citizen activist groups in the United States and several other countries, leading to new potential problems for all who generate RF energy, including radio amateurs. Citizen activists are now suing the FCC in federal court, alleging that the FCC's 1996 rules are grossly inadequate to protect public health. They want the FCC to adopt far more stringent RF exposure standards. Some of the demands now being made by these citizen activists, if granted, could end amateur radio as we know it. 


Much has already been written about the new rules themselves, including Ed Hare's definitive technical summary in the January, 1998, issue of QST.1 The FCC itself has published a detailed 44-page document describing the rules as they relate specifically to amateur radio and providing a variety of charts and formulas to facilitate compliance.2 I also published an article describing the new rules, with a simple computer program (written in BASIC) that the FCC staff reviewed for accuracy and accepted as a satisfactory way for amateurs to evaluate the RF fields at their stations.3 

To avoid needless repetition, this summary of the rules and their history will be brief. In its Report and Order in ET Docket 93-62 and in two follow-up Memorandum Opinions, the FCC updated its previous RF safety rules, adopting new standards that had been previously recommended by scientific bodies and--significantly for amateur radio--eliminating our former categorical exemption from the requirement to do routine evaluations of our stations. 

The FCC first adopted RF safety rules in 1985 in Gen. Docket 79-144. The Commission has been under a Congressional mandate to "evaluate the effects of (its) actions on the quality of the human environment" ever since the National Environmental Policy Act of 1969 was signed into law by then-President Richard Nixon. In its 1985 rules, the FCC adopted a 1982 American National Standards Institute (ANSI) standard for RF exposure, a standard that was ten times as strict as the previous ANSI standard in the VHF spectrum (30-300 MHz). The Commission required all licensees to comply with this standard to assure that employees and members of the public would not be exposed to RF energy levels exceeding the standard. However, in the 1985 rules amateurs were exempted from actually doing anything to determine whether their stations met the standard. For many other licensees, the 1985 rules required engineering studies and in some cases field measurements to assure compliance. 

By 1991, there had been considerable new research that raised questions about the effects of RF energy on human health. As a result, a standard-setting committee of the Institute of Electrical and Electronic Engineers (IEEE) adopted a new two-level standard that made a distinction between occupational and public exposure to RF energy. The IEEE standard was adopted the next year by ANSI as its new standard on RF exposure, C95.1-1992. At the frequencies of most concern to amateur VHF-UHF enthusiasts, the new standard for "controlled environments" (such as workplaces) was left essentially unchanged from the 1982 ANSI standard. However, a new standard that is five times stricter than the 1982 standard (and therefore, 50 times stricter than the pre-1982 standard) was adopted for "uncontrolled environments" where the general public may be exposed to RF energy. 

In 1993, the FCC responded to these developments by proposing to rewrite its RF safety rules in Docket 93-62. When it ultimately acted on this proposal in 1996, the FCC adopted most of the 1992 ANSI standard, while incorporating some provisions of another standard recommended by the National Council for Radiation Protection and Measurement. From an amateur radio perspective, here are the highlights of the new rules: 

*Five test questions concerning RF safety have been added to each of three amateur radio licensing examination elements: elements 2, 3A and 3B. 

*Like other licensees, amateurs must meet maximum permissible exposure (MPE) limits based on the 1992 ANSI standard. An amateur's own property is treated as a controlled environment; neighbors' properties and public places are treated as uncontrolled environments (i.e., amateurs must meet this stricter standard beyond their own property line). 

*Amateurs are no longer categorically exempted from doing routine evaluations of the RF fields at their stations. However, mobile stations using push-to-talk transmitters still need not do evaluations. Fixed stations must do routine evaluations only if the PEP power input to their antennas exceeds the following levels: 

160, 80 and 40 meters             500 watts PEP 

30 meters                             425 watts PEP 

20 meters                             225 watts PEP 

17 meters                             125 watts PEP 

15 meters                             100 watts PEP 

12 meters                             75 watts PEP 

10, 6, 2 and 1 1/4 meters        50 watts PEP 

70 centimeters                     70 watts PEP 

23 centimeters                     200 watts PEP 

*For amateurs who must do a routine evaluation, the procedure involves nothing more than using a chart or a computer program to assure that the permitted MPE limits are not exceeded. To do this, amateurs must determine that the average power density of their signal, averaged over six minutes on their own properties and over 30 minutes beyond their property line, does not exceed the limit as determined by a chart or computer program (which takes into account the frequency, average power, antenna gain, the presence or absence of ground reflections and the distance to places accessible to humans). 

*Although this is not spelled out in the rules, it has been widely suggested that amateurs make a record of what they have done to perform a routine evaluation--and keep it on file in case anyone should ever inquire. 


In the two years since the FCC announced the new rules, it has become clear that most amateurs can comply without making major modifications of their station and antenna configurations. Table I, accompanying this article, shows the required separation distances from several typical VHF antennas at various power levels, assuming a worst-case scenario in which the main lobe of the antenna illuminates a populated area subject to ground reflections. (The table also includes the separation distances that would be required under a hypothetical safety standard advocated by some citizen activists; this is discussed later). 

The table is based on calculations using the FCC-recommended far-field formula; the FCC has concluded that these numbers represent an acceptable estimate for near-field exposures as well. If the precise pattern of an antenna is known, the actual gain in the relevant direction may be used in lieu of the antenna's maximum forward gain in making calculations of the power density at a given distance from the antenna. 

A full discussion of the evaluation process is beyond the scope of this paper; it is covered in depth both in Hare's QST article and the FCC's Supplement B, previously cited. However, as a practical matter, it should be noted here that the power averaging provisions make it relatively easy for most amateurs to show that their stations do not exceed the MPE limits even if their antennas are not as far from their property lines as Table I might seem to require. In conversational SSB communications, for instance, the FCC permits the use of 20 percent of PEP as the average power during transmission periods. If the station is only transmitting half of any six-minute (or 30-minute) period, a further 50 percent reduction in the average power is permitted. Under these procedures, a station running 1500 watts PEP output, for example, may have an average power of 200 watts or less. 

Given all of these considerations, the FCC staff has not been inclined to devote significant resources to oversight of amateur compliance. In fact, William Cross, the FCC Wireless Telecommunications Bureau official most intimately involved with amateur radio matters, recently indicated that he did not know of any amateur who had relocated an antenna or made other major changes in station parameters because of Docket 93-62.4 

Shortly after the new rules were announced, many amateurs expressed the fear that the existence of these rules would cause neighbors and local public officials to initiate numerous lawsuits against amateurs, alleging that their operations are hazardous. In reality, that does not appear to be happening. But on the other hand, the FCC standards give amateurs new leverage in dealing with recalcitrant local officials. 

One of the reasons many other FCC licensees supported the FCC's original proposal to establish RF safety standards--and the reason why some amateurs (including this author) supported Docket 93-62--was because local communities have sometimes adopted arbitrary and unreasonable rules restricting RF fields near FCC-licensed facilities. When I worked on this issue as a member of the legal staff at the National Association of Broadcasters during the early 1980s, for example, many in the broadcast industry saw Docket 79-144 as a way to prevent the proliferation of unreasonable local rules. Several states, cities and counties had already adopted rules that seemingly had no scientific basis whatever--but that could make it difficult or impossible for broadcasters to remain on the air in those jurisdictions. Having uniform, scientifically based federal standards was seen as a far better alternative. 

For amateurs, these problems may be even worse than they are for broadcasters: few amateurs can afford the engineering and legal support needed to ward off overzealous local regulators. To illustrate what amateurs can face, here is the relevant provision of the municipal code of one California city: 

Sec. 9141.1. Radioactivity or Electrical Disturbance

Devices which radiate radio-frequency energy shall be so operated as not to cause interference with any activity carried on beyond the boundary line of the property upon which the device is located. 

Further, no radiation of any kind shall be emitted into the atmosphere, the ground, or sewerage systems in quantities which is dangerous to humans.5 

Local regulations such as these, which flatly ban interference and harmful "radiation" but provide no standard whatever to guide local officials, can put an amateur in an impossible predicament: there may be no way to prove that an amateur's station complies with such vague rules. While the FCC has not yet expressly preempted local rules that regulate amateur radio stations for RF safety, the fact that there is a federal RF safety standard with which most amateurs can comply can only give amateurs added leverage in dealing with local officials. (The regulation of RF interference, on the other hand, has long been federally preempted, although that does not stop local officials from attempting to legislate in that area--until a court tells them not to). 

It remains to be seen how Docket 93-62 will affect amateur radio in the longer term. At this point, it is clear that it has not created serious difficulties for most amateurs. And it seems likely that being able to show compliance with a federal standard for RF safety will help rather than hinder amateurs who may face challenges from neighbors or local officials. And the FCC's goal in Docket 93-62 of fostering greater amateur awareness of good RF safety practices can only benefit amateurs and their communities. 


This author's papers in both the 1993 and 1996 Proceedings of the Central States VHF Conference6,7 dealt at length with research that had been done on questions of electromagnetic fields (EMFs) and health. Since 1996, the pace of research on EMFs has increased substantially--but the health questions remain controversial and unresolved. 

Recently several prominent research entities have completed major studies of the possible health hazards of low-frequency EMFs--leading some of the news media to proclaim those questions settled. Some scientists, on the other hand, have vociferously objected to that conclusion. And the more relevant question for radio amateurs--about the safety of EMFs at radio frequencies--are becoming more controversial as a result of some troubling and widely publicized new research. 

Some of the news media said "case closed" in late 1996, when a prestigious 16-member committee the National Research Council, an affiliate of the National Academy of Sciences, announced the results of a major study of low-frequency EMFs in residential areas, a study that was commissioned by Congress. In a 384-page hard-cover book, the NRC committee summarized its analysis of about 500 previous studies of the health effects of low-frequency EMFs that had been conducted over 17 years.8 

The NRC committee concluded that exposure to residential EMFs does not cause cancer or otherwise threaten human health. Although children living close to the highest voltage power lines do have about a 50 percent higher than normal risk of developing childhood leukemia, the NRC study concluded that EMFs had not been shown to be the cause. Nor did the study find any conclusive evidence that low-frequency EMFs cause reproductive or developmental abnormalities. Among other things, the NRC committee noted that elevated childhood leukemia rates and certain developmental abnormalities are statistically associated with other factors including air quality and even family income. Older, less expensive homes tend to be near high-tension lines--and these neighborhoods often have relatively poor air quality as well. 

The NRC study was widely assailed by some activists on EMF and health issues. Paul Brodeur, the author of two controversial books on EMFs and health (including Currents of Death), was quoted in the media as saying the study used "distortions and omissions" in an attempt to reassure the public. 

More specific objections were raised by Dr. Samuel Milham, a scientist who became widely known among radio amateurs after he conducted a study that found radio amateurs to have an abnormally high mortality rate from certain kinds of cancer.9 (As noted in the author's 1993 and 1996 papers in the Central States Proceedings, Dr. Milham's "silent keys" study, published 10 years ago, did not attempt to prove that there was a causal link between amateur radio and cancer. He said his findings could well be attributable to occupational exposure to EMFs rather than to amateur radio.) 

When the Seattle Times proclaimed the question of EMFs and health resolved as a result of the NRC study, Dr. Milham responded with a letter to the editor that said: 

I take strong objection to your editorial of Nov. 7 on electric and magnetic fields... (I)f you had read the National Research Council report, you would have discovered that the committee chose, or more likely, was instructed to ignore the entire body of occupational EMF research in coming to its conclusions. They ignored over half of the human EMF research, and the only research which had the benefit of good EMF measurement. In the residential studies which they reviewed, almost no individual EMF monitoring was done. I have reviewed all the EMF studies, especially the human epidemiologic studies, both residential and occupational, and come to the conclusion that EMF poses a real health hazard. I did not always hold this view. 

Most of the research in this field, including mine, is published in peer-reviewed scientific literature. If it is "junk science," then all science is in doubt. Congratulations on your recent induction into the Flat Earth Society. 

-Samuel Milham, M.D., M.P.H.10 

Before the debate over the NRC study subsided, the National Cancer Institute weighed in with new research on childhood leukemia and high-tension lines--research that was published in the prestigious New England Journal of Medicine.11 After an eight-year, $5 million project, the National Cancer Institute reported that children living near high-tension lines had no greater risk of developing cancer than other youths. NCI identified 600 children under age 15 who had acute lymphoblastic leukemia and compared them to a matched control group of 600 other children who were healthy. NCI researchers went to the present and former homes of the children in both groups and measured EMFs. They found no significant difference in EMF levels in the homes of the two groups of children after the largest study of this type ever conducted. 

At about the same time as the NRC and NCI studies, a large-scale epidemiological study in Finland reached a similar conclusion about residential EMFs and cancer--but among adults. This study, commissioned by a Finnish power company, identified nearly 400,000 people who had lived within 550 yards of an overhead high-tension line over a 20-year period. The researchers reported that these people had cancer rates equal to or less than those expected among the general adult population of Finland. However, unlike the NCI study, this project involved only a statistical analysis of health patterns, not field measurements inside homes. 

As a result of these recent studies of EMFs and cancer, public concern about EMFs from power lines seems to have gradually subsided. However, a potentially greater concern for radio amateurs may be the growing body of research about RF fields and health. Several troubling new studies in this area have been published in the last two years. 

Perhaps the most widely noted and credible study of RF fields and health was one done in Australia--a study funded by Australia's leading provider of cellular telephone services and conducted by scientists who had previously said they doubted that low-level RF energy posed any serious health hazard. But their study concluded that laboratory mice exposed to 900 MHz RF energy appeared to have almost double the cancer rate of mice who were not exposed.12 

The Australian study was conducted by Dr. Michael Repacholi, head of the World Health Organization's Electromagnetic Fields Project, and colleagues including Dr. Antony Basten. They exposed 100 mice to digitally pulsed cellular telephone-type signals at power densities designed to approximate those experienced by cellphone users. A separate control group of 100 mice was not exposed. Both groups had been genetically altered to increase their susceptibility to cancer in order to make indications of the disease visible to researchers more quickly. Of the RF-exposed group, 43 percent developed cancer, compared to 22 percent of the control group. 

This study received wide publicity, both because of its dramatic results and because the scientists involved were highly respected. And the fact that an industry-funded study reached this result only added to its perceived credibility. However, the scientists who conducted the study went to great lengths to emphasize that mice and humans absorb energy from RF fields very differently, and that the results obtained with genetically altered mice might not be replicated in normal mice. 

Soon after the Australian study was reported, world press attention again focused on work by Dr. Ross Adey (K6UI), long a prominent expert in this field (and a colleague of this author on the former ARRL Bio-Effects Committee). Dr. Adey presented a paper in Italy in 1997 reporting a study in which he and his staff at Loma Linda University exposed laboratory rats to cellphone-like RF energy.13 In this study, the rats exposed to RF actually had a lower cancer rate than those in an unexposed control group. However, Dr. Adey pointed out in media interviews that his new study was different in some important ways from the Australian study--and that it did in fact demonstrate certain biological effects of RF exposure. His study utilized analog cellphone signals as well as digital signals with a much lower pulse rate than that used in the Australian study (50 as opposed to 217 pulses per second). Dr. Adey has often reported that differences in waveform (e.g., the presence or absence of low-frequency modulation on an RF signal, the pulse rate or even the precise frequency of low-frequency energy) may alter the biological effect of EMFs. 

An earlier study at the University of Washington had also demonstrated biological effects of low-level RF--and provoked controversy in the cellphone industry. Drs. Henry Lai and Narendra Singh reported on a study of laboratory rats exposed to 2.45 GHz RF energy for two hours per day for 120 to 200 days, at levels approximating the 1992 ANSI standard.14 They identified DNA damage, including both single- and double-strand DNA breaks (the double-strand breaks were considered the more serious because they are often precursors to cancer). 

While many previous studies had failed to produce any hard evidence of health hazards associated with the use of cellphones (or other exposures to RF energy at similar power densities), these studies surely heightened the public concern over RF safety issues. But on the other hand, by 1998 about 50 million Americans were using cellphones regularly, three times the number who were using cellphones when a lawsuit triggered the first cellphone cancer scare in 1993. (That lawsuit was eventually dismissed, as were several others alleging cellphone-induced health problems, when the plaintiffs could not prove that any health hazards existed.) 


While all of this recent research on RF energy was being reported in professional journals and publicized in the news media, a confrontation was growing between citizen activists and the cellphone industry, among others. 

Soon after the Lai-Singh study was announced, a confidential memorandum written by a Motorola executive was leaked to the press, and it caused a serious public relations setback for the industry. In the memo, the executive said, "I think we have sufficiently war-gamed the Lai-Singh issue..." (emphasis added). To journalists and citizen activists, that was smoking-gun proof that the cellphone industry was trying to cover up health hazards caused by their product. When a research council funded by the cellphone industry then tried to review and critique the methodology used by Drs. Lai and Singh, both activists and some journalists cried foul--and some activists redoubled their efforts to impose stricter RF safety standards on the cellphone industry (and everybody else who transmits radio signals). 

Dozens of grassroots organizations have sprung up across the United States and in other countries to battle for drastically stricter RF exposure standards--and to oppose cellphone companies' and others' applications for towers. Citizen groups have been known to oppose cellular towers even in the face of proof that the RF exposure will be a thousand times lower than the current ANSI standard. Hard scientific evidence is not necessarily persuasive to angry citizens. 

One activist group is currently suing the FCC in federal appellate court, charging that the FCC failed to heed what the group considers relevant scientific evidence and therefore adopted a grossly inadequate RF safety standard.15 This group, the Ad Hoc Association of Parties Concerned About the Federal Communications Commission Radiofrequency Health and Safety Rules, is not just challenging the FCC in court. It has also conducted community gatherings and organized opposition to cellphone, broadcast and other tower applications. Fig. 1 is a flyer circulated by the Ad Hoc Association to publicize presentations by Dr. Neil Cherry, a local public official, university researcher and activist in New Zealand. The Ad Hoc Association flew Dr. Cherry to San Francisco to help organize opposition to tower applications in the United States. 

A computer search of the New Zealand media revealed a litany of stories about Dr. Cherry's activism there. A Canterbury Regional Councillor and candidate for mayor of Christchurch, Dr. Cherry has been quoted in the media on everything from the effect of weather on people's moods to the hazards of very low level RF energy. In one case he vocally opposed a cellular tower about 300 feet from a school. Dismayed New Zealand Telecom authorities tried to explain that the RF fields from this installation would be about 100 times lower than the applicable safety standard at the schoolyard boundary, but to little avail. Dr. Cherry also campaigned against RF fields in Australia, prompting an Australian senator to attack him as a "charlatan" and "snake-oil merchant" who engaged in "scaremongering campaigns." These charges were reported in both Australian and New Zealand newspapers. 

The Ad Hoc Association's founder, David Fichtenberg, has said, "Our goal is to give local government back its planning and zoning rights on wireless telecommunications facility sitings and RF exposure limits. The federal government should be required to reexamine available studies of RF and effects on biological systems..."16 In pursuing this agenda, the Ad Hoc Association has formed alliances with a number of other citizen activist groups in the United States and abroad. 

The Ad Hoc Association appears to favor an RF exposure standard of 2 microwatts per square centimeter--100 times more stringent than even the uncontrolled environment standard adopted by the FCC for the VHF spectrum.17 The right-hand column in Table I shows calculations of the separation distances that would be required under a 2 microwatt standard instead of the standard adopted by the FCC. Under these separation distances, most radio amateurs could not hope to remain on the air: this would effectively end amateur radio as we know it. Such a stringent standard would also eliminate everything from law enforcement communications to broadcasting as we know it. 

After hundreds of studies and the expenditure of millions of dollars, documented evidence of actual health hazards to humans from RF energy at levels below the 1992 ANSI standard remains elusive. The research to date has been inconclusive; even scientists who have reported biological effects from low-level energy have usually been quick to point out the limitations of their research. If the claims of some citizen activist groups were accurate, the epidemiological evidence of a link between EMFs and cancer would be overwhelming, not inconsistent and tentative. 

There is much that we do not know about EMFs and health; more research is clearly in order. So is taking common-sense precautions to minimize exposure to RF energy in the name of prudent avoidance. But if community activists should succeed in persuading governments (or the courts) to mandate an unrealistic RF exposure standard without a broad scientific consensus that it is necessary, much that is central to modern life could be taken away from us in response to irrational fears, not scientific evidence. 


1. Hare, Ed, "FCC RF-Exposure Regulations--the Station Evaluation," QST, January, 

1998, page 50. 

2. Federal Communications Commission Office of Engineering & Technology, Evaluating 
Compliance with FCC Guidelines for Human Exposure to Radiofrequency Elec- 
tromagnetic Fields, Additional Information for Amateur Radio Stations, Supple- 
ment B to OET Bulletin 65 (Edition 97-01). This document may be downloaded at <www.fcc.gov/oet/rfsafety>. 

3. Overbeck, Wayne, "Complying with the FCC's New RF Safety Rules," CQ VHF
January, 1997, page 30. The BASIC computer program contained in this article may 
be downloaded at <ftp://members.aol.com/cqvhf/97issues/rfsafety.bas>. 

4. E-mail communication with William Cross, FCC Wireless Telecommunications Bureau, 
April, 1998. 

5. Zoning regulations of the City of Grover Beach, Calif. 

6. Overbeck, Wayne, "EMR and Weak Signal DXing: The FCC May Change the Rules," 
Proceedings of the 27th Conference of the Central States VHF Society, Okla- 
homa City, 1993, page 26. 

7. Overbeck, Wayne, "EMR, Health and Weak Signal DXing: New Rules and New Re- 
search," Proceedings of the 30th Conference of the Central States VHF Society
Bloomington, MN, 1996, page 88. 

8. Committee on the Possible Effects of Electromagnetic Fields on Biologic Systems, 
National Research Council, Possible Health Effects of Exposure to Residential 
Electric and Magnetic Fields, Bethesda, MD: National Academy Press, 1997. 

9. Milham, Samuel, "Increased Mortality in Amateur Radio Operators due to Lymphatic 
and Hematopoietic Malignancies," American Journal of Epidemiology, 1988; 

10. Milham, Samuel, "Do Your Homework -- Statements on EMF Threat Overlook Much 
of Research," letter to the editor in the Seattle Times, Nov. 15, 1996. 

11. Linet, M.S. et al., "Residential Exposure to Magnetic Fields and Acute Lymphoblastic 
Leukemia in Children, New England Journal of Medicine, 1997 July 3; 337:1-7. 

12. See research report by Repacholi, Michael et al., Radiation Research, 1997 May; 

13. This research was summarized in a paper by Adey, W.R., at the Second World 
Congress for Electricity and Magnetism, Bologna, Italy, June, 1997. 

14. See research report by Lai, Henry et al., International Journal of Radiation Biology
May, 1996. 

15. Ad Hoc Association et al. v. Federal Communications Commission et al., United States 
Circuit Court of Appeals for the District of Columbia Circuit, No. 97-1683. 

16. Quoted from a brochure published by the Ad Hoc Association, P.O. Box 7577, 
Olympia, WA 98507. 

17. Telephone interview with David Fichtenberg, May 3, 1998. 

TABLE I. Antenna separation distances required to meet FCC MPE limits and a hypothetical 2 microwatt/cm.2 standard at 144 MHz (based on FCC's far field formula). 

Quarter-wave ground plane or whip (estimated gain 1 dBi) 

POWER (watts) Distance (ft) Distance (ft) Distance (ft) 

(controlled) (uncontrolled) (hypothetical std) 

10 1.7' 3.7' 37.2' 

50 3.7' 8.3' 83.1' 

150 6.4' 14.4' 143.9' 

17-element, 5-wavelength Yagi (estimated gain 16.8 dBi) 

POWER (watts) Distance (ft) Distance (ft) Distance (ft) 

(controlled) (uncontrolled) (hypothetical std) 

10 10.2' 22.9' 229.1' 

100 32.4' 72.4' 724.4' 

500 72.4' 162' 1619.8' 

E.M.E. array of eight 17-element Yagis (estimated gain 24 dBi) 

POWER (watts) Distance (ft) Distance (ft) Distance (ft) 

(controlled) (uncontrolled) (hypothetical std) 

150 90.9' 203.3' 2032' 

500 166' 371.1' 3710.8' 

1500 287.4' 642.7' 6427.3' 

NOTE: The first two columns are taken from FCC OET Bulletin 65, Supplement B, pages 30-31. The right-hand column in each table is based on a 2 microwatt/cm2 standard, advocated by some citizen activists. All are worst-case calculations that include ground reflections and assume the main lobe illuminates a populated area. If only sidelobes illuminate populated areas or if ground reflections are not included, much smaller separation distances would be required. The power should be averaged (including listening periods) and should take into account the duty cycle (the FCC recommends using 20% of PEP for "conversational" SSB and 40% for "conversational" CW).