Ideally, an antenna should be one-half the wavelength of the transmitting frequency. Some manufacturers call these "sub-channels". If you have a very snsitive radio, you might not benefit at all from the antenna amplifier. Also digital signals can be modulated to radio frequency carrier.
You can call us toll-free at ; fax your order to ; or send e-mail to pubsales arrl. Check out the full ARRL publications line. This seminar educated engineers about the Standard and its development. SCC now has about active members. SCC considers a large number of input sources and research papers.
It evaluates these against scientific criteria. For example, they exclude papers that do not include measured RF field levels. The result included about papers. SCC considered the topics and conclusions in these papers and combined them with the substantial collective knowledge of their learned membership.
Finally, they reached a consensus that a standard for exposure could be set and did so. This is the approximate level at which several animal species demonstrate temporary difficulty in performing complex tasks.
With removal of the field, he soon decided he was hungry, after all. The Committee deems these to be thermal effects. Human volunteers exposed to such fields usually asked, "Who turned on the sun? The Committee applied a safety factor of 10, setting an SAR of 0. The MPEs in the Standard and regulations account for how much energy the human body absorbs over different frequency ranges. Some have suggested that this whole topic is unfounded--there are no adverse effects of RF energy.
Several ARRL committees and other technical experts advise us that these Standards are realistic and we should heed them. I serve on two US standards bodies, and have participated in others. I know how difficult it is to find common ground in a large group. Given that members of SCC agreed upon this Standard, it is almost certainly based on sound scientific principles. The FCC simply did not follow the "rules to make the rules. There are petitions "on the plate" from industry and the amateur community.
When the regulations were first announced, ARRL filed an emergency petition for relief from an implementation error that required question pools revision well before the effective date of the regulations. We found many errors and flaws in the requirements as written.
The W threshold for categorical exclusion is arbitrary: While the MPEs vary with frequency, the W level does not. We ask that the W level be increased at some frequencies, consistent with the MPEs. Some other services have exclusions when the antenna location is 10 meters from areas of exposure. At HF, W to any antenna would be unconditionally safe when the antenna is 10 meters from areas of exposure--with a significant safety margin. We asked the FCC to add these criteria to the W criterion already in the regulations.
We did not ask for any change to the W criterion at VHF and higher, because some station and antenna configurations could result in fields that exceed the MPEs.
We considered higher limits, for HF, with a greater antenna separation. A safety margin similar to that for the W scenario would require a rather great distance at some frequencies. We backed off this path because it might be misinterpreted. Local officials might assume that the worst-case distance for such high-power stations should apply to all amateur stations. The congressional mandate to the FCC included the requirement to develop preemption of local regulation of RF exposure resulting from the operation of radios in the Personal Communications Services of which we're not.
In order to do so, they needed the federal RF-exposure regulations. The result is that the Amateur Radio Service bears the burden of these new regulations without the benefits of preemption. As the FCC and amateur communities wrestled with understanding the requirements and rewriting Bulletin 65, it became apparent that neither the FCC nor the amateur community could meet the January 1, , implementation date.
If the FCC manages to complete Bulletin 65 by the target date of December 1, , that would give amateurs only four weeks to obtain it, read it, understand it, perform the needed calculations and take steps to correct any problems.
For example, if a ham wants to move a tower, it could require zoning approval and other paperwork. In some areas of the country, winter would prevent completion. The ARRL then joined the growing number of organizations and individuals seeking relief from the short deadlines for these regulations.
At press time, there has been no decision on any of the petitions for reconsideration before the FCC although this may have all been decided by the time you read this. Secure Site Login Forgot Password? Exposure "Environments" The regulations define two primary RF-exposure environments: Categorical Exclusions All Amateur Radio stations must comply with the MPE limits, regardless of power, operating mode or station configuration. Amateur stations using a transmitter power of less than 50 W PEP at the transmitter output terminal.
Mobile or portable stations using a transmitter with push-to-talk control. Paperwork Other than a short certification on Form station applications, the regulations do not normally require hams to file proof of evaluation with the FCC. Examinations The regulations add five questions on the topic of RF exposure to each Amateur Radio examination for Novice, Technician and General class licenses.
Routine Station Evaluation The regulations require amateur operators, whose stations are not categorically excluded, to perform a routine analysis of compliance with the MPE limits. This means the equivalent far-field strength that would have the E- or H-field component calculated or measured. It does not apply well in the near field of an antenna.
Back to Top Having Trouble? RF Exposure Regulations News. Although Amateur Radio is basically a safe activity, in recent years there has been considerable discussion and concern about the possible hazards of electromagnetic radiation EMR , including both RF energy and power frequency Hz electromagnetic fields. Extensive research on this topic is underway in many countries. It summarizes what is now known and offers safety precautions based on the research to date.
All life on Earth has adapted to survive in an environment of weak, natural low-frequency electromagnetic fields in addition to the Earth's static geomagnetic field. Natural low-frequency EM fields come from two main sources: But in the last years, man-made fields at much higher intensities and with a very different spectral distribution have altered this natural EM background in ways that are not yet fully understood.
Much more research is needed to assess the biological effects of EMR. Both RF and Hz fields are classified as nonionizing radiation because the frequency is too low for there to be enough photon energy to ionize atoms. Still, at sufficiently high power densities, EMR poses certain health hazards.
It has been known since the early days of radio that RF energy can cause injuries by heating body tissue. In extreme cases, RF-induced heating can cause blindness, sterility and other serious health problems. These heat-related health hazards are called thermal effects. In addition, there is evidence that magnetic fields may produce biologic effects at energy levels too low to cause body heating. The proposition that these athermal effects may produce harmful health consequences has produced a great deal of research.
In addition to the ongoing research, much else has been done to address this issue. For example, the American National Standards Institute, among others, has recommended voluntary guidelines to limit human exposure to RF energy.
And the ARRL has established the RF Safety Committee, a committee of concerned medical doctors and scientists, serving voluntarily to monitor scientific research in the fields and to recommend safe practices for radio amateurs.
Body tissues that are subjected to very high levels of RF energy may suffer serious heat damage. These effects depend upon the frequency of the energy, the power density of the RF field that strikes the body, and even on factors such as the polarization of the wave.
At frequencies near the body's natural resonant frequency, RF energy is absorbed more efficiently, and maximum heating occurs. In adults, this frequency usually is about 35 MHz if the person is grounded, and about 70 MHz if the person's body is insulated from the ground. Also, body parts may be resonant; the adult head, for example is resonant around MHz, while a baby's smaller head resonates near MHz.
Body size thus determines the frequency at which most RF energy is absorbed. As the frequency is increased above resonance, less RF heating generally occurs. However, additional longitudinal resonances occur at about 1 GHz near the body surface. Nevertheless, thermal effects of RF energy should not be a major concern for most radio amateurs because of the relatively low RF power we normally use and intermittent nature of most amateur transmissions.
Amateurs spend more time listening than transmitting, and many amateur transmissions such as CW and SSB use low-duty-cycle modes. In any event, it is rare for radio amateurs to be subjected to RF fields strong enough to produce thermal effects unless they are fairly close to an energized antenna or unshielded power amplifier.
Specific suggestions for avoiding excessive exposure are offered later. Nonthermal effects of EMR may be of greater concern to most amateurs because they involve lower level energy fields. Research about possible health effects resulting from exposure to the lower level energy fields, the athermal effects, has been of two basic types: Scientists conduct laboratory research into biological mechanisms by which EMR may affect animals including humans.
Epidemiologists look at the health patterns of large groups of people using statistical methods. These epidemiological studies have been inconclusive. By their basic design, these studies do not demonstrate cause and effect, nor do they postulate mechanisms of disease. Instead, epidemiologists look for associations between an environmental factor and an observed pattern of illness.
For example, in the earliest research on malaria, epidemiologists observed the association between populations with high prevalence of the disease and the proximity of mosquito infested swamplands. It was left to the biological and medical scientists to isolate the organism causing malaria in the blood of those with the disease and identify the same organisms in the mosquito population.
In the case of athermal effects, some studies have identified a weak association between exposure to EMF at home or at work and various malignant conditions including leukemia and brain cancer. However, a larger number of equally well designed and performed studies have found no association.
A risk ratio of between 1. Epidemiologists generally regard a risk ratio of 4. For example, men who smoke one pack of cigarettes per day increase their risk for lung cancer tenfold compared to nonsmokers, and two packs per day increase the risk to more than 25 times the nonsmokers' risk. However, epidemiological research by itself is rarely conclusive.
Epidemiology only identifies health patterns in groups-it does not ordinarily determine their cause. And there are often confounding factors: Most of us are exposed to many different environmental hazards that may affect our health in various ways. Moreover, not all studies of persons likely to be exposed to high levels of EMR have yielded the same results.
There has also been considerable laboratory research about the biological effects of EMR in recent years. For example, it has been shown that even fairly low levels of EMR can alter the human body's circadian rhythms, affect the manner in which cancer-fighting T lymphocytes function in the immune system, and alter the nature of the electrical and chemical signals communicated through the cell membrane and between cells, among other things.
Much of this research has focused on low-frequency magnetic fields, or on RF fields that are keyed, pulsed or modulated at a low audio frequency often below Hz. Several studies suggested that humans and animals can adapt to the presence of a steady RF carrier more readily than to an intermittent, keyed or modulated energy source. There is some evidence that while EMR may not directly cause cancer, it may sometimes combine with chemical agents to promote its growth or inhibit the work of the body's immune system.
None of the research to date conclusively proves that low-level EMR causes adverse health effects. Given the fact that there is a great deal of research ongoing to examine the health consequences of exposure to EMF, the American Physical Society a national group of highly respected scientists issued a statement in May based on its review of available data pertaining to the possible connections of cancer to Hz EMF exposure. This report is exhaustive and should be reviewed by anyone with a serious interest in the field.
Among its general conclusions were the following:. Later in the same chapter they write: Studies of human populations have not demonstrated any reliably effected end point.
Readers may want to follow this topic as further studies are reported. Amateurs should be aware that exposure to RF and ELF 60 Hz electromagnetic fields at all power levels and frequencies may not be completely safe. Prudent avoidance of any avoidable EMR is always a good idea.
However, an Amateur Radio operator should not be fearful of using his equipment. If any risk does exist, it will almost surely fall well down on the list of causes that may be harmful to your health on the other end of the list from your automobile. How much EM energy is safe? Scientists have devoted a great deal of effort to deciding upon safe RF-exposure limits.
This is a very complex problem, involving difficult public health and economic considerations. The recommended safe levels have been revised downward several times in recent years-and not all scientific bodies agree on this question even today. It replaced a American National Standards Institute guideline that permitted somewhat higher exposure levels.
ANSI-recommended exposure limits before were higher still. This new IEEE guideline recommends frequency-dependent and time-dependent maximum permissible exposure levels. Unlike earlier versions of the standard, the standard recommends different RF exposure limits in controlled environments that is, where energy levels can be accurately determined and everyone on the premises is aware of the presence of EM fields and in uncontrolled environments where energy levels are not known or where some persons present may not be aware of the EM fields.
The graph depicts the new IEEE standard. It is necessarily a complex graph because the standards differ not only for controlled and uncontrolled environments but also for electric fields E fields and magnetic fields H fields. Basically, the lowest E-field exposure limits occur at frequencies between 30 and MHz.