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Journals from The Book Company Whether choosing a journal from our journal collections, or having our team design a unique custom journal for you, The Book Company has the perfect journal for your next project. In a pure technical point of view, remember that the temperature of a CPU and any other electronic semiconductor components is a critical factor that affects the good functioning of your equipment, hence the use of a fan on both the CPU and on the cabinet of your transceiver, amplifier or the one of your computer, to extract the excess of heat.
These are not simple accessories; they are mandatory and must remain operational if you want that your system works in good conditions. Thermal radiation from electronic components. So, as we all expect a very long life for our ham equipment, better to use oversized and powerful fans, and why not adding an extra fan on the cabinet if you noticed that your system is rather hot after have used it heavily.
Athermal effects of EMR. 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: epidemiological research and laboratory research. 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 EMR 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. However, epidemiological research by itself is rarely conclusive.
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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. 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.
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. Their conclusions have not changed with years. At left a sideview, at right from the end.
Among its general conclusions were the following:. The scientific literature and the reports of reviews by other panels show no consistent, significant link between cancer and powerline fields.
No plausible biophysical mechanisms for the systematic initiation or promotion of cancer by these extremely weak Hz fields has been identified. While it is impossible to prove that no deleterious health effects occur from exposure to any environmental factor, it is necessary to demonstrate a consistent, significant, and causal relationship before one can conclude that such effects do occur.
‘Earth’s most uninhabitable place found’
Later in the same chapter they write: "Although the data base has grown substantially over the past decades, much of the information concerning nonthermal effects is generally inconclusive, incomplete, and sometimes contradictory. Studies of human populations have not demonstrated any reliably effected end point. Readers may want to follow this topic as further studies are reported.
Prudent avoidance of any avoidable EMR is always a good idea. However, an Amateur Radio operator should not be fearful of using his or her 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.
At left a sideview, at right from top. Safe Exposure Levels. Under what energy level an EM 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.
one woman's thoughts about life on the spectrum
The recommended safe levels have been revised downward several times in recent years—and not all scientific bodies agree on this question even today. The main bodies involved in these measurements are next :. Among the supranational institutions having a consultative or legal function, name :. It replaced a ANSI 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 next 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 and magnetic fields. Basically, the lowest E-field exposure limits occur at frequencies between 30 and MHz. The lowest H-field exposure levels occur at MHz. Higher power densities are permitted at frequencies below 30 MHz below MHz for H fields and above MHz, based on the concept that the body will not be resonant at those frequencies and will therefore absorb less energy.
In general, the IEEE guideline requires averaging the power level over time periods ranging from 6 to 30 minutes for power-density calculations, depending on the frequency and other variables. The ANSI exposure limits for uncontrolled environments are lower than those for controlled environments, but to compensate for that the guideline allows exposure levels in those environments to be averaged over much longer time periods generally 30 minutes. This long averaging time means that an intermittently operating RF source such as an Amateur Radio transmitter will show a much lower power density than a continuous-duty station for a given power level and antenna configuration.
Predicted radiation directivity pattern RDP of an S-band antenna array 3. Document Lambda Science, Inc. Time averaging is based on the concept that the human body can withstand a greater rate of body heating and thus, a higher level of RF energy for a short time than for a longer period. However, time averaging may not be appropriate in considerations of nonthermal effects of RF energy. The IEEE guideline excludes any transmitter with an output below 7 W because such low-power transmitters would not be able to produce significant whole-body heating.
However, recent studies show that hand-held transceivers often produce power densities in excess of the IEEE standard within the head. There is disagreement within the scientific community about these RF exposure guidelines. The IEEE guideline is still intended primarily to deal with thermal effects, not exposure to energy at lower levels. A small but significant number of researchers now believe athermal effects should also be taken into consideration. Several European countries and localities in the United States have adopted stricter standards than the recently updated IEEE standard.