Thanks, ab3a, for some good summaries of these issues.
However, there's a big difference between chemicals you can choose to buy or not to buy and bring into your home, and RF signals bathing your house, your car, and everywhere you go in a city without your consent. I think that's a large part of why those people are making so much noise.
And yet another problem is that the researchers who do these studies often don't understand the engineering side of the problem and the engineers don't understand the research side of the problem. I can remember reading about one study where the researchers ended up cooking their lab rats with relatively small levels of RF because they used far-field assumptions instead of near field equations for the antenna radiation patterns.
One approach worth considering is to assume antenna reciprocity with MRI images. This would give people some idea of how much of what frequencies of energy the human body would absorb most highly. Right now the radiation standards are pretty broad and are based upon some crude thermal assumptions, with a fudge factor thrown in for good measure.
We might do well to consider limiting exposure to those frequencies that are most highly absorbed by the human tissues. And while we're at it, examine whether it is feasible to allow exposure to greater amounts of radiation as long as those wavelengths are not easily absorbed human tissues.
Also, we make the assumption that pulsed power averaged over time won't hurt anything. However some parts of the body may not conduct heat away all that well (making the assumption that the heat conductivity of human tissues can be approximated by saline water may not be all that well founded)
I agree that there is still much that we can do to improve RF safety --but in the scheme of things that can hurt or kill people, I think other research deserves priority. If we studied everyday household chemicals with half as much fervor as people have about this stuff, why, I'm sure we could lengthen the average human life span by a whole year. (OK, I'm being a bit sarcastic here, but only a little).
I think one of the main problems in trying to have a meaningful discussion about the possible biological effects of RF or EMF is that there are so many different kinds of radiation/electromagnetic frequencies and they are apparently not at all the same in their potential for affecting living beings. Another problem, partially dependent on the first one, is that not all studies are created the same, making it difficult to compare their results. A third is that biological systems are extraordinarily complex, especially compared to machines, and are subject to huge amounts of variables.
As the RF spectrum becomes more and more crowded proper pre-selector filtation becomes more important, but it also becomes expensive. Very steep skirts are required to separate out services that abutt each other. And filters introduce their own amomlies, ripple, group delay, etc. Multi-pole cavity filters of the type used for microwave systems such as C-band satellite, are labor intensive as each pole has to be hand tuned during assembly. They are not cheap. The waveguide flanges, the semi rigid inter cavity coaxial cable links and the pickups on either end add to the cost.
You are protecting a wide band low noise amplifier and down converter. In the past 25 years the cost has dropped from $100,000 for a nitrogen cooled parametric amplifier to under $300 for very quiet room temperature LNA or LNB of better specs! Adding $600 for for a front end filter to a $300 LNB will not make your product competative in the marketplace even if it is better.
RF radiation is called non ionizing as its energy level, based upon frequency (wavelength), cannot normally bump electrons from valence rings of atoms. Thus the chemical reaction effects are considered to be non existent. RF is part of the same electromagnetic spectrum as X-rays gamma rays and visible light. The real question is, are there rare circumstances where RF energy can cause other biological changes. And are those events frequent enough that they should be addressed. Probably not. But we do need long term studies to get results above the noise and decide once in for all if more or less caution is appropriate.
Remember it is only in the past few years that we're all being exposed long term to SHF wavelengths from our cell phones, cordless phones, WiFi AP's etc. Also, remember that with digital modulation the peak energy level is much higher than the average level. So, if we are not dealing with tissue thermal effects, the average level becomes irrelevent. Peak RF fields have to be treated differently. When I specify a test load for a digital RF signal I need to know not only the average power dissipation required but the peak RF level in that waveform. The peak results in higher voltage stress of the resistor. Dummy loads known to work well at CW power levels have failed over time when subject to digital RF energy of the same average power because the peaks provided significantly higher voltage.
Human activity always results in benefits and problems. Life is a tradeoff. If we are too careful as a species we'll never progress. If we are too cavaliere, we may end our reign on this planet way too soon.
I agree that the mass media often gets it wrong and contributes to mass hysteria about technology. Problem is when there are alleged experts with opposing opinions the unwashed have nowhere to turn as they do not have the expertise to research the answers for themselves. I put the blame squarely on the US education system both high school and college. Liberal arts majors should be exposed to life skills knowledge that incluse science and technology for the non technologist. And it should be a requirement, not an elective.
Ironically, those that protest cell tower placement increase their exposure to RF from their handsets by forcing them to put out more power to reach more distant cell sites. They do not understand the physics or the technology and thus make the wrong decisions regarding RF exposure concerns.
But as a product designer that routinely sees thier device used in the situation you describe below, one would think that they would put in a brick wall RF filter that would shunt everything from about 800mhz and above.
Any first year EE student could design a passive filter that would do the job and it would cost all of $0.50 to implement. Unfortunately the 'consumer' electronics industry has a long history of paring down designs for cost reasons, typically resulting in degraded or poor performance of the product.
It is the 21st century and RFI susceptance as you properly point out is a real and continuing issue. And the problem will only get worse as more and more wireless devices are unleashed and cost pressures continue to drive designs towards minimalist levels.
I have been a ham for 35 years. I've seen a lot of research. An epidemiological study of ham radio operators would have to take a whole lot of other extenuating circumstances in to the picture. Don't forget about the wonderful materials we use to make electronic components and what happens to them if they burn up. Don't forget that they often set up their stations in the basement, where radon is commonplace. Don't forget that this is often a very sedentary activity.
There are lots of reasons why you might find that ham radio operators may not be in the best of health, and none of them have anything to do with RF.
That said, knowledge of RF in general, is rapidly disappearing. Few people understand much about how the radio spectrum propagates, about impedance, about the practical limits to dynamic range and so many more very technical subjects.
Instead we have people who think they understand the time domain and they're reinventing all the frequency domain stuff to fit in those terms so that they can make software of the radio. I can hardly wait until the first of these people encounters a less than ideal amplifier and exclaims "I don't get it --I've got 18 bits of dynamic range!"
The beauty of the CDMA standards in use here in the US is that they don't make those pulsed transmissions that are so easily picked up by poorly shielded audio wiring. Another good thing is that while RF is more ubiquitous today, it generally runs less power because it only needs to get to the nearest network node. After that, some other networking takes over and routes it to the destination.
I sympathize with those who feel that RF is the cause of their weirdness. I should remind everyone that by definition, RF radiation is NON-IONIZING. Aside of heating effects, no-one has ever shown that RF radiation is dangerous to humans, plants, or animals despite nearly a century of research. I'm not saying that such an effect can not exist, but I have to point out that this electrosensitivity research, despite nearly a century of effort by many different people, has yet to produce any consistent and reproducible results.
In my post, I did point out that to my knowledge there has not been any study of hams re longevity or cancers; I think it could definitely be a worthwhile effort regardless of the results. I've been out of the RF business myself, professionally speaking, for MANY years (over 35; even the last few years I was with Motorola, I had "graduated" to system-level design), so I don't have any personal stake in this battle. I live in the Atlanta area, and right now, every night it seems the evening news is running yet another story about hysterical parents near-rioting over having cell towers anywhere near schools or residential areas. Last night, one of those stated that there were 159 existing cell towers within 4 miles of the one she was protesting about. The clear implication is "why do they need so many?" Cell sites are NOT cheap to erect OR maintain; this particular one would result in $4 million INCOME to the school district (badly needed) over the next 10 years. It's needed because of the CONSUMER DEMAND (strongly encouraged by the current US administration) for vast increases in broadband data infrastructure. The only way to do that is by cell-splitting (which incidentally REDUCES the radiated power from each cell site!); ergo, more cell sites and towers, covering the same geographic area. The only way to stop this would be to outlaw smartphones (a "modest proposal" of Swiftian dimensions)!
This is a needless pot-stirring (IMHO) by the technically-illiterate mass media. EVERYONE who does understand the technical issues involved needs to help educate the illiterati and the public to forestall this sort of "pitchforks and torches" activism before it results in a further shackling of our ability to IMPROVE our lives and lifestyles with advancing technology by ill-advised and misguided policies.
Transfers the control of a large number of motion axes from one numerical control kernel to another within a CNC system, using multiple NCKs, and enables implement control schemes for virtually any type of machine tool.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.