On Sat, 2007-02-10 at 20:04 +0000, Paul Smith wrote: > Dear All > > Sorry, but this post is out of topic. > > In the building where I live, the building administration is intending > to install at its top an antenna for irradiating the signal for > wireless Internet users. Can those antennas interfere with the health > of the people living in the building? > > Thanks in advance, > > Paul > Highly unlikely. The signal is fairly low power, and is spread spectrum, so it is nothing like the signal from a Radar or microwave oven, which is high power cw (pulsed in the case of a radar). There are people that spread rumors about RF stuff, but all the documented evidence for the wlan and wifi spectrums shows no effects at their power levels, at least up to now as far as I know. If you google for problems, you can find some sites, but if you track back the science, you will find most of it hails from a few college reports, and then look carefully at their numbers. Field densities in RF are measured in generally uW/sq meter. Most of the sites that herald problems talk about microwats per square cm, which are probably falicios, especially with the longer wavelengths (<30Ghz in frequency) because with insufficient wavelength you will not measure anything, and factoring to get square cm is not appropriate, nor does it give you anything useful or repeatable, except an exercise in mathematics. For example to couple 144Mhz into free space a standard dipole is 36" long. While you can receive with a "smaller" antenna, in reality to achieve coupling from free space, the effective aperture (capture area) must still meet the critical halfwave. This is accomplished by tuning, and the tuning elements become part of the capture area. This is why radar antennas are so large even though their frequencies are in the gigahertz region. To get the signal to focus, you need a sufficient area of control either through elements or through reflection (the typical radar antenna uses reflection) and reflection generally requires a surface largen than 1/2 wavelength in at least one dimension. Since this can (and probably will) turn into a "flame" thread, I won't say any more. There are people who are sensitive, but they are rare. Generally the symptoms are psychosomatic, and if the antenna is hidden the symptoms go away even though the signal density stays the same or increases. Notice I did not say "all", but generally. YMMV And while I am not an engineer, I am a reasonable expert on antennas and radiation. I am not a biologist. I do not pretend to know everything about cellular response to EMF. However, I do have over 36 years experience in the RF field in measurement, transmission and reception. Regards, Les H
