Re: OT: can antennas for wireless Internet cause damage to health?

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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

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