Dear Fiona Crowley, Imelda & Klaus,
N.B. In Sweden, electrosensitivity
is an officially acknowledged handicap.
Thus, since you do not loose your handicap status travelling
e.g. inside the EU, a treatment indicated below should immediately be
legally reported to the EUs handicap-ombudsman.
Best regards
Yours
Olle
(Olle Johansson, assoc. prof. The Experimental
Dermatology Unit. Department of Neuroscience
Karolinska Institute. 171 77 Stockholm. Sweden)
Klaus,
I would like to respond to some of the concerns
raised about intensification of RF fields by presence of metallic objects.
The textbook entitled "Antenna Theory Analysis
and Design" by C.A. Balanis, Wiley and Sons, New York (1982) has
a very comprehensive chapter about the fields from antennas over partially
conducting ground. The same basic arguments apply to fields near partially
conductive structures. The field enhancement due to interaction of the
direct and reflective fields is dependent on the antenna size (dipole
length), relative to the wavelength of the radiation, the distance of
the antenna from the ground or partially conducting structure, the polarization
of the antenna, and the dielectric constant and electrical conductivity
of the bounding surface (ground) or partially conductive structure.
For an AM broadcast radio tower, the antenna is nearly
always a straight dipole, for TV stations and some FM radio stations,
there may be more complex structures than just dipoles, but the analysis
of their emitted fields can usually be represented as arising from multiple
dipole sources (e.g., log periodic antenna) or as an emitting element
plus reflective and directive rods (Yagi antenna).
Sources such as cell towers usually have antennas that
are of two types: 1) either whip antennas (long straight dipoles) that
may or may not have flat reflectors (when the antennas are mounted on
the sides of buildings) and 2) antennas that have rectangular folded dipoles
encased in weather proofing plastic. The latter antennas resemble flat
blades, and they produce a directional emission pattern. The relation
between the essential parameters of a folded dipole and those of linear
dipoles are given in the Balanis book, so that one can compute approximate
radiation patterns, allowing for the effect of the finite conductivity
of nearby objects or boundary surfaces.
Most AM broadcast stations have vertically polarized
(direction of the emitted electric field) antennas, TV station antennas
often have horizontal polarization, sometimes circular or elliptical poalrization.
Cell tower antennas are usually either vertically polarized or else have
polarization at 45 degrees with respect to the axis of the antennas. However,
the polarization axis is usually tilted slightly downward from what I
described, because either the antennas are tilted a few degrees toward
the ground, or else the antenna design includes an electrial tilt of the
radiation pattern.
Incidentally, if one knows the manufacturer and model
number of a transmitting antenna, the design parameters and the radiation
patterns can usually be obtained from the internet. In the rare instances
when those data were not available from the internet, I have found the
manufacturers are glad to oblige by sending the requestor the data.
I urge those who are mathematically inclined to get
this reference book and make estimates of the field enhancment under various
circumstances, rather than speculating on whether using a tractor (for
example) increases the radiation dose significantly when working near
various types of RF sources.
I set up a calculation as I have described above and
found that even a linear dipole begins to have complex radiation patterns
as the length of the dipole increases beyond the wavelength of the radiation.
By the way, a typical length for the kind of folded dipole used in cell
towers is about 4 times the wavelength. The calculation model I set up
also allowed me to consider the effect of various types of soil on the
radiation field near the ground, as well as the effect of the wetness
of the soil. Similar considerations appear in Balanis' book and in a much
earlier classic engineering textbook on antennas by Krauss. I hope this
information is helpful to someone on this list.
I am a retired physicist and one of the founding board
members of the EMR Network, a national charitable organization in the
U.S. that is working to help people with concerns about RF radiation and
health. Much useful information can be obtained from the website www.emrnetwork.org.
I also presented a paper at the International Conference on Cell Tower
Siting held in Salzburg, Austria in June, 2000. All papers presented at
that meeting can be downloaded from the web site www.land-sbg.gv.at/celltower.
I urge your readers to read these papers. Among the
outstanding contributions are those by Prof. Neil Cherry.
Bill P. Curry, Ph.D. Physics is fun
(630) 858-9377 Fax (630) 858-9159
EMSciTek Consulting Company
I have proposed to participate in the revision of Application
of the next 24 February 2003, the first day, in Luxembourg.
The description and evaluation of NINE
DEGREES OF HEALTH HAZARD (see attached)
can help to recognize and accommodate the diverse disciplines necessary
for successful implementation of Precautionary Principle.
Best regards
Miguel Muntané
HELP STOP A WAR: SEND A VALENTINE
We've launched a new website opposing a war in Iraq:
http://www.greenpeace.org/campaigns/intro?campaign_id=135724
We've also set up a discussion thread about volunteering
to help stop a war here:
http://act.greenpeace.org/1044275002/index_html
We encourage you all to participate in the world wide
demonstrations against a war on Saturday, 15 February. To find out more,
please visit:
http://www.unitedforpeace.org/article.php?id=725
Please send our new Valentine-themed e-card to your
friends and colleagues (not just your special someone!) from:
http://act.greenpeace.org/ecs/s2?i=485&sk=std
The e-card asks people to thank the Presidents of France,
Russia and China for opposing a war in Iraq.
Please thank these Presidents yourself from:
http://act.greenpeace.org/ams/e?a=486&s=blue2s
You can send a letter to the 15 members of the UN Security
Council here:
http://act.greenpeace.org/ams/e?a=476&s=blue2s
and to UK Prime Minister Tony Blair here:
http://act.greenpeace.org/ams/e?a=478&s=blue2s
You can participate in a general discussion about a
possible Iraqi war here:
http://act.greenpeace.org/1044892516
|