"T. T." <(E-Mail Removed)> hath wroth:
>Recently after reading some articles I have some concerns about 802.11G
>WLAN health issue:
>http://arstechnica.com/news.ars/post/20060222-6235.html
>http://www.netstumbler.org/archive/i...p/t-12052.html
Concern and demonstrable proof are quite different. At the power
levels of a typical Wi-Fi system, I would say that you and the baby
are safe.
Let's pretend that there is an effect. According to inverse square
law, the exposure is proportional to the square of the distance.
Double the distance, 1/4th the exposure. 4 times the distance, and
1/16th the exposure. That means keep your distance and you're much
safer.
However, you're not built in only 2 dimensions. RF absorption (as
opposed to exposure) is proportional to the cube of the distance.
Double the distance and you absorb 1/8th the RF. 4 times the
distance, and you absorb 1/64th the energy. This is roughly how the
SAR (specific absorption rate) is calculated for cell phones.
After distance, the next most important parameters are power and duty
cycle. Power is easy. If the transmitter is on the air all the time,
it's 100% duty cycle and you get the maximum absorption. However, if
your transmitter is a GSM cell phone, it only transmits 1/8th the
time. Therefore, you only get 1/8th the exposure. Wi-Fi varies in
duty cycle. With no traffic, the duty cycle is something like 1/100th
where all that gets transmitted are the beacon frames. Download
furiously and it approaches 100% duty cycle.
Now, let's warp some numbers. The sun cranks out 1000 watts of energy
per square meter at noon. The average wireless access point transmits
about 15 milliwatts (0.015 watts) of RF. At a distance of 1 meter,
that's a fabulous 15 milliwatts per square meter exposure. Therefore
the sun delivers 66,666 times more power than your wireless access
point. Sure, it's at different frequencies, but if the tin foil hat
crowd can ignore frequency effects, then so can I. Like I said, "warp
some numbers".
The Canadian university president declared that some unreferenced
Calif PUC study said "more research is necessary". Well, yes... more
research is always necessary. That's how researchers get their grant
funding. There's no end to research and every research paper I've
ever read has ended in "more research is necessary".
Anyway, enough numbers and educational politics. If you're seriously
worried about RF exposure and don't want to take any chances, then
running CAT5 is the obvious alternative. Just ignore the RF coming
from TV, AM, FM, cellular, military, radar, aviation, and commercial
wireless systems. Depending on your location, such RF levels can
easily exceed your Wi-Fi levels.
Let's do some more math. How far would an FM broadcast station need
to be away from your house to have the same RF exposure levels as your
Wi-Fi at a distance of 1 meter. Well, the math is simple enough:
Power_1 / Power_2 = Distance_1 ^2 / Distance_2 ^2
0.015 watts / 50,000 watts (ERP) = 1 meter^2 / Distance_2 ^2
Distance_2 = 1800 meters
So, if you have an FM broadcast station within about a mile, it's
producing about the same RF exposure level as your wireless access
point at 1 meter. Actually the FM station is producing quite a bit
more because it runs at 100% duty cycle while Wi-Fi averages much
less, but I'll use worst case just like all the alarmist reports.
So, what can you do to reduce RF exposure? Aluminum foil wall paper
is available. Frequency selective wallpaper can be found:
|
http://www.newscientist.com/article.ns?id=dn6240
You can turn your house into an RF screen room with RF absorbent
non-reflective material. Actually, that might not be a bad idea if
the kid turn out to be a chronic screamer.
Another easy fix is to simply turn off the transmitter when it's not
being used. Carbon filled tubing slipped over the antenna works
nicely. If you get a separate wireless access point and router, then
you can just unplug the wireless part when it's not being used.
>Is Wifi or WLAN verified to have some health issues with humans?
Verified by the FCC, NIH, or a peer reviewed medical publication? To
the best of my limited knowledge, no such study has been verified. The
problem is that most of the studies are epidemiological, where the
research report attempt to correlate medical abnormalities with RF
exposure. Since this takes a long time, the sample grouping is never
differentiated by a single factor, and the preponderance of a
multitude of other contributory factors, the chances of an
epidemiological study finding something interesting *AND* repeatable,
is zilch.
>We
>have a baby (13 months) at home so we really don't want to take any
>risk.
Read what I wrote in terms of the baby. Distance is the most
important factor. That means what you feed the kid and his immediate
environment is most important. Worry about those and not
environmental issues that fade rapidly with distance. There's also
more than a hint that growing up requires early exposure to bugs,
filth, chemicals, and toxins to build up a survivable immunity. That
which doesn't kill the kid make him/her stronger.
>Because of this, I'm thinking of giving up our current wireless LAN and
>use fixed line instead. However, although I'm a family handyman, but I
>have never did category-5 home wiring project before.
It's not that difficult but does take some practice. Since you have a
kid, you should plan to redecorate or move things around about every 5
years. Might as well get used to running and terminating wires.
>I don't want to
>drill a hole on the wall only to find out that there is a water pipe
>behind the wall!!!
Drill a small hole in the wall and shove a coat hanger in to see what
you're getting too close to. There are field detectors and toners for
locating AC wiring (that's not in conduit). You can hear water pipes
with a stethoscope. If you have money, you can get a fiber optic
inspection viewer. Lots of ways to sniff around inside a wall.
Incidentally, you biggest problem will not be hitting a wire or pipe.
It will be hitting a stud or firebreak with the drill. Unlike hanging
pictures on the wall, you want to avoid the studs when running CAT5.
Use a stud finder.
>So, is this some kind of project that I could do
>myself or I better hire a professional electrian or handyman to do the
>job??
Your lack of imagination suggests limited abilities to do this right
the first time. Perhaps having an electrician show you how to do it
would be better than Learn by Destroying(tm).
>Is there any online resources or advices that people could give
>me about this kind of home project? Many thanks!
Yes. Google found a few. Lots of vendors have tutorials under their
"structured wiring" products. Dmitri has his site. You should be
able to find something.
--
Jeff Liebermann
(E-Mail Removed)
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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