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Re: wifi radiation

 
 
JohnO
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      05-23-2007
On May 23, 7:06 am, Shane <(E-Mail Removed)-a-geek.net> wrote:
> I seem to recall getting a fair amount of... ribbing.. for having concern
> about wifi installations at home/school
> There was even suggestion that there is more radioactivity associated with a
> mobile phone than a wifi ap.
>
> Whilst that may be true, the british study which first concerned me found
> the following:http://www.nzherald.co.nz/section/1/...jectid=1044127...
>
> Radiation levels from wireless internet in schools are being investigated
> after a British study found emissions in a classroom there three times
> higher than those from a mobile phone mast.
>
> It followed the discovery by BBC researchers that the maximum signal
> strength one metre from a Wi-Fi laptop in a classroom was three times that
> measured 100m from a mobile phone mast nearby.



Hardly surprising given that radiated signal strength must be
inversely proportional to the cube of the distance from source.

So the sensible way to view all this is that is that if WiFi radiation
is low then cellphone tower radiation is infinitessimal.

>
> I certainly hope my mobile phone isnt emitting the same as a mast, and
> granted the mast was measured 100m away, and the wifi AP 1m away. Still,
> it could be HT powerlines instead...


Just wear a tinfoil hat and tinfoil undies and you'll be fine.

>
> --
> Q: What do you get when you cross a mosquito with a rock climber?
> A: Nothing. You can't cross a vector and a scalar.



 
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Roger_Nickel
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      05-23-2007
On Tue, 22 May 2007 19:41:20 -0700, JohnO wrote:

> On May 23, 7:06 am, Shane <(E-Mail Removed)-a-geek.net> wrote:
>> I seem to recall getting a fair amount of... ribbing.. for having concern
>> about wifi installations at home/school
>> There was even suggestion that there is more radioactivity associated with a
>> mobile phone than a wifi ap.
>>
>> Whilst that may be true, the british study which first concerned me found
>> the following:http://www.nzherald.co.nz/section/1/...jectid=1044127...
>>
>> Radiation levels from wireless internet in schools are being investigated
>> after a British study found emissions in a classroom there three times
>> higher than those from a mobile phone mast.
>>
>> It followed the discovery by BBC researchers that the maximum signal
>> strength one metre from a Wi-Fi laptop in a classroom was three times that
>> measured 100m from a mobile phone mast nearby.

>
>
> Hardly surprising given that radiated signal strength must be
> inversely proportional to the cube of the distance from source.


Inverse square actually; the wavefront spreads out on the surface
of an expanding sphere. WiFi is legally limited to 1 watt effective
radiated power and most of the computer cards are well below this
because they use inefficient patch antenna. Getting a signal above
background noise levels is often a problem!. Cell phones are right
against the head and allowed to radiate up to 2 watts (but don't usually).
The mobile phone mast is probably 50 metres away beaming out
toward the horizon using a phased array of small aerials and is the
least of any problem.

 
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Lawrence D'Oliveiro
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      05-23-2007
In message <(E-Mail Removed) o.nz>,
Roger_Nickel wrote:

> On Tue, 22 May 2007 19:41:20 -0700, JohnO wrote:
>
>> On May 23, 7:06 am, Shane <(E-Mail Removed)-a-geek.net> wrote:
>>> I seem to recall getting a fair amount of... ribbing.. for having
>>> concern about wifi installations at home/school
>>> There was even suggestion that there is more radioactivity associated
>>> with a mobile phone than a wifi ap.
>>>
>>> Whilst that may be true, the british study which first concerned me
>>> found the
>>>

following:http://www.nzherald.co.nz/section/1/...jectid=1044127...
>>>
>>> Radiation levels from wireless internet in schools are being
>>> investigated after a British study found emissions in a classroom there
>>> three times higher than those from a mobile phone mast.
>>>
>>> It followed the discovery by BBC researchers that the maximum signal
>>> strength one metre from a Wi-Fi laptop in a classroom was three times
>>> that measured 100m from a mobile phone mast nearby.

>>
>>
>> Hardly surprising given that radiated signal strength must be
>> inversely proportional to the cube of the distance from source.

>
> Inverse square actually; the wavefront spreads out on the surface
> of an expanding sphere.


A bit difficult, that, since all the radio antennas humans have managed to
invent have been dipoles.
 
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Richard
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Posts: n/a
 
      05-23-2007
Roger_Nickel wrote:

> Inverse square actually; the wavefront spreads out on the surface
> of an expanding sphere. WiFi is legally limited to 1 watt effective
> radiated power and most of the computer cards are well below this
> because they use inefficient patch antenna. Getting a signal above
> background noise levels is often a problem!. Cell phones are right
> against the head and allowed to radiate up to 2 watts (but don't usually).
> The mobile phone mast is probably 50 metres away beaming out
> toward the horizon using a phased array of small aerials and is the
> least of any problem.


4 watts effective, 1 watt radio output is the limit. Easily obtainable
on a big antenna but the chip antennas on wifi cards is usually 2dBi if
your lucky. The APs usually have something a bit better, a 3dBi dipole
or something like that, still thats only up to 2 watts effective.

Most school environs have the power lowered down so that stations don't
try to associate with accesspoints in the next room, since there is no
provision in the wifi specs to remotely set the cards carrier sense
level or hand over threshholds its basically the only way to get the AP
density needed for good thruput without having cards holding off all the
time because of transmissions 3 rooms over on the same channel.

I get -50dBmW when near the APs at tech, whereas my one at home at the
same distance will give me -30 - thats 20dB difference, or 100 times the
power at home. No worries on the school ones IMO, more worried about the
card thats mere inches from me then the AP on the walls in the classrooms.
 
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Shane
Guest
Posts: n/a
 
      05-23-2007
Roger_Nickel wrote:

> On Tue, 22 May 2007 19:41:20 -0700, JohnO wrote:
>
>> On May 23, 7:06 am, Shane <(E-Mail Removed)-a-geek.net> wrote:
>>> I seem to recall getting a fair amount of... ribbing.. for having
>>> concern about wifi installations at home/school
>>> There was even suggestion that there is more radioactivity associated
>>> with a mobile phone than a wifi ap.
>>>
>>> Whilst that may be true, the british study which first concerned me
>>> found the
>>>

following:http://www.nzherald.co.nz/section/1/...jectid=1044127...
>>>
>>> Radiation levels from wireless internet in schools are being
>>> investigated after a British study found emissions in a classroom there
>>> three times higher than those from a mobile phone mast.
>>>
>>> It followed the discovery by BBC researchers that the maximum signal
>>> strength one metre from a Wi-Fi laptop in a classroom was three times
>>> that measured 100m from a mobile phone mast nearby.

>>
>>
>> Hardly surprising given that radiated signal strength must be
>> inversely proportional to the cube of the distance from source.

>
> Inverse square actually; the wavefront spreads out on the surface
> of an expanding sphere. WiFi is legally limited to 1 watt effective
> radiated power and most of the computer cards are well below this
> because they use inefficient patch antenna. Getting a signal above
> background noise levels is often a problem!. Cell phones are right
> against the head and allowed to radiate up to 2 watts (but don't usually).
> The mobile phone mast is probably 50 metres away beaming out
> toward the horizon using a phased array of small aerials and is the
> least of any problem.


As I posted previously, the university is using consumer grade wifi cards to
transceive across distances of over 20 Km (I think its more than that,
Uni -> Mt Pirongia)

--
Q: What is often used by Canadians to help solve certain differential
equations?
A: the Lacrosse transform.

 
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