Re: Is there any harmful effect from wifi (802.11.x) radiation? Any definitive proof?
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
||||||||||||||||
|
Posted by Bert Hyman on September 25, 2008, 10:59 am
Please log in for more thread options dcs@lumbercartel.com (D. C. Sessions) wrote in >> Is there any _PROVEN_ harmful effect stemming from the wireless
>> radiation of WIFI, be it in the 2.4GHz band (for 802.11b and >> 802.11g) and in the 5GHz band (for 802.11n) ? >> >> Although I am part of the team deploying the city-wide wifi >> coverage, I want to be sure that what I am doing would NOT cause >> any harmful effect to the people of this city. >
> The frequencies used for WiFi are the same as those used for mobile > telephones. Not really. Phones generally operate in two bands, 800-900Mhz and 1800-1900Mhz. These numbers are vague enough to cover the US and the rest of the world, and GSM and whatever they call the CDMA services popular in the US. The data services are often elsewhere, but not at 2.4GHz or 5GHz, so far as I know. > The number of telephones obviously *vastly* exceeds the number of
> WiFi hotpoints, they have the same transmit power, and they are > located closer to people. But WiFi APs and computer WiFi NICs radiate continuously, while phones will transmit only while in a call, or make periodic short transmissions while inactive. Radiation from a cell transmitters will probably be continuous though. As to proximity, your PC's NIC might be sitting on your lap, and depending on where you are, the AP might be hanging on the ceiling, directly overhead. All that said, I have no reluctance to carry a cellphone in my pocket or use it whenever I need to, nor to use my WiFi equipped laptop for hours at a time. -- Bert Hyman | St. Paul, MN | bert@iphouse.com | ||||||||||||||||
|
Posted by Jeff Liebermann on September 25, 2008, 2:29 pm
Please log in for more thread options >But WiFi APs and computer WiFi NICs radiate continuously, while phones
>will transmit only while in a call, or make periodic short >transmissions while inactive. Radiation from a cell transmitters will >probably be continuous though. Wrong on all counts. 802.11 has a specific duty cycle which varies by the type of traffic. When there's no traffic, all you see are 10 short beacons per second and some other broadcast traffic (mostly ARP requests). When saturated at full bandwidth (i.e. downloading), there has to be spaces between transmissions or there's no way to create a shared channel system. The timing varies but typical is 50% (which shows up as a the conventional wisdom of TCP thruput is equal to about 50% of the data rate). So, the worst case duty cycle for Wi-Fi is about 50% and more typically (my guess) is about 1%. Cell phones have different timing schemes but basically they can't be on the air all the time or your battery won't last very long. GSM has 8 time slots, so you automatically have a 12.5% tx duty cycle. They are also required to have adaptive power control to reduce handset tx power depending on the cell sites received signal strength. In general, todays handsets cannot output more than perhaps 250 milliwatts and tend to typically operate in the 50 mw region. If your handset has a diagnostic mode, you can possibly display the actual value. My guess(tm) is that the typical cell phone averages about 50mw RF with a 15% duty cycle. Radiation from a cell site is not continuous but is close. There are usually multiple 250 watt power amplifiers. Each user gets up to 2 watt of RF from the cell site per channel (varies with service and band). If there are 100 active users, the cell site is spewing up to 200 watts. If there are none, such as might happen at night, the cell site is spewing next to nothing. The 2 watt carriers are also subject to the same power control requirement as the handset and can be much less power output. Electricity to run a cell site is expensive and vendors are always trying to save on power. You can be sure they're running as economically as possible. >As to proximity, your PC's NIC might be sitting on your lap, and
>depending on where you are, the AP might be hanging on the ceiling, >directly overhead. Yep. Think inverse square law. Double the distance and you get 1/4th the exposure. Distance is far more important the power. >All that said, I have no reluctance to carry a cellphone in my pocket
>or use it whenever I need to, nor to use my WiFi equipped laptop for >hours at a time. Hmmm... You need a personal RF safety dosimeter: <http://www.satimo.fr/eng/index.php?categoryid=140> (top 2 products)
Paranoia sells well.
<http://www.narda-sts.us/products_personal_main.php> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 | ||||||||||||||||
>