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AM Radio Waves May Be Harmful?
Klar writes "Wired News reports that: 'Korean scientists have found that regions near AM radio-broadcasting towers had 70 percent more leukemia deaths than those without.' The article continues: 'The study, to be published in an upcoming issue of the International Archives of Occupational and Environmental Health, also found that cancer deaths were 29 percent higher near such transmitters.' While 'their study did not prove a direct link between cancer and the transmitters', the FDA and the World Health Organization are urging more studies, especially of radio waves from cell phones."
1) Assume a cell phone antenna is 1 inch away from your head.
2) Assume a 50,000 watt AM transmitter
3) Assume a 1 watt cell phone.
4) We know radio energy diminishes from the source outward at 1/r^2.
5) The square root of 50,000 is approx 224.
So, the energy being pumped into your head by your cell phone is roughly equivalent to standing 224 times farther away from the AM transmitter than your cell phone is from your head (which is one inch).
224 inches is around 19 feet. A 1 watt cell phone pumps more energy into your head than standing 20 feet away from a 50,000 watt AM transmitter.
It pumps more energy into your head than standing 27 feet away from a 100,000 watt transmitter.
-- "A chicken is an egg's way of making another egg."
/me Runs to the calculator...
.10 m from the phone, then the power passing through it is roughly 8 watts / m^2. (Determining the cross-sectional area of a brain and computing actual power is left as an exercise for the reader.) A 50 kW AM transmitter achieves this density of power at a radius of about 22 meters. So, if the tower is more than 22 meters high, it is safer to stand directly under it than it is to talk on a cell phone.
Well, the power spreads out at a rate proportional to the square of the radius. So, if your brain averages
Unknown host pong.
or
3. "But think of the children"
I actually worked with a group doing mobile phone testing. We found that the radio waves penetrated very deeply into the skulls of children 12 years and younger. At the time it wasn't a problem because there were very few kids of this age with mobiles.
As to whether it caused damage or not... no idea. We just did the physics.
Norman Cook's Ode to Sl
In any case, the amount of power the human body absorbs from a 1500kHz AM signal is phenomenally small. The body is small compared to the signal wavelength (2m/200m=0.01 wavelength), which means it absorbs almost none of the radiated power. The only way it is likely to be a hazard is if you touch a conductor with considerable RF voltage on it. That could give you an RF burn.
A handheld cellular phone emits a maximum of 600mW, but rarely does so in an urban setting. (Remotely mounted antennas are allowed to transmit up to 3W or 4W.) The power emitted is adjusted based upon the tower's reported reception strength. Not only does this conserve battery power, but it helps reduce congestion in the cell network by keeping your signal from straying into the next cell over.
"But it's RF!" you say. So, what is it that RF does? It induces current, and mostly in a conductor the same length (or fraction of the length) as the wavelength of the signal. Now, the 350mm wavelength emitted by an 850mHz transmitter (300,000,000 m/s / 850,000,000Hz = 0.353 meters, or a half length of 0.167 meters (~6-1/2 inches) is actually pretty close to the width of the average skull, so we can assume that the skull will effectively absorb some of that energy. How much?
Interesting ... A quick trip to Google found an Amateur Radio RF Safety Calculator and I entered the following values: 600mW, 2.2dBi gain antenna, 0.1 feet from antenna and 850 mHz, and it tells me that I'm not in the "safe zone" -- I need to be 0.22 feet from the antenna. According to the FCC, the maximum permissible exposure in a controlled area is 2.84 mw/cm^2, but the cell phone is exposing me to 8.5293 mw/cm^2.
I may have to rethink my cell phone usage... :-(
John