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decibels
# Posted: 5 Dec 2006 16:35
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They keep saying things are fine because the levels are (for example) 0.001 (a thousandth) of the "safe" limit but this ignores the way power ratios work in the real world.

There's a HUGE difference between the power transmitted, and the power received - that's how radio manages to work at all in the first place. A 1MW TV transmitter is putting out 90dBm (decibels relative to a milliWatt or 1/1000 of a Watt), whereas GSM phones lose contact with a base station at -110dBm. Although that's comparing apples to oranges in some respects, that still shows that there's a difference in power of 200dB between what *can* be transmitted and the lower limit of cellphones.

200dB is simply the ratio 100,000,000,000,000,000,000 expressed in more managable terms. That's an awfully large number, isn't it? Puts things into perspective?

Try this for size, too :
The ear responds to power levels (of sound) in a log (orders of magnitude) way too, with levels also expressed in dB. Here are some example levels
160 Perforation of eardrum
140 Jet Aircraft Taking Off
120 Human Threshold of Pain
120 Loud Rock Concert
110 Moderate rock concert, dance club
100 Motorcycle
-- extended listening above 85-90dB leads to hearing loss --
90 Lawnmower, loud home stereo
85 Jackhammer at 15 meters (50 feet)
80 Moderate home stereo, ringing telephone
75 Average City Street

Here we see that instant damage to the ear occurs at 160dB, a whole 40dB higher than the level at which loud sound become painful. However, the danger of long-term hearing loss starts at 85dB, which is yet another 35dB lower. That's at least 3000 times difference between the safety limit and the onset of pain, and another 10,000 before severe damage - a combined ratio of 30 million! Now, does it really seem so far fetched to be concerned when we're fobbed off with excuses that a mast's power levels are only 1000 times lower than the safe limit - especially when we're not so much concerned about The Heating Effect (that the limits are based on) but the *possible* biological effect that could occur with lower powered long-term exposure?

It's like being told there's nothing to worry about at the rock concert because 120dB won't do any harm because at the most it's a bit uncomfortable - but we know that it's 3000 times louder than it takes for long term hearing loss if you listen for too long at that level.

decibel
# Posted: 5 Dec 2006 18:43
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http://www.ericsson.com/ericsson/corporate_responsibility/health/files /English/EN_brochure_Base_station_antenna_sites_2004.pdf
- this seems to revel in levels being less than 1% of the limit being safe - yet that's only 20dB lower than the limit!

The difference between a 100m distance and 300m? 3 times the distance allows the signal to spread out 9 times (it's an area thing with a squared relationship), which gives you 9.5dB less power levels.

Different national limits :
( from http://test1.contenttest.net/grenzwerte_d_en.shtml )
0,001 W/mē "Precautionary limit" in Austria
0,02 W/mē Exposure limit in Russia
0,09 W/mē ECOLOG recommendation 1998 (Germany)
0,1 W/mē Exposure limit in Poland
0,16 W/mē Exposure limit in Italy
0,24 W/mē Exposure limit in CSSR
2 W/mē Exposure limit in New Zealand
3 W/mē Exposure limit in Canada (Safety Code 6, 1997)
9 W/mē Exposure limit in Germany and ICNIRP recommendation 1998

that's a 9000 times difference between ICNIRP and Austria's precautionary limit - which is 39.5dB!!

Anonymous
# Posted: 10 Dec 2006 05:43
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Whats the limit in the USA?

decibels
# Posted: 11 Dec 2006 13:56
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The UK currently uses ICNIRP limits of roughly 4.75 Watts per square metre for GSM-900 (935-960MHz), 9.3 W/mē for GSM-1800 (1805-1880MHz), and 10 W/mē for 3G (over 2GHz). These are power densities over an area facing the transmitter. Field strengths can also be measured in one less dimension, as a voltage along a 1 metre distance. The above values correspond to a whopping 42.3V/m, 59.2V/m and 61.4V/m (Power in Watts = voltage squared / impedance, where the impedance of free space (i.e. in the air) is 377 Ohms. Try squaring 42.3 and then divide by 377, the result is 4.75)

dBm are sometimes used for power values, these are decibel values relative to 1 milliwatt (0.001W). So the 4.75 W/mē limit for GSM-900 would be 4750mW/mē = 36.7dBm/mē (press the log button on the calculator and multiply by 10)

Now, with 37dBm spread over a square metre in front of you, how much signal would a mobile phone or piece of test equipment receive? Here we need to consider the size of the aerial in comparison with that square metre. At 950MHz, the 'aperture' of the simple (no gain) aerial is such that levels in the equipment will be about 21dB lower than the W/mē in the air.
aperture = wavelength squared, divided by 4 pi ... GSM-900 wavelength is 0.316m.. squared and / by 12.56 = 0.0079, which is just under a hundredth (0.01), a ratio of -21dB

So, on this test equiment, the ICNIRP limit of 37dBm/mē will appear as a received (measured) power of around +16dBm (about 40mW = 0.04W = roughly 100 times less then the power density in the air) bear in mind that received signal strengths vary quite a lot as you move about even slightly. Precise accuracy is very difficult, it's a bit of an art and typical average values are the best you can hope for in practical terms

At a typical mast this ICNIRP limit only really reaches a few metres around the aerial, as levels fall away rapidly as the signal spreads out. My equipment is unable to read higher than between -30 to -20dBm (the accuracy is questionable at this levels), so I'm about 40dB short of being able to measure up to the limit (-24 is 10,000 times away from +16dBm).

I have seen such -20-something values when VERY close to a mast, such as a pico-cell at street level. But near any sites mounted on a pole, or panels on a building or mast, I've never seen higher than -30dBm, in fact as I drive around on the roads closest to most sites (even a road right next to a telegraph pole mast), it's seldom more than -40dBm. to put this into perspective, a GSM phone will work down to a cut-off point at -110dBm, which is 70dB lower (10,000,000 less power)
Yes, the signal from nearby a picocell in the street can be 100 to 1000 times more, or even higher (at close range) than those you get driving past a large of TV transmitter size. I'd rather live across the road from a large lattice mast (typically -50dBm) than have a small 10m mast at the end of the garden (possibly 20dB more at -30dBm).

So if, typically, the general public are never bathed in more than about -34dBm (measured), this is 50dB less then the ICNIRP safety limit (about 100,000 times less). Those unfortunate cases of masts very close by (next building, at same level) will get much more than this, however.
Note that on my single-channel receiver this is the level of just one broadcast channel (continuous pulsed signal used for control purposes and text messages) and doesn't include the traffic channels (additional radio channels used for calls), or the sum of all signals from other sites too.

So these are the facts, for what it's worth, I'm just trying to help by putting some numbers to it all. Residents about 20 to 100m around a site are getting no more than the order of magnitude of between 10,000 and 100,000 times less signal than the ICNIRP says is safe - which is only considering the heating effect - and not all that far away from the extra precautionary limit 0.001 W/mē in Austria.

If there is a problem with biological sensitivity to pulsed microwaves (and I see no reason not to suspect this until far more unbiased work is done on the subject) then it happening at levels a tiny fraction of what's considered safe by those who keenly accept what they're told at present. Just as epilpsy can be triggered with flashing light levels just high enough to be brighter than the ambient lighting, it could be that pulses of microwaves on a continuous basis significantly higher than background levels (especially within several hundred metres of a mast) may be having an effect. It could be a small effect for some, which would take years for damage to accumulate, or it could be actually felt by those particularly sensitised to it. More experiments, surveys and studies are most definitely required before any real conclusion can be drawn. In the meantime, it would be callous disregard for the public's safety to continue with some of the situations we have at present.

I await further developments with interest.

decibels
# Posted: 11 Dec 2006 14:12
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I believe the USA uses the ICNIRP limit too, but it was so difficult to Google for it, I gave up! Try http://en.wikipedia.org/wiki/Mobile_phone_radiation_and_health and the many links there.

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