New study warns of risks from emissions, suggests towers be kept away from homes - Page 2 - Canadian TV, Computing and Home Theatre Forums

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post #16 of 38 (permalink) Old 2010-11-11, 09:09 PM
 
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I haven't read the article, but most of you have missed a point here. A cell phone tower (base station) does not only transmit on the cellular frequencies, but also on microwave via the microwave dishes for the backhaul. The dishes are directional and such there should be little stray RF energy going elsewhere except to the other dish far far away, but it is still possible there is some stray energy that is radiated to nearby area.

If the study is about microwave, then this is the microwave energy that I will be thinking of. No cellphones today utilize microwave frequency range (1.9GHz is close but not microwave yet).

Your home microwave oven operates in the 2.3GHz spectrum (close to the WiFi / ISM 2.4GHz one), as a comparison.

What RF energy is dangerous or not, depends on many factors, the intensity of the energy, and possibly the frequency but so far science is far from a consensus. Yes, I have been following this bit since the 80's myself.
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post #17 of 38 (permalink) Old 2010-11-15, 08:00 AM
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^^^^
The microwave links don't run that much power and are focused into a beam by a parabolic antenna Also, "microwave" is an arbitrary term, usually meaning frequencies above 1 GHz. There won't be much of a difference in characteristics between a signal at 1.9 GHz and 2.4, other than frequency.
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post #18 of 38 (permalink) Old 2010-11-15, 10:28 AM
 
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Microwave links are not hazardous to the public because of the restrictions imposed by safety code 6. All the radio energy sources are taken into account when making this calculation. As you can imagine it gets really complicated for locations like the CN Tower with dozens of transmitters and the requirement to determine exposure levels on nearby buildings. There are meters to measure RF exposure to ensure that the calculations reflect reality. The safety code 6 calculations are required as part of the licensing process and periodic site surveys with a meter may be required.

That said, the area in front of a microwave dish can be hazardous because the energy is focused into a small area just like light in front of a flashlight. The effective radiated power in the main beam of the antenna can be in the kilowatt range. Microwave antennas are usually located where public access is not available like the top of a tower or the roof of a building. If the safety code 6 calculations show that RF energy levels exceed code where a person might go then signs and physical barriers may be required.

The world has been dealing with microwave energy for over 60 years so the health issues are generally understood. Safety codes exist that protect the general population from casual exposure and workers from occupational exposure.
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post #19 of 38 (permalink) Old 2010-11-15, 12:04 PM
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^^^^
On the microwave level of the CN Tower, the space behind the microwave dishes is shielded, with warning signs on access doors to where the antennas are (behind that huge white "donut"). Also, the telecom office up there, where I'd occasionally go to do some work, was inside a Faraday cage. When the CBC built their building on Front St. W., across from the CN Tower, they had to install a lot of shielding to prevent interference.

BTW, work with microwaves actually (slightly) predates WW2. Many of the WW2 radars used microwave frequencies even back then. It was the British invention of the http://en.wikipedia.org/wiki/Magnetron that made those radars possible.
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post #20 of 38 (permalink) Old 2010-11-15, 12:20 PM
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I went looking for the safety code because i thought it might be relavent to the discussion here, but i see it was revised in 2009 and health canada has it for sale, not for download. The 1999 version is available for download from other sites.
Safety code 6, published by health Canada isn't law itself. But since it has been referenced in MOL court procedings, it has become the law of the land.
It would be interesting to see what the differences are between the 1999 and 2009 versions.
Inseresting to note that the new version comes with "Technical Guide for Interpretation and Compliance~" that sounds like a CYA.
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post #21 of 38 (permalink) Old 2010-11-15, 01:57 PM
 
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Originally Posted by fortissimo View Post
I haven't read the article, but most of you have missed a point here. A cell phone tower (base station) does not only transmit on the cellular frequencies, but also on microwave via the microwave dishes for the backhaul.
Of course, the use if microwave backhaul is far from industry wide. Lot's of fibre-optic and copper backhaul too.
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post #22 of 38 (permalink) Old 2010-11-16, 06:06 AM
 
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I remain quite skeptical. If this were accurate, UHF broadcast would have killed us all long ago.
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post #23 of 38 (permalink) Old 2010-11-16, 10:21 AM
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And if you sat beside a UHF transmitter for a few years, you'd be dead by now.

Folks really need to read the report before commenting.

All electronic transmission devices pose a potential danger, the point is to employ these devices in a safe manner. Heck toothpaste is something we let our kids use twice a day but if they swallow a tube of it, it could kill them. Even "safe" products can be dangerous if used or implemented incorrectly.

I would hope that Industry Canada (or relevant government body) has very specific regulations about transmission towers and their proximity to people. My sense is they do not.



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post #24 of 38 (permalink) Old 2010-11-16, 10:45 AM Thread Starter
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I would hope that Industry Canada (or relevant government body) has very specific regulations about transmission towers and their proximity to people. My sense is they do not.
I think they call it "Specification Creep". Given enough time and the absence of standards, safety will always give way to function.
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post #25 of 38 (permalink) Old 2010-11-18, 12:44 PM
 
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Originally Posted by hugh View Post

I would hope that Industry Canada (or relevant government body) has very specific regulations about transmission towers and their proximity to people. My sense is they do not.
Well you'd be wrong.

"To protect the general public, Health Canada maintains its guideline document entitled Limits of Human Exposure to Radiofrequency Electromagnetic Energy in the Frequency Range from 3 kHz to 300 GHz, which is commonly referred to as Safety Code 6. This document has been adopted by many organizations across Canada and is referred to in several regulations. Industry Canada has adopted this guideline for the purpose of protecting the general public. "

You can get the whole rundown here:

http://www.ic.gc.ca/eic/site/smt-gst...f08792.html#s4
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post #26 of 38 (permalink) Old 2010-11-18, 12:48 PM
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so robsaw you are saying that they do have "specific regulations about transmission towers and their proximity to people"

So what is the minimum recommended distance from humans for cellphone towers?



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post #27 of 38 (permalink) Old 2010-11-18, 01:06 PM Thread Starter
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So what is the minimum recommended distance from humans for cellphone towers?
Judging from the last diagrams the answer is 0m at ground level. Hmm?

http://www.ic.gc.ca/eic/site/smt-gst...e/Picture2.jpg
http://www.ic.gc.ca/eic/site/smt-gst...e/Picture3.jpg
http://www.ic.gc.ca/eic/site/smt-gst...e/Picture4.jpg
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post #28 of 38 (permalink) Old 2010-11-18, 02:39 PM
 
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The safety regulations are not stated in terms of the proximity (distance)of people to sources of radio energy rather they deal with exposure to radio energy. Exposure levels are determined by calculations including such parameters as frequency, number of channels, antenna patterns and effective radiated power. The calculations show the locations, if any, where the level of exposure exceeds accepted standards. The calculations are 3 dimensional as antennas are typically on towers or building tops. Antennas usually have gain which in practical terms means the vertical radiation pattern of the antenna is compressed so more power goes out toward the horizon and much less goes to the ground. The power is focused much like the beam from a flashlight.

Each transmission site has its own considerations for exposure levels. Most towers don't have enough transmitters or ERP to create exposures at ground level in excess of the standards. Problems are more likely to occur on the roof tops of buildings from high power broadcast transmitters located on top of a nearby building. No single minimum distance rule will be appropriate because it will inevitably be based on worst case assumptions and needlessly prevent companies from locating transmission sites where they are needed to serve the public.

BTW, Industry Canada does not make the rules about acceptable levels of exposure, that's a health issue, but I believe they are responsible for ensuring they are followed.
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post #29 of 38 (permalink) Old 2010-11-18, 02:53 PM
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GeorgeMX, so are those regulations completely applicable to Cell phone towers?

Personally, as a Canadian citizen, I am just concerned that Canadians are being protected with a generous allowance. Cell phone towers on top of apartment buildings or office buildings seem to be in close proximity to people (as opposed to radio towers which are often well away from people) so I think its important that we are vigilant.



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post #30 of 38 (permalink) Old 2010-11-18, 10:06 PM
 
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Originally Posted by hugh View Post
GeorgeMX, so are those regulations completely applicable to Cell phone towers?

Personally, as a Canadian citizen, I am just concerned that Canadians are being protected with a generous allowance. Cell phone towers on top of apartment buildings or office buildings seem to be in close proximity to people (as opposed to radio towers which are often well away from people) so I think its important that we are vigilant.
As far ask I know they apply to all licensed radio base station sites which includes cellular. I don't know if they have exempted the micropower sites used indoors and on street corners. The ERP per channel on these sites is comparable to cell phone levels.
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