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Could Broadband Over Power Lines be Dangerous?
falconfighter writes " Broadband over Powerlines, once touted as the solution to many internet problems (developing 3rd world countries, etc.) has a new hazard. The system basically involves putting high amounts of modulated RF on a power line. The Amateur Radio Relay League has the most informative page on the topic.
The hazards include exceeding MPE (maximum permissable exposure), RF burns, and disrupting the HF bands of radio. This last one would also work in reverse, meaning hams, airplanes, or the military keying up their radios could take out large areas of internet service (with airplanes, potentially over several hundred miles)."
Being near a hot unshielded antenna lead of sufficient power output is bad news...
Do note that the problems of interference goes both ways: broadband over powerlines will jam HF communications (including emergency services some places). But at the same time a HF jammer or a HF over-the-horizon radar will jam broadband over powerlines.
HF being global means a jammer in the Pacific can take out broadband in Europe.
HF radio is *the* communication medium for many life-critical situations. It is the only affordable communication line for many NGOs operating in third world countries, and HF equipment is much easier to setup and more rubust than satellite equipment.
Until now, the HF spectrum has been carefully regulated to avoid harmful interference. It is just not acceptable to sacrifice it simply to get a cheaper Internet access. There are a good set of broadband technologies available which almost do not interfere with HF users.
Let's hope politicians don't wait to do anything until a true emergency happens...
>>esr>>
Oh goody so now the power companies will have even more control as they blat out most LF/HF wireless within a certain distance of their transmission lines (or should that be antena lines now?)...
Not to mention won't people who choose not to receive broadband via power still be able to tap into the transmission signal and so monitor other peoples traffic easier than trying to splice into the fiber backbone (oh hang on.... wonder if the gov't might not be keen for this very reason)...
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My grandfather was an air-crash investigator, and once investigated a european crash (May have been Switzerland in around 1970, apologies, I don't have any details) in which an airliner had apparently tried to land on the side of a mountain. It was proved that the accident happened due to the local electricity generating grid using high frequency modulation to carry messages over power lines. The chosen frequency was a close enough match to the Instrument Landing System on the aircraft to cause it to engage. I hope modern airliners have better ILS.....
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I know most of the big cities have their power lines underground (at least mine did). The broadband company took it to their challenge to even put the broadband cables underground. I guess that could provide sufficient shield along with the shielding on the cable itself. Now the question is cost of doing this over the entire country, which I have no clue. Again I am just curious as to how will these two cable interact because it is failing my general electromagnetic knowledge.
What some power companies here (norway) have done is to use a special kind of machine (it looks like a really clever invention) that "spins" fibre optic cable(s) around high voltage power lines. This doesn't work for buried power cables, ofcourse. This technique gives several advantages: Cheap, the cost is the cable and a helicopter, no digging, no new cable masts, no buying right of way. Security (I'd think twice before trying to mess with a cable wrapped around a high voltage line :D ). And since light won't be disturbed by the magnetic fields generated by the current there is no need to worry about power and data interfering with each other
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The hazards of RF exposure are still being debated. Hazards from BPL would need years of study. That being said people are probably at more risk from intentional radiators like WiFi points. This is due to the way the body absorbs RF. The absorbtion is a function of the wavelength of the RF and the size of the human body. I don't remember the exact data but the shorter the wavelength the better the absorbtion. This does have some exceptions but I do remember a strong absorbtion around the 1Ghz range.
The interference problem is the greater of the two. Yes it will interfere with radio communications but the interference will be worse for BPL. Aircraft have the potential to cause interference over a wide area due to their altitude, but the tranmitter is relatively low power. The real problems will start when a ham operator can't talk to his buddy 20 miles away. They get tired of the interference so they kick in the linear amplifiers. Since the max leagal power for most of the bands is 1500 watts they have the potential to take out BPL in a very large area.
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I agree that MPE limits and RF burns should not be a problem. I'm not sure where the original poster got that from - I also don't see it on the ARRL site.
HOWEVER, the interference concern is VERY real. 250mW can go a long way - I'm not sure where you get your "few hundred meters" figure from. I know people who operate "QRP", a low-power mode, who regularly use similar power levels to talk to ham operators hundreds of miles away!
Let's not forget, a "transmission line" at 60 Hz is much more like an ANTENNA at HF! Powerlines will radiate VERY well.
What's so different about the interference from BPL is that its broadband - that is to say the signal is several tens of MHz wide, spanning all of the HF bands. A spur from another local noise source or unlicensed device is less of a problem because you can simply use another frequency - with BPL this is not possible.
Make no mistake, BPL poses a real problem to HF communication.