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FCC Approves BPL Despite Interference Concerns
goosman writes "The ARRL is reporting that the FCC has approved revised Part 15 (unlicensed services) rules to specifically regulate the deployment of broadband over power line (BPL) technology. The Commission adopted a Report and Order in ET Docket 04-37 when it met in open session today. At the same time, three members of the Commission, including Chairman Michael K. Powell, specifically mentioned the concerns of Amateur Radio operators at the open meeting and expressed either assurances or hope that the new BPL rules will adequately address interference to licensed services."
Historically, amateur radio has been used as "emergency frequencies" in natural disasters. Especially when standard infrastructure (like, you know, phone and power lines) no longer work.
Finkployd
Trials of this technology were abandoned in the UK in 1998/1999 (I seem to recall), due to the problem of street lights acting as transmitters, causing significant interference with emergency services transmissions.
It was accepted at the time that the cost of adding the necessary filters to each streetlight was too much to continue with the project.
Of course, technolgy has improved significantly in the last few years, maybe this has now been resolved. But it's quite possible that the system may be able to work in some areas and not in others simply because of the way your road's street lights are wired up.
Jolyon
Please read my Canon EOS tech blog at http://www.everyothershot.com
The twisted lines you saw and the twisted lines that would supposedly stop interference are two different things:
- A standard power cable is a long steel cable with an outer layer of aluminum strands twisted around it serving as conductor.
- A "twisted pair" of lines are two lines, corresponding to the signal line and the return path, that are twisted around each other. The idea is that if the same signal travels in both directions, the lines will each generate an equal but with opposite sign EM field (which is what causes interference), and these two fields will effectively cancel eachother out.
Unfortunately, if you twisted power lines, you'd need insulation tens of centimeters if not meters thick to prevent arcing. High voltage lines can run up to 400kV, and standard insulators between those and the cable towers are a good 3 or 4 meters long...
Jw
So, screw HAM radio, right?
<echo mike>
I guess CB Ray-dee-yo is all the communikashuns you ever needed there, good buddy!!
</echo mike>
NEVER underestimate the needs of Amateur Radio in catastrophic situations. BPL interference can propagate great distances. If there is a state of emergency in an area, even if there is no power for many miles, BPL can still affect the reception of signals coming FROM the emergency area. The receiving area, with power, would have trouble picking up the shortwave frequencies due to the BPL that will most likely be present. A lot of the popular VHF/UHF emergency frequencies, apparently not affected as much as shortwave frequencies, are difficult to use in hilly or mountainous regions.
An article By UK Columnist Peter Cochrane last year give a nice list of why this technology won't work, even though it has been claimed as "Proven" many times:
- Power cables employ low-grade plastic that is unfriendly to high-frequency signals as the absorption per unit length is very high. This alone precludes transmission of high-speed data over significant distances.
- Power cables are not physically symmetrical and are therefore very effective antennas. They radiate energy from high-speed data signals which becomes a source of interference for wireless services including broadcast radio as well as emergency, maritime, aeronautical, military and navigation services. By reciprocity they also suck in energy from every local radio source which further degrades data signals.
- As signals propagate along cables they become weaker but the switching transients from washings machines, refrigerators, vacuum cleaners, electric drills, light switches and other appliances are huge, do not decay at the same rate and swamp data signals.
- Switching transients on power grids with generators going on and off line, dynamic load sharing, fault and maintenance work, all induces massive transients that also swamp data signals.
- Cable joints, transformers, power meters, the on/off nature of electrical appliances and the topology of power grids create large load changes and multiple signal reflection points. This creates a dynamic echo environment where the transmitted signal is further corrupted.
- Real time communications of any kind - whether by telephone, radio or TV - are taken out by the huge voltage transients inherent to power lines and ultimately the data rates achievable for non-real time are also very low.
- Transformers and power meters require a workaround as they present an absolute block to any high frequency signals.
Parent poster is correct, and well explained. Here's another way to look at the twisted-pair concept.
Any electrical circuit forms a loop; you can trace the current going out from the power source, through the load, and back to the other side of the power source.
For an electric power transmission line, this "loop" is the wires on the left and right sides of the power-line crossbar (OK, not all lines look like that, but the principle is the same). You can trace an imaginary line down one side of the power line and back on the other, enclosing a loop 12 feet wide and many miles long, with enormous area. This is one reason power lines are a bad idea for carrying RF signals; they make a GREAT antenna.
For radio interference, the area enclosed by this loop is an important factor; reduce the loop area, and you reduce the radiated interference. The DIRECTION of the current in the loop also counts; a clockwise loop radiates with a phase opposite that of a counterclockwise loop and can cancel it out if the two are right next to one another.
Now imagine twisting the two wires around each other; you get many very tiny loops with alternating CW/CCW directions of current flow in the loop; their net radiating effects cancel out.
Interesting note: Cross-country power lines ARE in fact twisted pairs, to prevent another interference type. At every Nth tower, you'll see the lines cross over so the left-hand line goes to the right. This results in loops of a half-mile length or so; useless for shielding from RF, but VERY important for protecting the grid from geomagnetic storms, where the Earth's magnetic field is pushed around by solar wind. Making the net loop area zero prevents the transmission line from acting as a giant DC generator and blowing out the switchgear, causing major blackouts (this happened in Canada in the 1970s, IIRC).
"My strength is as the strength of ten men, for I am wired to the eyeballs on espresso."
"Twisted pair" refers to both conductors being twisted together.
The idea is that the magnetic field (H-field) and electric field (E- field) from the one conductor, where the signal is travelling one direction, will cancel out the H and E fields from the other conductor, where the returning signal is traveling the other way, leaving no net signal at distances "far" from the conductor (where "far" is defined by the signal frequency).
In a power line, you CANNOT twist the two conductors into that kind of close proximity, as the insulator required to keep the power from going ZZAAP is too large and/or costly to deploy.
Furthurmore, one of the assertions of BPL - that by using BPL "every power plug is an Internet plug" is bullshit. The BPL signal will not cross a transformer - the transformer is designed to pass 60 Hz (US - 50 Hz in the UK) ONLY. Therefor, for the signal to pass the transformer there needs to be a device installed that takes the signal from one side, regenerates and amplifies it, and injects it on the other side.
The only "advantage" of BPL is the idea that you can carry the signal along the long haul high tension runs without extra infrastructure costs. However, that is being determined to be BS as well, as they are finding that they have to install signal repeaters every few km to boost the signal.
If the power companies want to get into the Internet business, great! Let them string fiber along the power lines - they will have MUCH more bandwidth than BPL gives them, much more reliability, much less interference to other services, AND they can apportion a section of the fiber for SCADA purposes (monitoring substations, controlling switching, reading your meter, etc. Note - that data would NOT be transiting the Internet, but would be in a seperate time slot or fiber, so it would not present a security risk.)
www.eFax.com are spammers
Well, here's a pretty good thesis on the topic:
Amateur Radio and Innovation in Telecommunications Technology The summary is "a hell of a lot", and if you want a comprehensive list, read the thesis.
It won't work that way. If BPL interferes with ham radio, the number of operators will decrease below the crticical mass necessary to provide emergency communications, worldwide.
Here's why:
BPL produces interference across the entire spectrum of "high frequency" (3-30Mhz) radio, and a little above and below in fact. The HF frequencies have special properties (on this planet, at least) of being reflected around the world by the ionosphere. A tiny sliver of these frequencies are used by amateur radio operators, but there are litterally thousands of other kinds of licensees worldwide.
BPL power lines radiate this interference, and when the ionosphere is highly reflective, the interference will be sent around the world. Since the FCC denied the request to have the BPL systems transmit identification, there won't be any way for anyone to identify which BPL installation is causig interference, since it might be halfway around the country, or halfway around the world.
There are BPL systems that don't use HF radio waves, but in all the rush to "Step 3: Profit" these technical issues have been ignored, and the comlpanies with the best lobbiests have won.