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Utility Cuts Short BPL Trial
fatboy writes "The ARRL is reporting that Alliant Energy has called an early end to its broadband over power line (BPL) pilot project in Cedar Rapids, Iowa. The "evaluation system" went live March 30, and plans were for it to remain active until August or September. Alliant shut it down June 25. Ongoing, unresolved HF interference from the system to retired engineer Jim Spencer, W0SR, and other amateurs prompted the ARRL to file a complaint to the FCC on Spencer's behalf demanding it be shut down."
This is exactly the same reason that a Broadband over power lines experiment was given up by one of the UKs power providers (The predecessor to Scottish power I think).
I wonder why someone thaught it would be different in the US, even with its more stringent laws about RF interference.
Do these people not do basic searches on prior work?
There is much more than sad lonely guys in their bunkers involed in interference on the HF bands. If you go to that link, most of the frequencies are labelled Army, Navy, Air Force, Coast Guard, emergency response, etc.. All these would be subject to inteference out by widespread BPL deployment.
I live in Cedar Rapids and participated in the program. I didn't RTFA so I'm not sure what it says about this, but the mailer I got a couple days ago didn't say anything about a complaint, it just basically said Alliant had met its goals for the program ahead of schedule, and after working out a few issues there is a possibility the system may be implemented on a larger scale.
On the 0th day, God created C
I've never understood why they were so gung-ho about this stupid idea in the first place when most power grids already have multi-core fiber optic cable hidden inside the neutral wire. (they use it to communicate between substations and most of the capacity is dark - I put hundreds of miles of this stuff in the air back in the mid-nineties so I know from whence I speak) The power company already has the most valuable easements. Couple that with their existing fiber grid and they could have fiber to the curb in every major market for a lot less than the phone or cable companies who very often have to mount on existing power poles and pay $1 or more per pole for easement rights.
That's how SPRINT became a major Playa in the long distance and later, the backbone market - they used their existing easements. (for those who live in a cave, SPRINT stands for Southern Pacific Railway INTernational - your phone call 'rides the rails'...or more precisely, runs over fiber optic plowed into the roadbed of their gigantic network of railroad tracks)
Nope, it doesn't appear to have been fully rejected. Scottish Hydro Electric appear to offer the service. Website with details here:
Cheers,Scottish Hydro
Mike
Unshielded transmission line will create signals that interfere with radio service.
Not necessarily so.
Unshielded balanced feeders have been widely used ever since the introduction of RF transmission and the losses can be lower than a sheilded cable if done properly. Leakage will always be slightly higher -- but can still be extremely low providing the lines are balanced properly.
Many years ago I built a balanced unsheilded RF link that was over a mile long on a farm for a CB radio. With an input power of 500mW and a matched dummy load on the other end, the leakage from that feeder was so low as to be almost undetectable beyond a few tens of yards.
I expect that the problem the BPL trials are having is that the power circuits are not balanced at the RF frequencies (or harmonics thereof) that are being used.
Achieving and maintaining high levels of balance across the entire spectrum being used is probably going to be a *major* problem that will stand in the way of this technology.
If you are truely a licensed Amateur AND a slashdot reader, then you have no excuse whatsoever to actually go and RTFA.
If you had done even a modicum of research into this, you would know that what the ARRL and others are complaining about is BPL or PLC in europe that uses the HF spectrum for transmission. Over long unshielded agind powerlines, this == big fscking antenna. Hence the bleed, and RF issues ensue.
They have also stated (the ARRL and others) repeatedly that they have no problem with BPL itself. They have problems with the power companies that are trying to roll this out to make an extra buck or two. I mean, lets face it, many power companies have problems just keeping the power going, let alone BPL... and to have to handle interference complaints as well?
But in any case, the people who are against BPL, as I said, are against the version that uses the HF spectrum. Not just parts of the HF spectrum, but the ENTIRE HF spectrum from around 3 to 30+MHz. They support other means readily, such as the BPL system that was being developed in the desert that used gigahertz transmission frequencies instead of HF freqs... or the aforementioned fiber wound around the power lines, and some companies ALREADY have cable wound around the powerlines that they use themselves.
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In theory, you can use almost any pair of wires to carry a broadband signal. That's because in theory, any pair of wires are perfectly conductive. Also, as soon as an extra electron tries to enter one end, another one drops out the other end, instantaneously, and if you try to pull an electron out of one end, another will be sucked in at the other end, equally instantaneously.
..... well, they don't have a word for it, they call an engineer to fix it. But what you need to remember is that the potential difference (voltage) across a capacitor can only change gradually, never suddenly; and the current through an inductor also can only change gradually, never suddenly.
It ain't like that in practice.
Imagine a drainpipe stuffed with tennis balls. When you try to push in an extra tennis ball, what happens is that all the other tennis balls give a little, and for one fleeting instant there really is an extra ball in the pipe. Then the balls expand back to normal size and one is shoved out the far end.
Now, any pair of wires will have a capacitance (since they are conductors separated by an insulator), an inductance (since they are wires; at low frequencies you need a full-on coil to get any effect, but at high frequencies any slight bend will do the job) and a resistance (since they aren't perfect conductors). It's what electrical engineers call a composite impedance, and what everybody else calls
For any given transmission line, if you stick a battery across the terminals at one end and a resistor across the terminals at the other end, look at each end with an oscilloscope and have some magical way of lining up the time axes, you won't see just a simple step change of voltage. When you apply the battery to the T.L., it looks like some composite impedance (which it is) and likely draws more current than the resistive load at the far end wants, since it's charging up the capacitance of the line -- or less than that, since it's charging through an inductance. One or the other phenomenon will win out every time.
Once the capacitance of the line has charged -- via the inductance and resistance of the line -- it then begins discharging into the resistor on the far end. Actually, it doesn't wait at all, but starts discharging as soon as it has begun charging. And what you may even see, is a pulse of current reflected back towards the battery, if too much current went in at first compared to what the resistor was expecting. You can even get multiple reflections if the first one isn't exactly right. What you essentially see on the scope traces is a damped sine wave at the frequency at which the resistance and capacitance of the line resonate -- and a delay between applying power from the source and seeing it at the load.
That's what you get with DC. With AC, the capacitance and inductance tend to distort the shape of the waveform, but not change the frequency -- though it's very likely that other frequencies will be added in. Also, anything under a few hundred kHz behaves mostly like DC -- albeit more-or-less-slowly-changing DC -- but broadband networks need carrier frequencies measured in MHz, and by the timed you get to that sort of frequency, the AC phenomena are well established.
Now if all you are concerned about is getting the maximum energy throughput, as are the electricity board for example, then you want to minimise resistance (which turns energy into heat -- capacitance and inductance just store it in electric and magnetic fields, respectively, then give it up again) even if that makes the line highly capacitive or inductive. All that will happen is that you'll get a huge reflection the first time you connect up, then a series of ever-decreasing ones, but most of the power from your source ends up in the load even if it takes awhile to make it down the line, and even if the shape of the waveform is significantly altered.
If you want a transmission line that does not
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