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 Seuss
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 Re: Piggybacking ethernet over power lines  [Re: Stonehenge]
#14384268 - 05/01/11 06:44 PM (12 years, 11 months ago) |
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> BH, the answer to that would depend on a lot of factors.
Power transformers tend to have a high inductance, therefore they act as low pass filters (they only allow low frequencies to pass through them).
> Cable tv signals seem to propagate quite easily.
Cable TV uses shielded coax cable and amplifiers.
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 johnm214
 
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Re: Piggybacking ethernet over power lines [Re: Stonehenge]
#14386884 - 05/02/11 04:54 AM (12 years, 11 months ago) |
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Quote:
Stonehenge said:
"They could have done just that, but apparently, HAM radio doesn't have an effective lobby as do the manufacturers of electronic equipment. So basically, when HAM amateurs complained about this unlucky selection of frequencies, they were just ignored by the authorities."
Then why don't we see it now?
Because the FCC somehow managed to mess up their own process so badly that it effectively violated the very tiny and insubstantial legal rights user's of the spectrum have. Basically: they did exactly what Koraks said: not only ignore the enthusiasts but ignore their own procedures and ignored their own research.
The FCC ruling was so ridiculous that it was ruled to be illegal- and that's saying something when you look at the anemic laws and how little rights they give the public.
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Seuss
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Re: Piggybacking ethernet over power lines [Re: Stonehenge]
#14386961 - 05/02/11 05:53 AM (12 years, 11 months ago) |
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I didn't have time to get into the science of this the other day. I have a few minutes this morning, so will highlight a couple of points. Unfortunately, this is pretty heady stuff that was taught in my electrical engineering fields and waves class; it is not easy to understand without a solid understanding of the foundations of electrical engineering. Trying to keep it simple...
> Why would no signal propagate down the wire?
In a nutshell, the lower the frequency of the signal on a wire, the less important the properties of the wire become. There are several factors that come into play as the frequency increases. Skin effect is one. As the frequency increases, the charge carriers distribute along the edge of the conductor rather than than being distributed evenly throughout the wire. Because of this effect, the diameter of the conductor can have a significant impact on inductance of the wire at the frequency of the signal. Another factor that comes into play as signal frequency increases are connectors. Most high power transmission lines are bolted together by a splicing connector. This type of connection is fine for low frequency, but higher frequency signals will bounce back rather than continuing to propagate. Another issue at higher frequencies is dielectric loss. Bends and twists in the power line is yet another issue of concern, again leading to signal reflection at higher frequencies. Noise is also a large concern. Power lines are large antennas that pick up noise from their surroundings. They also carry noise generated by the things that they power... every time a motor turns on or off there is a "click" generated on the line. Higher frequency signals are much more sensitive to noise than lower frequency signals. The list goes on...
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Stonehenge
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Re: Piggybacking ethernet over power lines [Re: Seuss]
#14387534 - 05/02/11 09:14 AM (12 years, 11 months ago) |
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Those are valid concerns but what frequency are we talking about?
"Cable TV uses shielded coax cable and amplifiers."
That goes over many miles of cable. This would be short distance. Skin effect would not matter much and the bounce back at spliced connectors is possible but may not be a factor. It depends a lot on how high a frequency you are using.
I think it comes down to economics. You can't just send the signal starting at the power distribution point and expect it to get to the consumer without problems such as the ones discussed in this thread already. You would have to have a receiver in each neighborhood possibly at each transformer to service just a few houses. They already have satellite receivers that you mount on the home. The main benefit of using power lines would be that they are already in place. If the frequencies that would be easiest to use are off limits, and very high frequencies run into problems necessitating units in each neighborhood, then the cost advantage is wiped out. Shielding the power lines can be done fairly easily but it adds to the cost as well.
At super high frequencies, above those used in microwave ovens, the impedance of a straight piece of wire becomes significant and traveling over 100' would not be practical. That's why i ask what frequency we are talking about because a few hundred megahertz can be dealt with but that may not provide the bandwidth needed or broadcast interference might come into play.
Obviously people more knowledgeable about all the factors have looked into it and decided it wasn't feasible. Or it may be that the cable companies have lobbied against it and political pressure was brought to bear. It is an interesting concept though. I'd like to know the reasons they gave it up because at one time it was being seriously considered.
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Seuss
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Re: Piggybacking ethernet over power lines [Re: Stonehenge]
#14387726 - 05/02/11 10:16 AM (12 years, 11 months ago) |
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> Those are valid concerns but what frequency are we talking about?
I'd have to run the numbers, but rough order would be in the 50MHz and up before things get really bad.
> That goes over many miles of cable. This would be short distance.
I'm talking about broadband over powerlines...
> You would have to have a receiver in each neighborhood possibly at each transformer to service just a few houses.
Then you might as well use phone lines instead. As you say, "it comes down to economics."
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koraks
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Re: Piggybacking ethernet over power lines [Re: Seuss]
#14387991 - 05/02/11 11:09 AM (12 years, 11 months ago) |
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I'm not sure why cable internet and ADSL won over Ethernet-over-Power, but the investments in high-speed data infrastructure by power companies is likely to have been an issue. While cable providers and telco's usually have the organizational infrastructure to manage those projects, the competencies of power companies tend to lie in other areas. I think that may have prevented EoP from enjoying a first-mover advantage, and I guess power companies are too occupied with keeping their primary service available to worry about expanding their portfolios too much. I suspect that here in The Netherlands, some EoP offerings will probably materialize in the next few years, as the network is being prepared for 'smart metering', which requires bi-directional data communication as well.
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Seuss
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Re: Piggybacking ethernet over power lines [Re: koraks]
#14388114 - 05/02/11 11:40 AM (12 years, 11 months ago) |
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> I'm not sure why cable internet and ADSL won over Ethernet-over-Power
A big part of it is available bandwidth and economics. It is much cheaper to push a lot of data down a phone line than it is to push a lot of data down a power line. The difference in cost is due to previously mentioned problems associated with power lines.
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Stonehenge
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Re: Piggybacking ethernet over power lines [Re: Seuss]
#14388160 - 05/02/11 11:49 AM (12 years, 11 months ago) |
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"I'm talking about broadband over powerlines..."
Broadband over power lines could mean you inject the signal at the distribution point or at the low voltage end or somewhere in between.
"I'd have to run the numbers, but rough order would be in the 50MHz and up before things get really bad."
50 mz is not that high. You can run a signal at that frequency and not worry too much about the things we discussed. Or you could engineer around the problems. Of course it still would not go through a transformer but you could put a bypass cheaply on each one.
"Then you might as well use phone lines instead."
They do. Phone lines are not shielded either so i wonder why not power lines? Seems like you could do it just as easily.
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“A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835)
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koraks
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Re: Piggybacking ethernet over power lines [Re: Stonehenge]
#14388235 - 05/02/11 12:08 PM (12 years, 11 months ago) |
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Quote:
Stonehenge said:
"I'd have to run the numbers, but rough order would be in the 50MHz and up before things get really bad."
50 mz is not that high. You can run a signal at that frequency and not worry too much about the things we discussed. Or you could engineer around the problems. Of course it still would not go through a transformer but you could put a bypass cheaply on each one.
50mc is difficult enough for infrastructure that is designed to carry 50 or 60Hz. Theoretically, it is possible to engineer around all problems discussed, but if it's economical to actually implement the solutions is another issue. For example, your earlier suggesting of slipping a shielding layer around power cables sounds pretty easy, but if you dig open the sidewalks, you might as well just drop in a bundle of fiberglass and be done with it. And that's exactly what's happening in certain areas.
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Stonehenge
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Re: Piggybacking ethernet over power lines [Re: koraks]
#14388379 - 05/02/11 12:37 PM (12 years, 11 months ago) |
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Both phone and power involve 2 conductors. If phone lines needed coax shielding that probably would not have gotten off the ground. But, and this is a big but, phone broadband has much smaller bandwidth than cable. It has it's built in limitations so we might assume the same limitations for power lines. Why build a system that is going to be inferior to start and will be more and more outmoded as time goes on? Phone lines do not have step up or down transformers in the way, making them simpler for broadband use.
20 or 30 years ago power broadband might have made sense but with all the competition today offering more bandwidth plus programming, it probably just does not make economic sense. It sounds simple at first and i still would like to know the real reasons they didn't do it. If they could just put the signal at the high voltage end and give everyone a modem, they could offer it cheap. Obviously there is more to it than that.
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“A democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship.” (attributed to Alexis de Tocqueville political philosopher Circa 1835)
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