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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here
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To: Sam Citron who wrote (888)5/19/1997 2:09:00 PM
From: WTC   of 12823
 
Many years ago there was a Bell System carrier system designed for rural telephony over power lines ('J' carrier as I recall, but I never had any personal exposure to it.) The inherent problem with power line carrier systems is you need to couple (probably capacitor couple) at the high-voltage side, because a transformer has very significant impedance to a high-frequency data carrier -- it's a giant inductor. The better answer seems to be using the power line poles for placing a power system fiber cable. On the really large high-voltage systems, it might be a fiber buried in the right-of-way, where the support tower spacing leaves you with more sag in the communications cable than you want to accommodate.

There are a few very high voltage DC transmission systems in the US - over 700kv. I would not want to mess with that kind of voltage but at least you don't have the same inductance problems as with the more usual AC systems.

There is an experimental powerline carrier system in Bali, Indonesia, that went in originally around 1990. It's low capacity for low density communications, as I remember, and I think it may have been supplied by Siemens. It is (was?)capacitor coupled with opto-isolators to the communications network,I believe, and the "power grid" on Bali never gets into really high voltages. Just judging by the insulators on the poles, I'd guess it was somewhere in the 68Kv range on the transmission backbone.
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