"tony sayer" wrote in message
...
To Tony. You're right. In recent years, the electricity companies have
installed fibre optic links,

Energis.. IIRC used to carry FM broadcast and TV to transmitters.

but I'm fairly sure that when they first
started using this method of communicating amongst themselves, they did
make
use of the full distribution network, including the supergrid, but I may
be
wrong on that. How much power volts are on the line, shouldn't make any
difference. It's still just a piece of wire, with HF skin effect, to the
comms signal. I believe that with the PLT internet trials, the injection
points were at central substations, so I guess that this must have been
working at up to at least the local 11kV distribution level. Just as an
aside, I think that the grid and supergrid operate at 275kV and 400kV,

Yep 400 kV. Even so it would be interesting to see how they get the RF
on and off the line;-!!! wouldn't go through the trannies too well
unless they were using Russ A MK-IV snake oil of course;-))

not
475kV. I also have a dim recollection of reading somewhere, that the 25kV
overhead lines on the uk rail nework, were also used for HF telemetry, but
again, I could be going off on one there.

Never heard of that?.

Suffering from CRAFTs disease,
don'tcha know ... !! d;~}

Errmm hate to admit I do know;-0

Arfa



--
Tony Sayer


I guess you would get it on and off capacitively. Not too difficult to make
a cap of a few decimals of a uF at several hundred kV working, I would have
thought. You'd then use these to bridge any high inductances in the way,
such as tranny windings, and to get the data on and off. Depending on the
frequencies involved, you may actually get away with a few hundred pF.

I'm sure that such caps must have existed when megawatt main UHF TV
transmitter sites, such as Sandy Heath, used valve transmitters at the
bottom of the mast ( perhaps still do ?? ). Also, maybe for use in high
pulse power radar ?

Arfa