This is good use for a scope.

The Southern Pacific Railroad connection with SPRINT was only for a few years, roughly between 1972 and 1982, when SPC merged with GTE. See the history at:

Running fiber optic cable along railroad right of way makes sense since the railroads seem to have cart blanche on their right of way. I don't know if they have an additional fiber optic sensor related to the tracks.

The power companies have been running fiber in ground wires for years, but it is probably dark.

It would be interesting to know just how much dark fiber there is and who owns it, but I suspect such a document doesn't exist.

of

tracks.

From my field experience, a lot of it is 80 to 90% dark. There are some cases where 50 to 75% is lit though.

?-)

I can't see why geometry would have much effect on the overall propagation delay. If one's concerned about the wave velocity, one need only perform the experiment from both ends. That gives the total propagation time for the cable, and thus the proportion of the cable traversed to the fault, provided, of course, that there's only one.

Sylvia.

It has a lot to do with it.

Power cables made with materials that are soft tend to not hold their wall thickness as they are twisted and bunched. Sending a fast raise pulse down the cable results in random readings from one length to another. If it were cables like molded twins or coax, you could then use that method, however, even molded twin laying on top of each other on a spool can cause that reading to be random.

Of course we are talking about lengths of 1000 feet or more.

After I thought of the idea originally, I then remembered that we tried experimenting with a TDR on these types of cables and it wasn't consistent enough to use. It works great on small signal twisted pairs and such.. Those types of cables must maintain their physical structure though out.

So it boils down to using a wheatstone bridge with HV if opens are to be found.

Jamie

Many years ago, when I was working on toll roads, they were trying to make a truck scale using fibers embedded in a rubber strip in the road. After spending quite a few bucks (including a test installation on the Autobahn) they finally figured out that the environment was too variable to get reliable measurements. Temperature, water, snow, rubber aging, they all changed the response significantly...

Charlie