Quote:
Originally Posted by Lobster Ring
Many thanks Escapee.
I have noticed that the rails are no longer disjointed, they put a thick wire and connect disjointed lines/pints on the side, no idea why.
Why can't they apply the short-wave idea used on the powerlines?
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I guess they could, but I think it would be limited bandwidth.
I think the comms they used on the rails long ago was just audio for communicating with the train drivers, this was multiplexed upto a higher frequency possibly to get extra channels and also to put it outside the human hearing range.
I'm not sure how their automatic signal system works, perhaps someone may know if its done via RF telemetry or some other method?
I'm not sure how they got around the fundamental problem of wooden sleepers being good insulators in the hot summer months, and fairly good conductors in the wet months. I couldn't see the system working for anything more than carrying audio or low speed data. I dont know how much of the rail network is now continuously welded rail ie: no joints, fish plates etc. But some of that used to use concrete sleepers, all this low frequency stuff below the HF band is not really an area I have ever got involved with. Putting LF/HF signals down the mains and relying on transformers and some capacitors to offer a high resistance to 50Hz is something I dont go near.
I would say putting LF/HF etc down a railway line wouldn't work, but apparently it does. I guess it was a matter of using what was available as a cheap implementation for communications, just the same as ADSL is.
PS: I wonder how they managed with comms when a train was on the line, ie: shorting the two lines together via the axle. I guess it could work because the frequency used wouldn't see it as a short unlike 50Hz or DC.