OvermodThe far-better short-term approach to LOS in DPU radio is to wire tunnels (and other 'problem' signal-integrity areas) with the same kind of re-radiating antenna setup used to provide FM radio in road tunnels.
The technology exists for the railroad bands in the form of "both directions amplifiers" (or "BDAs") used for bringing public safety signals into buildings.
Many of the digital public safety frequencies only reach a short distance into buildings. Being a repeater based system, a radio (ie, hand-held) has to hit the repeater to be heard, unless simplex mode is used. BDAs make that possible.
I believe the technology is used by the subway folks as well.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
caldreamerI am suprised that the railroads are not using satellite communications which would eliminate dead spots.
The technology is most certainly not a cure-all for many of the reception problems that affect either full-integrity signalling or train control. This is not the same thing as either satellite TV or satellite radio in that uplink as well as reception is involved, and the round-trip latency is already restricted by speed-of-light considerations. The relatively high frequency and very low signal strength make reception more than usually directional, and if I recall correctly there is strong absorption through water vapor or precipitation in cloud of any particular depth; you still have the problem of providing repeaters or passive antennas in tunnels or other 'attenuated-signal' areas, and providing some method of resolving multipath considerations... now at GHz frequencies instead of railroad-band with current forms of modulation.
One of the great promises after the 2008 mandate was that it would make possible an effort by 'the railroads' (perhaps orchestrated by an industry representative organization like the AAR or a regulator like FRA) to develop a highly accurate communications network along its lines that would enable high-accuracy differential GPS in conjunction with reasonably-harmonized GIS available to local communities as a business. There have been a number of good local atomic time standards for the required differential beacons for nearly the whole time of the mandate. As far as I know, all this opportunity has been frittered away, or the effort compromised by other aspects of PTC as it has come to be implemented.
The far-better short-term approach to LOS in DPU radio is to wire tunnels (and other 'problem' signal-integrity areas) with the same kind of re-radiating antenna setup used to provide FM radio in road tunnels. Reasonably redundant if that proves to be desirable. Ought to help with voice-radio communications and probably the SDR radio frequencies and modulation used by PTC, too.
Locomotives do (data)
caldreamer I am suprised thet the railroads are not using satelitte communications which would eliminate dead spots. The technology has been ou there for years. Caldreamer
I am suprised thet the railroads are not using satelitte communications which would eliminate dead spots. The technology has been ou there for years.
Caldreamer
And even out in the wide open, there are a couple of signaled intersections where, if I get stopped, I lose the satellite radio.
Brian (IA) http://blhanel.rrpicturearchives.net.
Even satellites have dead spots, e.g. tunnels, natural and concrete canyons.
Even if everything is working properly, propogation can be bad. Some days I can hit one of our amateur radio repeaters loud and clear (it's about 45 miles away).
Sometimes it might as well be in Timbuktu. I can't hear it, and it can't hear me.
Both railroad radio and two meter amateur radio are in the same basic band, about 10 MHz apart.
caldreamerAre there times when trains loose communications with the dispatchers due to dead spots just like you get with cell phones?
Dead spot locations for RR radio coverage are well known by both the crews and the regular dispatchers of the territories. All concerned do their best to work around the situations when necessary.
The reality is all forms of radio are subject to dead spots - in my own neck of the woods - whenever I drive the 4 blocks that constitute 'downtown' of my city - that is a near deadspot for commercial FM radio reception from transmitters that are East or West of the town. Since I don't routinely listen to stations that have their transmitters North or South of town, I don't know if they are also affected. Downtow is in a valley that is nominally created by hills on all 4 geograpnical directions which are bisected by the Patapsco River.
Never too old to have a happy childhood!
Absolutely...better than it used to be.
Are there times when trains loose communications with the dispatchers due to dead spots just like you get with cell ohones?
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