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Mobile phone signals seem to be interrupted very often when travelling by train. I have been wondering why exactly, and found two reoccuring explanations online:

  • The train acts as a faraday cage, and so blocks radio waves.

  • The train is moving too fast for a clear signal to be received.

Both of these arguments, however, seem also to hold for cars (inside which I have never experienced signal loss). I have seen the faraday argument debunked for cars, and assuming that trains then are also not really faraday cages, I am left in the dark as to why my phone loses signal in a train. Any ideas?

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Could it be simply that there are a higher density of signals within a train carriage and fewer phone masts to service them at once?

That is, you often have a dense crowd of people in a small space, none of whom are occupied with driving, and who are more likely than the average car driver to be wishing to conduct business on the phone?

Plus the train is more substantial in construction, so the signal attenuation may be slightly greater than inside a car.

Also, trains frequently travel through extremely deep and steep cuttings, whereas roads rarely have these features?

Trains also travel through extremely secluded areas at times, where the phone infrastructure may be extremely modest. Roads are rarely so secluded from populated areas.

There is also a public safety incentive to ensure coverage along secluded stretches of motorways, to cope with crashes and such, whereas trains have separate communication infrastructure for their staff (which have full lineside coverage).

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  • $\begingroup$ Your first three suggestions make sense, the others rely on the actual signal (right outside the train) would be worse. I experienced this signal loss in Flanders, Belgium where there are hardly any landscape features blocking signal, and signal coverage is above 90%. So i conclude that it must be the traincarriage itself blocking the signal. $\endgroup$ – Simon Feb 20 '18 at 12:47
  • $\begingroup$ @Simon, if you ask me, the density is then the most credible explanation of all those I have mentioned. By your own logic, if there are no landscape features, and if there is signal within the carriage mostly, then the most likely explanation is simply that the masts are being overloaded by too many people in one place wanting to access a particular mast. And because the overload is literally transient, there is no justification for adding further mast capacity. The masts have a fixed capacity - and there are also a fixed number of channels, can be as little as a few score per mast. $\endgroup$ – Steve Feb 20 '18 at 12:52
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Cell towers are much more frequently built near highways than near railways, largely because so many more people travel by car than by train.

The range of an average cell tower is much shorter than most people think. In populous areas it can be under a mile (the range is artificially shortened to keep the tower's radios from being overwhelmed). It is also directional in many cases, so just being close to a tower is not good enough to guarantee coverage. As a result, as soon as a railway gets distant from a highway there is a good chance that the area won't be covered.

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  • $\begingroup$ It's from a few years ago, but a study showed that motorway and rail were actually very comparable in coverage: bbc.co.uk/news/technology-27484561 $\endgroup$ – Steve Feb 21 '18 at 4:56
  • $\begingroup$ @Steve I'd be interested in seeing something similar for other countries. My experience on this topic is in the US, and I wouldn't be terribly surprised if it were different in the UK. $\endgroup$ – Chris Feb 21 '18 at 5:03
  • $\begingroup$ Very true. There is a site (on which the BBC report is based) that contains data for all countries: opensignal.com/networks. But I couldn't find comparable statistics to those quoted by the BBC for here in the UK. $\endgroup$ – Steve Feb 21 '18 at 5:24
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In the UK most lines on which fast trains travel have 25,000 volt overhead line equipment. Might the electromagnetic field from this be enough to disrupt the signal your phone obtains? I actually work as a railway engineer (but civils though) and although we have never had anything to do with the effects of high voltage on phone signal, there are rules that you cannot run signalling cables and the feeder wire for the 25kV overhead lines closer than a metre to one another as it causes interference and can make signalling unreliable (which you REALLY don't want). It doesnt seem such a stretch that the same electromagnetism would mess up your phone signal.

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That is probably as you are running parallel, and its a long metal conductor.

Using a phone, which would probably transmit to the mast perpendicular or diagonal wrt to the 25kV cable should pose no problem. The cross sectional area is minimal, and the wavelengths different.

Thats about as much as I can recall from wavelength stuff from years gone by.

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