[time-nuts] Recording mains frequency/phase [WAS: No GPS satellites]

[Mark Sims]

Yes, it has been done...  and it has some very interesting real world uses:
http://www.theregister.co.uk/2014/07/03/tinfoil_hatters_spook_says_nsa_can_track_whistleblowers_through_power_lines/

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If we all did this, then I realize that we could identify the different power grids. However, I wonder if there is any interesting variation *within* a grid. As the electricity flows vary throughout the day, it seems possible that the phase difference between two people on the same 
grid would actually change (a bit).

Has anybody done this experiment?