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Old September 8th 16, 10:30 PM posted to uk.railway,uk.rec.gps
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Posts: 10
Default GPS receivers and possible OHLE interference

We've just got a dashboard camera for the car, and it also has a GPS
receiver. I was looking at the tracks of my wife's journey to work. At one
point she passes under a long bridge beneath many OHLE-electrified (*)
railway tracks close to a station. The GPS track seems to go haywire,
showing her going roughly opposite to the real direction, and this begins
just *before* she goes under the tracks and therefore while she still
theoretically has GPS reception.

Intriguingly, the "dilution of precision" figures (a measure of how much
error there may be in each reading) does not get worse when she approaches
the bridge and the tracks, even though as she starts to turn north, the GPS
track shows her turning south.

Does the radiation from OHLE lines (presumably 50 Hz with lots of harmonics
and noise due to arcing) corrupt GPS signals in such a way as to still show
a reliable GPS signal (low DOP) but with lat-long coordinates varying in the
wrong direction? I'd have expected (if anything) a loss of signal (no GPS
fix) or else points that were distributed at random causing a very wiggly

This is the track - the green
arrows show what was actually recorded and I've drawn a red line that shows
where she actually went.

(*) 25 kV AC overhead electrification, for non-railway people in uk.rec.gps