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GPS receivers and possible OHLE interference
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NY
Sep 8, 2016, 5:30:34 PM9/8/16
to
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
line.
This is the track https://s15.postimg.org/d2qin2m3v/GPS.png - 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
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
line.
This is the track https://s15.postimg.org/d2qin2m3v/GPS.png - 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
BevanPrice
Sep 8, 2016, 6:20:18 PM9/8/16
to
get the same effect with hand-held GPS units in trains when they are in
cuttings (especially tree-surrounded), or inside tunnels. Except in some
types of train (e.g. Voyagers), these GPS units generally perform O.K.
on either electrified or non-electrified lines.
(Voyagers and some other trains have window coatings that largely block
the GPS signal.)
Recliner
Sep 8, 2016, 6:54:02 PM9/8/16
to
but not in new ones, which must have coated windows.
Charles Ellson
Sep 8, 2016, 11:08:59 PM9/8/16
to
partly screened from the full range of available satellites by the car
body. There should be a noticeable difference between getting a fix of
position after switch-on inside the car and doing the same standing in
the open, better demonstrated if it has the mode (usually involving a
hidden menu) available showing satellite positions.
Jeremy Double
Sep 9, 2016, 2:28:59 AM9/9/16
to
buildings in that area, which might be either shielding or reflecting the
signal from one or other GPS satellite. That would explain why the track
goes astray before entering the tunnel.
--
Jeremy Double
NY
Sep 9, 2016, 3:46:16 AM9/9/16
to
"Jeremy Double" <jmd.n...@btinternet.com> wrote in message
news:988477433.495094816.930213...@news.individual.net...
be right. My experience with GPS problems is that you either fail to get a
lock at all (too few usable satellites in range) or else you get "random
walk" tracks which show a lot of lateral jitter about the track that you are
supposed to be taking, or else there is a horizontal offset - the line
follows the route that you are taking but is displaced sideways from it.
I've never seen a case where the recorded track actually turns round and
heads in the opposite direction, which is why I suspected some interference
from the OHLE.
I'm very familiar with the problem of getting GPS reception inside a train
with heat-reflecting windows. I've found that the best thing is to start
recording before you get on the train, while there is still good reception
and plenty of visible satellites, and then the track will continue (maybe
with a bit more jitter) when you get on the train. If I leave it until I'm
on the train before turning on my phone's GPS receiver, it never gets a GPS
fix.
news:988477433.495094816.930213...@news.individual.net...
> If you look at the map that the o.p. provided, there are some tall
> buildings in that area, which might be either shielding or reflecting the
> signal from one or other GPS satellite. That would explain why the track
> goes astray before entering the tunnel.
Ah, so you think it's just the tall buildings causing reflections? You may
> buildings in that area, which might be either shielding or reflecting the
> signal from one or other GPS satellite. That would explain why the track
> goes astray before entering the tunnel.
be right. My experience with GPS problems is that you either fail to get a
lock at all (too few usable satellites in range) or else you get "random
walk" tracks which show a lot of lateral jitter about the track that you are
supposed to be taking, or else there is a horizontal offset - the line
follows the route that you are taking but is displaced sideways from it.
I've never seen a case where the recorded track actually turns round and
heads in the opposite direction, which is why I suspected some interference
from the OHLE.
I'm very familiar with the problem of getting GPS reception inside a train
with heat-reflecting windows. I've found that the best thing is to start
recording before you get on the train, while there is still good reception
and plenty of visible satellites, and then the track will continue (maybe
with a bit more jitter) when you get on the train. If I leave it until I'm
on the train before turning on my phone's GPS receiver, it never gets a GPS
fix.
Recliner
Sep 9, 2016, 4:37:56 AM9/9/16
to
train, you'll periodically lose it during the journey when the train is in
tunnels, deep cuttings and covered stations. The device will then have to
attempt to get a new fix, which will fail if the windows are shielded or
you don't hold it near a window.
Conversely, in something like the Mk 1 carriage I was travelling in
yesterday, even in an aisle seat you get a good fix. Perhaps surprisingly,
you also get a good fix in Shinkansen trains, on the rare occasions they're
not in tunnels.
NY
Sep 9, 2016, 5:43:58 AM9/9/16
to
"Recliner" <recli...@btinternet.com> wrote in message
news:426162798.495102694.431198...@news.eternal-september.org...
on the train because of the ability to read the "almanac" of currently
available satellites and their locations while there's still good reception.
I've got a little app called GPS Status which can download A-GPS info over
the internet which speeds up time to first lock considerably. Because of the
power consumption of leaving my phone's GPS receiver turned on all the time,
I tend to turn it on only when I need it, so it always needs to get an
up-to-date almanac. If I left it going all the time I'd probably get better
results, but my battery would only last a couple of hours. Making it last
from 8 AM to 6 PM (ie times when I can't be tethered to the charger), even
with GPS, wifi and mobile data normally turned off, is a problem out here in
the country because the phone uses so much power winding up the gain on the
mobile phone receiver to listen for incoming calls - oh to be in an area
that has good mobile reception.
GPS comes into the category of PFM (pure f***ing magic): the maths involved
in calculating your position based on time delays from satellites which
themselves are moving round the earth (*) makes my brain hurt! The fact that
it works at all, even with little quirks like going off course when you get
reflections or can only see a few satellites, is a miracle.
(*) For a long time, I thought that GPS satellites were geostationary, like
Sky satellites. Then I found out that they're not...
news:426162798.495102694.431198...@news.eternal-september.org...
>> Even if you have a fix with six it more satellites before getting on the
> train, you'll periodically lose it during the journey when the train is in
> tunnels, deep cuttings and covered stations. The device will then have to
> attempt to get a new fix, which will fail if the windows are shielded or
> you don't hold it near a window.
Good point. Maybe I get better results by getting a lock-on before getting
> train, you'll periodically lose it during the journey when the train is in
> tunnels, deep cuttings and covered stations. The device will then have to
> attempt to get a new fix, which will fail if the windows are shielded or
> you don't hold it near a window.
on the train because of the ability to read the "almanac" of currently
available satellites and their locations while there's still good reception.
I've got a little app called GPS Status which can download A-GPS info over
the internet which speeds up time to first lock considerably. Because of the
power consumption of leaving my phone's GPS receiver turned on all the time,
I tend to turn it on only when I need it, so it always needs to get an
up-to-date almanac. If I left it going all the time I'd probably get better
results, but my battery would only last a couple of hours. Making it last
from 8 AM to 6 PM (ie times when I can't be tethered to the charger), even
with GPS, wifi and mobile data normally turned off, is a problem out here in
the country because the phone uses so much power winding up the gain on the
mobile phone receiver to listen for incoming calls - oh to be in an area
that has good mobile reception.
GPS comes into the category of PFM (pure f***ing magic): the maths involved
in calculating your position based on time delays from satellites which
themselves are moving round the earth (*) makes my brain hurt! The fact that
it works at all, even with little quirks like going off course when you get
reflections or can only see a few satellites, is a miracle.
(*) For a long time, I thought that GPS satellites were geostationary, like
Sky satellites. Then I found out that they're not...
Peter Crosland
Sep 9, 2016, 7:04:21 AM9/9/16
to
GPS. The better ones have accelerometers built in that keep track during
signal interruptions. Others also use them to assume that you will
continue on the road you are on. I have never seen such weird results as
shown in the map you listed.
--
Peter Crosland
Reply address is valid
Sam Wilson
Sep 9, 2016, 7:13:53 AM9/9/16
to
In article <gf-dncTSd--pCk_K...@brightview.co.uk>,
Peter Crosland <g6...@yahoo.co.uk> wrote:
> ... The better [GPSs] have accelerometers built in that keep track during
trying to work out where it is when it's on a train? I've only seen it
once a long time ago but it was quite entertaining.
Sam
--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
Peter Crosland <g6...@yahoo.co.uk> wrote:
> ... The better [GPSs] have accelerometers built in that keep track during
> signal interruptions. Others also use them to assume that you will
> continue on the road you are on. I have never seen such weird results as
> shown in the map you listed.
Have you ever seen a GPS receiver with the "I must be on a road" setting
> continue on the road you are on. I have never seen such weird results as
> shown in the map you listed.
trying to work out where it is when it's on a train? I've only seen it
once a long time ago but it was quite entertaining.
Sam
--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
Tony Mountifield
Sep 9, 2016, 7:14:30 AM9/9/16
to
In article <FuudndBkqNfAGU_K...@brightview.co.uk>,
I always considered that the battery got drained faster in poor signal areas
because the phone winds up its transmit power in order to make itself heard
by the base station. It gets warmer for the same reason.
And it's not just in the countryside. EE is pretty poor in the west half of
Winchester too, and has been since they turned off some of their base stations
after merging Orange and T-Mobile.
Cheers
Tony
--
Tony Mountifield
Work: to...@softins.co.uk - http://www.softins.co.uk
Play: to...@mountifield.org - http://tony.mountifield.org
NY <m...@privacy.net> wrote:
> the country because the phone uses so much power winding up the gain on the
> mobile phone receiver to listen for incoming calls - oh to be in an area
> that has good mobile reception.
Changing the gain on a receiver shouldn't make much difference to consumption.
> the country because the phone uses so much power winding up the gain on the
> mobile phone receiver to listen for incoming calls - oh to be in an area
> that has good mobile reception.
I always considered that the battery got drained faster in poor signal areas
because the phone winds up its transmit power in order to make itself heard
by the base station. It gets warmer for the same reason.
And it's not just in the countryside. EE is pretty poor in the west half of
Winchester too, and has been since they turned off some of their base stations
after merging Orange and T-Mobile.
Cheers
Tony
--
Tony Mountifield
Work: to...@softins.co.uk - http://www.softins.co.uk
Play: to...@mountifield.org - http://tony.mountifield.org
Martin Coffee
Sep 9, 2016, 7:30:27 AM9/9/16
to
On 09/09/16 12:14, Tony Mountifield wrote:
> In article <FuudndBkqNfAGU_K...@brightview.co.uk>,
> NY <m...@privacy.net> wrote:
>> the country because the phone uses so much power winding up the gain on the
>> mobile phone receiver to listen for incoming calls - oh to be in an area
>> that has good mobile reception.
>
> Changing the gain on a receiver shouldn't make much difference to consumption.
> I always considered that the battery got drained faster in poor signal areas
> because the phone winds up its transmit power in order to make itself heard
> by the base station. It gets warmer for the same reason.
>
> And it's not just in the countryside. EE is pretty poor in the west half of
> Winchester too, and has been since they turned off some of their base stations
> after merging Orange and T-Mobile.
>
Switching off the wifi can help improve GPS on some services. The on
> In article <FuudndBkqNfAGU_K...@brightview.co.uk>,
> NY <m...@privacy.net> wrote:
>> the country because the phone uses so much power winding up the gain on the
>> mobile phone receiver to listen for incoming calls - oh to be in an area
>> that has good mobile reception.
>
> Changing the gain on a receiver shouldn't make much difference to consumption.
> I always considered that the battery got drained faster in poor signal areas
> because the phone winds up its transmit power in order to make itself heard
> by the base station. It gets warmer for the same reason.
>
> And it's not just in the countryside. EE is pretty poor in the west half of
> Winchester too, and has been since they turned off some of their base stations
> after merging Orange and T-Mobile.
>
board wifi can give a false approximate location to "seed" the GPS. As
I recall gWr's wifi placed me in Victoria, London the last time I used
their wifi.
NY
Sep 9, 2016, 9:09:08 AM9/9/16
to
"Martin Coffee" <mar...@pyntyn.pincerlicken.com> wrote in message
news:nqu6gh$103t$1...@gioia.aioe.org...
determined by wifi and/or mobile networks" on Settings | Location Services
page was turned on. I got some *very* bizarre results that placed me several
thousand miles away: it alternated between perfectly accurate and being a
long way away.
I googled for the symptom and found that I should turn this option off.
Never had any problems since then.
news:nqu6gh$103t$1...@gioia.aioe.org...
> Switching off the wifi can help improve GPS on some services. The on
> board wifi can give a false approximate location to "seed" the GPS. As I
> recall gWr's wifi placed me in Victoria, London the last time I used their
> wifi.
When I first got my Android phone, "Use wireless networks: Locaton
> board wifi can give a false approximate location to "seed" the GPS. As I
> recall gWr's wifi placed me in Victoria, London the last time I used their
> wifi.
determined by wifi and/or mobile networks" on Settings | Location Services
page was turned on. I got some *very* bizarre results that placed me several
thousand miles away: it alternated between perfectly accurate and being a
long way away.
I googled for the symptom and found that I should turn this option off.
Never had any problems since then.
houn...@yahoo.co.uk
Sep 9, 2016, 9:14:40 AM9/9/16
to
EMU? You can tell when a train is coming even before it makes itself heard.
Basil Jet
Sep 9, 2016, 9:17:45 AM9/9/16
to
On 2016\09\09 12:13, Sam Wilson wrote:
> In article <gf-dncTSd--pCk_K...@brightview.co.uk>,
> Peter Crosland <g6...@yahoo.co.uk> wrote:
>
>> ... The better [GPSs] have accelerometers built in that keep track during
>> signal interruptions. Others also use them to assume that you will
>> continue on the road you are on. I have never seen such weird results as
>> shown in the map you listed.
>
> Have you ever seen a GPS receiver with the "I must be on a road" setting
> trying to work out where it is when it's on a train? I've only seen it
> once a long time ago but it was quite entertaining.
I saw something similar when my TomTom mistakenly thought for several
> In article <gf-dncTSd--pCk_K...@brightview.co.uk>,
> Peter Crosland <g6...@yahoo.co.uk> wrote:
>
>> ... The better [GPSs] have accelerometers built in that keep track during
>> signal interruptions. Others also use them to assume that you will
>> continue on the road you are on. I have never seen such weird results as
>> shown in the map you listed.
>
> Have you ever seen a GPS receiver with the "I must be on a road" setting
> trying to work out where it is when it's on a train? I've only seen it
> once a long time ago but it was quite entertaining.
minutes that I was 2km north of where I actually was. It tracked my
west-east progress progress correctly and tried to fit it onto the road
network where there weren't many east-west roads.
Roland Perry
Sep 10, 2016, 5:18:14 AM9/10/16
to
In message <Sam.Wilson-DE27F...@88-209-239-213.giganet.hu>,
at 12:13:53 on Fri, 9 Sep 2016, Sam Wilson <Sam.W...@ed.ac.uk>
remarked:
>trying to work out where it is when it's on a train? I've only seen it
>once a long time ago but it was quite entertaining.
I experienced it once on the train from Nottingham to Grantham, using
the now hard to get Microsoft Autoroute and a separate GPS dongle, on my
laptop. It was also perhaps a function of the railway line roughly
following (average about half a km north of) the A52 most of the way.
--
Roland Perry
at 12:13:53 on Fri, 9 Sep 2016, Sam Wilson <Sam.W...@ed.ac.uk>
remarked:
>> ... The better [GPSs] have accelerometers built in that keep track during
>> signal interruptions. Others also use them to assume that you will
>> continue on the road you are on. I have never seen such weird results as
>> shown in the map you listed.
>
>Have you ever seen a GPS receiver with the "I must be on a road" setting
That's more of a setting in the Satnav software than the GPS receiver.
>> signal interruptions. Others also use them to assume that you will
>> continue on the road you are on. I have never seen such weird results as
>> shown in the map you listed.
>
>Have you ever seen a GPS receiver with the "I must be on a road" setting
>trying to work out where it is when it's on a train? I've only seen it
>once a long time ago but it was quite entertaining.
the now hard to get Microsoft Autoroute and a separate GPS dongle, on my
laptop. It was also perhaps a function of the railway line roughly
following (average about half a km north of) the A52 most of the way.
--
Roland Perry
Roland Perry
Sep 10, 2016, 5:18:14 AM9/10/16
to
In message
<426162798.495102694.431198...@news.eternal-septe
mber.org>, at 08:37:54 on Fri, 9 Sep 2016, Recliner
<recli...@btinternet.com> remarked:
their sensitivity, they aren't nearly as homogenous as the GSM
receivers.
--
Roland Perry
<426162798.495102694.431198...@news.eternal-septe
mber.org>, at 08:37:54 on Fri, 9 Sep 2016, Recliner
<recli...@btinternet.com> remarked:
>> I'm very familiar with the problem of getting GPS reception inside a train
>> with heat-reflecting windows. I've found that the best thing is to start
>> recording before you get on the train, while there is still good reception
>> and plenty of visible satellites, and then the track will continue (maybe
>> with a bit more jitter) when you get on the train. If I leave it until I'm
>> on the train before turning on my phone's GPS receiver, it never gets a GPS
>> fix.
>
>Even if you have a fix with six it more satellites before getting on the
>train, you'll periodically lose it during the journey when the train is in
>tunnels, deep cuttings and covered stations. The device will then have to
>attempt to get a new fix, which will fail if the windows are shielded or
>you don't hold it near a window.
Remember also that the GPS receivers in phones vary considerably in
>> with heat-reflecting windows. I've found that the best thing is to start
>> recording before you get on the train, while there is still good reception
>> and plenty of visible satellites, and then the track will continue (maybe
>> with a bit more jitter) when you get on the train. If I leave it until I'm
>> on the train before turning on my phone's GPS receiver, it never gets a GPS
>> fix.
>
>Even if you have a fix with six it more satellites before getting on the
>train, you'll periodically lose it during the journey when the train is in
>tunnels, deep cuttings and covered stations. The device will then have to
>attempt to get a new fix, which will fail if the windows are shielded or
>you don't hold it near a window.
their sensitivity, they aren't nearly as homogenous as the GSM
receivers.
--
Roland Perry
Roland Perry
Sep 10, 2016, 5:28:14 AM9/10/16
to
In message <nqu6gh$103t$1...@gioia.aioe.org>, at 12:30:16 on Fri, 9 Sep
2016, Martin Coffee <mar...@pyntyn.pincerlicken.com> remarked:
>Switching off the wifi can help improve GPS on some services. The on
>board wifi can give a false approximate location to "seed" the GPS. As
>I recall gWr's wifi placed me in Victoria, London the last time I used
>their wifi.
My local buses have "free wifi", and if used for geolocation by mapping
software puts me in a village ten miles away which I presume is where
their depot is.
--
Roland Perry
2016, Martin Coffee <mar...@pyntyn.pincerlicken.com> remarked:
>Switching off the wifi can help improve GPS on some services. The on
>board wifi can give a false approximate location to "seed" the GPS. As
>I recall gWr's wifi placed me in Victoria, London the last time I used
>their wifi.
software puts me in a village ten miles away which I presume is where
their depot is.
--
Roland Perry
Roland Perry
Sep 10, 2016, 5:28:14 AM9/10/16
to
In message <nqu5i0$dmc$1...@softins.softins.co.uk>, at 11:14:08 on Fri, 9
Sep 2016, Tony Mountifield <to...@mountifield.org> remarked:
EE), but recently they've rationalised base stations and I can only
"see" one rather T-Mobile one (with the added joy that's it's officially
intermittent but the can't be bothered to fix it).
As a result they've lost three lucrative accounts to O2 - having tried
3, which was a rather frying pan into the fire experience.
--
Roland Perry
Sep 2016, Tony Mountifield <to...@mountifield.org> remarked:
>And it's not just in the countryside. EE is pretty poor in the west half of
>Winchester too, and has been since they turned off some of their base stations
>after merging Orange and T-Mobile.
Yes, where I live used to have good coverage on Virgin (over the top of
>Winchester too, and has been since they turned off some of their base stations
>after merging Orange and T-Mobile.
EE), but recently they've rationalised base stations and I can only
"see" one rather T-Mobile one (with the added joy that's it's officially
intermittent but the can't be bothered to fix it).
As a result they've lost three lucrative accounts to O2 - having tried
3, which was a rather frying pan into the fire experience.
--
Roland Perry
Martin Coffee
Sep 10, 2016, 11:14:56 AM9/10/16
to
rationalised their masts there. I rather like staying with them as no
one can contact me!
Peter Crosland
Sep 10, 2016, 1:43:25 PM9/10/16
to
On 09/09/2016 12:13, Sam Wilson wrote:
> In article <gf-dncTSd--pCk_K...@brightview.co.uk>,
> Peter Crosland <g6...@yahoo.co.uk> wrote:
>
>> ... The better [GPSs] have accelerometers built in that keep track during
>> signal interruptions. Others also use them to assume that you will
>> continue on the road you are on. I have never seen such weird results as
>> shown in the map you listed.
>
> Have you ever seen a GPS receiver with the "I must be on a road" setting
> trying to work out where it is when it's on a train? I've only seen it
> once a long time ago but it was quite entertaining.
Yes! More modern algorithms can usually distinguish between road and rail.
> In article <gf-dncTSd--pCk_K...@brightview.co.uk>,
> Peter Crosland <g6...@yahoo.co.uk> wrote:
>
>> ... The better [GPSs] have accelerometers built in that keep track during
>> signal interruptions. Others also use them to assume that you will
>> continue on the road you are on. I have never seen such weird results as
>> shown in the map you listed.
>
> Have you ever seen a GPS receiver with the "I must be on a road" setting
> trying to work out where it is when it's on a train? I've only seen it
> once a long time ago but it was quite entertaining.
Clank
Sep 10, 2016, 3:31:46 PM9/10/16
to
NY <m...@privacy.net> wrote:
> 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
> line.
Many years ago when I lived in Leeds I used to run along the canal towpath
> 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
> line.
from the city out in to the west. After a couple of km you pass a large
electricity distribution place (where I guess the UHV lines from the pylons
get stepped down to mere HV - it's a big old load of pylons, transformers
and cables anyway.) Running past here the GPS tracks from my mobile phone
would always go completely haywire (I think I achieved a top speed of
100mph according to one such track - eat your heart out, Usain Bolt...)
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