Gps Signal

I'm on the train and wanted to know where I was. Phone flat against the train window and it cant get a fix om my position, yet it says it can see 8 satellites

Satellites in view 8

Satellites in use 0

Why is this? I thought it just needed to see 3 to triangulate a position.

I have the same problem with mine indoors but works perfectly outside or in the car?????

Yep mine too, my tomtom will just about work on the window sill in my home office.

The sats may be getting picked up but the signal will be to weak to make a decent connection. Used to get it alot with my old stand alone gps receiver as u could go into the phone sat nav settings and see the signal wasnt good enough to make a connection.

Bump, interested in the scientific explanation on this one if anyone understands how GPS works.

Originally Posted by -Ralph-

Bump, interested in the scientific explanation on this one if anyone understands how GPS works.

Thousand foot, very basic explanation:
The GPS satellite works by transmitting an accurate time signal & it's location.

The receiver unit then calculates the time taken to receive the message against the time it got sent, and the location of the satellite. It needs the messages of 4 satellites to produce coordinates.

My guess would be that even if you can see 8 satellites intermittently, it's not getting a full fix on them or some of the messages may be corrupted because of interference or barriers (your house).

Dan

Out of curiosity. What train was it? You dont need to specify a particular class but which company..where were you going?
Virgins Voyagers (and its Meridian/Pioneer stablemates) have a solar-reflective coating on the saloon windows which has been known to cause bother with mobile phone signals and maybe to blame for your GPS drama.

Fear not, Im a train driver, not a bobble hat wearing trainspotter

Thanks. My old sat nav sometimes took a while to get a fix, and it had a screen that showed you where in the sky the satellites where and a dynamic bar graph like a audio graphic equaliser, that showed you how many sats and how strong the signal was. You could watch it and it would have a clear view of the sky, have anything between 8 and 12 satellites, all with signals over 50%, but it would still take two minutes or so to decide where it was.

I've often watched it thinking, and so if you can see all that, why can't you tell me where I am?

My car on the other hand has a built in sat nav, with an external GPS receiver and I've never know it to loose signal other than in a tunnel, and it is usually operational before I've pulled off my driveway.

The train was one of these http://en.wikipedia.org/wiki/British_Rail_Class_222 East Midlands St Pancras to Kettering. It is impossible to hold a telephone conversation on that route, but I have followed the train's route on the phone using GPS before. I'm one of those geeky people interested in Geography, when on a train or plane, I like to know what I'm looking at.

Originally Posted by -Ralph-

Thanks. My old sat nav sometimes took a while to get a fix, and it had a screen that showed you where in the sky the satellites where and a dynamic bar graph like a audio graphic equaliser, that showed you how many sats and how strong the signal was. You could watch it and it would have a clear view of the sky, have anything between 8 and 12 satellites, all with signals over 50%, but it would still take two minutes or so to decide where it was.

Was it an old Navman? I had one of those for a couple of days until I took it back because it was so rubbish. Garman Nuvi 310 I had was a lot better. I have the 1490 now and I really miss the screen that says which satellites you're picking up, saying that it usually finds the signal and you're good to go inside 10 seconds most of the time. I have a hand held Garmin walking GPS that can take a minute or two to work out where you are, but I've even had it work indoors a few times.

Originally Posted by Bedhead

Was it an old Navman? I had one of those for a couple of days until I took it back because it was so rubbish. Garman Nuvi 310 I had was a lot better. I have the 1490 now and I really miss the screen that says which satellites you're picking up, saying that it usually finds the signal and you're good to go inside 10 seconds most of the time. I have a hand held Garmin walking GPS that can take a minute or two to work out where you are, but I've even had it work indoors a few times.

It was a V7 PMD 1400