Problems with GPS Abroad

[shiltonpig]

Hola

 

Went to Barcelona at the weekend and encountered a few problems with my GPS....I have a basic model the Garmin Geko 301.

 

When I switched it on abroad it took a long time to set up...I presume this is normal, could someone kindly confirm? Then it was fine and we recorded our first spanish cache.

 

Next day we were walking up the main street in Barcelona and we couldn't acquire any satelittes to gain a reading. It was completely cloudy, some tree cover though not too bad and the building were very tall overcasting the street.

 

Later on in the day it was sunnier and out more in the open and worked fine.

 

Could anyone answer my questions please:

 

How much would a cloudy sky affect my GPS?

Would tall building affect my readings?

Am I doing anything wrong?

As I have a basic model would a more advanced model be more effective?

 

Any other advice much appreciated

 

Apart from that had a great time caching abroad!

[+Father Jack]

Taking a long time to get a reading when you move more than 100 miles or so is normal. It has something to do with the gps thinking it is still at home and not seeing the satellites it expects so it has to gather new information from the sky, this takes time, up to half and hour so I’ve heard in some cases.

 

Tall buildings will affect GPS coverage. Remember, your GPS needs line of sight with the satellites, if a building is in the way then you will get low/no signal.

 

you are not doing anything wrong.

 

A more advanced model would be better but it would still need line of sight to the satellites and take a while to start up if you move a long distance.

[+chizu]

When we got our GPSr it thought we were in Hong Kong for about an hour!

[+dino-irl]

How much would a cloudy sky affect my GPS?

AFAIK clouds and weather in general don't have a great effect on a GPSr and it's ability to receive signal. Just as well considering I live in NW Ireland

 

IIRC from a similar discussion before it's something to do with the wavelength of the signal. I'm sure someone else will either correct me if I'm wrong or totally confuse you with detail if I'm correct!

 

Would tall building affect my readings?

Most definitely if they are blocking your line of sight to the satellites. It's commonly known as the "Urban Canyon". Basically they block the signal in the same way that you will struggle to get signal under trees in a wood/forest or a natural canyon.

 

Am I doing anything wrong?

I doubt it if you were able to get good signal in open areas. Also you managed to find at least one cache....you did remember to enjoy yourself?.....that's very important

 

As I have a basic model would a more advanced model be more effective?

Only if it has a better chipset which has a more sensitive receiver. The new "H" range from Garmin or a GPSr with a SirfIII chip (usually the higher end models) will cope much better in the situation you describe. Whether the expense is worth it is up to you to decide.

[+Amberel]

When I switched it on abroad it took a long time to set up...I presume this is normal, could someone kindly confirm?

 

Next day we were walking up the main street in Barcelona and we couldn't acquire any satelittes to gain a reading. It was completely cloudy, some tree cover though not too bad and the building were very tall overcasting the street.

 

Later on in the day it was sunnier and out more in the open and worked fine.

 

Could anyone answer my questions please:

 

How much would a cloudy sky affect my GPS?

Would tall building affect my readings?

Am I doing anything wrong?

As I have a basic model would a more advanced model be more effective?

 

 

Cloudy sky should be no problem. Tall buildings could be, especially if they are all around. They might obstruct the signal, or might reflect it, giving a false position.

 

Are you doing anything wrong? No, not really. All I would suggest is that if you have trouble getting a lock, try standing still. Lot's of GPSrs don't get a lock so easily while moving, even at walking speed. Once you have a lock, no problem.

 

Your basic model should be OK.

 

The reason it took a long time when you first used it in Spain was because it was "looking" for the wrong satellites at the wrong frequencies. Your GPSr holds a thing called the "almanac", which tells it roughly where the satellites are. When you switch it on, it uses the last known position and the current time to work out which ones should be in view. If you've moved a long way since it was last used it will be looking for the satellites that would be visible at the location where you last switched it off It then has to do a search for all satellites, and it's pot luck how soon it hits the jackpot. A more expensive GPSr might be better than a cheap one here, as it might have more electronic "correlators" to search for lots of satellites at the same time.

 

Once it has a lock it will update your "last known position". All satellites broadcast almanac data for themselves and all the other satellites. The almanac data gradually gets out of date, so if you've not used it for a few months it might have to search for all satellites as above. It takes several minutes to download a new almanac.

 

As well as the almanac the satellites broadcast "ephemeris". This is highy accurate information about the position of the satellite, and it gets out of date very quickly, i.e. a few hours. Each satellite broadcasts only its own ephemeris. When you switch your GPSr on for the first time that day first it has to search for the satellites. Then you may see it has a signal from several satellites but still isn't giving you a position solution. That's because it is still downloading the ephemeris - as soon as it has the ephemeris for 3 or 4 satellites, it will tell you where you are. It takes half a minute or so to download the ephemeris, and this is where it's a good idea to keep still, so the ephemeris download isn't interrupted by you walking under a tree or something like that.

 

If you turn your GPSr off and then on again within an hour, you should get a fix much more quickly because it can immediately use the ephemeris from when it was last on.

 

Rgds, Andy

[+Travers]

You have some very in depth answers here but from our non-techy perspective sometimes the GPS takes a while to 'cotton on' to the fact you have moved quite a distance and gets quite uppity and refuses to get a fix on the satellites.

 

We tend to help the wee gadget along by giving it a hint (not too much of a hint though) as to where it actually is - something along the lines of...you are in Europe, you're getting warmer, the country is Spain, you're getting quite hot etc - then it finally figures it out. It seems to save time and is an option on both our Magellan and Garmin (look under the setup menu or similar).

 

Tall buildings are a pain as they can block the signal and leave you wandering helplessly back and forth (probably looking more than a little foolish to innocent passers by). Sometimes standing still until you have a lock on one or two satellites is a good remedy, then move about a bit to get a couple more - there must be a proper name for this??

[+Simply Paul]

I believe you can also get 'echo' signals, bounced off tall buildings, which can throw a GPSr out, especially if it's struggling to get a lock and work out where it is. When I was caching in Barcelona in February, my etrex yellow took quite a while to get a lock (because of the travel and the lack of sky in the city) and once it had, it still took a while to settle down and give sensible readings. I don't think I was doing anything wrong, and I don't think you did either.

 

Newer, better GPSrs would probably get a faster and better lock because of newer firmware and improved antennas, but unless yours is due for replacement, I'd not personally bother upgrading.

[+Maple Leaf]

When I switched it on abroad it took a long time to set up...I presume this is normal, could someone kindly confirm? Then it was fine and we recorded our first spanish cache.

I have an Etrex Legend and use the facility 'New Location' on the Satellite Page options menu.....

 

In the manual it states .......If you are more than 600miles from where you last used the unit, select the 'New Location' and then the 'Use Map' options to appoximate your location. This gives the unit reference information and speeds satellite acquisition.