GPS as a backup / start-up times etc.

[Wal]

Bit of a newbie at this, but hope you can help - I’d like to take a GPS with me on my trip, but mainly for backup, not general navigation – I’d like to be able to pack it away and only turn it on occasionally to confirm where I am. .

The questions I have are:

1) If I were to pack my GPS away for a few days, and then fire it up, would it take a long time to get an accurate fix? - i.e. would that be equivalent to a cold start-up – Time to First Fix (TFF) I think the term is?

2) Does it store information on the last location it was used, and use that as a short-cut to guess where to start looking for satellites?

3) If so, how does it know how much time has passed since it was turned on - does it have an internal clock of some sort that it maintains even when it’s turned off (like a PC), and does that mean that sooner or later there is an internal battery to replace?

Any advice you can give would be much appreciated.

Thanks … Wal

[AliBaba]

1) 30 secs (depends on type)

2) Yes

3) There is a battery but the GPS has probably been outdated/lost/stolen/ruined before you have to replace it, mine has lasted for three years...

[Wal]

Thanks for the reply - much appreciated

[PanEuropean]

AliBaba is generally correct in his reply, however, there are a few additional considerations.

1) If you are in the same place as you were when you turned it off, it will figure out where it is pretty quickly, as long as it has not been turned off longer than about a month. If you have changed location considerably (more than 200 km), it pretty much needs to start from scratch. Not scratch like the first time it was ever turned on, but the satellites won't be where it expects them to be, because you moved the GPSR without telling it. So, expect it to be slow to figure out its position if you have moved it more than 200 km's.

2) Almost all of them do. Some GPSR's that don't have a soft power down feature won't write their last position to non-vol memory before they are turned off. But they will have already written the last satellite almanac to memory, which accomplishes 90% of what writing the last position does, again, presuming you don't move it a great (100's of km's) distance between shutdown and startup.

3) Even if the internal battery fails, the GPSR will get the correct time from the first satellite it picks up. But, in the case of older GPS units (typically pre 2001) that did not write the waypoints, tracks, etc. to non-vol but relied on the battery to keep this information alive, you will lose any user settings, waypoints, tracks, etc. if your battery goes dead.

The battery issue is kind of moot - sort of like batteries in PC's - by the time the internal battery goes dead, the hardware is so out of date you probably will have upgraded anyway.

PanEuropean