slowjett

Hello,
I was driving to a gig in Boston the other day using iGuidance and my GPSlim 240 (Which normally is VERY accurate) and when I was in the city my location on the screen kept jumping all around, even when stopped, it would say I was doign 5mph and moving around on the nearby streets.

I would like to use GPS when footing it as well in the city, should I expect this problem?

Why does this happen?

And what can I do to fix the problem?


Thanks so much,
Josh

edge777

I had that happen with my Holux 236, and as far as I could tell, there were two things that caused it: Really tall sky-scrapers in downtown (where I usually had 9-10 active satellites, I would be down to 2 or 3), or when I was in close proximity to overhead transit power lines for the train or electric busses. The signal would mostly work while moving, but get a little confused while stopped.

JakeRich

It's a phenomenon from the signal bouncing all around in the urban canyon. Since the way GPS computes location is through timing signals, just a few nanoseconds of bounce or delay can cause the fix to wander around. For more information, you can look at the two tutorials in my sig.