[ntp:questions] Re: GPS signal quality

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Tue Nov 16 14:33:08 UTC 2004

"Richard B. Gilbert" <rgilbert88 at comcast.net> writes:

> Helmut Wollmersdorfer wrote:
> > Today I tried two consumer level GPS mice in my location.
> > One is a Fortuna U2 and the other a Holux GM-210.
> > For convenience I used the demo software under WinXP.
> >
> > There is not much free view to the sky. It took some hours, that three
> > satellite signals could be received. More than 80% of the time only one or
> > none is usable. Accuracy is poor as the satellites can only be "viewed" in
> > the north-east quarter.
> >
> > Compared with the calculated coordinates from an 1:25000 map the accuracy
> > seems ~100 m, altitude from GPS is 229-265 m against 205 m.
> >
> > Given this situation, would it be worth to try Oncore, or would it be waste
> > of time and money? For me GPS will only make sense if I can get more
> > accuracy than my well working DCF receivers provide.
> >
> > Helmut Wollmersdorfer
> It sounds very much as if you have a poor location for your antenna!  If the

Not necessarily: Precise timing required a precise refernce oscillator, and
the position is eventually derived from time information. I guess these cheap
devices are made...well...cheap.  Basically I agree that GPS works best with
a clear view to the sky.


> location you are using is the best available, you would be wasting your money
> on the Oncore.  If, on the other hand, you can place an antenna where it will
> have a 360 degree view horizontally and 160 degrees vertically (from 10
> degrees above the horizon all the way around, GPS will work quite well.  Can
> you place the antenna on the highest point of the building you are in?
> I have learned from experience that even foliage will block the GPS signal!
> Now that most of the leaves have fallen from the trees, I can receive a usable
> signal fifty percent of the time, versus thirty percent earlier in the year.
> You MUST have that clear view of the sky in order for GPS to work reliably.
> When GPS does work reliably; e.g. when you have a good quality signal from
> four satellites, your clock can synchronize to within 40 microseconds or
> better.  Your mileage may vary; the computer hardware and the operating system
> also affect the performance!

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