[ntp:questions] Re: GPS signal quality

Richard B. Gilbert rgilbert88 at comcast.net
Wed Nov 10 19:07:37 UTC 2004


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 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!




More information about the questions mailing list