Unruh wrote: > "Richard B. Gilbert" <[email protected]> writes: > >> David J Taylor wrote: >>> Richard B. Gilbert wrote: >>> [] >>>> Assuming a GPS *TIMING* receiver, and that it can be installed with >>>> the antenna having a good view of MOST of the sky, you can expect >>>> results that are *almost* as good as the atomic clocks on board the >>>> satellites! >>>> You do need to run a "site survey" to establish your location as >>>> exactly as possible! Once your location is known, the calculation of >>>> the "speed of light delay from your selected satellite to you can be >>>> done quickly and easily. >>> I didn't have such difficulties when using today's sensitive GPS devices >>> - e.g. GPS 18x LVC: >>> >>> http://www.gpsw.co.uk/details/prod2402.html >>> >>> Having a view of, say, a 180-degree arc of southern sky is probably good >>> enough. I have mine indoors, sitting on top of a PC on the top floor of >>> my building. No separate antenna. The earlier GPS 18 LVC sits on the >>> roof. The GPS determines its location all by itself - no site survey >>> required. Microsecond accuracy. >>> >> That is what a "site survey" is. The GPS determines its location a few >> hundreds of times over the course of a day and does a "least squares" >> calculation to get a reasonable approximation of your latitude and >> longitude. > >> Cellular phone base stations do a more extended site survey, thirty days >> instead of one. This gives them a MORE reasonable approximation. When >> I did my site survey (24 hours) the locations plotted a locus about 300 >> feet long in an East-West direction and with a width of about thirty feet. > > Yee gads. My "survey" in my location gives me a location whose bounds are > about 3mX3m scatter > at worst. The centre is about 4m off from where Googleearth claims my > rooftop location is, but that could well be > Googleearth's problem. This is with a Garmin GPS18 with a view of about 50% > of the full sky. > (roughly 50 N, 120 W) I am surprized your error box is that large. <snip>
I did this years ago and I think it might have been while DOD was still encrypting the low order bits in the data. It might be faster and easier today but what I have works and I'm not going to mess with it! _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
