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. If I had had the patience and if I had required sub microsecond accuracy I could probably have trimmed that locus further. . . . . It is enough, for me, that my little herd of computers agree as to approximately what time it is. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
