"Didier Juges" <[EMAIL PROTECTED]> wrote: > I would have thought the GPS receiver averages the readings when it locks on > multiple satellites. Are you saying it only uses one at a time?
Average is perhaps too simple of a word. The good GPS receivers (here I'm assuming we aren't talking about Trimble SV6!) look at all the satellites in view and in mask, throw out obvious outliers, and average among the remaining. > If so, > what's the point of a self survey? ??? If you're wrong by 1000 feet about where you are, then that could be hundreds of nanoseconds in time error. And that hundreds of nanoseconds would jump around like the dickens as you chose different satllites or the chosen satellite pans across the sky. > I talk about WWV because most ham operators have a receiver that receives > WWV, so it is an inexpensive and convenient way to get an absolute > reference, even though it is not as good as GPS. WWV is great. But again, you gotta know where you are to have the right time. Fluctuations in propogation will change path length and if you don't know the path length, it is NOT an absolute reference in the nanosecond or even microsecond range. For typical conditions the propogation delay for WWV cannot be estimated much better than the tens of microseconds; combining WWV with a better "absolute" clock in fact lets you study propogation by studying the shifting of the various ionospheric layers. (There have been ham operators who do this, including me!) Tim. (N3QE) _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
