Magnus, Thanks for the explaination. I forgot about ionispheric latency effects. I'll look for the book you mentioned.
Joe KA5ZEC On Wed, Sep 30, 2009 at 4:11 AM, Magnus Danielson <[email protected]> wrote: > Dear Joe, > > Joseph Gray wrote: >> >> Does anyone know if any of those all-in-one hockey puck GPS receivers >> put out PPS on the serial cable? The type that has the antenna and GPS >> together, with a serial cable hanging off of it. I'm thinking about >> using one for a timing project. The more sensitive, the better, as it >> will be used indoors. >> >> While I'm on the subject of GPS units, a question comes to mind. I >> know that WAAS enhances position accuracy. Does it do anything for >> time? My first thought would be no, as that comes directly from the >> standard GPS satellites. > > It does. It improves the GPS position in [XYZT]. However, it does not work > its magic in a direct sense to time itself. The fast corrections adjust the > pseudo-range measures comming out the channels. Ionspheric errors is also > corrected by transmitting grid-based data and the receiver interpolates the > correction value for its (coarse) location and make individual corrections. > SBAS (WAAS is one of several SBAS systems) also corrects for satellite orbit > parameters, and UTC offsets. > > These corrections all aids to improve the GPS position in [XYZT] where the > improvement in T is for most users a side-effect. A GPS with fixed position > can (if the receiver supports time-only mode) get a quicker and more > accurate fix (modulus local multipath) and then produce more accurate time > value as the SBAS aiding reduces the biasing errors and fluctuations of > those. Using a LBAS broadcast could improve the state further. > > Dip your nose into the Kaplan & Hegarty book for instance. That is what I > used to reinforce my recollection of things. There are better sources. > > Cheers, > Magnus > > _______________________________________________ > 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. > > _______________________________________________ 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.
