On 2015-02-07, David Woolley <[email protected]> wrote: > On 07/02/15 08:24, Rob wrote: >>> >And a side question: Is it the GPS module that calculates when the PPS >>> >goes active? Is this signal compensated for the time it takes the signal >>> >from the sats in the module, or on the SV? >> Yes, the module calculates the position and time fix from the signals of >> at least 4 SVs, and then outputs the PPS related to the calculated time. > > Which is the key to how GPS does the P. GPS receivers need to know > where the satellites were when the signal was launched, and the orbits > are specified in terms of the satellite times. It then has to work out, > from the relative delay times, from at least four satellites, the > current time and three spatial coordinates (four unknowns). I'm not > sure it actually needs the time part of the solution (it probably does > for detailed corrections) but that is going to drop out of solving for > the spatial position.
Some receivers allow you to feed in the current location, and then the receiver can use only one sattelite to determine the time > > What the satellites do do is to to transmit some additional information > about ionospheric propagation, which allows for receiver to compensate > for the signals travelling slower than the speed of light in vacuo. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
