[ntp:questions] Shared PPS source/Multiple PPS sources

William Unruh unruh at invalid.ca
Sat Feb 7 18:15:32 UTC 2015


On 2015-02-07, David Woolley <david at ex.djwhome.demon.invalid> 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.



More information about the questions mailing list