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.
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.
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