[time-nuts] Newbie question about GPS

[Bob kb8tq]

Hi


> On Mar 2, 2020, at 7:14 AM, Anton Moehammad via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi All,I hope some one can help me to find the answer.1. Let say some one can extract the L1 carrier frequency 15xx MHz and convert it down to let say 1MHz and put it to phase comparator and made the PLL to generated the LO to convert and extract the carrier. Is this possible ? Have some has do it ? Can share any thoughts ?

The carrier is significantly doppler shifted due to the way the satellites orbit the earth. Without
correcting for that, the carrier makes a poor reference. This is only the first of *many* corrections
applied…..

> 2. In the UCenter or almost any software control for GPS module/receiver we can find data for next pps, why if the software can calculate the PPS should be they do not use it to adjust the PPS output so the PPS jitter is minimal ?

The correction information can get the PPS to error levels dimensioned in picoseconds. Doing
that with some sort of external corrector is complex and expensive (if it can be done at all). The
way they do it is quite adequate for a GPSDO application. It costs them next to nothing to do. 

> 3. Why if we use real time RTK for better accuracy in term of position the PPS is not changed ? ( At least in my setup) ?Are the RTK software only process data and show the result in the screen without change anything in module/receiver ?Any software can do a real change to receiver for better PPS out based from any corrections available (ionosphere, Tidal etc) ?

It depends on which RTK streams you are using. Are you bringing in a clock correction stream?
In any case, the change in the PPS is going to be very small. You would need a very good reference
to compare to to see it happen. 

Bob


> Thank YouAnton
> 
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