could minimize phase noise the smallest division factor? phase noise could be the same if the frequency for the phase detector is 8khz or 125khz? I know about LEA-M8F.
The basic problem here is that the phase noise of the high frequency output is only corrected by the GPS signal at a very low bandwidth, like 5Hz if the update rate is 10Hz which some receivers support. So above this frequency, phase noise is dominated by the GPS receiver's oscillator and NCO.
So there is zero advantage to using an oscillator frequency above the receiver's update rate and in practice because of the limited accuracy of the GPS solution, the bandwidth should be limited to a point significantly below the update rate.
I read a lot of ublox papers and I understand that the output signal is generated by the NCO based on satellites data calculations and does not derive simply from the division of the internal clock of 48Mhz, if I understood correctly, obviously the signal is affected by the granularity of the 48Mhz.
David Hess: which frequency would you choose?
it could be useful to flip a coin?
Choosing a frequency which is an even division of 48MHz helps with short term jitter but does not solve the problem outlined above because the high frequency clock is not updated any faster than the GPS solution is produced. The 48MHz internal clock creates a granularity in the timing signal which is where the 20 nanosecond timing specification comes from and that can be reduced by using the timing error reported by the GPS unit for every update but if the GPSDO oscillator is good, then the optimum noise performance will require a time constant slower than the 1Hz or 10Hz update rate anyway.
What does work well for simple designs is to divide the 10MHz GPSDO down to a lower frequency and then phase lock that to the 1 or 5 or 10Hz output with a time constant slower than 1Hz. Dividing down to a medium frequency gives some of the benefit of a jam mode to quickly lock onto the GPS timing signal without implementing a separate jam mode. If you divided down to 1 or 5 or 10Hz, then it could take a long time for the phase of the low frequency outputs to come into alignment.