Hi You can update the EFC a billion times a second. Update rate and bandwidth are not the same thing. If you want good ADEV, the loop better not have a bandwidth greater than 0.01 Hz. GPS ADEV is pretty awful at 1 and 10 seconds. It is starts to be good past a few thousand seconds. Yes, older modules are a bit worse than newer ones. Also sawtooth correction can make things a bit better.
Bob Sent from my iPad > On Aug 17, 2016, at 2:51 PM, Nick Sayer via time-nuts <[email protected]> > wrote: > > Updating the EFC more quickly reduces the ADEV, though. I find that the > fiddly part of tuning a GPSDO design is balancing the ADEV against phase > control. If you want keep an iron fist on the phase, you can only do so by > constantly swatting around the frequency. > > I won't say that getting more frequent phase feedback is a bad thing, but if > you're trying to get the PLL time constant to be longer rather than shorter > that it won't help a lot. > > Sent from my iPhone > >> On Aug 17, 2016, at 9:57 AM, Peter Reilley <[email protected]> wrote: >> >> You can get crystal oscillators that have a frequency control signal and are >> more >> stable than the run of the mill oscillators. Changing the GPS oscillator >> would >> require modifying a very tightly populated circuit board. Perhaps not >> possible. >> >> What about some of the SDR (software defined radio) projects that aim to >> implement GPS functionality? If you used the GPS chipping rate (1.023 MHz) >> to dicipline the 10 MHz oscillator then you are less sensitive to crystal >> instabilities. >> You are updating the crystal one million times a second rather than once per >> second. >> This is assuming that the chipping rate of the transmitter is just as good >> as the >> 1 PPS signal. This info from here; >> https://www.e-education.psu.edu/geog862/node/1753 >> and here; >> https://en.wikipedia.org/wiki/GPS_signals >> >> Even using the 50 bits/sec data rate of the GPS signal would allow updating >> the >> GPSDO faster than the 1 PPS signal. >> >> Pete. >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
