Well, on a practical level, if you update the EFC that frequently then the DAC change glitches will dominate the actual output even if you’re not actually moving the needle much.
> On Aug 17, 2016, at 2:53 PM, Bob kb8tq <kb...@n1k.org> wrote: > > 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 <time-nuts@febo.com> >> 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 <preilley_...@comcast.net> 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 -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.