); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY "Tom Van Baak" <[EMAIL PROTECTED]> wrote: > > Jerry > > > > It is amusing/distressing to see that the myth that using an FLL to lock > > an oscillator to the PPS output of a GPS receiver is a good approach > > still persists. > > The optimum solution is a phase lock loop. > > Whilst building an FLL is instructive/educational, if you want the best > > GPSDO performance you should really use a PLL. > > > > Bruce > > It would seem for timekeeping applications, a PLL-based > GPSDO will inherit the long-term accuracy of GPS with > great fidelity. > > But for many frequency (e.g., transmitters) or time interval > applications (e.g., frequency counters with finite gate times), > I'd like to understand, in detail, what the difference between > a PLL- and FLL-based GPSDO really is. > > Can someone point me to real data or even simulations > with plots that show rms or adev differences between the > two camps?
I can think of a couple applications that use FLL's rather than PLL's, and it's never for good statistics. It's all about either: 1. Artificially speeding up lock 2. Power conservation (surprisingly common concern in consumer battery operated items) 3. Given a choice between a simplistic single-loop PLL with very low reference frequency or a FLL, they chose FLL because of better phase noise performance #3 has become less and less an issue because the fraction of the world confining themselves to single-loop synthesizers has become smaller and smaller. Still, the latest ARRL Handbook shows a clever example by N6NWP. (They call it "frequency stabilized" rather than "frequency locked"). Now there are other some other applications that simply ignore frequency and only lock phase through discrete jumps, that some of us call "phase-jerk loops", that have incredibly bad phase noise characteristics (meaning that if you listen to the result on a speaker it sounds like a million screaming banshees!) but work fine for clock and data recovery state machines. Incidentally, the LCD WWVB-locked clocks at discount stores fall into this category - they simply jerk their phase to lock to WWVB, and do no frequency correction. Tim. > > Thanks, > /tvb > > > _______________________________________________ > 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.
