[time-nuts] GPSDO Question

Tom Van Baak tvb at LeapSecond.com
Sun Sep 2 16:13:39 EDT 2007

> 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?


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