[time-nuts] New Subscriber, DIY GPSDO project (yes, another one)

[Matthias Welwarsky]

On Montag, 9. März 2020 15:04:40 CET Bob kb8tq wrote:
> Hi
> 
> If you go that way, just run a pure FLL for the “main loop” and do the phase
> on top of that. Assuming you are disciplining an OCXO, it works pretty well
> …. Even more so if you keep time tagged phase ( to do frequency from phase)
> and can look at some very long tau “frequency” as a section of the loop.

Not sure about the merit of this. As soon as your LO is close to the "true"  
frequency, the phase error will become dominant. Which means the FLL part will 
contribute nothing and the whole thing will effectively become a PLL.

BR,
Matthias

> 
> Bob
> 
> > On Mar 9, 2020, at 9:44 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
> > 
> > --------
> > 
> > In message <1593455.IjMom2WFaZ at linux-5fgm.suse>, Matthias Welwarsky 
writes:
> >>> Backing up a bit …. the objective is not to minimize overshoot or
> >>> keep the loop from oscillating. The issue here is optimizing the noise
> >>> output of the combination of GPS + OCXO when combined via
> >>> the control loop. It’s a very different objective ….
> >> 
> >> Absolutely. The GPS will introduce a ton of noise and the objective for
> >> the
> >> control loop is mainly to keep the influence of this noise away from the
> >> GPSDO output for small tau. You want the GPS only have an influence for
> >> large tau, ideally only countering the aging of the LO.
> > 
> > Has anybody ever played seriously with separate frequency and phase
> > adjustments ?
> > 
> > I'm thinking 24h (to minimize GPS periodicities) frequency measurement
> > and adjustment, with a continuous very weak proportional phase adjustment
> > to come with measurement noise and rounding errors ?
> 
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