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

[Bob kb8tq]

Hi

In this case the “phase” is phase correction of the output rather than PLL ….

Bob

> On Mar 9, 2020, at 10:58 AM, Matthias Welwarsky <time-nuts at welwarsky.de> wrote:
> 
> 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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> 
> 
> 
>