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

[Magnus Danielson]

Hi,

On 2020-03-09 22:31, Poul-Henning Kamp wrote:
> --------
> In message <20200309222553.e5b65b79daa2ee195cf13419 at kinali.ch>, Attila Kinali writes:
>> On Mon, 09 Mar 2020 13:44:59 +0000
>> "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:
>>
>>> 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 ?
>> Please correct me if I'm wrong, but that sounds like a
>> simplified version of a Kalman filter, with the only
>> predicted variable being the frequency of the LO.
> I think this has many names.
>
> Dave Mills called it a FLL - Frequency Locked Loop.
>
> I'm not sure a Kalman filter would really do much extra for the
> basic GPS+(OCXO|RB) case, unless you get advanced and also feed it
> temperature and air pressure.
>
> Once you have more than two references, Kalman makes a lot of sense.
>
>
The Kalman filter has the benefit of auto-tuning on itself as you
run-in, but for a time-frequency system, it's just a self-tuning
PI-loop, so when it have stabilized, the difference is very small. It
took a bit of re-drawing of the processing, but when it showed up on the
sketch-book it was very clear what was going on.

Cheers,
Magnus