[time-nuts] Re: GPSDO - GPS1300-10-1000 by RFX Ltd. UK

[Lux, Jim]

On 3/1/22 12:54 AM, John Moran, Scawby Design wrote:
> David - thanks for the reply, but these seem designed for SDR and I wanted 1pps. Nice and cheap though.
>
> Paul - thanks too; it seems that you are saying that the performance of all GPSDOs are the same, but that wasn't the impression I had got from listening to discussion here. Fine when the thing is locked (except for sawtooth stuff and these hanging bridge things, and digital vs analogue (British) control loops, etc.) but what about hold-up performance when it's not.


Holdover performance is going to be determined by the oscillator's 
stability. The time error is essentially = tau * ADEV(tau)Â  - so if you 
have a ADEV(1000sec) of 1E-9, after 1000 seconds, the uncertainty of 
your 1pps would be 1E-6 seconds after 1000 seconds of holdover.

A more subtle effect is "what happens when the GNSS signal returns" - 
Does your 1 pps abrubptly snap back to GNSS epoch within a few ns? Or 
does it gradually drift back to sync. Downstream uses might care.