[time-nuts] Re: The STM32 GPSDO, a short presentation

[Lux, Jim]

On 3/31/22 2:40 PM, Bob kb8tq wrote:
> Hi
>
> The gotcha of looking at one GPSDO against another is that
> the GPS side of things is “common mode” to all of the devices.
>
> Bob


We all know that GPS is "truth" and has no errors, common or otherwise 
<grin>...



But seriously, three cornered hats work best if all the sources have 
similar statistics, but say you compare 2 GPSDOs against OCXO, even if 
the OCXO is an order of magnitude or two worse (at long tau), where does 
it fall in the "trying to discipline a wet noodle" territory.

One might also be able to do different tau ranges - GPS is not so hot in 
the short run (1000 seconds) but is quite good in the long run (days), 
while an OCXO is the reverse (which is why we make GPSDOs at all). So, 
if you're looking to measure the performance of a new GPSDO, can one do 
two sets of measurements - one against OCXO and one against GPS, and 
then see how you do against each of the component curves.  After all, 
the hope is that the GPSDO is better than either of the other two.