[time-nuts] TIC resolution impact on GPSDO's performance

[Dr Bruce Griffiths]

Poul-Henning Kamp wrote:
> In message <459054DC.8030701 at xtra.co.nz>, Dr Bruce Griffiths writes:
>
>   
>>> A quantum of 1ns is not a concern if the attack point for the PLL
>>> is on the order of hours.
>>>   
>>>       
>> This statement is only true when one is disciplining or monitoring 
>> relatively with sufficiently large frequency and/or phase instabilities.
>> When one wishes to discipline an Oscilloquartz 8607 OCXO for example 
>> every nanosecond or fraction thereof matters.
>>     
>
> As far as I can see on TVB's site, the 8607 is about 5e-13 at 1000 sec,
> so 1ns/1h sounds perfectly good to me.
>
>   
Only true when one only considers the data available on Tom's site.
Quartzlock have a GPS disciplined BVA OCXO that achieves considerably 
better stability, admittedly their carrier phase tracking GPS receiver 
has a resolution of a few picoseconds for an integration time of 1 second.
>> Its not the coherence of the sawtooth but the coherence between the 
>> oscillator clocking the timer used to position the PPS signal and the 
>> frequency of the PPS signal itself.
>>     
>
> Yes, those are non-coherent, that is why we need the negative sawtooth
> in the first place.  If they were coherent, we could just have
> used a formula.
>   
But they are not sufficiently incoherent as hanging bridges and the 
quasi periodic form of the sawtooth error amply demonstrate.

Bruce