[time-nuts] Question about precise frequency / phase measurement

SAIDJACK at aol.com SAIDJACK at aol.com
Thu Apr 19 20:52:46 UTC 2012


Depends on the scope..
 
if your scope has 100ps A-to-B measurement resolution, then waiting 5  
minutes in this scenario would give 0.83ns drift, with 100ps uncertainty IF your 
 oscillators were synced to ~3ppt which is very tough to do with a 
free-running  OCXO (It would be unrealistic to get that stability from the two 
sources if they  are free running).
 
A more realistic scenario would give say 100ns drift in 5 minutes, then a  
0.1ns resolution on the scope would give a very accurate reading in just 5  
minutes (100ns +/-0.1ns = +/-0.1% error). The result would be 3.33E-010,  
+/-3.33E-013. Who needs more resolution than that as the OCXO will likely 
wander  much more than that in 5 minutes..
 
bye,
Said
 
 
In a message dated 4/19/2012 12:52:07 Pacific Daylight Time,  
azelio.boriani at screen.it writes:

Yes,  and, as you can see, you have to wait 1 hour.

On Thu, Apr 19, 2012 at  9:49 PM, <SAIDJACK at aol.com> wrote:

> Hi  Wolfgang,
>
> one of the easiest and very accurate ways to do this  is simply to measure
> the drift of the two 10MHz signals on an  oscilloscope. Adjust the OCXO so
> that this drift between the two  traces is as slow as you can get it. Then
> simply  measure it over  time. Use one signal for trigger, the other to
> display
>  if  you only have a one channel scope.
>
> If you get say  10ns drift over 1 hour (which you can easily measure even
> with the  cheapest scopes), that is a resolution of 10ns/3600s =  
2.78E012.
>
> Or in other words 27.7uHz!
>
> This has  been discussed before and documented in the time nuts archives
> some  time ago.
>
> bye,
>  Said
>



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