[time-nuts] Low-Cost Rubidium Performance

Javier Herrero jherrero at hvsistemas.es
Thu Feb 9 21:04:39 UTC 2012


El 09/02/2012 21:06, Magnus Danielson escribió:
> I was just thinking about that. For these more modern 5680A, just the 
> Q of the resonance and the loop filter / loop bandwidth would not 
> allow for so much high frequency side-bands of the DDS to pass through.
The loop filter at least should have good rejection to the 1400Hz 
frequency presumed to be used for the detection... although in the phase 
noise plots I've not seen a very significant spur at that frequency.
> The low frequency DDS variations will go through however.
Yes :)
> I'd expect that the DDS noise creeps onto the 10 MHz signal one way or 
> another, such as the CPLD or other location where separation is poor.
> It would be a bit fun to hunt around and see where the noise creeps in.
Quite a bit. Would be helpful to see how bad is the 60MHz signal 
available inside :) All those 1Hz spaced spurs (and multiples...) could 
be originated by the CPLD.
> It would also be fun to see what a mixer based PI-loop OCXO cleanup 
> (using say a spare 10811) would do. Using a pre-filter and mixer (to 
> avoid severe intermodulations) while still getting a decenting 
> filtering effect. 
Also... perhaps using the 60MHz instead if it is cleaner... I've a spare 
10544 and a 10811 that would love to use for cleaning up the output (but 
lack of time for now to play around as much as I would like :) )



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