[time-nuts] 10MHz Rubidium reference source for frequency counter

mike cook michael.cook at sfr.fr
Wed Oct 29 14:03:05 EDT 2014

Le 29 oct. 2014 à 08:32, Karen Tadevosyan a écrit :

> Thanks again for your explanations and advices.
> I raised this question as a ADEV measurement result of my GPSDO/NEO-7M is about 1E-9 for tau = 1sec http://www.ra3apw.ru/wp-content/uploads/2014/10/NEO7M_OCXO_MV89A_10M_2h0_ADEV.jpg and it isn't meet my expectation. 
> In my understanding (before I published my question here) the reason for this is not a good enough short range stability of my frequency counter's reference OCXO that's why I had an idea to use external rubidium source.
> Now I see that even my internal reference OCXO provides a good ADEV value 1E-10 for tau =1 sec (according Pendulum CNT-91 with opt.19 datasheet).   
> If so what can be a reason of not a good ADEV result of GPSDO/NEO-7M?

Without GPS steering, the oscillator that you have should be able to give you low 10^12 stability at tau 1s once it has been running for a few days. Have you measured it to see if it is reasonably stable when free running?, at least with a consistent drift. If it is not then GPS won't help. If it is a good rock , then try using a pot vary the frequency. If it won't steer then there maybe something wrong in the box, or if the osc is old, maybe you have hit the min/max adjustment limits. Have you monitored your EFC corrections? You may have a too short time constant or too course adjustments causing overshoots.

> Karen, ra3apw
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