In this case a (roughly) 375 MHz reference with say 5 ps rms jitter would do just fine. The 375 MHz is not set in stone, but I'd like to end up with something in that ballpark.
regards, Fred ----- Original Message ---- From: ew <[email protected]> To: [email protected] Sent: Thu, March 17, 2011 7:42:55 PM Subject: Re: [time-nuts] Thunderbolt vs Motorola M12+T It depends what your definition of low jitter is. There are low noise CRO's coupled with a PLL that will do a credible job. You may also considder a multiple of 375 if a good CRO is available and devide it down. Look for close in phase noise. Plenty of good PLL's available since you will not have to use fraction. Bert Kehren -----Ursprüngliche Mitteilung----- Von: Tijd Dingen <[email protected]> An: Discussion of precise time and frequency measurement <[email protected]> Verschickt: Do., 17. Mrz. 2011, 14:01 Thema: Re: [time-nuts] Thunderbolt vs Motorola M12+T With regard to your mentioning of "a reference is not 10MHz" ... Suppose one is after a good quality ~ 375 MHz reference with low jitter and high frequency accuracy, what would be the best bang for buck time-nut approved way be? For now I would settle for a 370 MHz reference, which would be obtained by multiplying from a 10 MHz source from say a thunberbolt. But possibly there are more economic ways to go about this... ----- Original Message ---- From: Chris Albertson <[email protected]> To: Discussion of precise time and frequency measurement <[email protected]> Sent: Thu, March 17, 2011 6:45:34 PM Subject: Re: [time-nuts] Thunderbolt vs Motorola M12+T On Thu, Mar 17, 2011 at 8:58 AM, Tijd Dingen <[email protected]> wrote: > Same here. A GPSDO like the thunderbolt is really nice from a system > integration point of view. Buy an easy thingy kit on ebay, and you have > your 10 MHz reference. However, cannot a lot be gained from using a > more up-to-date design with newer gps engine? > > On the one hand we have a thunderbolt which you can view as blackbox > that has a nice stable 10 MHz as output. On the other hand we have for > example a Motorola M12+T where you have to do your own oscillator > disciplining. At this point I am more inclined to go for the thunderbolt > since it solves a lot of problems. However I feel that with a modern > gps engine with better pps signal + a good quality XO you could get > a better 10 MHz signal. Any thought/experience/tips? I've only read reports of experiments and I think in general the result is that there is an inherent limit to what you can expect from a GPSDO that is around 10E-12 and that all the GPSDOs if you let them run, get somewhat close to that limit. What seems to matter the most is the quality of the VXCO used. So asking if the t-bolt or mt12 is best may not be the important question as gps may not be not the weak link, it's the oscillator. That said I thing the quality of the GPS' PPS determines how long you need to let the GPSDO run. I've been thinking recently that if the ultimate goal is a reference that is not 10MHz you might be best off building a GPDDO that runs at the desired frequency then trying to lock to a 10MHz. -- ===== Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
