Hi This comes back (very much) to:
What is your objective? If the full performance delivered by a surplus part is your objective, then the Miller is not what you are after. Since it sells for about 2X the current crop of surplus parts … that is a bit of an issue as well. There are a *lot* of different aspects of these devices beyond what any one plot can show. That is why the testing part of it is an issue. It is not a deal breaker. It is not something to stop you dead. It’s something to plan and budget for. Bob > On Apr 5, 2016, at 2:16 AM, Dimitri.p <dimi...@dotp.com> wrote: > > Miller GPSDO vs HP Z3801A, Jackson Labs Fury GPSDO, vs Trimble Thunderbolt > compared Feb 2008 > > http://leapsecond.com/pages/gpsdo > > It seems the Miller GPSDO, for an "unlikely" design, it can hold its own > pretty good. > > > > At 06:56 PM 4/4/2016, you wrote: >> Don wrote: >> >>> 5. Design a voltage tracking / filter to match the OCXO >>> control requirements. >>> 6. And, ...ta-dah; >>> 7. You have a 10MHz, bench frequency standard that will >>> rival all others >> >> Not very likely. The whole point of a GPSDO is for the frequency to be >> controlled by the more stable source (OCXO or GPS) at all integration times >> (tau). But the OCXO will typically be more stable than the GPS for tau less >> than several hundred seconds (see graph below -- black line is GPS, brown >> line is a typical OCXO). So, the PLL needs to have a time constant of >> hundreds of seconds. Such a PLL filter cannot practicably be designed in >> the analog domain, so one needs to design a digital filter with appropriate >> time constant and damping. Because of the very long time constant, it is >> almost necessary for the filter to have more than one, switchable time >> constants to avoid extremely long lock times. >> >> Very few home builders are capable of designing a proper digital filter >> suitable for this application (the counter-based loops of most published DIY >> GPSDO designs are not proper digital filters). >> >> So, no -- it is very unlikely that a home-built GPSDO will "rival all >> comers," whether the builder designs his or her own circuit or uses one of >> the many published circuits. >> >> Best regards, >> >> Charles >> >> >> Graph below. Note that a properly designed GPSDO would show stability that >> follows the OCXO (brown line) at low tau, and the GPS (black line) above the >> point where they intersect -- here, about 350 seconds. Note that a loop >> filter with proper damping will NOT exhibit a "hump" near the crossover >> (many GPSDOs do exhibit a pronounced hump, betraying that their loop filters >> are not properly designed). >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
