bang-bang servos do depend on inherent low-pass filtering by the controlled device. Don
saidj...@aol.com > Tom, > > airflow, or changes in airflow are typically much worse for ADEV than > actual ambient temperature changes in still air. > > In still air for example a typical Eurocan DOCXO will have a case temp of > about 55C to 60C at 25C ambient. > > Turn on any kind of significant airflow over that part and the air > temperature will be nearly the same as before, but the case of the DOCXO is > now > very quickly cooled to 30C to 40C by the airflow. > > This affects mostly TCXO and single-oven units (including Rb's etc), it > does very little to DOCXO units typically because the outer oven takes the > brunt of the temp change and insulates the inner oven. There are other > components on the PCB though next to the DOCXO that will be affected such as > the > DAC, DAC reference, EFC filters, current ground loops due to changing > heater-current on the ground pin, etc. > > This even affects TCXO's because they are typically heated by themselves > and other components on the PCB, and any kind of airflow change will cause an > instant temp change on the TCXO due to cooling. > > So in my opinion a bang-bang controlled fan near any kind of oscillator is > about the worst thing one can do for short term stability. > > bye, > Said > > > In a message dated 6/24/2014 13:35:21 Pacific Daylight Time, > t...@leapsecond.com writes: > >> However it is disappointing that no one has stepped up to tackle the >> temperature problem. how many have looked at the temperature attachment > and >> clicked on the N5TNL link. Let me make it clear that yes the GPSDO will > work but >> there will be one or two orders of magnitude degradation without active >> fan temperature control unless the internal temperature compensation is > >> disabled. > > Can you clarify the "two orders of magnitude" claim? That's hard for me to > believe, I think, without seeing the ADEV plots or actual lab report. > > I mean, even a cheap XO or TCXO or OCXO can be disciplined against GPS and > achieve superb results. Temperature (or rather, temperature rate of > change) has little effect short-term. Temperature also has little to zero > effect > long-term. So it's only in the, what, tau 100 to 1000 or maybe 10000 second > range that temperature even matters. As long as the LO is locked to GPS; I > assume you're not talking about holdover. > > Obviously you'd want a slightly shorter loop time constant for a > non-temperature-controlled Rb than a fancy temperature-controlled Rb. But > does this > really make a one or two *orders of magnitude* difference? > > /tvb > > > _______________________________________________ > 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. > > -- "The power of accurate observation is commonly called cynicism by those who have not got it." -George Bernard Shaw Dr. Don Latham AJ7LL Six Mile Systems LLC 17850 Six Mile Road Huson, MT, 59846 mail: POBox 404 Frenchtown MT 59834-0404 VOX 406-626-4304 Skype: buffler2 www.lightningforensics.com www.sixmilesystems.com _______________________________________________ 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.