Hi Most GPSDO’s do some sort of “slew” to an average DAC value when they go into holdover. Freezing at the last value is not (in general) a good idea. Often things degrade before there is a dropout. Your final DAC value may not be a good one to maximize holdover duration.
Some setups try to “learn” temperature or aging. That gets fed into the DAC when in holdover. The value of this depends a lot on the quality of the training process. Separating this and that input to get a good value for a specific parameter is rarely done with good accuracy. The exception to that rule are oscillators that have a large TC or a very high drift rate. In most cases those are not the ones you pick for a GPSDO. Bob > On Oct 25, 2017, at 7:46 PM, Bob Martin <[email protected]> wrote: > > The holdover state is a DAC set to the last value of the analog control > voltage that adjusts the oscillator frequency. Some designs > use an analog control loop and switch the DAC into the control loop. > Others use the DAC to set the control voltage at all times. This can result > in a steps in the control voltage (output frequency). > I've used both methods and prefer the latter. > > Bob M > > On 10/25/2017 5:30 PM, Mark Sims wrote: >>> No, you set up an oscillator so that is why you have that problem. >> I hooked the two rubidiums together just to see what would happen. It >> pretty much did what I expected... chaos... the time-nut equivalent of a >> naughty schoolboy putting a microphone up to the speaker of the public >> address system. I't's a tough job, but somebody gotta do it ;-) >>> No, not really. The rubidium would be the real hold-over clock. >> Symmetricom calls the disciplining state where it can't lock to the 1PPS >> signal the "holdover" state. It's sort of like a GPSDO holdover state. >> Their discipline firmware does let you set the time constant and damping >> values. I tried a little playing around with them, but never found any >> settings that worked consistently well with the LEA-5T. >> _______________________________________________ >> 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.
