Guys, be aware, first of all, that to correctly test your new GPSDO you need an already running GPSDO as a reference (and a 10 digits-per-second interpolating counter). Don't forget/overlook the reference: start always with a known, good reference.
On Mon, Nov 5, 2012 at 9:12 PM, WarrenS <[email protected]> wrote: > Chris > > Q>I can measure the control voltage change over time and convert that into > a frequency drift? > > Yes, no problem as long as the discipline loop is working OK. > It is very easy to plot the oscillator's long term drift per day, by just > plotting the "filtered" analog EFC control voltage. > Typical 10811 EFC sensitivity I've seen is 0.25Hz / volt > > Q>Is this type of behavior an indication of dire problems with my 10811 > oscillator? > > Depends how long it has been runing. A high ageing rate per day is typical > for a Oscillator that has not been used for a while. > > Depending on the size of the step, If you still have the same problem > after running continuously a few weeks, > The "dire problems" may have more to do with your control loop tuning > method than the 10811. > > If the 3 hr integrating time is also the update cycle time, then no wonder > there are 'large' steps at each update. > 10K sec is too long of an update rate to get the best performance from a > HP10811. > As an example, good settings for a TBolt when disciplining an external > HP10811 is about 1000 sec integration time with an update rate of once per > second. > > Generally it is better to use small steps and update the EFC voltage more > often, maybe more like one per minute, > and then reduce the overall "feedback gain" to increase the control loop > time constant until it is around ~1000 seconds > > One of the easy ways to improve most everything, is to limit how much EFC > voltage change you allow. > After the oscillator has been running a few weeks continuously, a total > change of well under 1 volt at the EFC input is plenty, > when there is a manual course frequency adjustment, like in the HP108111, > that can be used to set the EFC control voltage to the center of it's range > . > > ws > ************************ > > > [time-nuts] getting a grip on 10811 drift (beginner-ish question) > Chris Howard chris at elfpen.com > > > I built a GPSDO using my own power supply, > a VE2ZAZ board, a Trimble Resolution T GPS > and a surplus HP 10811 oscillator. > > > I'm having a bit of trouble with it. I have it set up and > it locks ok and stays in lock so far. But the recommended > long-term integration setting is not working for me. > I think it is about 3 hours. At the end of every cycle > it does a control voltage adjustment, always in one direction. > If I understand it right, the oscillator is slowing and needs > an incremental bump downward of control voltage every time. > > That seems like it is more than just long term drift. But > I don't have my head around the quantities I'm looking at. > > I can measure the control voltage change over time. Can I convert that > into a frequency drift? Or do I need to stop the voltage > adjustments and allow the drift to occur then do a measurement > of that directly somehow? > > Is this type of behavior an indication of dire problems > with my 10811 oscillator? > > Chris Howard > w0ep > > _______________________________________________ > 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.
