Hi Bob, better use an FIR. Your rolling average didn't smooth out enough because it doesn't have a cutoff low enough. Hysteresis is not going to help here that I know of.
Cheers, D. On Wed, Feb 26, 2014 at 6:05 PM, Bob Stewart <[email protected]> wrote: > Hi Atilla, > > The GPSDO is VE2ZAZ's circuit with new code. It detects phase crossings to > change the DAC, so it has a phase crossing for every update. I'm working on > a TIC design but haven't started on the hardware. In the interim, I hooked > up an LM34 thermistor and have been playing with that. In the 8 hour plot > below, there are no frequency updates, only temperature updates. I've tried > a rolling average, but it doesn't smooth it enough, so I'll have to try > hysteresis next. The orange/green/blue line is the DAC. The red line is the > thermistor. The cyan smear is the phase plot of 1PPS from my Adafruit > (MT3339) against the OCXO (Trimble 34310-T). The units on the right > correspond to the temperature - 100 degrees at the EFC divider directly > beneath the OCXO. Also, they correspond to the wrapped phase, where 0-20 is > 0-360 degrees. The OCXO is limited to a swing of about +/- 1.1Hz at the > moment. > > http://www.evoria.net/AE6RV/TempComp/GPSDO.png > > In the plot below is the ADEV. Hopefully it's self explanatory. The phase > has varied a bit more than 180 degrees during the test. > > > http://www.evoria.net/AE6RV/TempComp/ADEV.png > > The biggest influence on temperature seems to be the low quality divider > resistors in the EFC divider chain. I have new low TempCo resistors but I > couldn't resist playing with these first. Without temperature compensation, > phase would vary through about one cycle every change to the red (thermistor) > line. > > > Bob - AE6RV > > > > >>________________________________ >> From: Attila Kinali <[email protected]> >>To: Bob Stewart <[email protected]>; Discussion of precise time and frequency >>measurement <[email protected]> >>Sent: Wednesday, February 26, 2014 10:23 AM >>Subject: Re: [time-nuts] Thermal Compensation: Digital vs Analog >> >> >>On Wed, 26 Feb 2014 08:09:44 -0800 (PST) >>Bob Stewart <[email protected]> wrote: >> >>> I've been experimenting with digital thermal compensation on my GPSDO. >>> The results have been favorable for a 14 bit dithered PWM-based DAC, but >>> leaves a bit to be desired in the big picture. And it takes up a lot of >>> program bytes on my PIC.. What's the general consensus on this? Should >>> thermal compensation be completely analog? >> >>Out of pure interest. Could you elaborate what results you got? >>Ie. what does your GPSDO look like? How do you compensate for the >>temperature coefficient? How much did that improve performance >>compared to non-compensated operation? Did you try any other approaches? >>Why? Why not? >> >>Yes, i'm a curious mind :-) >> >>Thanks in advance >> >> Attila Kinali >> >>-- >>The trouble with you, Shev, is you don't say anything until you've saved >>up a whole truckload of damned heavy brick arguments and then you dump >>them all out and never look at the bleeding body mangled beneath the heap >> -- Tirin, The Dispossessed, U. Le Guin >> >> >> > _______________________________________________ > 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.
