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 <att...@kinali.ch> >To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency >measurement <time-nuts@febo.com> >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 <b...@evoria.net> 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 -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
