Hi Nick, Jim Millers design is very clever and as I see can give results as good as a digital approach but it has the same limitations: The GPS jitter and the oscillator jitter in combination with the loop bandwidth. The only ADEV I have seen for the Miller GPSDO is this one http://www.leapsecond.com/pages/gpsdo/ . Can anyone point me to other tests? The ADEV I see on leapsecond.com indicates for me a time constant of around 200seconds. That is what you get with a OCXO range of 0.25ppm. You don´t need to have a large RC-filter. The original R1-C1 time constant with 16 seconds time constant will work as long as the internal oscillator in the Jupiter-T is at least some Hz away from a multiple of 10kHz. If that is true the sawtooth out of the Jupiter will have enough high frequency to be easily filtered by the RC. This is of course a risk. See for example: https://www.febo.com/pipermail/time-nuts/2005-August/019106.html . If you get a hanging bridge you have at least as much trouble as a non sawtooth corrected GPSDO and probably much worse as the RC filter is only 16s. In the digital approach the prefilter may filter away the hanging bridge (in best case). As I understand the Miller GPSDO with a OCXO with a 0.25ppm range and 10kHz into an XOR phase detector and 16s RC will be very similar to a digital approach with a TIC (Time interval counter ) with +-25us range followed by a prefilter with time constant 16s and a loop with just the P-term with a time constant of 200secs. As it has no I-term it will have slightly less noise but the output phase will drift as soon as the OCXO drifts (as a FLL). The resolution of the XOR phase detector (TIC) will be limited by the noise but as 0.1mV is 1ns the resolution can be seen as better than 1ns is my conclusion. A problem might be that the output of the XOR drifts with the 5V supply but this can be seen as the same problem as the DAC drift in a digital approach. My conclusion (without testing) is that the Jupiter-T 10kHz is very good but not better than the sawtooth corrected outputs from M12 or LEA6T receivers. That is the ADEV can be approximated by 1E-9/Tau (1E-12 at 1000s) in good conditions. My experience with the Venus838-T is only 2 weeks but disappointing. This can also be guessed from the datasheet ADEV curve, that I guess is sawtooth corrected values as it starts at 3E-9 at 1s, but is only 1E-11 at 1000s a factor 10 worse than I get with the LEA-6T with the same antenna and setup. If anyone have ADEV-MDEV curves to share I would be glad to see what can be achieved with the venus838-T. My conclusion is also that sawtooth correction is useless on my 838-T. Lars >Nick wrote: >Jim Miller's 10 kHz GPSDO that’s been referenced here has either solved this problem, or the 10 kHz output of the >Jupiter is substantially better than the Venus’ 10 MHz output, or the design doesn’t give the results time-nuts expect >from a GPSDO. Which of those applies?

Hi Lars. I own a G3RUH (Miller) GPSDO. From what I can recall.... While testing mine with my collection of HP5370B's and my assortment of references the performance of mine while locked was generally comparable to the one in the link you provided. I never tested it "un locked." I couldn't measure phase noise and the performance of my test setup at taus of less than 100 seconds or so was probably a limitation as well. My references (BVA OCXO, PRS10 rb and a cherry picked Z3805 GPSDO) probably weren't really good enough either. It is a nice unit that I have currently loaned out to a local amateur radio operator. Acquiring it lead to me spending a sizeable amount of time and money on time nuts pursuits over the years. Sent from my iPhone > On Sep 16, 2016, at 1:13 PM, Lars Walenius <lars.walenius@hotmail.com> wrote: > > Hi Nick, > > Jim Millers design is very clever and as I see can give results as good as a digital approach but it has the same limitations: > The GPS jitter and the oscillator jitter in combination with the loop bandwidth. > > The only ADEV I have seen for the Miller GPSDO is this one http://www.leapsecond.com/pages/gpsdo/ . > Can anyone point me to other tests? > > The ADEV I see on leapsecond.com indicates for me a time constant of around 200seconds. That is what you get with a OCXO range of 0.25ppm. You don´t need to have a large RC-filter. The original R1-C1 time constant with 16 seconds time constant will work as long as the internal oscillator in the Jupiter-T is at least some Hz away from a multiple of 10kHz. If that is true the sawtooth out of the Jupiter will have enough high frequency to be easily filtered by the RC. This is of course a risk. See for example: https://www.febo.com/pipermail/time-nuts/2005-August/019106.html . If you get a hanging bridge you have at least as much trouble as a non sawtooth corrected GPSDO and probably much worse as the RC filter is only 16s. In the digital approach the prefilter may filter away the hanging bridge (in best case). > > As I understand the Miller GPSDO with a OCXO with a 0.25ppm range and 10kHz into an XOR phase detector and 16s RC will be very similar to a digital approach with a TIC (Time interval counter ) with +-25us range followed by a prefilter with time constant 16s and a loop with just the P-term with a time constant of 200secs. As it has no I-term it will have slightly less noise but the output phase will drift as soon as the OCXO drifts (as a FLL). The resolution of the XOR phase detector (TIC) will be limited by the noise but as 0.1mV is 1ns the resolution can be seen as better than 1ns is my conclusion. A problem might be that the output of the XOR drifts with the 5V supply but this can be seen as the same problem as the DAC drift in a digital approach. > > My conclusion (without testing) is that the Jupiter-T 10kHz is very good but not better than the sawtooth corrected outputs from M12 or LEA6T receivers. That is the ADEV can be approximated by 1E-9/Tau (1E-12 at 1000s) in good conditions. > > My experience with the Venus838-T is only 2 weeks but disappointing. This can also be guessed from the datasheet ADEV curve, that I guess is sawtooth corrected values as it starts at 3E-9 at 1s, but is only 1E-11 at 1000s a factor 10 worse than I get with the LEA-6T with the same antenna and setup. If anyone have ADEV-MDEV curves to share I would be glad to see what can be achieved with the venus838-T. My conclusion is also that sawtooth correction is useless on my 838-T. > > Lars > > >> Nick wrote: > >> Jim Miller's 10 kHz GPSDO that’s been referenced here has either solved this problem, or the 10 kHz output of the >Jupiter is substantially better than the Venus’ 10 MHz output, or the design doesn’t give the results time-nuts expect >from a GPSDO. Which of those applies? > > > _______________________________________________ > 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. >

At the risk of inviting everyone to say “I told you so,” I’ll report here my experimental results from trying this concept out. Since there was a great deal of doubt about the outcome, I hedged my bet a bit and designed for the DOT050V rather than the OH300. If it worked out for the TCXO, then I could try with the more expensive one. The results aren’t very good. With a short TC loop filter, the PLL does lock up, but obviously the jitter of the Venus’ 10 MHz output comes through. With a longer TC, the PLL never locks - or at least if it does lock, it’s locking significantly off frequency. That’s with a 10 µF cap and varied resistors between 10k and 1M. The best I got was at 200k - a TC of 2s. That resulted in this video. Unlike other videos I’ve made comparing two GPSDOs, this one is not a time-lapse. The reference is an OH300 based GPSDO. https://www.youtube.com/watch?v=hiHRp0dCJ64 <https://www.youtube.com/watch?v=hiHRp0dCJ64> A time constant of 10s (1M resistor) just doesn’t work at all. But the real nail in the coffin here is that the price of the PLL chip is still more expensive than the microcontroller and all of the components it replaces. In the end, I’m glad I tried, but I don’t think I’m going to invest any more time in the design. I could try configuring the venus for a 10 kHz output and see if it’s better able to phase lock with a divided TCXO output, but I don’t think I have any reason to believe that would be more likely to succeed.

> On Sep 16, 2016, at 1:13 PM, Lars Walenius <lars.walenius@hotmail.com> wrote: > > > > My experience with the Venus838-T is only 2 weeks but disappointing. This can also be guessed from the datasheet ADEV curve, that I guess is sawtooth corrected values as it starts at 3E-9 at 1s, but is only 1E-11 at 1000s a factor 10 worse than I get with the LEA-6T with the same antenna and setup. If anyone have ADEV-MDEV curves to share I would be glad to see what can be achieved with the venus838-T. My conclusion is also that sawtooth correction is useless on my 838-T. Are you talking about the PPS output or the frequency output (10 MHz by default)? I haven’t attempted to get ADEV plots of the PPS output mainly because I’m not sure the best experimental setup. I could (try to) capture time differences between the PPS output of a thunderbolt and the PPS output of the Venus, but would taking the ADEV of that give correct results? > > Lars > > >> Nick wrote: > >> Jim Miller's 10 kHz GPSDO that’s been referenced here has either solved this problem, or the 10 kHz output of the >Jupiter is substantially better than the Venus’ 10 MHz output, or the design doesn’t give the results time-nuts expect >from a GPSDO. Which of those applies? > > > _______________________________________________ > 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.

Is there a schematic showing what you attempted? I went back through the discussion thread and it was not real clear to me which design you implemented. On Mon, 26 Sep 2016 21:18:25 -0700, you wrote: >... > >The results aren’t very good. > >With a short TC loop filter, the PLL does lock up, but obviously the jitter of the Venus’ 10 MHz output comes through. > >With a longer TC, the PLL never locks - or at least if it does lock, it’s locking significantly off frequency. > >That’s with a 10 µF cap and varied resistors between 10k and 1M. The best I got was at 200k - a TC of 2s. That resulted in this video. Unlike other videos I’ve made comparing two GPSDOs, this one is not a time-lapse. The reference is an OH300 based GPSDO. > >https://www.youtube.com/watch?v=hiHRp0dCJ64 <https://www.youtube.com/watch?v=hiHRp0dCJ64> > >A time constant of 10s (1M resistor) just doesn’t work at all. > >But the real nail in the coffin here is that the price of the PLL chip is still more expensive than the microcontroller and all of the components it replaces. > >...

What kind of capacitor is used for the 10 µF cap - electrolytic or film? Bill Hawkins -----Original Message----- From: Nick Sayer via time-nuts Sent: Monday, September 26, 2016 11:18 PM With a short TC loop filter, the PLL does lock up, but obviously the jitter of the Venus’ 10 MHz output comes through. With a longer TC, the PLL never locks - or at least if it does lock, it’s locking significantly off frequency. That’s with a 10 µF cap and varied resistors between 10k and 1M. The best I got was at 200k - a TC of 2s. That resulted in this video. Unlike other videos I’ve made comparing two GPSDOs, this one is not a time-lapse. The reference is an OH300 based GPSDO. https://www.youtube.com/watch?v=hiHRp0dCJ64 <https://www.youtube.com/watch?v=hiHRp0dCJ64> A time constant of 10s (1M resistor) just doesn’t work at all.