Hello everyone, I have just re-joined the list after being on pendulum-nuts for a while (where I still am!). I was impelled to join as I'm thinking about a new clock timer, I have dabbled in the past with an OCXO and one of TVB's picPETs. I just got some new surplus OCXOs and the thought crossed my mind of disciplining it to GPS - why not start another project? Tom directed me to a number of websites with GPSDO designs and the "Lars DIY GPSDO" looks interesting being relatively simple and Arduino based. One thing about it does puzzle me though and I thought I'd seek your collective wisdom. It uses a 4046 PLL chip just for its RS-flipflop type phase comparator which then drives a simple time interval comparator (TIC). What surprises me is that it doesn't use the 3-state phase/frequency detector - in principle this has the benefit of automatically frequency locking. This is the type of PD I have used in synthesisers in the past. Is there a reason why the unit works this way, can anyone advise please? Have a great Christmas everyone, and Happy New Year. * John Haine

Hi In a GPSDO, you are comparing 1 pps signals. The typical PLL chips really aren’t made for doing this sort of thing. There are several very simple ways to do an adequate job of measuring the time difference between the two PPS signals. One of the reasons for wanting to read the time difference directly is to incorporate the sawtooth correction output from your GPS module. The other big reason is the difficulty of coming up with R/C filters that get you out to the hundreds of seconds range …. Bob > On Dec 22, 2022, at 12:22 PM, john.haine--- via time-nuts <time-nuts@lists.febo.com> wrote: > > Hello everyone, I have just re-joined the list after being on pendulum-nuts > for a while (where I still am!). I was impelled to join as I'm thinking > about a new clock timer, I have dabbled in the past with an OCXO and one of > TVB's picPETs. I just got some new surplus OCXOs and the thought crossed my > mind of disciplining it to GPS - why not start another project? > > > > Tom directed me to a number of websites with GPSDO designs and the "Lars DIY > GPSDO" looks interesting being relatively simple and Arduino based. One > thing about it does puzzle me though and I thought I'd seek your collective > wisdom. It uses a 4046 PLL chip just for its RS-flipflop type phase > comparator which then drives a simple time interval comparator (TIC). What > surprises me is that it doesn't use the 3-state phase/frequency detector - > in principle this has the benefit of automatically frequency locking. This > is the type of PD I have used in synthesisers in the past. Is there a > reason why the unit works this way, can anyone advise please? > > > > Have a great Christmas everyone, and Happy New Year. > > > > * John Haine > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com

You will notice that Lars' design divides the 10 MHz down to 1MHz then uses the R-S flip flop phase comparator in the HC4046 chip with the 1 pps from the GPS to make a pulse every second that goes high on the rising edge of the PPS and goes low on the next rising edge of the 1 MHz. A simple diode - R-C circuit produces a voltage proportional to the pulse width and thus the phase difference, and an A/D converter in the Arduino measures this voltage each second. The HC4046 phase comparator with the 1 MHz gives it a lock-in range of 1 usec, which helps it acquire and maintain a lock. On Thu, Dec 22, 2022 at 1:32 PM Bob Camp via time-nuts < time-nuts@lists.febo.com> wrote: > Hi > > In a GPSDO, you are comparing 1 pps signals. The typical PLL chips really > aren’t made for doing > this sort of thing. There are several very simple ways to do an adequate > job of measuring the time > difference between the two PPS signals. > > One of the reasons for wanting to read the time difference directly is to > incorporate the sawtooth > correction output from your GPS module. The other big reason is the > difficulty of coming up with > R/C filters that get you out to the hundreds of seconds range …. > > Bob > > > On Dec 22, 2022, at 12:22 PM, john.haine--- via time-nuts < > time-nuts@lists.febo.com> wrote: > > > > Hello everyone, I have just re-joined the list after being on > pendulum-nuts > > for a while (where I still am!). I was impelled to join as I'm thinking > > about a new clock timer, I have dabbled in the past with an OCXO and one > of > > TVB's picPETs. I just got some new surplus OCXOs and the thought > crossed my > > mind of disciplining it to GPS - why not start another project? > > > > > > > > Tom directed me to a number of websites with GPSDO designs and the "Lars > DIY > > GPSDO" looks interesting being relatively simple and Arduino based. One > > thing about it does puzzle me though and I thought I'd seek your > collective > > wisdom. It uses a 4046 PLL chip just for its RS-flipflop type phase > > comparator which then drives a simple time interval comparator (TIC). > What > > surprises me is that it doesn't use the 3-state phase/frequency detector > - > > in principle this has the benefit of automatically frequency locking. > This > > is the type of PD I have used in synthesisers in the past. Is there a > > reason why the unit works this way, can anyone advise please? > > > > > > > > Have a great Christmas everyone, and Happy New Year. > > > > > > > > * John Haine > > > > > > > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe send an email to time-nuts-leave@lists.febo.com > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com -- --Jim Harman

Hi Since you only get one sample per second, no matter what you do, why bother with the 4046 at all? 1 us will roll over at 1 ppm off frequency ( which is very possible with an OCXO ). You still need “something else” to get things close. Bob > On Dec 22, 2022, at 7:52 PM, Jim Harman via time-nuts <time-nuts@lists.febo.com> wrote: > > You will notice that Lars' design divides the 10 MHz down to 1MHz then uses > the R-S flip flop phase comparator in the HC4046 chip with the 1 pps from > the GPS to make a pulse every second that goes high on the rising edge of > the PPS and goes low on the next rising edge of the 1 MHz. A simple diode - > R-C circuit produces a voltage proportional to the pulse width and thus the > phase difference, and an A/D converter in the Arduino measures this voltage > each second. > > The HC4046 phase comparator with the 1 MHz gives it a lock-in range of 1 > usec, which helps it acquire and maintain a lock. > > On Thu, Dec 22, 2022 at 1:32 PM Bob Camp via time-nuts < > time-nuts@lists.febo.com> wrote: > >> Hi >> >> In a GPSDO, you are comparing 1 pps signals. The typical PLL chips really >> aren’t made for doing >> this sort of thing. There are several very simple ways to do an adequate >> job of measuring the time >> difference between the two PPS signals. >> >> One of the reasons for wanting to read the time difference directly is to >> incorporate the sawtooth >> correction output from your GPS module. The other big reason is the >> difficulty of coming up with >> R/C filters that get you out to the hundreds of seconds range …. >> >> Bob >> >>> On Dec 22, 2022, at 12:22 PM, john.haine--- via time-nuts < >> time-nuts@lists.febo.com> wrote: >>> >>> Hello everyone, I have just re-joined the list after being on >> pendulum-nuts >>> for a while (where I still am!). I was impelled to join as I'm thinking >>> about a new clock timer, I have dabbled in the past with an OCXO and one >> of >>> TVB's picPETs. I just got some new surplus OCXOs and the thought >> crossed my >>> mind of disciplining it to GPS - why not start another project? >>> >>> >>> >>> Tom directed me to a number of websites with GPSDO designs and the "Lars >> DIY >>> GPSDO" looks interesting being relatively simple and Arduino based. One >>> thing about it does puzzle me though and I thought I'd seek your >> collective >>> wisdom. It uses a 4046 PLL chip just for its RS-flipflop type phase >>> comparator which then drives a simple time interval comparator (TIC). >> What >>> surprises me is that it doesn't use the 3-state phase/frequency detector >> - >>> in principle this has the benefit of automatically frequency locking. >> This >>> is the type of PD I have used in synthesisers in the past. Is there a >>> reason why the unit works this way, can anyone advise please? >>> >>> >>> >>> Have a great Christmas everyone, and Happy New Year. >>> >>> >>> >>> * John Haine >>> >>> >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe send an email to time-nuts-leave@lists.febo.com >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-leave@lists.febo.com > > > > -- > > --Jim Harman > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-leave@lists.febo.com