[time-nuts] Advantages of GNSS ???
I have several questions for the group, since there are several members that have been able to start evaluating the uBlox F9P and perhaps the F9T GNSS receivers. For the purposes of time and frequency determination, is there an advantage to using the GNSS receivers, relative to just the US GPS? It appears that a really good GPS (only) based GPSDO can get into the 1e-11 and perhaps the 1e-12 accuracy range. Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou (China), and plus Galileo (Europe), actually provide any improvement in time/frequency accuracy? Is that what the F9P actually does, or only some sub-combinations of the above? Down at that level of accuracy, do the four systems agree within 1 e-12, anyway? Is there any advantage to using the GNSS for time/frequency? Does using the RTCM Corrections, needed to achieve the ~ 1 cm positioning accuracy also improve time/frequency accuracy? The underlying question I am trying to get at is: Will a GNSS based GPSDO have any advantage over a GPS-only, or a dual band L1/L2 GPS-only GPSDO? Thanks, --- Graham == ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Advantages of GNSS ???
Here is screen grab of an F9T tracking GPS/GLONASS/GALILEO/BEIDOU. In the max sig level display the sats that the F9T says do L2 ionospheric corrections are shown in GREEN. Note that the F9T thinks that it is seeing signals from PRNs 192..202 These are the Japanese QZSS sat PRNs. Obviously, these are not visible from the USA. I'm not sure why it thinks it sees signals from these. Perhaps its correlators ate tricked by signals from other sats. It never actually tracks them. --- > On the F9P you have the specific issue of L1 / L2 with older GPS satellites. > The device only does L2C. That cuts the “population” roughly in half.___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Advantages of GNSS ???
A big issue with using the sawtooth correction message from a GPS receivers is the issue of just what that sawtooth value is related to and how to apply it to the measured PPS value / phase. I added the ability to Lady Heather to calculate a sawtooth corrected "paper clock" by applying the sawtooth correction message value to the PPS output measured by an external counter like the TAPR TICC. There are around a dozen different combinations of sawtooth value and PPS measurements... only one of which minimizes the PPS error. Do you add or subtract the sawtooth value to the PPS measurement? Do you apply the sawtooth value to the previous/current/next PPS measurement? Do you apply the sawtooth correction to the PPS itself or the accumulated phase of the PPS? I don't think that I have ever seen what to do with the sawtooth value documented in any receiver documentation... Heather has default receiver dependent correction strategies or lets you specify the correction strategy to use. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hey Graham, I'm gonna start a project soon to evaluate a F9P as a Time Transfer GNSS receiver. For now i haven't too much answers for you but only i know is: the BIPM uses all labs that participate from UTC to make corrections of GNSS satellites frequency, also for the TAI use. I think GNNS T&F is a good and reliable source for many projects. Here in my lab with Septentrio's Pola RX 3 Tr we have a very low Time Dilution Of Precision when the Glonass and all anothers becomes enabled, so our frequency if compared to all GNSS constallations is good, i think the same logic can be applied for frequency generation / distribution. What i want to say is: with more satellites of different constellations you can have a better end signal (more stable and reliable). Tests should be done. I hope can help more in the future. Best regards, Luiz Em sex, 5 de jul de 2019 às 23:00, Graham / KE9H escreveu: > I have several questions for the group, since there are several members > that have been able to start evaluating the uBlox F9P and perhaps the F9T > GNSS receivers. > > For the purposes of time and frequency determination, is there an advantage > to using the GNSS receivers, relative to just the US GPS? > > It appears that a really good GPS (only) based GPSDO can get into the 1e-11 > and perhaps the 1e-12 accuracy range. > > Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou > (China), and plus Galileo (Europe), actually provide any improvement in > time/frequency accuracy? > > Is that what the F9P actually does, or only some sub-combinations of the > above? > > Down at that level of accuracy, do the four systems agree within 1 e-12, > anyway? > > Is there any advantage to using the GNSS for time/frequency? > > Does using the RTCM Corrections, needed to achieve the ~ 1 cm positioning > accuracy also improve time/frequency accuracy? > > The underlying question I am trying to get at is: Will a GNSS based GPSDO > have any advantage over a GPS-only, or a dual band L1/L2 GPS-only GPSDO? > > Thanks, > --- Graham > > == > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi On the F9P you have the specific issue of L1 / L2 with older GPS satellites. The device only does L2C. That cuts the “population” roughly in half. This is not a great thing for a “GPS only” setup with that device. BIPM does not directly control or feed timing into the various GNSS systems. They do use highly specialized gear to do time transfer. Some of that is via GNSS sats. What they do is a bit different than what a typical timing user would do. Frequency of any GNSS output on the F9P is limited by the accuracy of the time pulse. Correction is only done once a second. The same “fraction of a nanosecond” sort of wobble you see in time gets you a “fraction of a PPB” frequency wobble. You will need a local standard to discipline in order to do very well. A commercial GPSDO is one way to do this. There are other approaches. Indeed this is just the first layer or two of the list of fun you are going to have :) Bob > On Jul 5, 2019, at 11:19 PM, Luiz Paulo Damaceno > wrote: > > Hey Graham, > > I'm gonna start a project soon to evaluate a F9P as a Time Transfer GNSS > receiver. For now i haven't too much answers for you but only i know is: > the BIPM uses all labs that participate from UTC to make corrections of > GNSS satellites frequency, also for the TAI use. I think GNNS T&F is a good > and reliable source for many projects. Here in my lab with Septentrio's > Pola RX 3 Tr we have a very low Time Dilution Of Precision when the Glonass > and all anothers becomes enabled, so our frequency if compared to all GNSS > constallations is good, i think the same logic can be applied for frequency > generation / distribution. What i want to say is: with more satellites of > different constellations you can have a better end signal (more stable and > reliable). Tests should be done. I hope can help more in the future. > > Best regards, > > Luiz > > Em sex, 5 de jul de 2019 às 23:00, Graham / KE9H > escreveu: > >> I have several questions for the group, since there are several members >> that have been able to start evaluating the uBlox F9P and perhaps the F9T >> GNSS receivers. >> >> For the purposes of time and frequency determination, is there an advantage >> to using the GNSS receivers, relative to just the US GPS? >> >> It appears that a really good GPS (only) based GPSDO can get into the 1e-11 >> and perhaps the 1e-12 accuracy range. >> >> Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou >> (China), and plus Galileo (Europe), actually provide any improvement in >> time/frequency accuracy? >> >> Is that what the F9P actually does, or only some sub-combinations of the >> above? >> >> Down at that level of accuracy, do the four systems agree within 1 e-12, >> anyway? >> >> Is there any advantage to using the GNSS for time/frequency? >> >> Does using the RTCM Corrections, needed to achieve the ~ 1 cm positioning >> accuracy also improve time/frequency accuracy? >> >> The underlying question I am trying to get at is: Will a GNSS based GPSDO >> have any advantage over a GPS-only, or a dual band L1/L2 GPS-only GPSDO? >> >> Thanks, >> --- Graham >> >> == >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
On Fri, 5 Jul 2019 19:49:59 -0500 "Graham / KE9H" wrote: > Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou > (China), and plus Galileo (Europe), actually provide any improvement in > time/frequency accuracy? There are multiple angles to this: 1) Galileo offers the widest bandwidth signal (E5a+b) of all the currently fully operational GNSS services. This brings huge advantages when it comes to mitigating multi-path (the largest contributor to uncertainty, even before ionospheric delay if you have a non-optimal antenna position). GPS, as far as I am aware of, has no plans for any such wide bandwith signal. 2) Galileo is currently the only service that has full L1+L5 coverage. It will take GPS a couple of years until there are enough block III birds up there to offer a similar coverage on L5. Where a couple is probably in the order of 10-20 years, if not longer (GPS satellites are too well made and don't die quickly enough). While L1+L2 works similarly well for ionospheric free solutions, L2 is not a protected GNSS band (it's even secondary user in some ITU regions) and may get interference from radar systems and microwave links. L5 is a protected GNSS band. Additionally, L2C (the civil L2 GPS signal) is currently only broadcast from 19 satellites. While this should probably be enough for a lot of cases, it does not provide full coverage of earth yet. My guess for full coverage (ie 24 birds with L2C) is in the order of 3-8 years. 3) If you are doing common-view time transfer, then you want to have as many visible satellites as possible to decrease errors due to noise and atmospheric disturbances. Thus having GPS+Galileo+Glonass+Beidu helps. Similar things apply for all-in-view time transfer. 4) Only GPS and Glonass are sofar in the standard IGS products. Galileo is only in the experimental MGES products. There aren't enough Beidu receivers out there to reasonably use Beidu for IGS yet. 5) Galileo has hydrogen masers as clocks, which offer improved stability compared to the rubidium masers (which all other GNSS use). But whether this actually results in better performance, I do not know. I'm sure there are studies on this out there, but I have not read any yet. 6) All but GPS and Glonass are fairly new systems and have not all kinks ironed out yet. While the Galileo quaterly performance reports look good, that does not mean that there aren't any hickups that might or might not trip up your receiver. Similar concerns can be raised for Beidu, which has the additional disadvantage, that it has been developed with a lot of secrecy around it. Ie a lot of the potential system performance analysis that scientists performed for GPS, Glonass and Galileo is missing for Beidu. 7) Local satellite based augmentation systems like QZSS, IRNSS, Beidu (the China-only part) give additional satellites that are high up in the sky, thus allowing to see additional satellites in urban areas (eg QZSS has one satellite at elevations >60° at all times). Attila Kinali -- The bad part of Zurich is where the degenerates throw DARK chocolate at you. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hello Luiz, (Did we meet at IFCS-EFTF in Orlando? If so, my apologies for not remembering your name, and for repeating here what you know). I presented some preliminary time-transfer data for the F9P at IFCS and wrote a short paper for the proceedings; if you’d like a copy, I am happy to send you one. For any other time-nuts interested in post processed GNSS time -transfer: Since the conference, I have been working on and off on adding dual frequency support to OpenTTP ( www.openttp.org), principally for the F9P/T and have four F9P receivers under test. The aim is to have a nice long data set for EFTF next year. Cheers Michael On Sat, 6 Jul 2019 at 2:02 pm, Luiz Paulo Damaceno < luizpauloeletric...@gmail.com> wrote: > Hey Graham, > > I'm gonna start a project soon to evaluate a F9P as a Time Transfer GNSS > receiver. For now i haven't too much answers for you but only i know is: > the BIPM uses all labs that participate from UTC to make corrections of > GNSS satellites frequency, also for the TAI use. I think GNNS T&F is a good > and reliable source for many projects. Here in my lab with Septentrio's > Pola RX 3 Tr we have a very low Time Dilution Of Precision when the Glonass > and all anothers becomes enabled, so our frequency if compared to all GNSS > constallations is good, i think the same logic can be applied for frequency > generation / distribution. What i want to say is: with more satellites of > different constellations you can have a better end signal (more stable and > reliable). Tests should be done. I hope can help more in the future. > > Best regards, > > Luiz > > Em sex, 5 de jul de 2019 às 23:00, Graham / KE9H > escreveu: > > > I have several questions for the group, since there are several members > > that have been able to start evaluating the uBlox F9P and perhaps the F9T > > GNSS receivers. > > > > For the purposes of time and frequency determination, is there an > advantage > > to using the GNSS receivers, relative to just the US GPS? > > > > It appears that a really good GPS (only) based GPSDO can get into the > 1e-11 > > and perhaps the 1e-12 accuracy range. > > > > Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou > > (China), and plus Galileo (Europe), actually provide any improvement in > > time/frequency accuracy? > > > > Is that what the F9P actually does, or only some sub-combinations of the > > above? > > > > Down at that level of accuracy, do the four systems agree within 1 e-12, > > anyway? > > > > Is there any advantage to using the GNSS for time/frequency? > > > > Does using the RTCM Corrections, needed to achieve the ~ 1 cm positioning > > accuracy also improve time/frequency accuracy? > > > > The underlying question I am trying to get at is: Will a GNSS based GPSDO > > have any advantage over a GPS-only, or a dual band L1/L2 GPS-only GPSDO? > > > > Thanks, > > --- Graham > > > > == > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Correction on all Ublox receivers including F9P is done at navigation rate which can be set as high as 20Hz. Leo > From: Bob kb8tq > Frequency of any GNSS output on the F9P is limited by the accuracy of the > time pulse. > Correction is only done once a second. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi They go absolutely crazy updating nav….. but they only come up with the timing correction once a second. From the latest version of the F9T Manual UBX-19005590 - R02 on page 43: The recommended configuration when using the UBX-TIM-TP message is to set both the measurement rate (CFG-RATE-MEAS) and the time pulse frequency (CFG-TP-*) to 1Hz. Since the rate of UBX-TIM-TP is bound to 1 Hz, more than one UBX-TIM-TP message can appear between two pulses if the time pulse frequency is set lower than 1 Hz. In this case all UBX-TIM-TP messages in between a time pulse T1 and T2 belong to T2 and the last UBX- TIM-TP before T2 reports the most accurate quantization error. In general, if the time pulse rate is not configured to 1 Hz, there will not be a single UBX-TIM-TP message for each time pulse. Sorry if the quote comes through a bit garbled. Sometimes this cut and paste stuff does not quite do the trick. Indeed it’s not 100% clear what they are doing from the docs. They say this and that here and there. The bottom line is still that you can only trust the sawtooth offset data to be correct at the one second point. Bob > On Jul 7, 2019, at 8:42 AM, Leo Bodnar wrote: > > Correction on all Ublox receivers including F9P is done at navigation rate > which can be set as high as 20Hz. > Leo > >> From: Bob kb8tq >> Frequency of any GNSS output on the F9P is limited by the accuracy of the >> time pulse. >> Correction is only done once a second. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Leo Bodnar writes: > Correction on all Ublox receivers including F9P is done at navigation > rate which can be set as high as 20Hz. If you are thinking of the sawtooth correction, then I think you'll find that this is only available for the full second. There is some mumbling in the manual that the timing firmware would really like you to only calculate one solution per second for best performance. Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ SD adaptation for Waldorf Blofeld V1.15B11: http://Synth.Stromeko.net/Downloads.html#WaldorfSDada ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Bob, what are you calling "time correction"? You are now quoting F9T which is not the product original statement related to (F9P.) If you refer to internal Ublox adjustment of instantaneous timepulse train then it is performed at navigation rate - up to 20Hz on F9P. F9P's rate of TP can be set from 0.25Hz to 10MHz according to the datasheet but in reality is usually wider. TP edge quantisation is a separate issue to TP base rate adjustment and it is done at TP rate. Leo > Subject: Re: [time-nuts] Advantages of GNSS ??? > They go absolutely crazy updating nav?.. but they only come up with the > timing correction once a second. > > From the latest version of the F9T Manual UBX-19005590 - R02 on page 43: > The recommended configuration when using the UBX-TIM-TP message is to set > both the measurement rate (CFG-RATE-MEAS) and the time pulse frequency > (CFG-TP-*) to 1Hz. > > Since the rate of UBX-TIM-TP is bound to 1 Hz, more than one UBX-TIM-TP > message can appear between two pulses if the time pulse frequency is set > lower than 1 Hz. In this case all UBX-TIM-TP messages in between a time pulse > T1 and T2 belong to T2 and the last UBX- TIM-TP before T2 reports the most > accurate quantization error. In general, if the time pulse rate is not > configured to 1 Hz, there will not be a single UBX-TIM-TP message for each > time pulse. > > Sorry if the quote comes through a bit garbled. Sometimes this cut and paste > stuff does not quite do the trick. > Indeed it?s not 100% clear what they are doing from the docs. They say this > and that here and there. The > bottom line is still that you can only trust the sawtooth offset data to be > correct at the one second point. > > Bob ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi Whatever they are doing to create an output is being done modulo the internal TCXO period. That gets you down to a +/- 4 ns error on either the F9T or the F9P. They can do that however often they like, it’s still a very coarse correction as far as I’m concerned. What matters is how often they come up with the data to tell you how far off from reality that magic edge *is* in reality. They do that to well under a nanosecond, both on the F9T and the F9P. That update info only is calculated / supplied once a second. This information *plus* the edge is (at lest to me) the only source of accurate time out of the device. It’s at least 10X better than what you get without the correction If indeed you *do* configure to let them modify the TCXO <-> pulse output at a greater rate than once a second, the connection between the sawtooth correction data and the actual pulse becomes a bit obscure. Only one edge has data for it. The rest have an offset of “who knows what”. Having a bunch of “unknown” edges in with one accurate one seems like a route to confusion. This all gets right back to the recommendation that I quoted about running the pulse rate at 1 pps for precision use. There are similar notes in similar documents going back at least to the LEA-5T era of modules. Are any of them 100% clear - nope. You have to either call up and ask “what does this really mean?” or guess a bit. Is this a knock of some sort on uBlox? Certainly not. No document ever written is ever going to be perfect. They are not the only outfit doing this (one second calculation of error). They aren’t any worse at explaining it than the other guys. They all do a pretty good job of describing what’s going on face to face. Bob > On Jul 8, 2019, at 9:51 AM, Leo Bodnar wrote: > > Bob, what are you calling "time correction"? > > You are now quoting F9T which is not the product original statement related > to (F9P.) > > If you refer to internal Ublox adjustment of instantaneous timepulse train > then it is performed at navigation rate - up to 20Hz on F9P. > F9P's rate of TP can be set from 0.25Hz to 10MHz according to the datasheet > but in reality is usually wider. > > TP edge quantisation is a separate issue to TP base rate adjustment and it is > done at TP rate. > > Leo > > >> Subject: Re: [time-nuts] Advantages of GNSS ??? >> They go absolutely crazy updating nav?.. but they only come up with the >> timing correction once a second. >> >> From the latest version of the F9T Manual UBX-19005590 - R02 on page 43: >> The recommended configuration when using the UBX-TIM-TP message is to set >> both the measurement rate (CFG-RATE-MEAS) and the time pulse frequency >> (CFG-TP-*) to 1Hz. >> >> Since the rate of UBX-TIM-TP is bound to 1 Hz, more than one UBX-TIM-TP >> message can appear between two pulses if the time pulse frequency is set >> lower than 1 Hz. In this case all UBX-TIM-TP messages in between a time >> pulse T1 and T2 belong to T2 and the last UBX- TIM-TP before T2 reports the >> most accurate quantization error. In general, if the time pulse rate is not >> configured to 1 Hz, there will not be a single UBX-TIM-TP message for each >> time pulse. >> >> Sorry if the quote comes through a bit garbled. Sometimes this cut and paste >> stuff does not quite do the trick. >> Indeed it?s not 100% clear what they are doing from the docs. They say this >> and that here and there. The >> bottom line is still that you can only trust the sawtooth offset data to be >> correct at the one second point. >> >> Bob > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Well now you can see one Bert Kehren In a message dated 7/8/2019 7:02:07 PM Eastern Standard Time, hol...@hotmail.com writes: A big issue with using the sawtooth correction message from a GPS receivers is the issue of just what that sawtooth value is related to and how to apply it to the measured PPS value / phase. I added the ability to Lady Heather to calculate a sawtooth corrected "paper clock" by applying the sawtooth correction message value to the PPS output measured by an external counter like the TAPR TICC. There are around a dozen different combinations of sawtooth value and PPS measurements... only one of which minimizes the PPS error. Do you add or subtract the sawtooth value to the PPS measurement? Do you apply the sawtooth value to the previous/current/next PPS measurement? Do you apply the sawtooth correction to the PPS itself or the accumulated phase of the PPS? I don't think that I have ever seen what to do with the sawtooth value documented in any receiver documentation... Heather has default receiver dependent correction strategies or lets you specify the correction strategy to use.___time-nuts mailing list -- time-n...@lists.febo.comTo unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
One what? I see that it is a Ublox unit, but see no reference to the interesting modern units like the 9 series. Also, I note that the only reference on the board to "ant" is on the lower right corner, while what I suppose to be the actual antenna connector appears to be an SMA near the upper right corner. And why does it look like several of the components have been resoldered or replaced or something? Dana On Mon, Jul 8, 2019 at 8:00 PM ew via time-nuts wrote: > Well now you can see one > Bert Kehren > > > In a message dated 7/8/2019 7:02:07 PM Eastern Standard Time, > hol...@hotmail.com writes: > > A big issue with using the sawtooth correction message from a GPS > receivers is the issue of just what that sawtooth value is related to and > how to apply it to the measured PPS value / phase. > I added the ability to Lady Heather to calculate a sawtooth corrected > "paper clock" by applying the sawtooth correction message value to the PPS > output measured by an external counter like the TAPR TICC. > > There are around a dozen different combinations of sawtooth value and PPS > measurements... only one of which minimizes the PPS error. Do you add or > subtract the sawtooth value to the PPS measurement? Do you apply the > sawtooth value to the previous/current/next PPS measurement? Do you apply > the sawtooth correction to the PPS itself or the accumulated phase of the > PPS? > I don't think that I have ever seen what to do with the sawtooth value > documented in any receiver documentation... Heather has default receiver > dependent correction strategies or lets you specify the correction > strategy to use.___time-nuts > mailing list -- time-n...@lists.febo.comTo unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow > the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Dana This was in response to Mark Sins " I don't think that I have ever seen what to do with the sawtooth value documented in any receiver documentation"I did this 4 years ago it, is a sawtooth corrected ublox. First pass. Always do a follow on board but never did any thing with it since there was no interest. We did it part of our GPSDO work but saw no improvement. Sorry my work offends you.I did the same with the Furuno GT and GN-87 without sawtooth since it is only 4 nsec. Ole tested it and we use it with very good results. Again I followed it up with a later design in case there is interest. I will not post the picture of the original one so not to offend you.I will not do a board on the ublox 9 since we are frequency not time nuts and see no need for it. Bert Kehren In a message dated 7/9/2019 12:05:14 AM Eastern Standard Time, k8yumdoo...@gmail.com writes: One what? I see that it is a Ublox unit, but see no reference to the interesting modern units like the 9 series. Also, I note that the only reference on the board to "ant" is on the lower right corner, while what I suppose to be the actual antenna connector appears to be an SMA near the upper right corner. And why does it look like several of the components have been resoldered or replaced or something? Dana On Mon, Jul 8, 2019 at 8:00 PM ew via time-nuts wrote: > Well now you can see one > Bert Kehren > > > In a message dated 7/8/2019 7:02:07 PM Eastern Standard Time, > hol...@hotmail.com writes: > > A big issue with using the sawtooth correction message from a GPS > receivers is the issue of just what that sawtooth value is related to and > how to apply it to the measured PPS value / phase. > I added the ability to Lady Heather to calculate a sawtooth corrected > "paper clock" by applying the sawtooth correction message value to the PPS > output measured by an external counter like the TAPR TICC. > > There are around a dozen different combinations of sawtooth value and PPS > measurements... only one of which minimizes the PPS error. Do you add or > subtract the sawtooth value to the PPS measurement? Do you apply the > sawtooth value to the previous/current/next PPS measurement? Do you apply > the sawtooth correction to the PPS itself or the accumulated phase of the > PPS? > I don't think that I have ever seen what to do with the sawtooth value > documented in any receiver documentation... Heather has default receiver > dependent correction strategies or lets you specify the correction > strategy to use.___time-nuts > mailing list -- time-n...@lists.febo.comTo unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow > the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Bert, My take on the issue is that Mark Sims had not seen manufacturer documentation on how specifically to use the sawtooth correction value. You posted a picture of what we now know was an implementation of a use of the correction value. Did you have manufacturer documentation on how the value was to be used before you did your design? If so, that's what Mark is looking for. Like me, Dana was confused by your picture of a GPS assembly, which was not an answer to Mark. Knowing Dana personally I'm not surprised he started down the 20 question path, and I doubt he was actually offended by your post. respectfully, Robert LaJeunesse > Sent: Tuesday, July 09, 2019 at 6:26 AM > From: "ew via time-nuts" > To: time-nuts@lists.febo.com > Cc: ew > Subject: Re: [time-nuts] Advantages of GNSS ??? > > Dana > This was in response to Mark Sins " I don't think that I have ever seen what > to do with the sawtooth value > documented in any receiver documentation"I did this 4 years ago it, is a > sawtooth corrected ublox. First pass. Always do a follow on board but never > did any thing with it since there was no interest. We did it part of our > GPSDO work but saw no improvement. Sorry my work offends you.I did the same > with the Furuno GT and GN-87 without sawtooth since it is only 4 nsec. Ole > tested it and we use it with very good results. Again I followed it up with a > later design in case there is interest. I will not post the picture of the > original one so not to offend you.I will not do a board on the ublox 9 since > we are frequency not time nuts and see no need for it. > Bert Kehren > > > In a message dated 7/9/2019 12:05:14 AM Eastern Standard Time, > k8yumdoo...@gmail.com writes: > > One what? I see that it is a Ublox unit, but see no reference to the > interesting > modern units like the 9 series. Also, I note that the only reference on > the board > to "ant" is on the lower right corner, while what I suppose to be the > actual antenna > connector appears to be an SMA near the upper right corner. > > And why does it look like several of the components have been resoldered > or replaced or something? > > Dana > > > On Mon, Jul 8, 2019 at 8:00 PM ew via time-nuts > wrote: > > > Well now you can see one > > Bert Kehren > > > > > > In a message dated 7/8/2019 7:02:07 PM Eastern Standard Time, > > hol...@hotmail.com writes: > > > > A big issue with using the sawtooth correction message from a GPS > > receivers is the issue of just what that sawtooth value is related to and > > how to apply it to the measured PPS value / phase. > > I added the ability to Lady Heather to calculate a sawtooth corrected > > "paper clock" by applying the sawtooth correction message value to the PPS > > output measured by an external counter like the TAPR TICC. > > > > There are around a dozen different combinations of sawtooth value and PPS > > measurements... only one of which minimizes the PPS error. Do you add or > > subtract the sawtooth value to the PPS measurement? Do you apply the > > sawtooth value to the previous/current/next PPS measurement? Do you apply > > the sawtooth correction to the PPS itself or the accumulated phase of the > > PPS? > > I don't think that I have ever seen what to do with the sawtooth value > > documented in any receiver documentation... Heather has default receiver > > dependent correction strategies or lets you specify the correction > > strategy to use.___time-nuts > > mailing list -- time-n...@lists.febo.comTo unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.comand follow > > the instructions there. > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Let's put the Bert vs. Dana misunderstanding aside. To me the key feature in Bert's photo is the Dallas/Maxim digital delay chip. Look carefully and see the DS1023-50, which is an 8-bit programmable delay line (~0 to ~127 ns in 0.5 ns steps). This is a technique used to remove sawtooth error without requiring a ns or sub-ns TIC and a PC. The trick: before each 1PPS the delay line is latched with the appropriately signed and scaled sawtooth correction number so that when the 1PPS arrives the leading edge is physically (electronically) delayed by exactly the right number of compensating ns. If you look inside one of Rick Hambly's GPS clocks [1] you will see this. Each second a PIC reads the binary sawtooth message from the receiver and programs the delay line just in time for the next 1PPS. The result is a sawtooth-free 1PPS without requiring a TIC or a PC. The idea has been around for 20 years, the era of the Motorola Oncore VP receiver. The performance of this "hardware" solution to sawtooth correction is simpler and nearly as good as the more complex "software" solution that's used today. For comparison plots see page 35 of: https://www.haystack.mit.edu/workshop/TOW2017/files/Seminars/tow-time2017.pdf The plot is beautiful. The reason this delay line technique isn't used much anymore is that AFAIK the Dallas chips are no longer produced. So almost every uses s/w sawtooth correction now. /tvb [1] https://www.cnssys.com/cnsclock/CNSClockII.php ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
On Tue, July 9, 2019 10:50 am, Tom Van Baak wrote: > chip. Look carefully and see the DS1023-50, which is an 8-bit > programmable delay line (~0 to ~127 ns in 0.5 ns steps). ... > The reason this delay line technique isn't used > much anymore is that AFAIK the Dallas chips are no longer produced. The original is not, there is a close variant still in production: https://www.maximintegrated.com/en/products/analog/clock-generation-distribution/DS1124.html "The DS1124 is an 8-bit programmable timing element similar in function to the DS1021-25. The 256-delay intervals are programmed by using a 3-wire serial interface. With a 0.25ns step size, the DS1124 can provide a delay time from 20ns up to 84ns with an integral nonlinearity of ±3ns. " Small package, would be a little difficult to prototype by hand, but not impossible. -- Chris Caudle ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
In message <8e74832c-58e6-c2ef-f68c-48e116718...@leapsecond.com>, Tom Van Baak writes: >The plot is beautiful. The reason this delay line technique isn't used >much anymore is that AFAIK the Dallas chips are no longer produced. So >almost every uses s/w sawtooth correction now. So... this is where it gets complicated isn't it ? If you saw-tooth compensate the PPS in hardware, and then use it to latch some digital counter, you may actually have made your performance worse, because you lost the "dithering" of the counter provided by the sawtooth, and all else being equal, just created a new "hanging bridge" problem. If instead you latch your counter on the uncompensated PPS and apply the saw-tooth compensation in software, you most likely dither the +/-1 count noise almost out of existence. Compensating the saw-tooth in hardware only[1] makes sense (IMO) if you feed the compensate PPS into an analog PLL and want to reduce the "hanging bridge" effect to the resolution of your delay-line. And if you implement an analog PLL in time-nuts territory where the timeconstants are measured in minutes and hours, you have far bigger challenges than the hanging bridge from the GPS... [1] Or, I guess, if you want to feed the PPS to your HP5370 without having to postprocess the TI measurements for the sawtooth. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
RobertThat was my wrong take, since as long as I have messed with timing GPS receivers the difference was price and the fact that saw tooth data was present in hardware. Juerg did his first M12/Dallas/Maxim in 2004 driving a PRS 10 only replacing it when he bought a Tbolt through TARP.Working 10 years ago with Richard Mc Corkle his GPS MAX used also a PIC to read M12 data adding it up for the time constant and adding the sum to his filter calculation. He also did a PIC for me using the D/M chip.Since something happened to Richard I set out to do a board to be used for our GPSDO. Tests did not show ant improvements. Did a Furuno board without saw tooth because it is only 4 nsec. Works great. In all cases the PIC also generated the survey command in order to work without a computer. The Furuno T does on power up an automatic survey. The N version also works great and is available at Berklin for 1/3 the price of T but does not survey. Only other one also with 1 pps. Looks like Berklin has a problem selling them, that why the price drop. All other ones more expensive.Bert Kehren In a message dated 7/9/2019 11:05:39 AM Eastern Standard Time, lajeune...@mail.com writes: Bert, My take on the issue is that Mark Sims had not seen manufacturer documentation on how specifically to use the sawtooth correction value. You posted a picture of what we now know was an implementation of a use of the correction value. Did you have manufacturer documentation on how the value was to be used before you did your design? If so, that's what Mark is looking for. Like me, Dana was confused by your picture of a GPS assembly, which was not an answer to Mark. Knowing Dana personally I'm not surprised he started down the 20 question path, and I doubt he was actually offended by your post. respectfully, Robert LaJeunesse > Sent: Tuesday, July 09, 2019 at 6:26 AM > From: "ew via time-nuts" > To: time-nuts@lists.febo.com > Cc: ew > Subject: Re: [time-nuts] Advantages of GNSS ??? > > Dana > This was in response to Mark Sins " I don't think that I have ever seen what > to do with the sawtooth value > documented in any receiver documentation"I did this 4 years ago it, is a > sawtooth corrected ublox. First pass. Always do a follow on board but never > did any thing with it since there was no interest. We did it part of our > GPSDO work but saw no improvement. Sorry my work offends you.I did the same > with the Furuno GT and GN-87 without sawtooth since it is only 4 nsec. Ole > tested it and we use it with very good results. Again I followed it up with a > later design in case there is interest. I will not post the picture of the > original one so not to offend you.I will not do a board on the ublox 9 since > we are frequency not time nuts and see no need for it. > Bert Kehren > > > In a message dated 7/9/2019 12:05:14 AM Eastern Standard Time, > k8yumdoo...@gmail.com writes: > > One what? I see that it is a Ublox unit, but see no reference to the > interesting > modern units like the 9 series. Also, I note that the only reference on > the board > to "ant" is on the lower right corner, while what I suppose to be the > actual antenna > connector appears to be an SMA near the upper right corner. > > And why does it look like several of the components have been resoldered > or replaced or something? > > Dana > > > On Mon, Jul 8, 2019 at 8:00 PM ew via time-nuts > wrote: > > > Well now you can see one > > Bert Kehren > > > > > > In a message dated 7/8/2019 7:02:07 PM Eastern Standard Time, > > hol...@hotmail.com writes: > > > > A big issue with using the sawtooth correction message from a GPS > > receivers is the issue of just what that sawtooth value is related to and > > how to apply it to the measured PPS value / phase. > > I added the ability to Lady Heather to calculate a sawtooth corrected > > "paper clock" by applying the sawtooth correction message value to the PPS > > output measured by an external counter like the TAPR TICC. > > > > There are around a dozen different combinations of sawtooth value and PPS > > measurements... only one of which minimizes the PPS error. Do you add or > > subtract the sawtooth value to the PPS measurement? Do you apply the > > sawtooth value to the previous/current/next PPS measurement? Do you apply > > the sawtooth correction to the PPS itself or the accumulated phase of the > > PPS? > > I don't think that I have ever seen what to do with the sawtooth value > > documented in any receiver documentation... Heather has default receiver > > dependent correction strategies or lets you specify the correction > > strategy
Re: [time-nuts] Advantages of GNSS ???
It's not very good, it is highly non-linear and even worse - nonmonotonous. It sometimes produces runt pulse glitches when you roll time backwards. I have used them in GPS clocks for many years but never enabled them for end user mode. It's really a very primitive delay line series and I don't regret seeing it gone. On top of this it is Maxim, doh! Leo Chris Caudle wrote: > The original is not, there is a close variant still in production: > > https://www.maximintegrated.com/en/products/analog/clock-generation-distribution/DS1124.html > > "The DS1124 is an 8-bit programmable timing element similar in function to > the DS1021-25. The 256-delay intervals are programmed by using a 3-wire > serial interface. With a 0.25ns step size, the DS1124 can provide a delay > time from 20ns up to 84ns with an integral nonlinearity of ±3ns. " > > Small package, would be a little difficult to prototype by hand, but not > impossible. > > -- > Chris Caudle ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Leo - I do believe you mean non-monotonic, rather than non-monotonous. Not being monotonous is a good thing. :-) David N1HAC On 7/9/19 1:20 PM, Leo Bodnar wrote: > It's not very good, it is highly non-linear and even worse - nonmonotonous. > It sometimes produces runt pulse glitches when you roll time backwards. > I have used them in GPS clocks for many years but never enabled them for end > user mode. > It's really a very primitive delay line series and I don't regret seeing it > gone. On top of this it is Maxim, doh! > Leo > > Chris Caudle wrote: >> The original is not, there is a close variant still in production: >> >> https://nam05.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.maximintegrated.com%2Fen%2Fproducts%2Fanalog%2Fclock-generation-distribution%2FDS1124.html&data=02%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C6a86facc79d243f1cd2308d7049fba48%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C636982956387678192&sdata=TmHZH%2FJQpSatDlFqHcbQp%2BPHrS9CGjFHe5oPNYzHbRQ%3D&reserved=0 >> >> "The DS1124 is an 8-bit programmable timing element similar in function to >> the DS1021-25. The 256-delay intervals are programmed by using a 3-wire >> serial interface. With a 0.25ns step size, the DS1124 can provide a delay >> time from 20ns up to 84ns with an integral nonlinearity of ±3ns. " >> >> Small package, would be a little difficult to prototype by hand, but not >> impossible. >> >> -- >> Chris Caudle > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > https://nam05.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.febo.com%2Fmailman%2Flistinfo%2Ftime-nuts_lists.febo.com&data=02%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C6a86facc79d243f1cd2308d7049fba48%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C636982956387678192&sdata=NQVVBCHNCkD3Ze5J7z6OXfR70zcz0nx3wj1XseqA7Jo%3D&reserved=0 > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
and non monitonicity in the device is the death of a control loops. My attempts at building good OCXOs using cheap AT crystals in the 90s was thwarted by non monotonic bending crystals ! And everytime they would wake up, the monitonicity would be in a different part of the control curve and they exhibited hysteresis, like defined steps , this seems to be the case with most crystals, the harder you looked, the more undesirable imperfections you found... On 10/07/2019 5:57 AM, David G. McGaw wrote: Leo - I do believe you mean non-monotonic, rather than non-monotonous. Not being monotonous is a good thing. :-) David N1HAC On 7/9/19 1:20 PM, Leo Bodnar wrote: It's not very good, it is highly non-linear and even wor ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
HI Actually a monotonous ( = un-exciting) GPSDO is a *really* good thing :) Having one that does exciting stuff from time to time is *not* at all what you are after :) Now we get to find out what auto spell check did to all of that …... Bob > On Jul 9, 2019, at 3:57 PM, David G. McGaw > wrote: > > Leo - > > I do believe you mean non-monotonic, rather than non-monotonous. Not > being monotonous is a good thing. :-) > > David N1HAC > > On 7/9/19 1:20 PM, Leo Bodnar wrote: >> It's not very good, it is highly non-linear and even worse - nonmonotonous. >> It sometimes produces runt pulse glitches when you roll time backwards. >> I have used them in GPS clocks for many years but never enabled them for end >> user mode. >> It's really a very primitive delay line series and I don't regret seeing it >> gone. On top of this it is Maxim, doh! >> Leo >> >> Chris Caudle wrote: >>> The original is not, there is a close variant still in production: >>> >>> https://nam05.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.maximintegrated.com%2Fen%2Fproducts%2Fanalog%2Fclock-generation-distribution%2FDS1124.html&data=02%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C6a86facc79d243f1cd2308d7049fba48%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C636982956387678192&sdata=TmHZH%2FJQpSatDlFqHcbQp%2BPHrS9CGjFHe5oPNYzHbRQ%3D&reserved=0 >>> >>> "The DS1124 is an 8-bit programmable timing element similar in function to >>> the DS1021-25. The 256-delay intervals are programmed by using a 3-wire >>> serial interface. With a 0.25ns step size, the DS1124 can provide a delay >>> time from 20ns up to 84ns with an integral nonlinearity of ±3ns. " >>> >>> Small package, would be a little difficult to prototype by hand, but not >>> impossible. >>> >>> -- >>> Chris Caudle >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> https://nam05.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.febo.com%2Fmailman%2Flistinfo%2Ftime-nuts_lists.febo.com&data=02%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C6a86facc79d243f1cd2308d7049fba48%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C636982956387678192&sdata=NQVVBCHNCkD3Ze5J7z6OXfR70zcz0nx3wj1XseqA7Jo%3D&reserved=0 >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
That is the dirty little secret of crystals. Manufacturers will test the temperature response in one direction, but if you heat and then cool crystals and measure the frequency, they do exhibit significant hysteresis. I've not been able to get a supplier of TCXOs for me to characterize this as I don't buy enough. I just have to test them myself and toss the 10% or so that don't meet their specs due to the hysteresis. If you cycle the temperature up and down multiple times, the effect lessens, but after letting them sit for a while, it comes back. I also saw jumps at particular temperatures, but that may be due to the TCXO compensation. Mark On Tue, Jul 9, 2019 at 4:00 PM Glen English VK1XX < glenl...@pacificmedia.com.au> wrote: > and non monitonicity in the device is the death of a control loops. > > My attempts at building good OCXOs using cheap AT crystals in the 90s > was thwarted by non monotonic bending crystals ! > > And everytime they would wake up, the monitonicity would be in a > different part of the control curve > > and they exhibited hysteresis, like defined steps , this seems to be the > case with most crystals, the harder you looked, the more undesirable > imperfections you found... > > > > On 10/07/2019 5:57 AM, David G. McGaw wrote: > > Leo - > > > > I do believe you mean non-monotonic, rather than non-monotonous. Not > > being monotonous is a good thing. :-) > > > > David N1HAC > > > > On 7/9/19 1:20 PM, Leo Bodnar wrote: > >> It's not very good, it is highly non-linear and even wor > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi Well, if you ever get back into it: You play games with varicap diodes to straighten out the curve. You may bias them, you might put them in parallel, you might put a coil or a cap across them. You can get the curve plenty flat enough for a control loop. Hopping / discrete steps generally means you have to much drive on the crystal or some other circuit gotcha. The crystal its self and the tuning diode have no steps in them. They just aren’t complex enough devices to get into stepwise behavior. Drive power on an OCXO will pretty much always be below a milli-watt. A typical design will be in the range of 1/10 to 1/100 of that power level. Bob > On Jul 9, 2019, at 5:36 PM, Glen English VK1XX > wrote: > > and non monitonicity in the device is the death of a control loops. > > My attempts at building good OCXOs using cheap AT crystals in the 90s was > thwarted by non monotonic bending crystals ! > > And everytime they would wake up, the monitonicity would be in a different > part of the control curve > > and they exhibited hysteresis, like defined steps , this seems to be the case > with most crystals, the harder you looked, the more undesirable imperfections > you found... > > > > On 10/07/2019 5:57 AM, David G. McGaw wrote: >> Leo - >> >> I do believe you mean non-monotonic, rather than non-monotonous. Not >> being monotonous is a good thing. :-) >> >> David N1HAC >> >> On 7/9/19 1:20 PM, Leo Bodnar wrote: >>> It's not very good, it is highly non-linear and even wor > > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi TCXO’s are very different beasts than OCXO’s. In an OCXO, the crystal is not exposed to any significant temperature change. Bob > On Jul 9, 2019, at 8:05 PM, Mark Goldberg wrote: > > That is the dirty little secret of crystals. Manufacturers will test the > temperature response in one direction, but if you heat and then cool > crystals and measure the frequency, they do exhibit significant hysteresis. > I've not been able to get a supplier of TCXOs for me to characterize this > as I don't buy enough. I just have to test them myself and toss the 10% or > so that don't meet their specs due to the hysteresis. If you cycle the > temperature up and down multiple times, the effect lessens, but after > letting them sit for a while, it comes back. I also saw jumps at particular > temperatures, but that may be due to the TCXO compensation. > > Mark > > > On Tue, Jul 9, 2019 at 4:00 PM Glen English VK1XX < > glenl...@pacificmedia.com.au> wrote: > >> and non monitonicity in the device is the death of a control loops. >> >> My attempts at building good OCXOs using cheap AT crystals in the 90s >> was thwarted by non monotonic bending crystals ! >> >> And everytime they would wake up, the monitonicity would be in a >> different part of the control curve >> >> and they exhibited hysteresis, like defined steps , this seems to be the >> case with most crystals, the harder you looked, the more undesirable >> imperfections you found... >> >> >> >> On 10/07/2019 5:57 AM, David G. McGaw wrote: >>> Leo - >>> >>> I do believe you mean non-monotonic, rather than non-monotonous. Not >>> being monotonous is a good thing. :-) >>> >>> David N1HAC >>> >>> On 7/9/19 1:20 PM, Leo Bodnar wrote: It's not very good, it is highly non-linear and even wor >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
> From: Bob kb8tq > Drive power on an OCXO will pretty much always be below a milli-watt. A > typical design will be in > the range of 1/10 to 1/100 of that power level. It depends whether OCXO is designed for long term stability and low ageing or low phase noise. Low ageing requires low drive but low phase noise needs as much drive as humanely possible - often approaching mW levels. Leo ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
I did, sorry, - it was a finger slip. Now, what I find kind of funny is that one of the meanings of "monotonous" is "repetitious or periodic" which is almost exactly the opposite of monotonic. Leo > From: "David G. McGaw" > Leo - > I do believe you mean non-monotonic, rather than non-monotonous. Not > being monotonous is a good thing.? :-) > David N1HAC ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi It depends a lot on the offset you are looking at. For close in phase noise, you probably don’t want high drive. If you are only after phase noise past 10KHz, you may not want / need an OCXO in the first place. Selecting crystals (like one in a hundred) for very high drive / low phase noise setups *is* done. It’s just not very practical. Bob > On Jul 10, 2019, at 3:49 AM, Leo Bodnar wrote: > >> From: Bob kb8tq >> Drive power on an OCXO will pretty much always be below a milli-watt. A >> typical design will be in >> the range of 1/10 to 1/100 of that power level. > > It depends whether OCXO is designed for long term stability and low ageing or > low phase noise. > Low ageing requires low drive but low phase noise needs as much drive as > humanely possible - often approaching mW levels. > > Leo > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hello, Why would you not want high drive level for best close-in noise? This is at odds with general thinking in the industry. Close-in in this context means from 0.1Hz to 1/f knee which is 1-100kHz depending on the design of the sustaining amplifier. There are few reasons why low phase noise "practical" oscillators are built as OCXOs: On one hand: - close-in noise depends on 1/f knee frequency - lowering knee frequency requires high-Q resonators - for classic 1MHz..100MHz range this means crystals - high-Q crystals require SC-cut On the other hand: - phase noise density is measured as a ratio referred to carrier level - increasing carrier level improves phase noise figure - increasing carrier level necessitates increasing drive level - maintaining reasonable ageing rate at higher drive levels requires SC-cut crystals Having established that SC-cut is preferred: - SC-cut has high temperature turning point. Its room temperature tempco is much worse than AT-cut's one making it mostly unusable as XO or TCXO - High temperature turning point requires oven Leo >> From: Bob kb8tq > It depends a lot on the offset you are looking at. For close in phase noise, > you probably don’t > want high drive. If you are only after phase noise past 10KHz, you may not > want / need > an OCXO in the first place. Selecting crystals (like one in a hundred) for > very high drive / > low phase noise setups *is* done. It’s just not very practical. > > > On Jul 10, 2019, at 3:49 AM, Leo Bodnar wrote: > > It depends whether OCXO is designed for long term stability and low ageing > > or low phase noise. > > Low ageing requires low drive but low phase noise needs as much drive as > > humanely possible - often approaching mW levels. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi Well part of it comes from designing, testing, and manufacturing a few thousand OCXO designs over the years. We likely built 10’s of millions of OCXO’s over the time I was doing / managing that. > On Jul 11, 2019, at 3:56 AM, Leo Bodnar wrote: > > Hello, / > > Why would you not want high drive level for best close-in noise? This is at > odds with general thinking in the industry. > Close-in in this context means from 0.1Hz to 1/f knee which is 1-100kHz > depending on the design of the sustaining amplifier. > > There are few reasons why low phase noise "practical" oscillators are built > as OCXOs: > > On one hand: > - close-in noise depends on 1/f knee frequency That is a quick approximation. There always will be a bit more to it. > - lowering knee frequency requires high-Q resonators That does help, but it’s far from the whole story > - for classic 1MHz..100MHz range this means crystals There are other exotic things you could do. Cost wise they get a bit crazy. There are materials other than quartz that give you higher Q. In some cases *much* higher Q without a massive cost penalty. > - high-Q crystals require SC-cut Actually not so much. An SC has a lower Q than an AT of similar size and design up to the point acoustic Q losses completely take over. If you are talking about sub 20 MHz OCXO’s with “doable” crystal package sizes, the AT will have the higher Q by a significant margin. > > On the other hand: > - phase noise density is measured as a ratio referred to carrier level True, that’s how it’s defined > - increasing carrier level improves phase noise figure Which is often how you get good phase noise far removed, since your circuit does not have issues as you increase the drive level. (if properly designed) > - increasing carrier level necessitates increasing drive level To the degree that “carrier level” in this case is defined to be exactly the same as drive level. > - maintaining reasonable ageing rate at higher drive levels requires SC-cut > crystals Not so much. Indeed there are a number of cuts that do well. The SC’s claim to fame is immunity to acceleration / stress effects in a single plane. (SC = Stress Compensated ). A side effect of the design is a shallow turn point at higher temperatures. There are other cuts that share this characteristic. Things like the FC do get used in OCXO’s. > > Having established that SC-cut is preferred: > - SC-cut has high temperature turning point. Its room temperature tempco is > much worse than AT-cut's one making it mostly unusable as XO or TCXO Depends on the XO, They get built into down hole gear as an XO. There are other “un heated” SC based applications. > - High temperature turning point requires oven Depending on the application and temperature spec. There *are* indeed low phase noise / SC based room temperature oscillators sold for some “interesting” applications. There’s a list member who has posted about their experience doing so. The bigger problem is that your approximation that drive always improves phase noise falls apart as you get closer to carrier. There are a lot of things that drive this. If they didn’t, the design task would simply be to have a low noise follower amp. There have been designs published in a lot of places for amps that are 50 db better than the noise of any OCXO at 1 Hz offset. Bob > > Leo > >>> From: Bob kb8tq >> It depends a lot on the offset you are looking at. For close in phase noise, >> you probably don’t >> want high drive. If you are only after phase noise past 10KHz, you may not >> want / need >> an OCXO in the first place. Selecting crystals (like one in a hundred) for >> very high drive / >> low phase noise setups *is* done. It’s just not very practical. >> >>> On Jul 10, 2019, at 3:49 AM, Leo Bodnar wrote: >>> It depends whether OCXO is designed for long term stability and low ageing >>> or low phase noise. >>> Low ageing requires low drive but low phase noise needs as much drive as >>> humanely possible - often approaching mW levels. > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
> Well part of it comes from designing, testing, and manufacturing a few > thousand OCXO designs over the years. We likely built 10’s of millions of > OCXO’s over the time I was doing / managing that. It might be just my personal opinion but credential swinging is better left out of technical discussion. > > - high-Q crystals require SC-cut > ... An SC has a lower Q than an AT of similar size > and design up to the point acoustic Q losses completely take over. > If you are talking about sub 20 MHz OCXO’s with “doable” crystal > package sizes, the AT will have the higher Q by a significant margin. Could you please back up this claim with verifiable facts? Leo ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Advantages of GNSS ???
Hi > On Jul 11, 2019, at 9:37 AM, Leo Bodnar wrote: > >> Well part of it comes from designing, testing, and manufacturing a few >> thousand OCXO designs over the years. We likely built 10’s of millions of >> OCXO’s over the time I was doing / managing that. > It might be just my personal opinion but credential swinging is better left > out of technical discussion. >>> - high-Q crystals require SC-cut >> ... An SC has a lower Q than an AT of similar size >> and design up to the point acoustic Q losses completely take over. >> If you are talking about sub 20 MHz OCXO’s with “doable” crystal >> package sizes, the AT will have the higher Q by a significant margin. > > Could you please back up this claim with verifiable facts? Order up a few 5 MHz 3rd overtones in HC-40 packages and see what you get. You also could send in an RFQ for a batch of each to any of the people who make them and see what comes back. Bob > > Leo > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
