Re: [time-nuts] Ublox neo-7M GPS
Thanks all for the replies to my initial query as to whether anyone had any firsthand experience with this device. The replies have been helpful. It is also clear that what some see as an apple, others see as an orange. A simple common truth perhaps which becomes very obvious when comparing the discussions of two groups each with a different focus where the subject is the same, in this case the Ublox Neo-7M. The other group which started my question has it's focus in the frequency domain and as to whether or not this device was suitable or not for use as a variable frequency signal source. That group has made some measurements and came to similar conclusions as some of those offered here. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Sorry but I disagree. Having done extensive work with the M7 and M6 in connection with the with GPSDO work we are doing we have characterized the units extensively. First from what we can see the difference between a SSR-6T and a $ 16 M6 is that one has a TCXO and outputs sawtooth correction data but uncorrected both are the same. Last year we did extensive work on Brooks GPSDO and it works well with uncorrected M12's and ublox $ 16 M6's. With a Morion we got 1 E-12. With a geometry shrink in the M7 silicon higher frequency is possible and also lower power. Ublox most likely wants lower power and higher performance but not necessarily lower sawtooth because those OEM's that need it will get a version with sawtooth data. Basic engine is still the same. Time nuts are not a big enough market. Sawtooth is smaller compared to the M6 doe to the higher clock frequency and it is safe to assume that when they come out with a M8 it will even be less. On the universal controller we have a GPS filter not correction on the input that does improve performance. I took a page out of Ulrich's work when I saw a picture of his GPSDO where he thermally isolated his M12. With the FE 5680 work I made the M12 part of the Rb by mounting it with metal stand offs to the backplate of the Rb.It in turn is temperature controlled. In the case of my FE 405B work I actually placed the M6 inside the OCXO took the battery off. I think I have a picture if interested. Not knowing that it can not be done I did what I call a GPS-PLL using a M7. Attached is the board layout on the right side is what we are presently using with the Morion, on the left is a version for 5 V OCXO's so Hams can use 12 Volt. The one on the right is driven by readily available parts for any Ham and no adjustments. Total cost not counting GPS and OCXO below $ 10. We are still fine tuning the filter but right out of the box we got 1 E-10. This is for Ham's not time nut standard. Data exceeds attachment limitations but any one can contact me off list and I will send it. We destroyed the M7 have not figured out how but a new one is on order and once testing is completed schematics will also be available. I have the bad habit layouts first documentation maybe second. Frustrating for the team, but I am getting better. As I said before mainly for Ham's and one of our Australian team member will roll it out to the Ham community. But any body is free to use it I just think time nuts can do better. Bert Kehren In a message dated 8/21/2014 1:30:50 A.M. Eastern Daylight Time, ed_pal...@sasktel.net writes: Thanks, Tony. That's good info. So now we've confirmed that the neo-7M has an NCO and it appears that it's resolution is 20 ns. The data sheet shows the 'Accuracy of time pulse signal' is 30 ns RMS and 60 ns for 99%, but it isn't clear whether they're referring to jitter or error with respect to GPS seconds. The original question was whether the neo-7M would make a good GPSDO. As we've seen, the answer is no. Cheap, yes. Good, no. Setting aside the NCO issue, the neo-7M isn't a timing receiver, it's a navigation receiver. That limits it's performance in many ways. Ublox sells timing receivers, but they're still NCO-based. They're also significantly more expensive than the navigation receivers. One example is Synergy Systems' SSR-6Tr if it's still available. It was announced, and discussed on this list, in 2012 but it still isn't listed on their web site so I don't know what it's status is. It's based on the LEA-6T timing receiver which has a spec for the 1 PPS is 'within 15 ns to GPS/UTC (1 sigma)'. That can be further reduced with some extra work. If the performance of an NCO-based unit isn't enough, you might want to consider Jackson Labs GPSTCXO which is a real GPSDO. More expensive than the NCO-based units, but you get what you pay for. No, I'm not associated with Synergy or Jackson labs. So Graham, if you survived the firestorm started by your simple question, are you any wiser? Ed On 8/20/2014 7:56 PM, Tony wrote: On 19/08/2014 16:11, Ed Palmer wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. FWIW, I just had a look at the timepulse on a NEO-7M. I configured it to 10MHz, 50:50 duty cycle when locked, disabled when out of lock. I don't have any of those Analyzers so I used an HP 54615B digital scope. The period of the majority of cycles was 104ns with 'random' cycles being 84ns. I did not observe any other cycle periods. I don't know how accurate the time measurements are on the scope, but it looks like the timing is derived from an approx
Re: [time-nuts] Ublox neo-7M GPS
Said, On 20/08/2014 15:42, saidj...@aol.com wrote: Hi Tony, that's consistent with what I remember. Do you have the capability to count the number of 10MHz pulses per second to see if it is phase-coherent with the UTC 1PPS pulse? I don't have any means to do that at the moment - when I get time I'll try programming my STM32F4 discovery board (168MHz ARM Cortex M4) to take some measurements. However as I haven't used the timers on that yet it'll take a bit of time to get it right! I am thinking that the software may be using statistics to approximate 10 million cycles per second, which would mean they may or may not be exactly 10 million cycles.. thanks, Said As I said, I measured the pulses at either 104ns (9.6MHz), with some being shorter at 84ns. I've just repeated the measurements on a Reyax RYN25AI (UBLOX MAX-7C) with the same results. Actually the scope measures the longer pulses at either 104.3ns or 105.2ns and the shorter pulses at 82.89ns or 83.82ns. Since it is a 1GS/s scope, the differences are almost certainly just the scope sampling uncertainties rather than actual jitter in the clock. Note that these measurements were with the clock free running as I can't get a GPS lock indoors. This time I had a closer look at the clocks using a slower sweep to show approx 19 cycles. It was then clear that there was always one short pulse followed by 4 long pulses. This makes sense - the xtal oscillator must be 48MHz (or more likely 24MHz multiplied up) so that the short pulses are 4 clocks (83.3ns) and the long pulses are 5 clocks (104.17ns), so 4 long plus 1 short = 24 of the 48MHz clocks. So 5 clocks out = 500ns, averaging 10MHz. How it distributes the short clock pulses (or if it makes phase changes larger than 21ns) when it has to lock to the GPS clock remains to be seen but is harder to measure and will require some sort of analyzer/timing capture tool. Perhaps if I get the time to program that ARM chip... Tony In a message dated 8/20/2014 11:07:59 Pacific Daylight Time, tn...@toneh.demon.co.uk writes: On 19/08/2014 16:11, Ed Palmer wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. FWIW, I just had a look at the timepulse on a NEO-7M. I configured it to 10MHz, 50:50 duty cycle when locked, disabled when out of lock. I don't have any of those Analyzers so I used an HP 54615B digital scope. The period of the majority of cycles was 104ns with 'random' cycles being 84ns. I did not observe any other cycle periods. I don't know how accurate the time measurements are on the scope, but it looks like the timing is derived from an approx 48MHz clock, and the timing phase/frequency adjusted by periodically deleting 48MHz clock cycles. Although I said random, I couldn't make any observations as to the statistics of the short and long cycles or their distribution - I guess I'll have to write some software for my STM32F4 discovery board for that. If I get time, I'll do the same with a Reyax RYN25AI receiver which has a UBLOX MAX-7C module. Tony ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
From: Tony As I said, I measured the pulses at either 104ns (9.6MHz), with some being shorter at 84ns. I've just repeated the measurements on a Reyax RYN25AI (UBLOX MAX-7C) with the same results. Actually the scope measures the longer pulses at either 104.3ns or 105.2ns and the shorter pulses at 82.89ns or 83.82ns. Since it is a 1GS/s scope, the differences are almost certainly just the scope sampling uncertainties rather than actual jitter in the clock. [] === Tony, any chance you could do a quick measurement at 8 MHz - I think that should be a more constant period. That's if I understood the data sheet correctly, and what applied to earlier models applies also to the ublox 7! Thanks, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
FYI. It is still available. Don't have it in hand yet, but one was ordered just a few days ago... Dan On 8/21/2014 6:34 AM, time-nuts-requ...@febo.com wrote: One example is Synergy Systems' SSR-6Tr if it's still available. It was announced, and discussed on this list, in 2012 but it still isn't listed on their web site so I don't know what it's status is. It's based on the LEA-6T timing receiver which has a spec for the 1 PPS is 'within 15 ns to GPS/UTC (1 sigma)'. That can be further reduced with some extra work. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hi Bert, I don't think we have any fundamental disagreement here. Maybe just a difference in emphasis. On 8/21/2014 4:34 AM, ewkeh...@aol.com wrote: Sorry but I disagree. Having done extensive work with the M7 and M6 in connection with the with GPSDO work we are doing we have characterized the units extensively. First from what we can see the difference between a SSR-6T and a $ 16 M6 is that one has a TCXO and outputs sawtooth correction data but uncorrected both are the same. I agree that uncorrected results will be basically the same. Note the specs I stated for the navigation receiver (30ns rms, 60ns max) vs. the timing receiver (15ns rms, 60ns max). Not a huge difference. But, timing receivers do have features that can improve performance over navigation receivers. Some that come to mind are position hold mode, TRAIM, maintaining performance with only one satellite locked, sawtooth correction, and precision survey. I haven't dug through the Ublox data sheets to see which ones they support. Some are only useful during degraded conditions so it might be difficult to test their effectiveness. Some are automatic while some, like sawtooth correction, require extra work to take advantage of. You mentioned the TCXO in the timing receiver. Ublox says that it helps with acquisition and maintenance of satellite lock, but I don't think it has any significant effect on the quality of the 1 PPS or the variable frequency which will still be limited by the timing resolution (i.e. period) of the TCXO. Is that right? Last year we did extensive work on Brooks GPSDO and it works well with uncorrected M12's and ublox $ 16 M6's. With a Morion we got 1 E-12. With a geometry shrink in the M7 silicon higher frequency is possible and also lower power. Ublox most likely wants lower power and higher performance but not necessarily lower sawtooth because those OEM's that need it will get a version with sawtooth data. Basic engine is still the same. Time nuts are not a big enough market. Sawtooth is smaller compared to the M6 doe to the higher clock frequency and it is safe to assume that when they come out with a M8 it will even be less. I won't be surprised to find that sawtooth correction becomes irrelevent due to higher clock speeds which results in small sawtooth size. The Navsync CW-12 has been around for some years now. It runs at 'up to 120 MHz', whatever that means. I've measured its' 1 PPS jitter as 4 or 5 ns (1 sigma) and about 20 to 25 ns max. It doesn't support sawtooth correction, but it hardly needs to. I tied it to an HP Z3817A GPSDO. That's not a typo. It's a strange beast that requires an external 1 PPS input. It includes an E1938 oscillator. The result was a 1 PPS jitter of 100 ps (1 sigma) and 1 ns max. That's better than my Z3801A or Tbolt. It might be capable of even better performance. There's a possibility that the E1938 oscillator is noisier than it should be. I should repeat that test with other GPS receivers to see if the output degrades due to the higher jitter on the older receivers. Another project to add to the list! Higher clock speeds will also allow more processing. I don't know if that will allow improved performance or if the receivers have already done everything that they can. On the universal controller we have a GPS filter not correction on the input that does improve performance. I took a page out of Ulrich's work when I saw a picture of his GPSDO where he thermally isolated his M12. With the FE 5680 work I made the M12 part of the Rb by mounting it with metal stand offs to the backplate of the Rb.It in turn is temperature controlled. In the case of my FE 405B work I actually placed the M6 inside the OCXO took the battery off. I think I have a picture if interested. Yes, if you look in the manual for Jackson Lab's GPSTCXO it says that shielding the board from drafts improves performance. You've taken that to the next level. Not knowing that it can not be done I did what I call a GPS-PLL using a M7. Attached is the board layout on the right side is what we are presently using with the Morion, on the left is a version for 5 V OCXO's so Hams can use 12 Volt. The one on the right is driven by readily available parts for any Ham and no adjustments. Total cost not counting GPS and OCXO below $ 10. We are still fine tuning the filter but right out of the box we got 1 E-10. This is for Ham's not time nut standard. Data exceeds attachment limitations but any one can contact me off list and I will send it. We destroyed the M7 have not figured out how but a new one is on order and once testing is completed schematics will also be available. Every project requires a sacrifice to ensure success. In my case, it's usually a blood sacrifice caused by stabbing or goring myself with some tool. :( Ed I have the bad habit layouts first documentation maybe second. Frustrating for the team, but
Re: [time-nuts] Ublox neo-7M GPS
David, No problem, its still set-up. As you'd expect its rock solid at 8MHz with no visible jitter. Can you point me to the datasheet you're referring to? The MAX-7 and NEO-7 datasheets don't provide any information on clocking. In the 'u-blox 7 Receiver Description Including Protocol Specification V14' the only clue as to the clocking characteristics is that the timepulse output must be configured with a minimum high or low time of 50ns or pulses may be lost. Make of that what you will! Tony On 21/08/2014 04:25, David J Taylor wrote: Tony, any chance you could do a quick measurement at 8 MHz - I think that should be a more constant period. That's if I understood the data sheet correctly, and what applied to earlier models applies also to the ublox 7! Thanks, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
On 21/08/2014 08:13, Ed Palmer wrote: But, timing receivers do have features that can improve performance over navigation receivers. Some that come to mind are position hold mode, TRAIM, maintaining performance with only one satellite locked, sawtooth correction, and precision survey. I haven't dug through the Ublox data sheets to see which ones they support. I just tried sending various TMODE and TMODE2 configuration messages to the NEO-7M. These allow you to select 'Disabled' 'Survey In' and 'Fixed Mode' where you can specify the receiver's lattitude and longitude. Not surprisingly, it replied with negative acknowledgements each time so they presumably aren't supported in this receiver. I was using the ublox u-center tool which should ensure the messages were formatted correctly. It's very unlikely, but its conceivable that it does actually support these modes but some other required configuration hadn't been done, causing a conflict. I've not yet found any detailed documentation specifying exactly which messages/features these modules do support. Tony H ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
On Thu, Aug 21, 2014 at 9:45 PM, Tony tn...@toneh.demon.co.uk wrote: I just tried sending various TMODE and TMODE2 configuration messages to the NEO-7M. These allow you to select 'Disabled' 'Survey In' and 'Fixed Mode' where you can specify the receiver's lattitude and longitude. Not surprisingly, it replied with negative acknowledgements each time so they presumably aren't supported in this receiver. Right, those are typically T version only commands. It should be in the documents as a note. The earlier list of timing attributes left out a critical one, being able to set your position to the accuracy of the receiver. While it's probably my poor anttenna siting the various self-surveys (Tbolt, Res-T, LEA-6T) I've done are all pretty poor. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Have not tried myself, but there are instructions around describing how to load T-firmware into non T ublox models. There also seem to be possible to patch the program ram to enable looked features on models without flash reprogramming capability. /Björn div Originalmeddelande /divdivFrån: Tony tn...@toneh.demon.co.uk /divdivDatum:2014-08-22 03:45 (GMT+01:00) /divdivTill: Discussion of precise time and frequency measurement time-nuts@febo.com /divdivRubrik: Re: [time-nuts] Ublox neo-7M GPS /divdiv /divOn 21/08/2014 08:13, Ed Palmer wrote: But, timing receivers do have features that can improve performance over navigation receivers. Some that come to mind are position hold mode, TRAIM, maintaining performance with only one satellite locked, sawtooth correction, and precision survey. I haven't dug through the Ublox data sheets to see which ones they support. I just tried sending various TMODE and TMODE2 configuration messages to the NEO-7M. These allow you to select 'Disabled' 'Survey In' and 'Fixed Mode' where you can specify the receiver's lattitude and longitude. Not surprisingly, it replied with negative acknowledgements each time so they presumably aren't supported in this receiver. I was using the ublox u-center tool which should ensure the messages were formatted correctly. It's very unlikely, but its conceivable that it does actually support these modes but some other required configuration hadn't been done, causing a conflict. I've not yet found any detailed documentation specifying exactly which messages/features these modules do support. Tony H ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Paul, How far from the equator are you? The farther you are, the more trouble GPS has measuring your latitude due to worsening geometry. By the way, does anyone know what the timing effects of that will be? Is it documented anywhere? I noticed that the GLONASS satellites have a higher orbital inclination than GPS. Would a GLONASS Disciplined Oscillator perform better at higher latitudes than a GPSDO? Ed On 8/21/2014 12:52 PM, Paul wrote: On Thu, Aug 21, 2014 at 9:45 PM, Tony tn...@toneh.demon.co.uk wrote: I just tried sending various TMODE and TMODE2 configuration messages to the NEO-7M. These allow you to select 'Disabled' 'Survey In' and 'Fixed Mode' where you can specify the receiver's lattitude and longitude. Not surprisingly, it replied with negative acknowledgements each time so they presumably aren't supported in this receiver. Right, those are typically T version only commands. It should be in the documents as a note. The earlier list of timing attributes left out a critical one, being able to set your position to the accuracy of the receiver. While it's probably my poor anttenna siting the various self-surveys (Tbolt, Res-T, LEA-6T) I've done are all pretty poor. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
On 21 Aug, 2014, at 16:27 , Tony tn...@toneh.demon.co.uk wrote: David, No problem, its still set-up. As you'd expect its rock solid at 8MHz with no visible jitter. Can you point me to the datasheet you're referring to? The MAX-7 and NEO-7 datasheets don't provide any information on clocking. In the 'u-blox 7 Receiver Description Including Protocol Specification V14' the only clue as to the clocking characteristics is that the timepulse output must be configured with a minimum high or low time of 50ns or pulses may be lost. Make of that what you will! Tony It sounds like this part is similar to the LEA-6T (including the 48 MHz reference oscillator). This white paper has some information about the frequency output of the latter: http://www.u-blox.com/images/downloads/Product_Docs/Timing_AppNote_%28GPS.G6-X-11007%29.pdf See, e.g., figures 11 and 12. I think the cleanliness of the 8 MHz phase is a little bit misleading, however, since the clean part isn't actually 8 MHz. It is instead the frequency of the free running 48 MHz reference divided by 6, and it will still be throwing in the occasional short or long cycle to correct the 48 MHz oscillator frequency error and make the long term average come out at a true 8 Mhz. In some sense this is the high frequency equivalent of the 1 PPS hanging bridge case. The output at any frequency has a phase error of +/- 10.5 ns but at 8 MHz the phase error of the output changes very slowly, and can hang near one of the extremes for long periods, so it requires very long integration times to reduce that to zero. If you were using this output to drive a cleanup PLL (which I would call the DO in a GPSDO) I think you would actually be better off using the output at 10 MHz since with that integrating over just a few microseconds of the jitter reduces the short term average phase error by a factor of 5, to +/- 2.1 ns, and an odder divider might be better still. Dennis Ferguson ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
tn...@toneh.demon.co.uk said: Tony, any chance you could do a quick measurement at 8 MHz - I think that should be a more constant period. ... No problem, its still set-up. As you'd expect its rock solid at 8MHz with no visible jitter. I don't think you have fixed the problem, just made it harder to see. Do you have a digital scope? If so, set it up with the infinite persistence mode, scroll the time delay out a long time, and wait a while. I'll bet you get one that is shifted by a cycle before long. If you wait long enough, you will see the short/long half-cycle on the scope. If I understand what's going on, it's a classic DDS. The basic idea is that you have a wide adder. Think of the binary point as being on the left. Each clock cycle you add a magic number. For a sine output, you take the top N bits of the adder, run them through a lookup table (ROM) and into a D/A converter. For a square wave output, just use the top bit. If you are adding 0.001 (binary) the top bit will toggle every 4 cycles. That's dividing by 8. If you add 0.0011, then occasionally you will only get 3 cycles between transitions. If you add 0.00011, then occasionally you will get 5 cycles. If you add 0.001001, then occasional changed to frequently and you can easily see it on a scope. There are a handful of interesting properties: Except for a few magic target frequencies, the output will have occasional (or frequent) missing or extra cycles. The output will be clean if you are dividing by a power of 2. (By switching from 10 MHz to 8 MHz, you have changed from frequent to occasional.) You can only get some output frequencies. For example, you can't divide by exactly 10. In binary, that turns into a repeating fraction.[1] With a wide enough adder, you can get very very close. If you pick a frequency that you can get, the long term ADEV output will be as good as your system clock. If your target is some other frequency, it will drift, but the long term drift will be as solid as your clock. In the time domain, those extra/missing cycles turn into spurs. If you take the magic number and throw away all the 0s on the left and right, the width of the remaining number tells you how close in the spurs will be. 1] With a FPGA, you could build a decimal adder rather than a binary one. That would allow a clean divide by powers of 10. If you are only interested in the clean cases, you could build a divide by N. It's just a down ounter that reloads to N on overflow. If N is odd, the output will not be 50-50 duty cycle. -- These are my opinions. I hate spam. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hal, Except for a few magic target frequencies, the output will have occasional (or frequent) missing or extra cycles. The output will be clean if you are dividing by a power of 2. (By switching from 10 MHz to 8 MHz, you have changed from frequent to occasional.) Not true that dividing by two cleans it up. If you change the cycle time from time to time as you would have to do even at 8MHz since the TCXO is free-running to GPS and then divide this by two you still get the non-standard cycle times, but these will now simply be twice as long on average. The divider will not magically remove the huge cycle to cycle jitter whenever the unit does a phase adjustment. Only a PLL with a very long time constant compared to the cycle time (e.g. 100ms versus 100ns) can clean up the phase jitter. Also, the number of adjustment cycles at 8MHz now depends on the frequency error of the TCXO versus UTC. Taking a heat gun and cold spray to the unit would show that easily. However at 8MHz with a 48MHz crystal you only need to add/shorten the cycle time to compensate for the error of the crystal versus UTC. This is similar to the sawtooth error we are all familiar with. At 10MHz you have to add cycle adjustments to both compensate for the frequency error of the TCXO as well as the N/M divider to generate 10MHz out of 48MHz. Wether you have 10,000's of phase adjustments per second or just a few doesn't change the fact that you are changing the cycle to cycle time by massive degrees/percentages/nanoseconds. The question is: does the hardware/software that calculates when to increase/shorten the cycle work with error-diffusion that keeps track of the overall phase error accrued, or does it simply try to get close enough by statistical averaging. In the former case, the 10MHz phase over long periods of measurement would stay in phase with the UTC 1PPS phase. In the later case the 10MHz phase would drift over time versus UTC which is really bad of course. Which way does the uBlox hardware compute the error? I don't know, and the documentation I have seen does not add any insight. bye, Said ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Quoting Tony tn...@toneh.demon.co.uk: I don't have any means to do that at the moment - when I get time I'll try programming my STM32F4 discovery board (168MHz ARM Cortex M4) to take some measurements. However as I haven't used the timers on that yet it'll take a bit of time to get it right! Be careful interpreting those results. I have a stm32f4 discovery and its timer occasionally wanders very far. The measurements I have are using the internal PLL as the timer's source, which is driven by the external crystal. I assume it wouldn't be an issue if you used an external clock source for the timer, but I haven't tested that. I captured timer measurments of PPS signals from a Navspark GPS over 20 hours with a timer capture channel on TIM2. TIM2 was setup with a 10.5Mhz rate (84Mhz / 8). Mostly the intervals between PPS were within 1ppm (10hz). Looking at a random 4 second interval where they were not within 1ppm: 10500782HZ (normal) 10499731HZ (-100ppm) 10501831HZ (+99ppm) 10500781HZ (normal) This happened 7 times within 20 hours, with the same pattern. This also happens when I switch out the Navspark GPS for a different navigation-grade GPS. In case you're interested in the stm32 code, it's based on the STM libraries: https://github.com/ddrown/usb-gps/blob/master/src/pps.c https://github.com/ddrown/usb-gps/blob/master/src/mytimer.c ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
On Thu, Aug 21, 2014 at 4:03 PM, Ed Palmer ed_pal...@sasktel.net wrote: How far from the equator are you? I believe 43.235262699 N (my median position) is about 4,809,051 meters from the equator. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Ed We may be talking past each other I had problems with the statement that the basic M6 and M7 are not suitable for GPSDO's. They are not GPSDO's in them self but great GPS engines even without saw tooth correction which is an impossibility since the data is not available. But as you observed as frequency goes up saw tooth comes down. But with frequency power goes up reduced by smaller chip geometry. For the majority of applications power is # 1 concern. We are a minority. Pure material cost of our universal controller is below $ 15 but once you add paying some one for kitting, shipping and handling it is a challenge to keep it below $ 50. Having in the past spend excessively for toys I get more pleasure by looking for very low cost solutions at top performance. That is what we do as a team. Bert Kehren In a message dated 8/21/2014 11:34:53 A.M. Eastern Daylight Time, ed_pal...@sasktel.net writes: Hi Bert, I don't think we have any fundamental disagreement here. Maybe just a difference in emphasis. On 8/21/2014 4:34 AM, ewkeh...@aol.com wrote: Sorry but I disagree. Having done extensive work with the M7 and M6 in connection with the with GPSDO work we are doing we have characterized the units extensively. First from what we can see the difference between a SSR-6T and a $ 16 M6 is that one has a TCXO and outputs sawtooth correction data but uncorrected both are the same. I agree that uncorrected results will be basically the same. Note the specs I stated for the navigation receiver (30ns rms, 60ns max) vs. the timing receiver (15ns rms, 60ns max). Not a huge difference. But, timing receivers do have features that can improve performance over navigation receivers. Some that come to mind are position hold mode, TRAIM, maintaining performance with only one satellite locked, sawtooth correction, and precision survey. I haven't dug through the Ublox data sheets to see which ones they support. Some are only useful during degraded conditions so it might be difficult to test their effectiveness. Some are automatic while some, like sawtooth correction, require extra work to take advantage of. You mentioned the TCXO in the timing receiver. Ublox says that it helps with acquisition and maintenance of satellite lock, but I don't think it has any significant effect on the quality of the 1 PPS or the variable frequency which will still be limited by the timing resolution (i.e. period) of the TCXO. Is that right? Last year we did extensive work on Brooks GPSDO and it works well with uncorrected M12's and ublox $ 16 M6's. With a Morion we got 1 E-12. With a geometry shrink in the M7 silicon higher frequency is possible and also lower power. Ublox most likely wants lower power and higher performance but not necessarily lower sawtooth because those OEM's that need it will get a version with sawtooth data. Basic engine is still the same. Time nuts are not a big enough market. Sawtooth is smaller compared to the M6 doe to the higher clock frequency and it is safe to assume that when they come out with a M8 it will even be less. I won't be surprised to find that sawtooth correction becomes irrelevent due to higher clock speeds which results in small sawtooth size. The Navsync CW-12 has been around for some years now. It runs at 'up to 120 MHz', whatever that means. I've measured its' 1 PPS jitter as 4 or 5 ns (1 sigma) and about 20 to 25 ns max. It doesn't support sawtooth correction, but it hardly needs to. I tied it to an HP Z3817A GPSDO. That's not a typo. It's a strange beast that requires an external 1 PPS input. It includes an E1938 oscillator. The result was a 1 PPS jitter of 100 ps (1 sigma) and 1 ns max. That's better than my Z3801A or Tbolt. It might be capable of even better performance. There's a possibility that the E1938 oscillator is noisier than it should be. I should repeat that test with other GPS receivers to see if the output degrades due to the higher jitter on the older receivers. Another project to add to the list! Higher clock speeds will also allow more processing. I don't know if that will allow improved performance or if the receivers have already done everything that they can. On the universal controller we have a GPS filter not correction on the input that does improve performance. I took a page out of Ulrich's work when I saw a picture of his GPSDO where he thermally isolated his M12. With the FE 5680 work I made the M12 part of the Rb by mounting it with metal stand offs to the backplate of the Rb.It in turn is temperature controlled. In the case of my FE 405B work I actually placed the M6 inside the OCXO took the battery off. I think I have a picture if interested. Yes, if you look in the manual for Jackson Lab's GPSTCXO it says that shielding the board from drafts improves performance. You've taken that
Re: [time-nuts] Ublox neo-7M GPS
Hi I would bet that they drop / add a cycle whenever the output gets ahead or behind GPS by the appropriate (TCXO period) amount. The output stays “in phase” with GPS (sort of). The output spectrum looks messy …. Why would I guess this - it’s the cheap / low computation way to do it. Playing around with pulse positions to “improve” the spectrum adds code. It also only really helps if you know there is a filter downstream. Bob On Aug 21, 2014, at 4:54 PM, saidj...@aol.com wrote: Hal, Except for a few magic target frequencies, the output will have occasional (or frequent) missing or extra cycles. The output will be clean if you are dividing by a power of 2. (By switching from 10 MHz to 8 MHz, you have changed from frequent to occasional.) Not true that dividing by two cleans it up. If you change the cycle time from time to time as you would have to do even at 8MHz since the TCXO is free-running to GPS and then divide this by two you still get the non-standard cycle times, but these will now simply be twice as long on average. The divider will not magically remove the huge cycle to cycle jitter whenever the unit does a phase adjustment. Only a PLL with a very long time constant compared to the cycle time (e.g. 100ms versus 100ns) can clean up the phase jitter. Also, the number of adjustment cycles at 8MHz now depends on the frequency error of the TCXO versus UTC. Taking a heat gun and cold spray to the unit would show that easily. However at 8MHz with a 48MHz crystal you only need to add/shorten the cycle time to compensate for the error of the crystal versus UTC. This is similar to the sawtooth error we are all familiar with. At 10MHz you have to add cycle adjustments to both compensate for the frequency error of the TCXO as well as the N/M divider to generate 10MHz out of 48MHz. Wether you have 10,000's of phase adjustments per second or just a few doesn't change the fact that you are changing the cycle to cycle time by massive degrees/percentages/nanoseconds. The question is: does the hardware/software that calculates when to increase/shorten the cycle work with error-diffusion that keeps track of the overall phase error accrued, or does it simply try to get close enough by statistical averaging. In the former case, the 10MHz phase over long periods of measurement would stay in phase with the UTC 1PPS phase. In the later case the 10MHz phase would drift over time versus UTC which is really bad of course. Which way does the uBlox hardware compute the error? I don't know, and the documentation I have seen does not add any insight. bye, Said ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
I'm at about 50 N. I used a Navsync CW-12 connected to a VIC-100 antenna to do a long site survey and got the following results: Latitude: 1.32 meters Std Dev., -1 to +4 meters total range Longitude: 1.18 meters Std Dev., -3 to +1 meters total range Height:3.90 meters Std Dev., +6.6 to -17 meters total range Since you're closer to the equator your results should be somewhat better than mine. You could use these numbers to help decide if you've got a problem or not. Ed On 8/21/2014 3:57 PM, Paul wrote: On Thu, Aug 21, 2014 at 4:03 PM, Ed Palmer ed_pal...@sasktel.net wrote: How far from the equator are you? I believe 43.235262699 N (my median position) is about 4,809,051 meters from the equator. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
On Thu, Aug 21, 2014 at 11:09 PM, Ed Palmer ed_pal...@sasktel.net wrote: Since you're closer to the equator your results should be somewhat better than mine. You could use these numbers to help decide if you've got a problem or not. I was unclear. My point was (since I'm really an absolute time person) is that the site survey option in various timing receivers seems fairly coarse so the ability to set a location seems like the more useful option. The position I gave you is purported to be inside a 10x10 cm box at my antenna center (of course it's not). I use raw data from a 6T and 7P for location fixes. I'm also sure it's a pointless exercise -- I'm just idly curious. -- Paul ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
David, No problem, its still set-up. As you'd expect its rock solid at 8MHz with no visible jitter. Can you point me to the datasheet you're referring to? The MAX-7 and NEO-7 datasheets don't provide any information on clocking. In the 'u-blox 7 Receiver Description Including Protocol Specification V14' the only clue as to the clocking characteristics is that the timepulse output must be configured with a minimum high or low time of 50ns or pulses may be lost. Make of that what you will! Tony === Tony, it's the note Dennis Ferguson mentioned. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Be patient as soon as we have finished rollout of the FE 5680A and FE 405 B GPSDO I will be off the list. Bert Kehren In a message dated 8/19/2014 9:31:50 P.M. Eastern Daylight Time, csteinm...@yandex.com writes: Bert wrote: I guess time nuts like to talk about it but not fix it. Will you PLEASE quit beating this tired old drum? All of us know this is your opinion, although many of us have other explanations for the phenomena you think it explains. We do not need you to repeat it every time you post, and it is offensive. Best regards, Charles ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
On 19/08/2014 16:11, Ed Palmer wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. FWIW, I just had a look at the timepulse on a NEO-7M. I configured it to 10MHz, 50:50 duty cycle when locked, disabled when out of lock. I don't have any of those Analyzers so I used an HP 54615B digital scope. The period of the majority of cycles was 104ns with 'random' cycles being 84ns. I did not observe any other cycle periods. I don't know how accurate the time measurements are on the scope, but it looks like the timing is derived from an approx 48MHz clock, and the timing phase/frequency adjusted by periodically deleting 48MHz clock cycles. Although I said random, I couldn't make any observations as to the statistics of the short and long cycles or their distribution - I guess I'll have to write some software for my STM32F4 discovery board for that. If I get time, I'll do the same with a Reyax RYN25AI receiver which has a UBLOX MAX-7C module. Tony ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hi Tony, that's consistent with what I remember. Do you have the capability to count the number of 10MHz pulses per second to see if it is phase-coherent with the UTC 1PPS pulse? I am thinking that the software may be using statistics to approximate 10 million cycles per second, which would mean they may or may not be exactly 10 million cycles.. thanks, Said In a message dated 8/20/2014 11:07:59 Pacific Daylight Time, tn...@toneh.demon.co.uk writes: On 19/08/2014 16:11, Ed Palmer wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. FWIW, I just had a look at the timepulse on a NEO-7M. I configured it to 10MHz, 50:50 duty cycle when locked, disabled when out of lock. I don't have any of those Analyzers so I used an HP 54615B digital scope. The period of the majority of cycles was 104ns with 'random' cycles being 84ns. I did not observe any other cycle periods. I don't know how accurate the time measurements are on the scope, but it looks like the timing is derived from an approx 48MHz clock, and the timing phase/frequency adjusted by periodically deleting 48MHz clock cycles. Although I said random, I couldn't make any observations as to the statistics of the short and long cycles or their distribution - I guess I'll have to write some software for my STM32F4 discovery board for that. If I get time, I'll do the same with a Reyax RYN25AI receiver which has a UBLOX MAX-7C module. Tony ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Thanks, Tony. That's good info. So now we've confirmed that the neo-7M has an NCO and it appears that it's resolution is 20 ns. The data sheet shows the 'Accuracy of time pulse signal' is 30 ns RMS and 60 ns for 99%, but it isn't clear whether they're referring to jitter or error with respect to GPS seconds. The original question was whether the neo-7M would make a good GPSDO. As we've seen, the answer is no. Cheap, yes. Good, no. Setting aside the NCO issue, the neo-7M isn't a timing receiver, it's a navigation receiver. That limits it's performance in many ways. Ublox sells timing receivers, but they're still NCO-based. They're also significantly more expensive than the navigation receivers. One example is Synergy Systems' SSR-6Tr if it's still available. It was announced, and discussed on this list, in 2012 but it still isn't listed on their web site so I don't know what it's status is. It's based on the LEA-6T timing receiver which has a spec for the 1 PPS is 'within 15 ns to GPS/UTC (1 sigma)'. That can be further reduced with some extra work. If the performance of an NCO-based unit isn't enough, you might want to consider Jackson Labs GPSTCXO which is a real GPSDO. More expensive than the NCO-based units, but you get what you pay for. No, I'm not associated with Synergy or Jackson labs. So Graham, if you survived the firestorm started by your simple question, are you any wiser? Ed On 8/20/2014 7:56 PM, Tony wrote: On 19/08/2014 16:11, Ed Palmer wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. FWIW, I just had a look at the timepulse on a NEO-7M. I configured it to 10MHz, 50:50 duty cycle when locked, disabled when out of lock. I don't have any of those Analyzers so I used an HP 54615B digital scope. The period of the majority of cycles was 104ns with 'random' cycles being 84ns. I did not observe any other cycle periods. I don't know how accurate the time measurements are on the scope, but it looks like the timing is derived from an approx 48MHz clock, and the timing phase/frequency adjusted by periodically deleting 48MHz clock cycles. Although I said random, I couldn't make any observations as to the statistics of the short and long cycles or their distribution - I guess I'll have to write some software for my STM32F4 discovery board for that. If I get time, I'll do the same with a Reyax RYN25AI receiver which has a UBLOX MAX-7C module. Tony ___ 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.
[time-nuts] Ublox neo-7M GPS
Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc Graham, Take a look at the data sheet. The waveforms at frequencies other than 8 MHz (IIRC in other modules) and sub-multiples may not be all you desire. However, I would be delighted to see testing of this box by a qualified frequency-nut! http://www.u-blox.com/en/download/documents-a-resources/u-blox-7-gps-modules-resources.html http://www.u-blox.com/images/downloads/Product_Docs/NEO-7_DataSheet_%28GPS.G7-HW-11004%29.pdf http://www.u-blox.com/images/downloads/Product_Docs/u-blox7-V14_ReceiverDescriptionProtocolSpec_Public_%28GPS.G7-SW-12001%29.pdf 73, David GM8ARV -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Graham, Those are not GPSDO's by definition. They are based on NCO technology. The difference being many orders of magnitude higher phase noise and ADEV noise. We tried to measure their phase noise and our TSC5125A could not even lock on to the 10MHz - they were so noisy. You can make a GPSDO out of them if you use a post filter oscillator loop locked with sufficient time constant (10s).. Sent From iPhone On Aug 19, 2014, at 9:20, Collins, Graham coll...@navcanada.ca wrote: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Said, Agreed, hence my reference as a very simple self-contained GPSDO. Even after a very quick first glance at the documentation it didn't seem like it would be much of threat to more traditional GPSDO's. It will be interesting to play around with and see what it can do. Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Said Jackson Sent: August-19-14 12:44 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ublox neo-7M GPS Graham, Those are not GPSDO's by definition. They are based on NCO technology. The difference being many orders of magnitude higher phase noise and ADEV noise. We tried to measure their phase noise and our TSC5125A could not even lock on to the 10MHz - they were so noisy. You can make a GPSDO out of them if you use a post filter oscillator loop locked with sufficient time constant (10s).. Sent From iPhone On Aug 19, 2014, at 9:20, Collins, Graham coll...@navcanada.ca wrote: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hi Graham, its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. This causes huge cycle-to-cycle phase jumps. One cycle maybe 100ns long, and the next adjacent cycle could only be 87ns long! Without filtering, I doubt the output is useful for much because it has phase jumps from cycle to cycle of 10's of nanoseconds or more. A true GPSDO (even the cheapest one) has cycle to cycle phase jumps of femtoseconds only due to oscillator jitter. You can easily make a GPSDO out of it though through a simple EXOR gate (74AC86), feeding a TCXO/VCXO through a low-pass filter, and designing a phase loop low-pass filter with less than say 10Hz bandwidth.. That approach has been discussed here in the past a couple of times and is very cost-effective. That is essentially what the Conner Winfield units do. The drawback is that you have very large phase and frequency jumps when going into and coming out of holdover on these units, because the unit does not have a holdover oscillator with any type of reasonable stability, and whatever high ADEV stability your filter oscillator has is lost due to the analog loop bandwidth of typically 10Hz meaning the internal $1 crystal of the GPS receiver itself determines ADEV. Bye, Said In a message dated 8/19/2014 10:03:27 Pacific Daylight Time, coll...@navcanada.ca writes: Said, Agreed, hence my reference as a very simple self-contained GPSDO. Even after a very quick first glance at the documentation it didn't seem like it would be much of threat to more traditional GPSDO's. It will be interesting to play around with and see what it can do. Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Said Jackson Sent: August-19-14 12:44 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Ublox neo-7M GPS Graham, Those are not GPSDO's by definition. They are based on NCO technology. The difference being many orders of magnitude higher phase noise and ADEV noise. We tried to measure their phase noise and our TSC5125A could not even lock on to the 10MHz - they were so noisy. You can make a GPSDO out of them if you use a post filter oscillator loop locked with sufficient time constant (10s).. Sent From iPhone On Aug 19, 2014, at 9:20, Collins, Graham coll...@navcanada.ca wrote: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’ usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’ expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow
Re: [time-nuts] Ublox neo-7M GPS
saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hal, I guess that depends on your definition of disciplined. The products that I am familiar with don't consider adjusting phase length of an asynchronously running oscillator on a cycle-to-cycle basis thousands of times per second to try to fit 10 million of them (or whatever your desired frequency is) disciplining. Best case you could call it phase/frequency hopping to try to achieve some sort of frequency average in my opinion. However if you used a DDS to adjust the frequency of an asynchronous clock digitally and control that frequency by digital adjustment that would be true disciplining of your frequency source. So analog versus digital has nothing to do with it. If your DAC had only a few bits you still would have many orders of magnitude less phase errors than the NCO approach; you can do the simple math: Let's say your VCXO had only 4 bits and a +/-20Hz frequency adjustment range. Pretty nasty considering any low-ball GPSDO these days has at least 21 bits EFC resolution. Now changing one LSB on our 4 bit DAC would thus result in a massive frequency change of +/-2.5Hz. This would result in a phase drift of 2.5E-07 or 250ns drift over ONE ENTIRE SECOND. That means 250ns divided by 10 Million (!!) cycles or a cycle to cycle change of only 25 femtoseconds when the DAC changes state. Theoretically that cycle length change would only happen ONCE if the system was a digital DDS type system. How does a single 25 femtoseconds cycle length change on our hypothetical 4 bit EFC DAC compare to a 10ns cycle to cycle change that happens thousands of times or more per second on typical NCO's? My point is we are talking performance differences of 5 or 6 orders of magnitude between a GPSDO (digital or analog) and an NCO. We are not comparing apples to apples. These are not even apples to oranges in my opinion. bye, Said In a message dated 8/19/2014 12:32:02 Pacific Daylight Time, hmur...@megapathdsl.net writes: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Knowing a litle bit about semiconductor production it is safe to assume that all 7M series divvices have the same chip and during production at ublox some features are disabled or enabled. The result is one mask set one chip run and one inventory. I did see a recent announcement where a 7M can be used as a GPSDO one of the intended markets is micro cell sites.Will require an external XO. In the meantime we have been playing with a $ 15 M7 ublox that can be programmed from 1 pps to 1 KHz and use it in a PLL. I call it a GPS PLL and is mainly intended for Ham's. Clark had years ago a similar circuits we have added some mods. Using a Morion 89 we get better than 1 E-10 per second on first try.. There have been recent claims using 1000 seconds which is easy but this is per second. Next steps are more fine tuning and lower cost XO's. Maybe even a VCTCXO. As I said before intended for Ham's, field day, uwave and SDR. Not really a time nut unit, but low cost off the shelf standard parts and no adjustments all on a 5 X 5 cm board. With a Morion you have to start off with 15 V but there are OCXO's out there for 5 V. Ideal for fieldday 12 V. Bert Kehren In a message dated 8/19/2014 12:20:40 P.M. Eastern Daylight Time, coll...@navcanada.ca writes: Good day all, On another list to which I subscribe, there has been chatter about the Ublox neo-7M GPS receiver. It seems that the device's configurable timepulse output is configurable from 0.25hz to 10 MHz as well as it's duty cycle and can also be set to be one condition when the GPS is not locked and a different condition when locked (i.e. 1 PPS if not locked, 10KHz when locked). This seems all too good to be true. Sounds like a very simple self-contained GPSDO. I don't know anything more about the device. I have just downloaded the documents and will be spending some time reading them. I am curious if any other list members were aware of this feature of this device and have had any first hand experiences with it. There is another model, the 7N. the 7M uses a simple crystal clock, the 7N a TXCO. Cheers, Graham ve3gtc This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’ usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’ expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hi Tom, last time I looked at these I tried figuring out what they were doing. It is very hard to get measurement data, our TSC did not converge on their signal, and looking at the output on a scope revealed only a bunch of crazy random phase jumps. I guess one could use a counter to measure how many time pulses are being sent in x seconds with x being a large number, or divide the output by 10 million and see how the pulse moves back and forth compared to the 1PPS UTC output.. Since I don't know the exact algorithm being used, I said adds/drops/extends/retards in my previous email. I did not mean to imply that the unit is doing all or any of those items. But that is exactly part of the problem isn't it, there is no clear description of what exactly is happening in the uBlox documents or the CW docs for that matter that I could find. I for one would not use that output to drive a processor or other digital device directly, who knows what happens if the processor sees a 100ns, then a 110ns, and then an 70ns pulse if it is only rated at 10MHz and 100ns pulse-width +/- a couple percent for example.. Without knowing the exact minimum phase time period specification that could come out of one of these NCO's, one should not properly use that signal in a digital design. My initial concern was that this is time-nuts, and we should call a GPSDO a GPSDO, and an NCO an NCO in my opinion. Nothing wrong with one or the other, but they sure are not the same thing - by 6 or more orders of magnitude in phase stability. We usually are concerned here about parts per trillion stability and accuracy, and now we are mixing things up that are millions of times worse than one another.. bye, Said In a message dated 8/19/2014 13:08:52 Pacific Daylight Time, t...@leapsecond.com writes: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Hi They are constrained by the same basic TCXO issues that give you sawtooth correction. They do not use EFC to get the TCXO on frequency. With sawtooth they give you a word that lets you know what’s going on. With the NCO’s they often are doing very crude synthesis. They don’t put a $48 DDS chip in a $10 GPS module. If you put one on a spectrum analyzer, it’s not pretty …. Bob On Aug 19, 2014, at 5:46 PM, Said Jackson saidj...@aol.com wrote: Tom, Btw part of my frustration with this is that we sometimes get calls from customers asking why they need our or others' GPSDOs for a couple 100 dollars when they can buy a CW or uBlox doing the same thing for a fraction of the cost. Most of them come back to us after evaluating these NCOs and finding that its not the same thing. You get what you pay for I guess.. Said Sent From iPhone On Aug 19, 2014, at 13:01, Tom Van Baak (lab) t...@leapsecond.com wrote: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
I recall when the LEA-M8F was announced that they mentioned a VCTCXO and maybe I wrongly assumed that they used it for sawtooth correction they also mention ability to control in addition an external OCXO. I previously suggested using saw tooth correction information to tune a TCXO but that would require a GPS module with sawtooth information and than it would be simpler to just use a PIC and delay chip. Still do not understand why no one took me up on the offer of chips and PCB. I guess time nuts like to talk about it but not fix it. How many receivers are out there. Bert Kehren. In a message dated 8/19/2014 5:51:30 P.M. Eastern Daylight Time, kb...@n1k.org writes: Hi They are constrained by the same basic TCXO issues that give you sawtooth correction. They do not use EFC to get the TCXO on frequency. With sawtooth they give you a word that lets you know what’s going on. With the NCO’s they often are doing very crude synthesis. They don’t put a $48 DDS chip in a $10 GPS module. If you put one on a spectrum analyzer, it’s not pretty …. Bob On Aug 19, 2014, at 5:46 PM, Said Jackson saidj...@aol.com wrote: Tom, Btw part of my frustration with this is that we sometimes get calls from customers asking why they need our or others' GPSDOs for a couple 100 dollars when they can buy a CW or uBlox doing the same thing for a fraction of the cost. Most of them come back to us after evaluating these NCOs and finding that its not the same thing. You get what you pay for I guess.. Said Sent From iPhone On Aug 19, 2014, at 13:01, Tom Van Baak (lab) t...@leapsecond.com wrote: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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. ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. http://www.febo.com/pipermail/time-nuts/2012-January/062913.html Remember the explanation of a GPSDO's Adev curve. At low values of Tau, the value is determined by the oscillator (whether OCXO or TCXO). At high values of Tau, the value is determined by the GPS system. I think of 'The GPS Line'. It's a line on the Adev graph that passes through 1e-10 @ 100 sec. with a slope of -1. Use a *really* fat pencil when you draw the line! Every GPSDO follows that line - nothing exists to the right of it. The oscillator determines where the curve for that particular GPSDO is on the left side of the line. When the oscillator performance hits the GPS Line, the graph turns down and to the right and follows the line. Since an NCO (Navsync, Ublox, whatever) has no internal oscillator, it just follows the GPS Line. That means that at a Tau of 1 sec. the Adev can't be any better than 1e-8. A low clock speed could make it worse due to limited resolution on the step size. Said's GPSTCXO has a nice TCXO oscillator which gives an Adev two orders of magnitude better than that at 1 second, but that difference disappears at 100 sec. Most GPSDO's use an OCXO which give even better performance at 1 sec. but eventually, the GPS line corrals everyone and imposes similar performance. For any particular application, the user has to decide what level of performance is necessary. If an NCO is good enough with it's cycle-to-cycle anomalies and limited low Tau performance, use it. If not, move up to a real GPSDO. Ed On 8/19/2014 3:23 PM, saidj...@aol.com wrote: Hi Tom, last time I looked at these I tried figuring out what they were doing. It is very hard to get measurement data, our TSC did not converge on their signal, and looking at the output on a scope revealed only a bunch of crazy random phase jumps. I guess one could use a counter to measure how many time pulses are being sent in x seconds with x being a large number, or divide the output by 10 million and see how the pulse moves back and forth compared to the 1PPS UTC output.. Since I don't know the exact algorithm being used, I said adds/drops/extends/retards in my previous email. I did not mean to imply that the unit is doing all or any of those items. But that is exactly part of the problem isn't it, there is no clear description of what exactly is happening in the uBlox documents or the CW docs for that matter that I could find. I for one would not use that output to drive a processor or other digital device directly, who knows what happens if the processor sees a 100ns, then a 110ns, and then an 70ns pulse if it is only rated at 10MHz and 100ns pulse-width +/- a couple percent for example.. Without knowing the exact minimum phase time period specification that could come out of one of these NCO's, one should not properly use that signal in a digital design. My initial concern was that this is time-nuts, and we should call a GPSDO a GPSDO, and an NCO an NCO in my opinion. Nothing wrong with one or the other, but they sure are not the same thing - by 6 or more orders of magnitude in phase stability. We usually are concerned here about parts per trillion stability and accuracy, and now we are mixing things up that are millions of times worse than one another.. bye, Said In a message dated 8/19/2014 13:08:52 Pacific Daylight Time, t...@leapsecond.com writes: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few
Re: [time-nuts] Ublox neo-7M GPS
Hi There are only two things they can be doing (since it’s not a tuned oscillator). 1) It’s a true DDS with a D/A on the output and you need to put a filter on it before you can do anything at all with it. 2) It’s a pulse drop / add NCO that drops or adds at the 20 to 30 ns level (28 to 50 MHz TCXO). Those are the only two choices there are. Both have significant issues as RF signal sources. Bob On Aug 19, 2014, at 7:11 PM, Ed Palmer ed_pal...@sasktel.net wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. http://www.febo.com/pipermail/time-nuts/2012-January/062913.html Remember the explanation of a GPSDO's Adev curve. At low values of Tau, the value is determined by the oscillator (whether OCXO or TCXO). At high values of Tau, the value is determined by the GPS system. I think of 'The GPS Line'. It's a line on the Adev graph that passes through 1e-10 @ 100 sec. with a slope of -1. Use a *really* fat pencil when you draw the line! Every GPSDO follows that line - nothing exists to the right of it. The oscillator determines where the curve for that particular GPSDO is on the left side of the line. When the oscillator performance hits the GPS Line, the graph turns down and to the right and follows the line. Since an NCO (Navsync, Ublox, whatever) has no internal oscillator, it just follows the GPS Line. That means that at a Tau of 1 sec. the Adev can't be any better than 1e-8. A low clock speed could make it worse due to limited resolution on the step size. Said's GPSTCXO has a nice TCXO oscillator which gives an Adev two orders of magnitude better than that at 1 second, but that difference disappears at 100 sec. Most GPSDO's use an OCXO which give even better performance at 1 sec. but eventually, the GPS line corrals everyone and imposes similar performance. For any particular application, the user has to decide what level of performance is necessary. If an NCO is good enough with it's cycle-to-cycle anomalies and limited low Tau performance, use it. If not, move up to a real GPSDO. Ed On 8/19/2014 3:23 PM, saidj...@aol.com wrote: Hi Tom, last time I looked at these I tried figuring out what they were doing. It is very hard to get measurement data, our TSC did not converge on their signal, and looking at the output on a scope revealed only a bunch of crazy random phase jumps. I guess one could use a counter to measure how many time pulses are being sent in x seconds with x being a large number, or divide the output by 10 million and see how the pulse moves back and forth compared to the 1PPS UTC output.. Since I don't know the exact algorithm being used, I said adds/drops/extends/retards in my previous email. I did not mean to imply that the unit is doing all or any of those items. But that is exactly part of the problem isn't it, there is no clear description of what exactly is happening in the uBlox documents or the CW docs for that matter that I could find. I for one would not use that output to drive a processor or other digital device directly, who knows what happens if the processor sees a 100ns, then a 110ns, and then an 70ns pulse if it is only rated at 10MHz and 100ns pulse-width +/- a couple percent for example.. Without knowing the exact minimum phase time period specification that could come out of one of these NCO's, one should not properly use that signal in a digital design. My initial concern was that this is time-nuts, and we should call a GPSDO a GPSDO, and an NCO an NCO in my opinion. Nothing wrong with one or the other, but they sure are not the same thing - by 6 or more orders of magnitude in phase stability. We usually are concerned here about parts per trillion stability and accuracy, and now we are mixing things up that are millions of times worse than one another.. bye, Said In a message dated 8/19/2014 13:08:52 Pacific Daylight Time, t...@leapsecond.com writes: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally
Re: [time-nuts] Ublox neo-7M GPS
Hi If you have to womp up a MCU anyway, there is no reason to put in a delay chip. It’s easier / faster / more accurate to just do it all in the MCU. You have to write and maintain custom code either way. Bob On Aug 19, 2014, at 7:53 PM, ewkeh...@aol.com wrote: I recall when the LEA-M8F was announced that they mentioned a VCTCXO and maybe I wrongly assumed that they used it for sawtooth correction they also mention ability to control in addition an external OCXO. I previously suggested using saw tooth correction information to tune a TCXO but that would require a GPS module with sawtooth information and than it would be simpler to just use a PIC and delay chip. Still do not understand why no one took me up on the offer of chips and PCB. I guess time nuts like to talk about it but not fix it. How many receivers are out there. Bert Kehren. In a message dated 8/19/2014 5:51:30 P.M. Eastern Daylight Time, kb...@n1k.org writes: Hi They are constrained by the same basic TCXO issues that give you sawtooth correction. They do not use EFC to get the TCXO on frequency. With sawtooth they give you a word that lets you know what’s going on. With the NCO’s they often are doing very crude synthesis. They don’t put a $48 DDS chip in a $10 GPS module. If you put one on a spectrum analyzer, it’s not pretty …. Bob On Aug 19, 2014, at 5:46 PM, Said Jackson saidj...@aol.com wrote: Tom, Btw part of my frustration with this is that we sometimes get calls from customers asking why they need our or others' GPSDOs for a couple 100 dollars when they can buy a CW or uBlox doing the same thing for a fraction of the cost. Most of them come back to us after evaluating these NCOs and finding that its not the same thing. You get what you pay for I guess.. Said Sent From iPhone On Aug 19, 2014, at 13:01, Tom Van Baak (lab) t...@leapsecond.com wrote: Hal, as long as you maintain long-term phase lock it's a disciplined oscillator. So, yes, a carrier tracking WWVB receiver with sufficiently stable flywheel LO is a WWVBDO. Said, too-short or too-long 100 ns cycles is one thing. Still ok for many applications. But tell me more about extra or missing pulses in the ublox-7. That sounds like a show stopper to me. /tvb (i5s) On Aug 19, 2014, at 2:05 PM, Hal Murray hmur...@megapathdsl.net wrote: saidj...@aol.com said: its not a GPSDO though, not even a simple one :) It does not discipline an oscillator. It generates the output by mathematically calculating how many phases it has to add/drop in a second, then digitally adds/drops/extends/retards the phase of the output clock to achieve an average of number of desired clock cycles. Is there something about the term GPSDO that says I have to do the D in the analog domain rather than the digital domain? I agree that current technology doesn't give results that are useful for many applications that currently use GPSDOs. What if the clock ran at a GHz? 10 GHz? Sure, it would have spurs, but would it be useful for some applications? Is a GPSDO still a GPSDO if the D/A driving the VCXO only has a few bits? How many bits does it need to be a real GPSDO? Is a battery powered wall clock listening to WWVB at 2 AM a WWVDO? It's got a pretty good ADEV if you go out far enough. -- These are my opinions. I hate spam. ___ 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. ___ 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. ___ 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. ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
I have a dozen ublox max-7's on hand and should have suitable PCB's for the analysis in a couple of days. Unfortunately I don't have the analyser, the test kit is currently limited to a HP5834A recently calibrated to Rb and a 100MHz DSO so probably not what your looking for. Let me know if I can help though. On Wed, Aug 20, 2014 at 9:11 AM, Ed Palmer ed_pal...@sasktel.net wrote: Does anyone have a neo-7M and an HP 5371A or a 5372A Analyzer? Use the Histogram Time Interval function to measure a block of samples. That will show the length of the samples with a resolution of 200 ps. That's what I did a couple of years ago when I analyzed the Navsync CW-12 with the old and new firmware. -- -- Teach your kids Science, or somebody else will :/ ja...@ball.net vk2...@google.com callsign: vk2vjb ___ 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.
Re: [time-nuts] Ublox neo-7M GPS
Bert wrote: I guess time nuts like to talk about it but not fix it. Will you PLEASE quit beating this tired old drum? All of us know this is your opinion, although many of us have other explanations for the phenomena you think it explains. We do not need you to repeat it every time you post, and it is offensive. Best regards, Charles ___ 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.
