[time-nuts] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
Take a look at this patent http://www.google.com/patents/US20130342278 and you will learn how to build the ultimate time and frequency reference. ___ 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] OCXO Voltage Input? (Bob Camp)
Hi Bob, your description oft he spurious coming from higher overtone of low-frequency modes is correct. I want to add, that all thickness-shear mode crystals (such as AT, BT and SC-cut) have so-called an-harmonic spurious modes, which is a whole ensemble of spurs located slightly above above the main mode (fundamental or overtone mode). slightly means starting at about 50 kHz to 200 kHz above for fundamental mode and about 30 ... 50 kHz above for overtone modes. These an-harmonic modes are relaled to the length and width of the active area (electrode). These spurious modes do not come only into play for wide-pull VCXO, but also in the case that the EFC input is used for modulation with signals in the audio frequency range. Remember that a frequency modulated signal has side-lines which are N* the audio frequency apart from the carrier. The amplitude of these side lines follows the so-called Bessel functions and varies with the modulation index. If it happens that such a Bessel-line for a particular modulation frequency coincides with such a spur, it comes to an interference, This means the modulation frequency response becomes a discontinuity (dip) at a sharp frequency. Such band breaks do even occur if the spurious is so weak that it can barely be seen on a network analyzer. Regards Bernd DK1AG AXTAL GmbH Co. KG www.axtal.com -Ursprüngliche Nachricht- Von: time-nuts [mailto:time-nuts-boun...@febo.com] Im Auftrag von Bob Camp Gesendet: Sonntag, 7. September 2014 04:21 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp) Hi Simple answer = crystals are never perfect. Longer winded, but very incomplete answer = A spurious response in a crystal normally refers to a mode that is not one of the “identified” modes of the crystal. An AT has a set of identified modes, an SC has a more complex set of modes. In the case of the AT it would be the fundamental and the odd overtones. In the case of the SC you have the A, B, C modes and their odd overtones. None of those are considered spurious. A spur can come from a lot of different places. One common one is higher order vibrations in a longer dimension face of the resonator. The 183rd overtone of the width of the blank is still a legitimate resonant mode. Another source are modes other than shear (like flex). Deriving a full catalog of all the modes of an arbitrary blank design is a major project. There are only a handful of people out there who are into that sort of thing (as opposed to simply cranking through some formulas). Practical answer = Don’t worry about it. Unless you are building a wide pull VCXO or a wide deviation VCXO (often the same thing) you will never notice them. Bob On Sep 6, 2014, at 9:13 PM, Hal Murray hmur...@megapathdsl.net wrote: kb...@n1k.org said: The biggest problem comes from crystal spurs rather than crystal Q. What's the mechanism for making spurs with a crystal? -- 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
On Tue, Sep 9, 2014 at 4:26 AM, Azelio Boriani azelio.bori...@screen.it wrote: Take a look at this patent http://www.google.com/patents/US20130342278 and you will learn how to build the ultimate time and frequency reference. Yes, but there was an error in he patent. The actual filing date was April 1, not March 16. -- Brian Lloyd Lloyd Aviation 706 Flightline Drive Spring Branch, TX 78070 br...@lloyd.aero +1.210.802-8FLY (1.210.802-8359) ___ 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
On Wed, Sep 10, 2014 at 9:42 AM, Azelio Boriani azelio.bori...@screen.it wrote: Really? Not noticed but then it makes sense, anyway a rather expensive April fools' as the patent was issued and I presume it was done at a cost. What you say is true. I was making a joke by suggesting that the patent itself is a joke. I skimmed through the patent but did not read it in detail. There may be some nugget in there that represents something new but nothing jumped out at me. The Patent system is now used aggressively and offensively. Patents are granted for things that actually represent common knowledge and/or prior art. The holders of these patents then use them to attack legitimate companies with successful products, hence the term patent trolls. So, mostly I was just making a joke. -- Brian Lloyd Lloyd Aviation 706 Flightline Drive Spring Branch, TX 78070 br...@lloyd.aero +1.210.802-8FLY (1.210.802-8359) ___ 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] OCXO Voltage Input? (Bob Camp)
Bernd, Brilliant point. Easy to miss if one has a to simple model of the oscillator at hand. Since it is a single-side-band mode, it will show up both as AM and PM with the same amplitude. Cheers, Magnus On 09/10/2014 03:27 PM, Bernd Neubig wrote: Hi Bob, your description oft he spurious coming from higher overtone of low-frequency modes is correct. I want to add, that all thickness-shear mode crystals (such as AT, BT and SC-cut) have so-called an-harmonic spurious modes, which is a whole ensemble of spurs located slightly above above the main mode (fundamental or overtone mode). slightly means starting at about 50 kHz to 200 kHz above for fundamental mode and about 30 ... 50 kHz above for overtone modes. These an-harmonic modes are relaled to the length and width of the active area (electrode). These spurious modes do not come only into play for wide-pull VCXO, but also in the case that the EFC input is used for modulation with signals in the audio frequency range. Remember that a frequency modulated signal has side-lines which are N* the audio frequency apart from the carrier. The amplitude of these side lines follows the so-called Bessel functions and varies with the modulation index. If it happens that such a Bessel-line for a particular modulation frequency coincides with such a spur, it comes to an interference, This means the modulation frequency response becomes a discontinuity (dip) at a sharp frequency. Such band breaks do even occur if the spurious is so weak that it can barely be seen on a network analyzer. Regards Bernd DK1AG AXTAL GmbH Co. KG www.axtal.com -Ursprüngliche Nachricht- Von: time-nuts [mailto:time-nuts-boun...@febo.com] Im Auftrag von Bob Camp Gesendet: Sonntag, 7. September 2014 04:21 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp) Hi Simple answer = crystals are never perfect. Longer winded, but very incomplete answer = A spurious response in a crystal normally refers to a mode that is not one of the “identified” modes of the crystal. An AT has a set of identified modes, an SC has a more complex set of modes. In the case of the AT it would be the fundamental and the odd overtones. In the case of the SC you have the A, B, C modes and their odd overtones. None of those are considered spurious. A spur can come from a lot of different places. One common one is higher order vibrations in a longer dimension face of the resonator. The 183rd overtone of the width of the blank is still a legitimate resonant mode. Another source are modes other than shear (like flex). Deriving a full catalog of all the modes of an arbitrary blank design is a major project. There are only a handful of people out there who are into that sort of thing (as opposed to simply cranking through some formulas). Practical answer = Don’t worry about it. Unless you are building a wide pull VCXO or a wide deviation VCXO (often the same thing) you will never notice them. Bob On Sep 6, 2014, at 9:13 PM, Hal Murray hmur...@megapathdsl.net wrote: kb...@n1k.org said: The biggest problem comes from crystal spurs rather than crystal Q. What's the mechanism for making spurs with a crystal? -- 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
On Tue, Sep 9, 2014 at 4:26 AM, Azelio Boriani azelio.bori...@screen.it wrote: Take a look at this patent http://www.google.com/patents/US20130342278 and you will learn how to build the ultimate time and frequency reference. The patent's owners don't appear to be very trustful in their idea, as they sell only a GPSDO as a time reference: http://www.onetastic.com/en/onetastic-otgps1.php Antonio I8IOV ___ 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
and if you look the claims of the patent, they are very close to the Shera design, which was a bit earlier idea 73 KJ6UHN Alex On 9/10/2014 10:12 AM, iov...@inwind.it wrote: On Tue, Sep 9, 2014 at 4:26 AM, Azelio Boriani azelio.bori...@screen.it wrote: Take a look at this patent http://www.google.com/patents/US20130342278 and you will learn how to build the ultimate time and frequency reference. The patent's owners don't appear to be very trustful in their idea, as they sell only a GPSDO as a time reference: http://www.onetastic.com/en/onetastic-otgps1.php Antonio I8IOV ___ 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
On 10 Sep 2014 17:36, Brian Lloyd br...@lloyd.aero wrote: On Wed, Sep 10, 2014 at 9:42 AM, Azelio Boriani azelio.bori...@screen.it wrote: I skimmed through the patent but did not read it in detail. There may be some nugget in there that represents something new but nothing jumped out at me. Maybe that is the trick to make money out of a good patent - make 99% of it rubbish, with the nugget well hidden. Then sue when people breach your patent. I looked but it is so boring and so badly written. I did learn one though - I thought Rb sources were used commercially, but according to that patent they are too expensive for that. Dave ___ 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
Rb sources are considered too expensive here in Italy for the TV broadcast market. The patent was issued by a small company that produces digital TV transmitters able to exploit the single frequency network specifications of the ETSI standard and so a stable and accurate time and frequency source is needed: usually a GPSDO with an OCXO at its heart. Very rarely do we see a disciplined Rb. On Wed, Sep 10, 2014 at 9:18 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 10 Sep 2014 17:36, Brian Lloyd br...@lloyd.aero wrote: On Wed, Sep 10, 2014 at 9:42 AM, Azelio Boriani azelio.bori...@screen.it wrote: I skimmed through the patent but did not read it in detail. There may be some nugget in there that represents something new but nothing jumped out at me. Maybe that is the trick to make money out of a good patent - make 99% of it rubbish, with the nugget well hidden. Then sue when people breach your patent. I looked but it is so boring and so badly written. I did learn one though - I thought Rb sources were used commercially, but according to that patent they are too expensive for that. Dave ___ 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] RFTG-u ref(1) stand-by
wa8ttm.radio wa8ttm.radio@... writes: I have the RFTG-u ref(1) and ref(0) with the interconnect cable. The pair are working except the ref(1) is in stand-by. How can make the ref(1) active ? Thanks, Ron I notice this, but also wonder... It may be correct operation, as Ref 0 is the default side. Ref 1 only becomes active (out of standby) if Ref 0 suffers a fault. At least that is how my RFTG works. But he RFTG also has a physical switch to select either side as default. The RFTG-U does not have that. ___ 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
If you run SFN you need phase-coordination between transmitters. This is typically done via GPS or distribution network. Rubidium isn't really needed anyway, it's more about having a good enough crystal. The ETSI SFN spec's seems to be miss-interpreted quite often, but the +/- 1 ppb spec is about correct. Phase errors could very well be several microseconds without great effect for the user, given that gap configuration is done correct. The reference side of DVB-T transmitters isn't well standardized. Cheers, Magnus On 09/10/2014 09:53 PM, Azelio Boriani wrote: Rb sources are considered too expensive here in Italy for the TV broadcast market. The patent was issued by a small company that produces digital TV transmitters able to exploit the single frequency network specifications of the ETSI standard and so a stable and accurate time and frequency source is needed: usually a GPSDO with an OCXO at its heart. Very rarely do we see a disciplined Rb. On Wed, Sep 10, 2014 at 9:18 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 10 Sep 2014 17:36, Brian Lloyd br...@lloyd.aero wrote: On Wed, Sep 10, 2014 at 9:42 AM, Azelio Boriani azelio.bori...@screen.it wrote: I skimmed through the patent but did not read it in detail. There may be some nugget in there that represents something new but nothing jumped out at me. Maybe that is the trick to make money out of a good patent - make 99% of it rubbish, with the nugget well hidden. Then sue when people breach your patent. I looked but it is so boring and so badly written. I did learn one though - I thought Rb sources were used commercially, but according to that patent they are too expensive for that. Dave ___ 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] Eureka, no more Cs, active or passive H-masers or GPSDOs needed
We've sold a bunch of GPSDO's into that market, and with the towers generally being placed on mountain tops lightning protection becomes a real challenge.. Maybe their GPS receivers are burning up all the time, and that's why they need some sort of none GNSS reference?! bye, Said In a message dated 9/10/2014 12:54:11 Pacific Daylight Time, azelio.bori...@screen.it writes: Rb sources are considered too expensive here in Italy for the TV broadcast market. The patent was issued by a small company that produces digital TV transmitters able to exploit the single frequency network specifications of the ETSI standard and so a stable and accurate time and frequency source is needed: usually a GPSDO with an OCXO at its heart. Very rarely do we see a disciplined Rb. ___ 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] OCXO Voltage Input? (Bob Camp)
Hi If you are modulating a normal OCXO EFC with audio, and the output frequency is not being multiplied up, the modulation index will be very low. Low modulation index means that the higher order FM sidebands will be quite far down. If you take “audio” to be 10 KHz, and a VHF OCXO to be 100 MHz: With a 10 ppm EFC range, you get 1.0 KHz of deviation. The modulation index is 1 a decade below your upper modulation frequency. That’s already a pretty wide swing OCXO and a fairly high modulation frequency for an EFC line. If you have a spur that is in the 50 to 150 KHz range, you are talking about the 5th to 15th sideband off of 10 KHz or the 50th to 150th sideband off of 1 KHz. At 50 sidebands out and an index of 1, you are in the “forget about it” region. Even at 10 KHz, the sideband is not likely to create much of an issue. The distortion from the non-linear EFC slope will be more of a problem in a practical sense. —— Since the modulation is single sideband, yes it converts PM - AM. It also will be impacted by any limiters in the system and will not multiply the same way as a pure PM modulation. The phase of the sideband will change as you go through the resonance, further messing up the multiplication / limiter math. Bob On Sep 10, 2014, at 12:50 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Bernd, Brilliant point. Easy to miss if one has a to simple model of the oscillator at hand. Since it is a single-side-band mode, it will show up both as AM and PM with the same amplitude. Cheers, Magnus On 09/10/2014 03:27 PM, Bernd Neubig wrote: Hi Bob, your description oft he spurious coming from higher overtone of low-frequency modes is correct. I want to add, that all thickness-shear mode crystals (such as AT, BT and SC-cut) have so-called an-harmonic spurious modes, which is a whole ensemble of spurs located slightly above above the main mode (fundamental or overtone mode). slightly means starting at about 50 kHz to 200 kHz above for fundamental mode and about 30 ... 50 kHz above for overtone modes. These an-harmonic modes are relaled to the length and width of the active area (electrode). These spurious modes do not come only into play for wide-pull VCXO, but also in the case that the EFC input is used for modulation with signals in the audio frequency range. Remember that a frequency modulated signal has side-lines which are N* the audio frequency apart from the carrier. The amplitude of these side lines follows the so-called Bessel functions and varies with the modulation index. If it happens that such a Bessel-line for a particular modulation frequency coincides with such a spur, it comes to an interference, This means the modulation frequency response becomes a discontinuity (dip) at a sharp frequency. Such band breaks do even occur if the spurious is so weak that it can barely be seen on a network analyzer. Regards Bernd DK1AG AXTAL GmbH Co. KG www.axtal.com -Ursprüngliche Nachricht- Von: time-nuts [mailto:time-nuts-boun...@febo.com] Im Auftrag von Bob Camp Gesendet: Sonntag, 7. September 2014 04:21 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] OCXO Voltage Input? (Bob Camp) Hi Simple answer = crystals are never perfect. Longer winded, but very incomplete answer = A spurious response in a crystal normally refers to a mode that is not one of the “identified” modes of the crystal. An AT has a set of identified modes, an SC has a more complex set of modes. In the case of the AT it would be the fundamental and the odd overtones. In the case of the SC you have the A, B, C modes and their odd overtones. None of those are considered spurious. A spur can come from a lot of different places. One common one is higher order vibrations in a longer dimension face of the resonator. The 183rd overtone of the width of the blank is still a legitimate resonant mode. Another source are modes other than shear (like flex). Deriving a full catalog of all the modes of an arbitrary blank design is a major project. There are only a handful of people out there who are into that sort of thing (as opposed to simply cranking through some formulas). Practical answer = Don’t worry about it. Unless you are building a wide pull VCXO or a wide deviation VCXO (often the same thing) you will never notice them. Bob On Sep 6, 2014, at 9:13 PM, Hal Murray hmur...@megapathdsl.net wrote: kb...@n1k.org said: The biggest problem comes from crystal spurs rather than crystal Q. What's the mechanism for making spurs with a crystal? -- 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] Update on my Arduino GPSDO / NTP server - going atomic
Bill, Since I accidentally let the smoke out of my Due, and I just *happen* to have an UDOO Dual sitting around, I decided to play with it while I wait for a replacement board to come around. UDOO ships an ARM version of Arduino IDE 1.5.4, which is a little bit too old to compile my code properly (I built against 1.5.7), but compiling the project on another machine with 1.5.7 and shipping the .bin to the udoo to upload with bossac works just fine. I removed the call to ether_init() since of course there's no W5100 Ethernet on the udoo. On the i.MX side of the UDOO I have Debian installed (UDOObuntu would work just fine, but it comes with loads and loads of unnecessary crap). First I tested using http://vanheusden.com/time/rpi_gpio_ntp/ which is a user-space daemon that listens for events from a Linux /sys/class/gpio device (Due pin 13 maps to Linux gpio40) and writes to an SHM segment compatible with the ntpd/chrony SHM refclock. That worked just fine, with about 5us jitter most of the time, but you could see that it was occasionally quite a bit higher. Then I worked on getting PPSAPI working. This requires rebuilding the kernel, but turned out to be relatively easy: there's a pps-gpio driver in Linux 3.2 that was easily backported to 3.0 just by applying the patch from LKML, and then it was just a little bit of work to init the device in the UDOO-specific board init function. My changes can be found at https://github.com/arodland/Kernel_Unico/compare/ppsapi if you're interested. With that in place, and the Rb sufficiently warm (I think) I'm seeing between 600ns and 1200ns RMS jitter on the PPS refclock as reported by chrony on the UDOO (pretty good!) and between 3us and 7us RMS jitter on the UDOO as measured over NTP from my desktop with 64-second polling, which is 4 or 5 us better than what I could get with the Due+W5100 combination. I bet at this point half of that figure is coming from instability on the desktop machine itself and nondeterministic ethernet switching delay. I still like the appeal of the bare metal approach, and when I get my new board (Taijiuino, a Due-alike board that routes the SAM3X's Ethernet MAC pins) I'm going to keep going with that, but this is pretty good performance for Linux, I'd say. Andrew On Sat, Sep 6, 2014 at 12:06 PM, Bill Dailey docdai...@gmail.com wrote: Will add it to my list of projects. Will touch bases when I get close. Sent from my iPad On Sep 6, 2014, at 10:18 AM, Andrew Rodland and...@cleverdomain.org wrote: Yes, the source is at http://github.com/arodland/Due-GPS-NTP-Server . It should be able to run just fine on the Due part of an Udoo, but you'll have to come up with a different arrangement for the Ethernet. One way would be to use chip-to-chip SPI to make the i.MX side of the Udoo act more-or-less like the W5100, translating between serial and Ethernet and interrupting the SAM3X when it gets packets. Another way would be to run regular ntpd on Linux (or FreeBSD?) on the i.MX side but give it a custom refclock driver that syncs to the Due (either by locking onto the generated PPS, or by asking the Due to timestamp events and reading the timecode back). If this works well, it could outperform my setup, since the i.MX is clocked quite a bit faster and has its Ethernet MAC on-chip :) Andrew On Sat, Sep 6, 2014 at 12:08 AM, Bill Dailey docdai...@gmail.com wrote: I was wondering if a board like the udoo would help your ntp performance. I have one and would be willing to try this configuration. Have you posted your source? I think I got confused as to who was doing this. I don't have a rubidium but I have a 6T on a breakout and a couple of very good ocxo's (mid 10-13 at 1s) that I could use. I have about 100 projects going on but a project like this has been on the back burner for awhile. I have a couple of furies I could test it against also. Bill Sent from my iPad On Sep 5, 2014, at 2:07 PM, Andrew Rodland and...@cleverdomain.org wrote: After some productive work, and some frustrating weeks spent fighting weird flakiness and needlessly replacing components, only to find that the problems went away after I reseated my main power connector, IT WORKS! Here's where I am now: * Main board: Arduino Due (ATSAM3X ARM Cortex-M3 CPU @ 84MHz) * Oscillator: Symmetricom X72. * GPS: Trimble Resolution T with a cheap Gilsson puck antenna. * Ethernet: Wiznet W5100. The X72 is used to externally clock one of the ARM's hardware timer/counters at 10MHz (I'm not multiplying it up and using it to clock the CPU). The same timer timestamps the rising edge of the PPS using capture mode, jitter free @ 100ns resolution. All the PLL is done digitally using these values and the adjustment is sent to the X72 over serial (DDS, 2 ppt resolution). After about a day's solid running, the PPS phase stays within +/- 100ns as measured on the board itself, even out to a PLL tau of 1 hour, and the frequency adjust
Re: [time-nuts] Update on my Arduino GPSDO / NTP server - going atomic
Cool. I have an udoo quad but am using it as a small mysql server for a medical project that is ongoing. I could just try another sd card. My biggest problem is time. I have about 5 simultaneous official work project, a new company that I am coding on an embedded jetson tk1 (computer vision) and a huge all digital phased array project that is on the back burner until we move (nov1) and get settled. Crazy life here. Keep up the good work... I will let you know when I catch up. Bill Sent from mobile On Sep 10, 2014, at 7:48 PM, Andrew Rodland and...@cleverdomain.org wrote: Bill, Since I accidentally let the smoke out of my Due, and I just *happen* to have an UDOO Dual sitting around, I decided to play with it while I wait for a replacement board to come around. UDOO ships an ARM version of Arduino IDE 1.5.4, which is a little bit too old to compile my code properly (I built against 1.5.7), but compiling the project on another machine with 1.5.7 and shipping the .bin to the udoo to upload with bossac works just fine. I removed the call to ether_init() since of course there's no W5100 Ethernet on the udoo. On the i.MX side of the UDOO I have Debian installed (UDOObuntu would work just fine, but it comes with loads and loads of unnecessary crap). First I tested using http://vanheusden.com/time/rpi_gpio_ntp/ which is a user-space daemon that listens for events from a Linux /sys/class/gpio device (Due pin 13 maps to Linux gpio40) and writes to an SHM segment compatible with the ntpd/chrony SHM refclock. That worked just fine, with about 5us jitter most of the time, but you could see that it was occasionally quite a bit higher. Then I worked on getting PPSAPI working. This requires rebuilding the kernel, but turned out to be relatively easy: there's a pps-gpio driver in Linux 3.2 that was easily backported to 3.0 just by applying the patch from LKML, and then it was just a little bit of work to init the device in the UDOO-specific board init function. My changes can be found at https://github.com/arodland/Kernel_Unico/compare/ppsapi if you're interested. With that in place, and the Rb sufficiently warm (I think) I'm seeing between 600ns and 1200ns RMS jitter on the PPS refclock as reported by chrony on the UDOO (pretty good!) and between 3us and 7us RMS jitter on the UDOO as measured over NTP from my desktop with 64-second polling, which is 4 or 5 us better than what I could get with the Due+W5100 combination. I bet at this point half of that figure is coming from instability on the desktop machine itself and nondeterministic ethernet switching delay. I still like the appeal of the bare metal approach, and when I get my new board (Taijiuino, a Due-alike board that routes the SAM3X's Ethernet MAC pins) I'm going to keep going with that, but this is pretty good performance for Linux, I'd say. Andrew On Sat, Sep 6, 2014 at 12:06 PM, Bill Dailey docdai...@gmail.com wrote: Will add it to my list of projects. Will touch bases when I get close. Sent from my iPad On Sep 6, 2014, at 10:18 AM, Andrew Rodland and...@cleverdomain.org wrote: Yes, the source is at http://github.com/arodland/Due-GPS-NTP-Server . It should be able to run just fine on the Due part of an Udoo, but you'll have to come up with a different arrangement for the Ethernet. One way would be to use chip-to-chip SPI to make the i.MX side of the Udoo act more-or-less like the W5100, translating between serial and Ethernet and interrupting the SAM3X when it gets packets. Another way would be to run regular ntpd on Linux (or FreeBSD?) on the i.MX side but give it a custom refclock driver that syncs to the Due (either by locking onto the generated PPS, or by asking the Due to timestamp events and reading the timecode back). If this works well, it could outperform my setup, since the i.MX is clocked quite a bit faster and has its Ethernet MAC on-chip :) Andrew On Sat, Sep 6, 2014 at 12:08 AM, Bill Dailey docdai...@gmail.com wrote: I was wondering if a board like the udoo would help your ntp performance. I have one and would be willing to try this configuration. Have you posted your source? I think I got confused as to who was doing this. I don't have a rubidium but I have a 6T on a breakout and a couple of very good ocxo's (mid 10-13 at 1s) that I could use. I have about 100 projects going on but a project like this has been on the back burner for awhile. I have a couple of furies I could test it against also. Bill Sent from my iPad On Sep 5, 2014, at 2:07 PM, Andrew Rodland and...@cleverdomain.org wrote: After some productive work, and some frustrating weeks spent fighting weird flakiness and needlessly replacing components, only to find that the problems went away after I reseated my main power connector, IT WORKS! Here's where I am now: * Main board: Arduino Due (ATSAM3X ARM Cortex-M3 CPU @ 84MHz) * Oscillator:
Re: [time-nuts] Update on my Arduino GPSDO / NTP server - going atomic
I apologize. I didn't mean for that last post to go through the list. Sent from my iPad On Sep 10, 2014, at 7:48 PM, Andrew Rodland and...@cleverdomain.org wrote: Bill, Since I accidentally let the smoke out of my Due, and I just *happen* to have an UDOO Dual sitting around, I decided to play with it while I wait for a replacement board to come around. UDOO ships an ARM version of Arduino IDE 1.5.4, which is a little bit too old to compile my code properly (I built against 1.5.7), but compiling the project on another machine with 1.5.7 and shipping the .bin to the udoo to upload with bossac works just fine. I removed the call to ether_init() since of course there's no W5100 Ethernet on the udoo. On the i.MX side of the UDOO I have Debian installed (UDOObuntu would work just fine, but it comes with loads and loads of unnecessary crap). First I tested using http://vanheusden.com/time/rpi_gpio_ntp/ which is a user-space daemon that listens for events from a Linux /sys/class/gpio device (Due pin 13 maps to Linux gpio40) and writes to an SHM segment compatible with the ntpd/chrony SHM refclock. That worked just fine, with about 5us jitter most of the time, but you could see that it was occasionally quite a bit higher. Then I worked on getting PPSAPI working. This requires rebuilding the kernel, but turned out to be relatively easy: there's a pps-gpio driver in Linux 3.2 that was easily backported to 3.0 just by applying the patch from LKML, and then it was just a little bit of work to init the device in the UDOO-specific board init function. My changes can be found at https://github.com/arodland/Kernel_Unico/compare/ppsapi if you're interested. With that in place, and the Rb sufficiently warm (I think) I'm seeing between 600ns and 1200ns RMS jitter on the PPS refclock as reported by chrony on the UDOO (pretty good!) and between 3us and 7us RMS jitter on the UDOO as measured over NTP from my desktop with 64-second polling, which is 4 or 5 us better than what I could get with the Due+W5100 combination. I bet at this point half of that figure is coming from instability on the desktop machine itself and nondeterministic ethernet switching delay. I still like the appeal of the bare metal approach, and when I get my new board (Taijiuino, a Due-alike board that routes the SAM3X's Ethernet MAC pins) I'm going to keep going with that, but this is pretty good performance for Linux, I'd say. Andrew On Sat, Sep 6, 2014 at 12:06 PM, Bill Dailey docdai...@gmail.com wrote: Will add it to my list of projects. Will touch bases when I get close. Sent from my iPad On Sep 6, 2014, at 10:18 AM, Andrew Rodland and...@cleverdomain.org wrote: Yes, the source is at http://github.com/arodland/Due-GPS-NTP-Server . It should be able to run just fine on the Due part of an Udoo, but you'll have to come up with a different arrangement for the Ethernet. One way would be to use chip-to-chip SPI to make the i.MX side of the Udoo act more-or-less like the W5100, translating between serial and Ethernet and interrupting the SAM3X when it gets packets. Another way would be to run regular ntpd on Linux (or FreeBSD?) on the i.MX side but give it a custom refclock driver that syncs to the Due (either by locking onto the generated PPS, or by asking the Due to timestamp events and reading the timecode back). If this works well, it could outperform my setup, since the i.MX is clocked quite a bit faster and has its Ethernet MAC on-chip :) Andrew On Sat, Sep 6, 2014 at 12:08 AM, Bill Dailey docdai...@gmail.com wrote: I was wondering if a board like the udoo would help your ntp performance. I have one and would be willing to try this configuration. Have you posted your source? I think I got confused as to who was doing this. I don't have a rubidium but I have a 6T on a breakout and a couple of very good ocxo's (mid 10-13 at 1s) that I could use. I have about 100 projects going on but a project like this has been on the back burner for awhile. I have a couple of furies I could test it against also. Bill Sent from my iPad On Sep 5, 2014, at 2:07 PM, Andrew Rodland and...@cleverdomain.org wrote: After some productive work, and some frustrating weeks spent fighting weird flakiness and needlessly replacing components, only to find that the problems went away after I reseated my main power connector, IT WORKS! Here's where I am now: * Main board: Arduino Due (ATSAM3X ARM Cortex-M3 CPU @ 84MHz) * Oscillator: Symmetricom X72. * GPS: Trimble Resolution T with a cheap Gilsson puck antenna. * Ethernet: Wiznet W5100. The X72 is used to externally clock one of the ARM's hardware timer/counters at 10MHz (I'm not multiplying it up and using it to clock the CPU). The same timer timestamps the rising edge of the PPS using capture mode, jitter free @ 100ns resolution. All the PLL is done digitally using these values and the
[time-nuts] Help understanding an ADEV
After spending a lot of effort trying to get some useful tuning figures for the PID in my GPSDO engine, I decided to capture the DAC output with my 3456A. And, of course I've made an ADEV plot. If I understand this correctly, it means that there is mostly justnoise out to 2 tau, and an area from about 4-5 tau is mostly noise, as well. Could someone tell me if I have this right? It matches what I'm seeing on the delta plot, and would explain why we couldn't get anything approaching reasonable stability from the OCXO, since the noise is larger than the increments being made to the DAC. I've ordered the PWM version of the PIC, and hopefully, since it's the motor control version (as opposed to the audio version) it will have much better noise performance. The red scatter is the EFC measured at the OCXO in tens of microvolts, and the blue line is the ADEV. I'm using a short shielded twisted-pair with mini-clipsas the probe. Hopefully I've got things scaled properly and have run the test properly. http://evoria.net/AE6RV/TIC/DAC.wander.png Bob - AE6RV ___ 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.
