Re: [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors
Hi Oddly enough, if you use a tantalum electrolytic as C2, it's not very happy in that circuit. Their leakage with low voltages on them can be pretty nasty. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-Henning Kamp Sent: Thursday, January 05, 2012 5:50 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors In message CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18=g...@mail.gmail.com , Azelio Boriani writes: I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning [Some op-amp] -+-R2-+-- || | - C2 | - || +---||---+ R1 | | - C1 - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@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] Thunderbolt? (re simple gpsdo.) capacitors
OK, note taken. Usually large capacitors are not available with tantalum dielectric, it seems that the last is a 1000uF 6.3V. On Fri, Jan 6, 2012 at 6:54 PM, Bob Camp li...@rtty.us wrote: Hi Oddly enough, if you use a tantalum electrolytic as C2, it's not very happy in that circuit. Their leakage with low voltages on them can be pretty nasty. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Poul-Henning Kamp Sent: Thursday, January 05, 2012 5:50 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors In message CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18=g...@mail.gmail.com , Azelio Boriani writes: I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning [Some op-amp] -+-R2-+-- || | - C2 | - || +---||---+ R1 | | - C1 - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@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] Thunderbolt? (re simple gpsdo.)
On Fri, 30 Dec 2011 22:54:26 -0800 Chris Albertson albertson.ch...@gmail.com wrote: I don't count anything with a computer and software inside as simple. My definition of a simple device is a capacitor or a transistor or I guess a single flip-flop or op-amp. A simple controller would some how use about two dozen or less of these kinds of components. I think, then the simplest solution is to use a LEA6-T, programm the second timing output to 8MHz (not 10!), and use a PLL and you get a GPSDO like the one James Millerd designed a few years ago, based on the Jupiter GPS. Here, the only time you need a computer is when you configure the LEA6-T, which can be done using USB or a serial port and the config can be stored in the EEPROM of the LEA. AFAIK the bigest catch here would be the update rate of the timing solution of the LEA and the introduced phase glitches. From what i know, the LEA provdies two modi for the freqency output, one is phase locked to the 1PPS, and the other is frequency locked. This together with the low update times, will require long integration constants for the PLL loop, which might make the thing problematic. Attila Kinal -- Why does it take years to find the answers to the questions one should have asked long ago? ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
Yes almost as long as you include ONE more Resistor, R2 added below. The dual cap thing does not get rid of leakage entirely, but close enough in most cases. That configuration is most useful for slow open loop filters when you want low leakage errors. It may be a bit of an overkill for a closed loop filters when a 10 % leakage would be tolerable. I tested a 10,000 sec TC filter using a 10 meg and 1000 uF, and got under 1% leakage error open loop. ws *** [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors Poul-Henning Kamp phk at phk.freebsd.dk The leakage current noise I measured was way below insignificant when things are properly scaled. Couldn't the double condensor from voltage references trick be used to eliminate the leakage entirely ? [Some op-amp] -+-R2-+-- | | | - | - | | +---||---+ | - - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? Thank you On Thu, Jan 5, 2012 at 9:18 PM, WarrenS warrensjmail-...@yahoo.com wrote: Yes almost as long as you include ONE more Resistor, R2 added below. The dual cap thing does not get rid of leakage entirely, but close enough in most cases. That configuration is most useful for slow open loop filters when you want low leakage errors. It may be a bit of an overkill for a closed loop filters when a 10 % leakage would be tolerable. I tested a 10,000 sec TC filter using a 10 meg and 1000 uF, and got under 1% leakage error open loop. ws *** [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors Poul-Henning Kamp phk at phk.freebsd.dk The leakage current noise I measured was way below insignificant when things are properly scaled. Couldn't the double condensor from voltage references trick be used to eliminate the leakage entirely ? [Some op-amp] -+-R2-+-- | | | - | - | | +---||---+ | - - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
Perhaps the dual cap is a differential implementation of the filter/integrator. ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
... don't know but judging from the very simple ASCII schematic I'll say no because the lower capacitor is grounded. There is some sort of feedback I can't figure out, too simple that schematic. On Thu, Jan 5, 2012 at 11:27 PM, li...@lazygranch.com wrote: Perhaps the dual cap is a differential implementation of the filter/integrator. ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
In message CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18=g...@mail.gmail.com , Azelio Boriani writes: I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning [Some op-amp] -+-R2-+-- || | - C2 | - || +---||---+ R1 | | - C1 - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors
Poul Thanks have been kind of following this thread and the diagram did not make a lot of sense. I figured I missed part of the thread. But this clears it up nicely. Regards Paul. WB8TSL On Thu, Jan 5, 2012 at 5:49 PM, Poul-Henning Kamp p...@phk.freebsd.dkwrote: In message CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18= g...@mail.gmail.com , Azelio Boriani writes: I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning [Some op-amp] -+-R2-+-- || | - C2 | - || +---||---+ R1 | | - C1 - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@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] Thunderbolt? (re simple gpsdo.) capacitors
Thanks. Me too: now I got it, sort of bootstrap and now I see that R2 is needed because the real filter is R2*C2 and the leakage is not totally compensated if C1 has to move to a new value - R*C1R2*C2. On Fri, Jan 6, 2012 at 12:00 AM, paul swed paulsw...@gmail.com wrote: Poul Thanks have been kind of following this thread and the diagram did not make a lot of sense. I figured I missed part of the thread. But this clears it up nicely. Regards Paul. WB8TSL On Thu, Jan 5, 2012 at 5:49 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18= g...@mail.gmail.com , Azelio Boriani writes: I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning [Some op-amp] -+-R2-+-- || | - C2 | - || +---||---+ R1 | | - C1 - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@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] Thunderbolt? (re simple gpsdo.)
Anyone contemplating building an analog loop for a GPSDO should consider that it can be very tricky and expensive to attain great performance. That's why the commercial ones are primarily digital - it puts the most severe performance requirements in the least amount of analog circuitry - the DAC, reference, output filter and buffer circuits. Years ago I had planned to build one using an OCXO and the 1 PPS signal from a Motorola Oncore GPS receiver. I had figured out pretty much the whole thing down to circuitry and critical components, BUT quickly concluded that to hold stability, the entire circuit needed to be ovenized - not hot, just held at constant temperature. There are a lot of tradeoffs involved in the parts - especially the opamps, large integrator caps, and references. Because of the large dynamic range and resolution needed, the component leakage, bias currents, noise, and tempcos were very significant. In my scheme I had to control the 10 MHz OCXO over +/- 2 Hz initially, coarse tuned with selected low TC resistors, then the remainder held with a large integrator. The 10 MHz was to be divided down to 1 PPS and compared to the GPS signal with a digital logarithmic phase detector down to 100 nSec, then an analog interpolator below that. I abandoned the project when I acquired a Z3801A, and was relieved to not have to build all of that stuff and thermally control it too. Even with a mostly digital system like the Z3801A, there are weaknesses in the small analog portion of the circuit that I think can be greatly improved. So, for slightly tweaking an oscillator with a very narrow tuning range, an analog loop is OK, using top notch performance opamps and integrator capacitors, but to outright replace the typical digital system is much more difficult. While it is true that most errors are inside the loop so are averaged and eliminated in the very long term, a lot can happen in the one second between those synchronizing pulses, and over the medium term 1000s of seconds, where each sample of correction signal has only a tiny effect, and the integrator is on its own to hold steady. Ed ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
I have used that trick also for HV supplies when leakage through a capacitor (typically the capacitor used to compensate the HV divider used for regulation) exposed to 10 or 20kV is hard to eliminate. At the time, I did not know it had already been invented... Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Poul-Henning Kamp p...@phk.freebsd.dk Sender: time-nuts-boun...@febo.com Date: Thu, 05 Jan 2012 22:49:55 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors In message CAL8XPmO76XuTETZC=33_v2YWuJGcw8gCvtTDHyae6E4MFb18=g...@mail.gmail.com , Azelio Boriani writes: I have googled extensively trying to find something about the dual capacitor method of reducing the leakage current... nothing found. Please, can you indicate anything for me to learn more? It is very simple: R1 charges C1 to the DC potential and therefore C2 sees (almost) no DC voltage, which means (almost) no leakage current. C2 is still a capacitor for any AC or dV component. I belive I picked this trick up from a datasheet or app-note relating to precision voltage references. Poul-Henning [Some op-amp] -+-R2-+-- || | - C2 | - || +---||---+ R1 | | - C1 - | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@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] Thunderbolt? (re simple gpsdo.)
Hal wrote: Does anybody know anything about the temperature coefficients of large caps? I'm not interested in the frequency shift of the filter as the temperature but the voltage shift due to a fixed charge as the capacitance changes. The common rule of thumb is thousands of ppm per degree C through their normal operating range (i.e., neglecting low temperatures where they are much worse). Here is what Cornell-Dubilier says about the temperature coefficient of capacitance of aluminum electrolytics : The capacitance varies with temperature. This variation itself is dependent to a small extent on the rated voltage and capacitor size. Capacitance increases less than 5% from 25 ºC to the high temperature limit. For devices rated 40 ºC capacitance declines up to 20% at 40 ºC for low-voltage units and up to 40% for high voltage units. Most of the decline is between 20 ºC and 40 ºC. For devices rated 55 ºC capacitance typically declines less than 10% at 40 ºC and less than 20% at 55 ºC. (see http://www.google.com/url?sa=trct=jq=aluminum+electrolytic+%22temperature+coefficient%22source=webcd=1ved=0CEwQFjAAurl=http%3A%2F%2Fwww.cde.com%2Fcatalogs%2FAEappGUIDE.pdfei=MwMDT728Jcfo0QGggpm4Agusg=AFQjCNEZwwiXQYXxoXbC_on3M5MlOh3ypg at p. 7) 5% is 50k ppm; an 85C cap would thus change 50k ppm over 60 degrees C, or a bit less than 1k ppm per degree C. Based on the timing circuits I've seen implemented with aluminum electrolytics, I'd say CDE is being optimistic here. For integrating in an environment where stability of parts in 10e10 or better is desired, you are likely to find that all of the other imperfections of electrolytic capacitors (leakage, noise, dielectric absorption, etc.) will stop you well short of the goal, never mind the tempco of capacitance. You might get by with wet-slug tantalums. 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.
Re: [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors
Hi Using electrolytic caps in timing applications is a bit exciting. Their leakage current changes each time you change the voltage on them. It's enough of a change to significantly impact long time constants. In some cases the capacitance changes with voltage as well. Temperature stability of capacitance for most processes is in the 10 to 20% change over 0 to 50C. Leakage at least doubles every 10C. Many ceramic bypass caps have similar TC and change in cap with voltage issues. NPO ceramics or *good* film capacitors are the stuff you make your analog computer out of. (Yes, I'm old enough that you had to check the course description to see if the computer course was analog or digital...) Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Hal Murray Sent: Monday, January 02, 2012 8:15 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect enough. Does anybody know anything about the temperature coefficients of large caps? I found data for ceramic caps, but when I added electrolytic all I got was lifetime stuff rather than capacitance change with temperature. I'm not interested in the frequency shift of the filter as the temperature but the voltage shift due to a fixed charge as the capacitance changes. -- These are my opinions, not necessarily my employer's. 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] Thunderbolt? (re simple gpsdo.) capacitors
On Tue, Jan 3, 2012 at 9:14 AM, Bob Camp li...@rtty.us wrote: Hi Using electrolytic caps in timing applications is a bit exciting. Their leakage current changes each time you change the voltage on them. It's enough of a change to significantly impact long time constants. In some cases the capacitance changes with voltage as well.. In general you are right. But in this case the electrolytic cap is inside a closed loop so as the temperature changes and the voltage in the cap changes, the loop will correct it, as long the temperature changes slowly compared to how frequently we measure the phase of the PPS signal. You could always place the entire system inside box and control it to a constant temperature. -- Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
Hi No argument there, but this thread has wandered a bit. If you are depending on the capacitor to provide a specific time constant, then you will have issues. If the control loop is not impacted by the changes, then they will track out. Often it's not quite an either / or, but a some of this and some of that. In any case the noise created by the leakage current in an electrolytic will be an issue outside the loop bandwidth and only will be reduced by the available gain... Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson Sent: Tuesday, January 03, 2012 12:35 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors On Tue, Jan 3, 2012 at 9:14 AM, Bob Camp li...@rtty.us wrote: Hi Using electrolytic caps in timing applications is a bit exciting. Their leakage current changes each time you change the voltage on them. It's enough of a change to significantly impact long time constants. In some cases the capacitance changes with voltage as well.. In general you are right. But in this case the electrolytic cap is inside a closed loop so as the temperature changes and the voltage in the cap changes, the loop will correct it, as long the temperature changes slowly compared to how frequently we measure the phase of the PPS signal. You could always place the entire system inside box and control it to a constant temperature. -- Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
this thread has wandered a bit. The thread was originally for Simple... Bottom line is that electrolytic caps can be made to work fine for a SIMPLE analog controller built for home NUT use, Not recommended for space or critical life support applications, or any production thing. Besides putting the crappie RC inside a closed loop the other thing that seems several are missing is to limit the correction range. If one sets up the simple loop to give say a 100 to 1 improvement, then all the other concerns become non-issues. The noise created by the leakage current in an electrolytic will be an issue outside the loop bandwidth and only will be reduced by the available gain... Loop Gain is not a problem when making a frequency lock loop, even with a P only controller, using any kind of phase detector because the gain is infinite. The leakage current noise I measured was way below insignificant when things are properly scaled. Such as when you scale it so you only care about a 1% of 5 volt change and not uv. If you're depending on a specific time constant for a SIMPLE controller using electrolytic caps then the problem is the design and not the caps. If you're want to make a 1e-10 to one correction with a simple controller the problem is not the cap but the configuration and the expectations. But making a 1e-13 correction to a 1e-9 Rb is no problem (1000 to one improvement) Hal Murray Posted: I'm not interested in the frequency shift of the filter as the temperature but the voltage shift due to a fixed charge as the capacitance changes. Interesting question, so I tried it. No effect on the One I tested. I charged a cheapie 1000uf, 50V cap to 5 volts then changed it's temperature which did changed it's capacitance and leakage, but had no effect on it's charge voltage. I guess the charge is not Fixed, so not the same thing as changing the value by paralleling the cap. ws ** [time-nuts] Thunderbolt? (re simple gpsdo.) capacitors Bob Camp lists at rtty.us Hi No argument there, but this thread has wandered a bit. If you are depending on the capacitor to provide a specific time constant, then you will have issues. If the control loop is not impacted by the changes, then they will track out. Often it's not quite an either / or, but a some of this and some of that. In any case the noise created by the leakage current in an electrolytic will be an issue outside the loop bandwidth and only will be reduced by the available gain... Bob *** On Behalf Of Chris Albertson Hi Using electrolytic caps in timing applications is a bit exciting. Their leakage current changes each time you change the voltage on them. It's enough of a change to significantly impact long time constants. In some cases the capacitance changes with voltage as well.. In general you are right. But in this case the electrolytic cap is inside a closed loop so as the temperature changes and the voltage in the cap changes, the loop will correct it, as long the temperature changes slowly compared to how frequently we measure the phase of the PPS signal. You could always place the entire system inside box and control it to a constant temperature. Chris Albertson Redondo Beach, California ___ ___ 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] Thunderbolt? (re simple gpsdo.) capacitors
In message 80B26DC756AA45DD84E4EB9E14B58998@Warcon28Gz, WarrenS writes: The leakage current noise I measured was way below insignificant when things are properly scaled. Really stupid question: Couldn't the double condensor from voltage references trick be used to eliminate the leakage entirely ? [Some op-amp] -++-- || | - | - | | +--||+ | - - | | GND -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Thunderbolt? (re simple gpsdo.)
Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect enough. Does anybody know anything about the temperature coefficients of large caps? I found data for ceramic caps, but when I added electrolytic all I got was lifetime stuff rather than capacitance change with temperature. I'm not interested in the frequency shift of the filter as the temperature but the voltage shift due to a fixed charge as the capacitance changes. -- These are my opinions, not necessarily my employer's. 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] Thunderbolt? (re simple gpsdo.)
On Mon, 02 Jan 2012 17:14:37 -0800, Hal Murray hmur...@megapathdsl.net wrote: Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect enough. Does anybody know anything about the temperature coefficients of large caps? I found data for ceramic caps, but when I added electrolytic all I got was lifetime stuff rather than capacitance change with temperature. I'm not interested in the frequency shift of the filter as the temperature but the voltage shift due to a fixed charge as the capacitance changes. That is not something you are likely to find specified because there is no need to test or guarantee it in the applications that electrolytic capacitors are generally used in. I would also expect problems because of dielectric absorption, leakage, and possibly noise. In the best case, you would probably need to qualify the capacitor yourself. I ended up doing that anyway with a polypropylene film capacitor used in a similar application because we needed to control leakage at high temperatures and that was not something that the manufacturer tested for or guaranteed. In that case, the integrator had a drift below 1 uV/sec at room temperature in a production environment using a 0.47uF polypropylene film capacitor and an equivalent time constant of about 5 seconds. The PC board used guard rings and the summing node was wired into the air although in a good environment that would not have been necessary. With care and the proper environment I think, 100 times better would not be out of the question but I suspect other factors like 1/f noise would become an issue. I think I would try a charge balancing scheme instead of integrating or averaging the output of the phase/frequency detector directly but maybe that is getting away from simple. ___ 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] Thunderbolt? (re simple gpsdo.)
For those who aren't familiar with this trick, it's easy to make a low pass filter in software: X = X*(1-k) + k*new Designing filters seems like an art. What is the frequency response of the above for different values of k? I tend to like FIR filters because I think I understand them better. I think yours is an IIR. It's a simple 1 pole filter. The corner frequency scales with the sample rate. If you have N samples per second and k is 1/K, then the time constant is K/N seconds. So with 1 PPS and an 8 bit shift, you get a time constant of 256 seconds. It's just a trick to add to your collection. It's only advantage is that it doesn't take many CPU cycles. It's just shifts and adds, no multiplies or floating point. I first saw it used to compute round trip times on early networking code. You do have to get the scaling right: if k is right shift by 8 bits, X has to be stored shifted left 8 bits so the right shift doesn't throw away too much info. You may need to store X shifted farther left, depending on the accuracy you need. (Or maybe you don't care about accuracy and don't need to shift.) It may be easier to think of X and a fraction with the binary point on the left of the word. Then instead of storing X shifted left, the question is how wide does X have to be. -- These are my opinions, not necessarily my employer's. 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] Thunderbolt? (re simple gpsdo.)
I too have been mulling over a minimal GPSDO. Has anyone mentioned a PWM DAC? Even a toy microcontroller like the Atmel AVRs can generate 16 bit resolution PWM, which sounds like it would be heaps. As long as the voltage reference is low noise, it does not matter if it drifts slowly, since the control loop adjusting the OCXO frequency will adjust it. Of course you will need a long time constant filter to smooth the PWM, but a 2 pole filter constructed from an opamp will do the job. The micro can also capture the 1PPS from the GPS if it is clocked by the OCXO, and use the value to close the control loop. So a minimal GPSDO looks like a simple microcontroller (I would use Arduino since we use these at work whenever we need to build something in an afternoon) with a filter for a PWM DAC, so one opamp and a few discretes. Of course as I write software for such beasts as a trade I am giving the software a zero cost. On 31 December 2011 06:46, Stanley timen...@n4iqt.com wrote: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Some sort of oscillator with a voltage control. CPU with a timer/counter that can capture the PPS. DAC. Software. How about MSC1200 : http://www.ti.com/lit/ds/symlink/msc1200y3.pdf Stanley ___ 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. -- Tom Harris celephi...@gmail.com ___ 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] Thunderbolt? (re simple gpsdo.)
On 01/01/2012 12:23 PM, Tom Harris wrote: I too have been mulling over a minimal GPSDO. Has anyone mentioned a PWM DAC? Even a toy microcontroller like the Atmel AVRs can generate 16 bit resolution PWM, which sounds like it .. So a minimal GPSDO looks like a simple microcontroller (I would use Arduino since we use these at work whenever we need to build something in an afternoon) with a filter for a PWM DAC, so one opamp and a few discretes. Of course as I write software for such beasts as a trade I am giving the software a zero cost. A 'bike light' sized microcontroller can do the job. Today I would have used something larger, and saved development time. On the other hand, having only room for 512 instructions prevented spending time on non-essential features. http://n1.taur.dk/simplexdo/ I used 8 bit PWM into a two-stage RC filter, making it easier to filter. To get 16 bit resolution I added delta-sigma modulation on top of the PWM. The ATTiny13 is not the right part for the job; It has no input capture. So space- and time consuming tricks are necessary to get cycle-accurate capture. Recently I discovered that some of the microcontrollers in the drawer would do nanosecond capture all on their own, but with a working tbolt, need has been lacking. /Kasper Pedersen ___ 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] Thunderbolt? (re simple gpsdo.)
Hi Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars…. No free lunch. Bob On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: As soon as you say Software the device is no longer simple.Even a microprocessor is a very complex device and so is its development system. The software inside the uP is not simple either if you count the number of possible paths through the code (2 raided to the power of the number of branches.) Yes and no... Software doesn't have to be big, bloated, ugly, and complicated. (But I agree that it often is.) If you have eight if statements you have 2^8 = 256 possible paths through the code. For a hobby application I goes you'd not bother to write up and run 256 test cases. This looks like fun to me, but I like writing that sort of code. Note that it doesn't need an OS or even any libraries. The context for simple wasn't well specified. Does simple refer to design or construction? I think simple means you can explain how it works in a few sentences. And if software is used you have to explain every calculation and decision point. With software design and construction is the same thing if you only build one unit. How good does the GPSDO have to be? (After all, this is time nuts.) What sort of adev at what sort of time scale? I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect enough. What's the input impedance of a VCXO or Rb unit? I assume we will need an op-amp to buffer the filter. I suspect you are right. The ugly problem in this area is that time constant to filter out phase detector noise overlaps the time constant needed to let environmental changes through. That doesn't matter if the filter is analog or digital. If the osc is stable (Rb) filter time constants of 1000s of seconds might make sense. That might help take care of some of the hanging bridges. The new $38 Rb units can only be adjust by RS-232 commands. So you need a digital controller. No choice there. The best oscillator for an analog controller would have to be a high quality ovenized crystal. About the time constants. If you are doing this in software then you can track performance inside the controller and adjust. Seems you shouod be able to tell the controller the tau you need and it should be able to optimize. Once you have a uP then more features are easy to do, like maybe using multiple GPS receivers or maybe fault detection and switching to holdover mode For those who aren't familiar with this trick, it's easy to make a low pass filter in software: X = X*(1-k) + k*new Designing filters seems like an art. What is the frequency response of the above for different values of k? I tend to like FIR filters because I think I understand them better. I think yours is an IIR. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
Hi Actually a minimalist GPSDO *could* be a person looking at a scope and tweaking a pot every so often. It all depends on what the desired result is (how accurate / how automated / how failure resistant). Is simplicity measured by low cost, low parts count, easy to find parts, or easy to work with parts? Do parts I already have (OCXO, Rb, GPS) count or not? Does time matter or just frequency? Is there a that's good enough level (as in do you need a GPSDO at all)? Does design time count / does it need to be an existing design? Without some definition, there really is no way to answer. Bob On Jan 1, 2012, at 6:23 AM, Tom Harris wrote: I too have been mulling over a minimal GPSDO. Has anyone mentioned a PWM DAC? Even a toy microcontroller like the Atmel AVRs can generate 16 bit resolution PWM, which sounds like it would be heaps. As long as the voltage reference is low noise, it does not matter if it drifts slowly, since the control loop adjusting the OCXO frequency will adjust it. Of course you will need a long time constant filter to smooth the PWM, but a 2 pole filter constructed from an opamp will do the job. The micro can also capture the 1PPS from the GPS if it is clocked by the OCXO, and use the value to close the control loop. So a minimal GPSDO looks like a simple microcontroller (I would use Arduino since we use these at work whenever we need to build something in an afternoon) with a filter for a PWM DAC, so one opamp and a few discretes. Of course as I write software for such beasts as a trade I am giving the software a zero cost. On 31 December 2011 06:46, Stanley timen...@n4iqt.com wrote: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Some sort of oscillator with a voltage control. CPU with a timer/counter that can capture the PPS. DAC. Software. How about MSC1200 : http://www.ti.com/lit/ds/symlink/msc1200y3.pdf Stanley ___ 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. -- Tom Harris celephi...@gmail.com ___ 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] Thunderbolt? (re simple gpsdo.)
Jim Williams did this in one of his designs for measuring low frequency reference noise. The large value low leakage wet tantalum capacitor he used was like $400 and it took 24 hours for the dielectric absorption to settle: http://www.linear.com/docs/28585 You can get the necessary time constant using a good 1uF film capacitor with good design and construction in this case. On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp li...@rtty.us wrote: Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars . On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect 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] Thunderbolt? (re simple gpsdo.)
Aren't there op-amp circuits that create a large capacitance? The gyrator? Don David Jim Williams did this in one of his designs for measuring low frequency reference noise. The large value low leakage wet tantalum capacitor he used was like $400 and it took 24 hours for the dielectric absorption to settle: http://www.linear.com/docs/28585 You can get the necessary time constant using a good 1uF film capacitor with good design and construction in this case. On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp li...@rtty.us wrote: Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars . On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect 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. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ 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] Thunderbolt? (re simple gpsdo.)
http://www.falstad.com/circuit/e-capmult.html I did not take the time to analyze... Don David Jim Williams did this in one of his designs for measuring low frequency reference noise. The large value low leakage wet tantalum capacitor he used was like $400 and it took 24 hours for the dielectric absorption to settle: http://www.linear.com/docs/28585 You can get the necessary time constant using a good 1uF film capacitor with good design and construction in this case. On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp li...@rtty.us wrote: Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars . On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect 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. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ 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] Thunderbolt? (re simple gpsdo.)
Hal posted:
For those who aren't familiar with this trick, it's easy to make a low pass
filter in software:
X = X*(1-k) + k*new orX = X - k*X + k*new
OR
Gives exact same results using only one multiply,
New_X = Last_X + k * (New_data - Last_X)
OR
For powers of square root of two 1.414 steps, which is close enough for GPSDO
control loops using only shifts can add:
New_X = Last_X + [ { (New_Data + 1/2* New_Data) - (Last_X + 1/2*
Last_Data) } divided by 2^N ]
I think the main problem in this area is building a low pass filter with a
long time constant.
Not At ALL, That can be the easiest part as long as it is in a CLOSED LOOP
system where accuracy is not very important.
As you stated, with digital filters you can go as slow as you want as long as
you do not let it loose LS_Bits when shifting and adding.
How do I build an analog filter with a time constant that long?
The TC filter is inside a loop so Most all the bad things that slow poor analog
filters do does not matter much at all.
100 meg and 10 uf Tantalum capacitor can work fine as a 0 to +5V, 1000 sec
analog filter inside a loop.
I've found that a 10 Meg resistors and most small, 10 cent ,1000uf caps work
fine for a closed loop 10K sec TC filter.
What's the input impedance of a VCXO or Rb unit? I assume we will need an
op-amp to buffer the filter.
No buffer usually needed, most are pretty Hi_Z, and many are floating inputs
such as the HP10811.
MOST of the time, for SIMPLE the best results are obtained by highly
attenuating the EFC input so high value filter resistors can be used.
The other thing that helps a lot is the less the EFC feedback gain the lower
the RC time constant need be for the same effective loop time constant.
example of simple and high performance:
Say you need a 10,000 second time constant analog filter when using the full
+5 to - 5V EFC range of a disciplined HP10811 osc.
You can get the same 10K sec Loop time constant using a +5 mv to -5 mv EFC
range and a 10 second filter time constant. (and a manual freq offset
adjustment)
Can make that using a couple 20 meg resistors, center taped with a 1uf cap (10
sec TC), connected to the EFC with a 40K ohm to ground (plus a RF bypass cap)
You get a 10,000 sec effective loop Time constant, low noise system that can be
controlled just fine with an 8+ bit dithered Dac, to performance a nut would
want.
There has been many postings of all sorts of possible bottle neck problems that
are true when making a overly complicated Rube Goldberg kind of nut
controller.
BUT for 'SIMPLE' with a little thought and compromise, most of these do not
need to apply, therefore they are not an issue even at the highest performance
levels.
ws
***
[time-nuts] Thunderbolt? (re simple gpsdo.)
Hal Murray hmurray at megapathdsl.net
Sun Jan 1 01:56:46 UTC 2012
As soon as you say Software the device is no longer simple.Even a
microprocessor is a very complex device and so is its development system.
The software inside the uP is not simple either if you count the number of
possible paths through the code (2 raided to the power of the number of
branches.)
Yes and no...
Software doesn't have to be big, bloated, ugly, and complicated. (But I agree
that it often is.)
This looks like fun to me, but I like writing that sort of code. Note that it
doesn't need an OS or even any libraries.
The context for simple wasn't well specified.
Does simple refer to design or construction?
How good does the GPSDO have to be? (After all, this is time nuts.) What sort
of adev at what sort of time scale?
I think the main problem in this area is building a low pass filter with a long
time constant.
The time constant of the filter has to be:
long relative to the noise from the phase detector
short relative to aging of the oscillator
short relative to environmental changes
(so the osc can track temperature and voltage
those changes may be in the PLL system rather than the osc)
If we are starting with PPS (rather than 10KHz), the filter time constant
needs to be 10s or 100s of seconds. How do I build an analog filter with a
time constant that long?
What's the input impedance of a VCXO or Rb unit? I assume we will need an
op-amp to buffer the filter.
The ugly problem in this area is that time constant to filter out phase
detector noise overlaps the time constant needed to let environmental changes
through. That doesn't matter if the filter is analog or digital.
If the osc is stable (Rb) filter time constants of 1000s of seconds might make
sense. That might help take care of some of the hanging bridges.
For those who aren't familiar with this trick, it's easy to make a low pass
filter in software:
X = X*(1-k) + k*new
or
X = X -k*X + k*new
where k is less than one. Smaller k makes a slower filter.
If you pick k as a (negative) power of 2, the multiplies can be done with a
shift so there is nothing complicated
Re: [time-nuts] Thunderbolt? (re simple gpsdo.)
Gyrators are usually used to create impractical inductances or frequency dependant negative resistances but I suppose you could. I do not think you would gain anything though since you would be trading one set of non-ideal behaviors for a different set. This is especially the case since the non-ideal behavior of inductors is almost always worse than the non-ideal behavior of capacitors. For example, you can sometimes avoid large feedback or input resistances by substituting a T-network but offset voltages and voltage noise will be multiplied accordingly. On Sun, 1 Jan 2012 13:52:27 -0700 (MST), Don Latham d...@montana.com wrote: Aren't there op-amp circuits that create a large capacitance? The gyrator? Don David Jim Williams did this in one of his designs for measuring low frequency reference noise. The large value low leakage wet tantalum capacitor he used was like $400 and it took 24 hours for the dielectric absorption to settle: http://www.linear.com/docs/28585 You can get the necessary time constant using a good 1uF film capacitor with good design and construction in this case. On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp li...@rtty.us wrote: Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars . On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect 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. ___ 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] Thunderbolt? (re simple gpsdo.)
Hi For some designs (like a Rb) the time constant may be in the days range…. Even for something simple, you can easily get out to several thousand seconds. You also need low noise past the cutoff time (for short times the cap may help you). That's going to get you into resistor noise and / or op amp noise. All of this will push up the capacitance required. Quick and dirty example: 1 pps comparison setup 10 ns jitter on the GPS ( 1x10^-8 at one second) 1x10^-11 as the desired GPSDO jitter at one second. … you need 1,000X attenuation of the jitter at one second. With a 1 uf cap, that's gets you to pretty noisy resistors. Most TBolt's are quite happy doing the sort of thing in the example. Bob On Jan 1, 2012, at 3:43 PM, David wrote: Jim Williams did this in one of his designs for measuring low frequency reference noise. The large value low leakage wet tantalum capacitor he used was like $400 and it took 24 hours for the dielectric absorption to settle: http://www.linear.com/docs/28585 You can get the necessary time constant using a good 1uF film capacitor with good design and construction in this case. On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp li...@rtty.us wrote: Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars…. On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect 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. ___ 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] Thunderbolt? (re simple gpsdo.)
Hi The answer is (as always) no free lunch. An op amp simulating a capacitor is always going to be performance limited. Different limitations come in with different circuits, but they all suffer from noise / drift / leakage. Put another way - for a long time constant, you are just as good off using the op amp as a buffer and dropping in a giant resistor. Bob On Jan 1, 2012, at 4:22 PM, David wrote: Gyrators are usually used to create impractical inductances or frequency dependant negative resistances but I suppose you could. I do not think you would gain anything though since you would be trading one set of non-ideal behaviors for a different set. This is especially the case since the non-ideal behavior of inductors is almost always worse than the non-ideal behavior of capacitors. For example, you can sometimes avoid large feedback or input resistances by substituting a T-network but offset voltages and voltage noise will be multiplied accordingly. On Sun, 1 Jan 2012 13:52:27 -0700 (MST), Don Latham d...@montana.com wrote: Aren't there op-amp circuits that create a large capacitance? The gyrator? Don David Jim Williams did this in one of his designs for measuring low frequency reference noise. The large value low leakage wet tantalum capacitor he used was like $400 and it took 24 hours for the dielectric absorption to settle: http://www.linear.com/docs/28585 You can get the necessary time constant using a good 1uF film capacitor with good design and construction in this case. On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp li...@rtty.us wrote: Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars…. On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect 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. ___ 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] Thunderbolt? (re simple gpsdo.)
Kasper, I like your style! Small ROM = no inessential features! I shall be studying this code, getting capture working with no capture hardware is a real pain. On 2 January 2012 00:53, Kasper Pedersen time-n...@kasperkp.dk wrote: On 01/01/2012 12:23 PM, Tom Harris wrote: I too have been mulling over a minimal GPSDO. Has anyone mentioned a PWM DAC? Even a toy microcontroller like the Atmel AVRs can generate 16 bit resolution PWM, which sounds like it .. So a minimal GPSDO looks like a simple microcontroller (I would use Arduino since we use these at work whenever we need to build something in an afternoon) with a filter for a PWM DAC, so one opamp and a few discretes. Of course as I write software for such beasts as a trade I am giving the software a zero cost. A 'bike light' sized microcontroller can do the job. Today I would have used something larger, and saved development time. On the other hand, having only room for 512 instructions prevented spending time on non-essential features. http://n1.taur.dk/simplexdo/ I used 8 bit PWM into a two-stage RC filter, making it easier to filter. To get 16 bit resolution I added delta-sigma modulation on top of the PWM. The ATTiny13 is not the right part for the job; It has no input capture. So space- and time consuming tricks are necessary to get cycle-accurate capture. Recently I discovered that some of the microcontrollers in the drawer would do nanosecond capture all on their own, but with a working tbolt, need has been lacking. /Kasper Pedersen ___ 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. -- Tom Harris celephi...@gmail.com ___ 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] Thunderbolt? (re simple gpsdo.)
Hi If you do a quick Google search for insulation resistance you get to: http://www.electrocube.com/support/insulation_resistance.asp or a bunch of similar information. The capacitor it's self (no external resistance at all) has a time constant between it's capacitance and internal leakage. There's nothing the op amp can do to take care of this. Indeed the leakage of the op amp *adds* to the cap's leakage. Unless it's a very good op amp, the op amp leakage will have a noticable negative impact. Bob On Jan 1, 2012, at 3:56 PM, Don Latham wrote: http://www.falstad.com/circuit/e-capmult.html I did not take the time to analyze... Don David Jim Williams did this in one of his designs for measuring low frequency reference noise. The large value low leakage wet tantalum capacitor he used was like $400 and it took 24 hours for the dielectric absorption to settle: http://www.linear.com/docs/28585 You can get the necessary time constant using a good 1uF film capacitor with good design and construction in this case. On Sun, 1 Jan 2012 15:11:04 -0500, Bob Camp li...@rtty.us wrote: Any real world capacitor will have a dielecric with an associated insulation resistance. It's a more money gets better performance sort of thing, but there are indeed limits. A 1000 uF cap that has a good insulation resistance number might cost you more than some new cars…. On Dec 31, 2011, at 11:54 PM, Chris Albertson wrote: On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect 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. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ 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] Thunderbolt? (re simple gpsdo.)
Here is another analog control example based on the quick and dirty example below. It is a simple and Very poor GPSDO Rb design as far as noise jitter goes because of the nonlinear and high Phase detector gain, and high 1e-8 noise jitter on the PPS, but still no problem to do with cheap basic parts. Given: 1) LPRO Rb with a + - 1e-9 range analog tuning range plus an internal freq adj pot with the same range. 2) 1pps GPS control signal with 10 ns noise at 1 second 3) Desired 1e-11 GPSDO jitter at one second 4) Total Attenuation needed from phase detector to EFC input 1000 to 1. Can be a combination of resistor and cap. 5) Use a 74HC74 D Flip-Flop phase detector whose 1ns sensitivity is good enough because it is much less than the 10 ns control signal jitter. 5a) 1 sec control signal to FF clk in, 10MHz divided by 100 using a 74HC390 to the FF D input (100KHz will give a 5us range before jumping a cycle) 6) limit range of fine EFC control input to + - 1e-10 freq change with resistor divider, and use the LPRO's course adj pot for course freq setting. 7) If Rb phase is before the control signal the 5V FF Q_not output will drive the Rb freq 1e10 lower in freq (1ns/10 seconds) 7a) if the Rb phase is later than the control signal, the 0 volts of the FF Q_not output will drive the Rb freq 1e-10 higher. 8) LPRO Rb EFC input Z is 50 Kohm with a 0 to 5V control, designed to be left open when not in use so resistor noise is not an issue (best to add a RF cap to gnd) 9) Output the FF thru a 10 sec low pass prefilter RC using 10K and 1000uf cap to give a 10 sec average of the 10ns phase noise 10) Feed the Rb EFC from this RC thru two 250K ohm resistors in series to give a 10 to one attenuation (500K to 50K) 11) Add the main slow LP filter as desired to the center of the 250K res center tap, with small resistor in series with a big cap. 12) use = 1000uf cap for 100 sec + TC, = 100 to 1 cap attenuation Plus 10 to one resistor attenuation = over all 1000 to one jitter attenuation Maybe no free lunch, but total controller cost can be under a dollar. Note that all the crappy LP filter RCs that many seem to be most concerned about are all Inside a closed loop, so their poor, less than ideal performance does not mater so long as the cap leakage is not so great that they never charge. ws * Hi For some designs (like a Rb) the time constant may be in the days range.. Even for something simple, you can easily get out to several thousand seconds. You also need low noise past the cutoff time (for short times the cap may help you). That's going to get you into resistor noise and / or op amp noise. All of this will push up the capacitance required. Quick and dirty example: 1 pps comparison setup 10 ns jitter on the GPS ( 1x10^-8 at one second) 1x10^-11 as the desired GPSDO jitter at one second. . you need 1,000X attenuation of the jitter at one second. With a 1 uf cap, that's gets you to pretty noisy resistors. Most TBolt's are quite happy doing the sort of thing in the example. Bob ___ 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] Thunderbolt? (re simple gpsdo.)
My FE-5680A and Thunderbolt have been well behaved for the last 16 hours. The Thunderbolt is using 3.00 FW and had its feedback settings optimized by Lady Heather. AMU mask is 7.0. No adjustments were made to the Rb during this run. -- Chuck Forsberg WA7KGX N2469R c...@omen.com www.omen.com Developer of Industrial ZMODEM(Tm) for Embedded Applications Omen Technology Inc The High Reliability Software 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 attachment: Rb60k2.gif___ 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] Thunderbolt? (re simple gpsdo.)
PI controllers can be implemented analog only. For the PPS they need large capacitors that are the equivalent of averaging (sum and accumulate) in a software implemented controller. On Sat, Dec 31, 2011 at 7:54 AM, Chris Albertson albertson.ch...@gmail.comwrote: On Fri, Dec 30, 2011 at 11:46 AM, Stanley timen...@n4iqt.com wrote: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Some sort of oscillator with a voltage control. CPU with a timer/counter that can capture the PPS. DAC. Software. How about MSC1200 : http://www.ti.com/lit/ds/symlink/msc1200y3.pdf I don't count anything with a computer and software inside as simple. My definition of a simple device is a capacitor or a transistor or I guess a single flip-flop or op-amp. A simple controller would some how use about two dozen or less of these kinds of components. Home heating thermostats can be simple of complex. Some use LCD displays and a computer. Other have a simple bimetallic spring inside. If this CAN'T be done. And if a computer is really required. I'm going to go all out and use a real computer. Something that can run an operating system and talk on the network. Here is an example of what I mean http://www.embeddedarm.com/products/board-detail.php?tab=optionsproduct=TS-7550# No one really wants a device that connects to a computer over a serial port. That was 20 years ago. The above board can host a web site and log data to a USB thumb drive and burns less then 2W of power But for now I'm looking for a controller that is much more like the bimetallic spring thermostat. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
In my opinion you have to look at it from the point of application. Hopefully I will be able to share the test results soon. For us DNL is key, INL is specked over the full range and since we use it in a filter application, based on the data that I have, can be ignored. In a Rb application I use 1.5 E-14 steps with a total range of 1 E-9, with OCXO's the steps are 1.5 E-13 and rage 1 E-8. In some applications I use smaller step sizes on the OCXO at the expense of range. Some OCXO's aging allow using 1.5 E -14. Do not forget that step sizes are 61 uV and take that into consideration when you look at the temperature specs. I also use it in an environment where temperature is better than + - .2 C. The other nice thing about the 1655 is that you have a reference output that is perfect for setting output range and even changing the output to + -. In a message dated 12/30/2011 9:48:38 P.M. Eastern Standard Time, davidwh...@gmail.com writes: Did you test the LTC1655 INL? The data sheet says plus or minus 20 counts maximum. I suspect Linear Technology designed those low DNL high INL parts for just this sort of application where only monotonic behavior really matters. Their equivalent current output DAC costs about twice as much not including a precision transimpedance amplifier but has an INL specification of plus or minus 1 count. Every couple years I consider the design of a digitally adjusted oscillator and do a search for likely parts. I wonder if it would be more cost effective to use an instrumentation ADC to correct a less expensive DAC design like one based on a PWM. On Fri, 30 Dec 2011 17:48:24 -0500 (EST), ewkeh...@aol.com wrote: Over the last two years along with two list members that may want to pipe in, I have spend a large amount of time on D/A's and we went as far as developing a test board using the LTC 2440 and testing numerous D/A's taking in to consideration performance, solderability, cost, availability and the winner is LTC 1655 by a long shot, is even available in a DIP with 16 bits more than you need for any Rb and if you want 20 bits, dithering is an option. My testing consistently shows with OCXO's aging that will in most cases allow operation of an OCXO for 3 years with out intervention. To top it off the LTC1655 cost less than $ 10. Testing the old AD 1861 was an eye opener but considering what its purpose was and its time the best choice. Bert In a message dated 12/30/2011 4:24:37 P.M. Eastern Standard Time, timen...@n4iqt.com writes: The DAC and it's voltage reference looks to be the weak link in the digital control and the simple goal. The CPU I mentioned before on closer look doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure you can find it in the same package as the CPU. The cheap Rb standards with digital control would not need a DAC and maybe this points to a simpler GPSDO that doesn't control the XO with analog but corrects it with a DDS but again finding them both in one chip is the problem. I have seen OCXO and DAC in the same package and even the DDS and OCXO combined but they didn't fit the simple goal. Not even sure how good they were. I know they are hard to find. Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
Chris Here is a GPSDO I built that better fits Your definition of Simple. I used this as my freq standard before getting a TBolt. 1) Feed the PPS output of an oncore GPS timing engine which has 1 Hz or better yet 100 Hz output to the clk of a D FlipFlop (74HC74) 2) Feed the FF's D from a 10 MHz osc which has been divided down to 100KHz or less using 74HC390. The FF output shows if the Phase of the Osc is greater or less than the GPS signal and the FF will toggle back and forth when the phases are near equal due to the typical 40 ns jitter on the GPS pulse signal. 3) Add a RC filter to the FF output using a big cap, so the voltage out of the RC filter is 0 to 5 volts depending on the duty cycle of the FF. (A small R in series with the cap will help stabilize it if a real Big cap is used). 4) Feed the filtered analog FF output voltage (No buffering necessary) to the EFC of an 10 MHz osc that has its EFC input desensitized with a couple of Rs and has been set to be real near 10 MHz at the nominal analog FF's 2.5 volts output using the Osc's mechanical tuning and/or add a fine freq adj pot. A couple basic ICs and a few Rs and Cs and you're done. This makes a basic PI controller that will cause the 10MHz osc to track the GPS PPS. The less you make the Osc's EFC tuning range the better this works, and Once it is tracking you can fine tune the freq adj pot every now and then to keep the Filtered FF voltage at near 2.5 volts if the Osc tends to drift outside of the control range. Not very high tech and there are Lots of possible ways to add more parts to improve it further, depending on what your goals are and how much you want to learn about GPSDO and PID control loops. If the definition of simple is less parts and more programming you can replace all the active parts with a simple PIC and get better performance by controlling the Osc's EFC using a software PID and PWM with an external RC filter as the Dac. ws Chris Albertson albertson.chris at gmail.com Sat Dec 31 06:01:38 UTC 2011 On Fri, Dec 30, 2011 at 10:16 AM, Hal Murray hmurray at megapathdsl.net wrote: Software. As soon as you say Software the device is no longer simple.Even a microprocessor is a very complex device and so is its development system. The software inside the uP is not simple either if you count the number of possible paths through the code (2 raided to the power of the number of branches.) I have nothing against software, that is what I do for a living, every day. But you can't count a uP with software indise as simple. And the point of this exercise is to find the simplest thing that can still work. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
I think this is the simplest design that can still work, just one flip flop, divider and a capacitor. What level of performance did you get?I think it depends on how big the integrating capacitor is and how stable the VCXO is. I guess if you switched to using the t-bolt the performance was not as good as a t-bolt. On Sat, Dec 31, 2011 at 10:23 AM, WarrenS warrensjmail-...@yahoo.comwrote: Chris Here is a GPSDO I built that better fits Your definition of Simple. I used this as my freq standard before getting a TBolt. 1) Feed the PPS output of an oncore GPS timing engine which has 1 Hz or better yet 100 Hz output to the clk of a D FlipFlop (74HC74) 2) Feed the FF's D from a 10 MHz osc which has been divided down to 100KHz or less using 74HC390. The FF output shows if the Phase of the Osc is greater or less than the GPS signal and the FF will toggle back and forth when the phases are near equal due to the typical 40 ns jitter on the GPS pulse signal. 3) Add a RC filter to the FF output using a big cap, so the voltage out of the RC filter is 0 to 5 volts depending on the duty cycle of the FF. (A small R in series with the cap will help stabilize it if a real Big cap is used). 4) Feed the filtered analog FF output voltage (No buffering necessary) to the EFC of an 10 MHz osc that has its EFC input desensitized with a couple of Rs and has been set to be real near 10 MHz at the nominal analog FF's 2.5 volts output using the Osc's mechanical tuning and/or add a fine freq adj pot... Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
Chris posted: What level of performance did you get? Correct it depends on what parts you use and how nutty you want to get. So much also depends on how you define performance, and where you want to compromise. Compared to WWV and WWVB it was much better, Compared to a correctly set up TBolt much worse. In a NUT-Shell, It is good of enough for most any REAL non-Nut application. Ball park numbers: Freq error of 1e-8 is simple, 1e-9 is easy, 1e-11 gets hard without some good parts and lots of care to details. Besides the GPS engine and the Osc, The time period the freq is averaged over is an important factor, because of the jitter. If you do not loose sync, like all GPSDO, over a long enough time period of many days or weeks, it is good enough to check and calibrate ANY Osc, because it can be set up so that there is NO long term accumulative drift, just short term freq jitter. just one flip-flop, divider and a capacitor. AND some resistors I'm looking for a controller that is much more like the bimetallic spring thermostat. For a Bang bang type two state controller like your bimetallic example, you don't even need the cap which is added to filter out freq jitter. Take out the filter cap, scale and adjust things right and what it does is if the freq is less than the GPS, when the FF toggles it will raise the freq above the GPS and then when the phase matches, it will toggle back and lower the freq below the GPS. This will continue forever keeping the AVERAGE Osc Freq dead nuts on bouncing back and forth between a couple frequencies in what then becomes a PWM like function of the OSC bouncing between two frequencies, one higher and one lower than 10.000 MHz. The freq step size and jitter is a function of the resistor divider used and the EFC sensitivity. The PWM cycle rate depends on freq step size, the speed of the PPS signal, the osc divider used and GPS PPS phase noise. Lots of other uses for this type of D FF as a basic ns hi-low Phase detector for low freq signals. Remove the EFC feedback, Reduce the 100 to 1 divider to two or so and you can use this to measure and/or manually set a Rb Osc to be on frequency if you have an accurate 1PPS signal. ws [time-nuts] Thunderbolt? (re simple gpsdo.) Chris Albertson albertson.chris at gmail.com Sat Dec 31 20:34:14 UTC 2011 I think this is the simplest design that can still work, just one flip flop, divider and a capacitor. What level of performance did you get?I think it depends on how big the integrating capacitor is and how stable the VCXO is. I guess if you switched to using the t-bolt the performance was not as good as a t-bolt. On Sat, Dec 31, 2011 at 10:23 AM, WarrenS warrensjmail-one at yahoo.comwrote: Chris Here is a GPSDO I built that better fits Your definition of Simple. I used this as my freq standard before getting a TBolt. 1) Feed the PPS output of an oncore GPS timing engine which has 1 Hz or better yet 100 Hz output to the clk of a D FlipFlop (74HC74) 2) Feed the FF's D from a 10 MHz osc which has been divided down to 100KHz or less using 74HC390. The FF output shows if the Phase of the Osc is greater or less than the GPS signal and the FF will toggle back and forth when the phases are near equal due to the typical 40 ns jitter on the GPS pulse signal. 3) Add a RC filter to the FF output using a big cap, so the voltage out of the RC filter is 0 to 5 volts depending on the duty cycle of the FF. (A small R in series with the cap will help stabilize it if a real Big cap is used). 4) Feed the filtered analog FF output voltage (No buffering necessary) to the EFC of an 10 MHz osc that has its EFC input desensitized with a couple of Rs and has been set to be real near 10 MHz at the nominal analog FF's 2.5 volts output using the Osc's mechanical tuning and/or add a fine freq adj pot... Chris Albertson Redondo Beach, California snip Home heating thermostats can be simple of complex. Some use LCD displays and a computer. Other have a simple bimetallic spring inside. But for now I'm looking for a controller that is much more like the bimetallic spring thermostat. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
OTH, if it's an OCXO, then the thermal time constants can be made large thermos bottles, etc.? Don WarrenS Chris posted: What level of performance did you get? Correct it depends on what parts you use and how nutty you want to get. So much also depends on how you define performance, and where you want to compromise. Compared to WWV and WWVB it was much better, Compared to a correctly set up TBolt much worse. In a NUT-Shell, It is good of enough for most any REAL non-Nut application. Ball park numbers: Freq error of 1e-8 is simple, 1e-9 is easy, 1e-11 gets hard without some good parts and lots of care to details. Besides the GPS engine and the Osc, The time period the freq is averaged over is an important factor, because of the jitter. If you do not loose sync, like all GPSDO, over a long enough time period of many days or weeks, it is good enough to check and calibrate ANY Osc, because it can be set up so that there is NO long term accumulative drift, just short term freq jitter. just one flip-flop, divider and a capacitor. AND some resistors I'm looking for a controller that is much more like the bimetallic spring thermostat. For a Bang bang type two state controller like your bimetallic example, you don't even need the cap which is added to filter out freq jitter. Take out the filter cap, scale and adjust things right and what it does is if the freq is less than the GPS, when the FF toggles it will raise the freq above the GPS and then when the phase matches, it will toggle back and lower the freq below the GPS. This will continue forever keeping the AVERAGE Osc Freq dead nuts on bouncing back and forth between a couple frequencies in what then becomes a PWM like function of the OSC bouncing between two frequencies, one higher and one lower than 10.000 MHz. The freq step size and jitter is a function of the resistor divider used and the EFC sensitivity. The PWM cycle rate depends on freq step size, the speed of the PPS signal, the osc divider used and GPS PPS phase noise. Lots of other uses for this type of D FF as a basic ns hi-low Phase detector for low freq signals. Remove the EFC feedback, Reduce the 100 to 1 divider to two or so and you can use this to measure and/or manually set a Rb Osc to be on frequency if you have an accurate 1PPS signal. ws [time-nuts] Thunderbolt? (re simple gpsdo.) Chris Albertson albertson.chris at gmail.com Sat Dec 31 20:34:14 UTC 2011 I think this is the simplest design that can still work, just one flip flop, divider and a capacitor. What level of performance did you get?I think it depends on how big the integrating capacitor is and how stable the VCXO is. I guess if you switched to using the t-bolt the performance was not as good as a t-bolt. On Sat, Dec 31, 2011 at 10:23 AM, WarrenS warrensjmail-one at yahoo.comwrote: Chris Here is a GPSDO I built that better fits Your definition of Simple. I used this as my freq standard before getting a TBolt. 1) Feed the PPS output of an oncore GPS timing engine which has 1 Hz or better yet 100 Hz output to the clk of a D FlipFlop (74HC74) 2) Feed the FF's D from a 10 MHz osc which has been divided down to 100KHz or less using 74HC390. The FF output shows if the Phase of the Osc is greater or less than the GPS signal and the FF will toggle back and forth when the phases are near equal due to the typical 40 ns jitter on the GPS pulse signal. 3) Add a RC filter to the FF output using a big cap, so the voltage out of the RC filter is 0 to 5 volts depending on the duty cycle of the FF. (A small R in series with the cap will help stabilize it if a real Big cap is used). 4) Feed the filtered analog FF output voltage (No buffering necessary) to the EFC of an 10 MHz osc that has its EFC input desensitized with a couple of Rs and has been set to be real near 10 MHz at the nominal analog FF's 2.5 volts output using the Osc's mechanical tuning and/or add a fine freq adj pot... Chris Albertson Redondo Beach, California snip Home heating thermostats can be simple of complex. Some use LCD displays and a computer. Other have a simple bimetallic spring inside. But for now I'm looking for a controller that is much more like the bimetallic spring thermostat. Chris Albertson Redondo Beach, California ___ 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. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com
Re: [time-nuts] Thunderbolt? (re simple gpsdo.)
As soon as you say Software the device is no longer simple.Even a microprocessor is a very complex device and so is its development system. The software inside the uP is not simple either if you count the number of possible paths through the code (2 raided to the power of the number of branches.) Yes and no... Software doesn't have to be big, bloated, ugly, and complicated. (But I agree that it often is.) This looks like fun to me, but I like writing that sort of code. Note that it doesn't need an OS or even any libraries. The context for simple wasn't well specified. Does simple refer to design or construction? How good does the GPSDO have to be? (After all, this is time nuts.) What sort of adev at what sort of time scale? I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? What's the input impedance of a VCXO or Rb unit? I assume we will need an op-amp to buffer the filter. The ugly problem in this area is that time constant to filter out phase detector noise overlaps the time constant needed to let environmental changes through. That doesn't matter if the filter is analog or digital. If the osc is stable (Rb) filter time constants of 1000s of seconds might make sense. That might help take care of some of the hanging bridges. For those who aren't familiar with this trick, it's easy to make a low pass filter in software: X = X*(1-k) + k*new or X = X -k*X + k*new where k is less than one. Smaller k makes a slower filter. If you pick k as a (negative) power of 2, the multiplies can be done with a shift so there is nothing complicated with making filters with a very long time constant. (You may have to use multi-precision arithmetic, but that's not a big deal.) -- These are my opinions, not necessarily my employer's. 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] Thunderbolt? (re simple gpsdo.)
On Sat, 31 Dec 2011 17:56:46 -0800, Hal Murray hmur...@megapathdsl.net wrote: This looks like fun to me, but I like writing that sort of code. Note that it doesn't need an OS or even any libraries. Both designs look fun to me but for different reasons. The analog design requires attention to leakage and noise while the digital design requires high resolution, good DNL, and attention to cycle accurate counting. My ongoing notebook doodles are tending toward using a simple PIC as a cycle accurate frequency comparator and high resolution low frequency oscillator to drive a high resolution frequency to voltage converter. The part I have not figured out is measuring phase below one cycle without frequency multiplication. There must be a better way than doing a time to voltage conversion. I figure I could get better than 17 bits of INL and 20 bits of DNL for the OCXO control signal. The context for simple wasn't well specified. Does simple refer to design or construction? I would say that simple means diagnosis can be performed with a multimeter and oscilloscope and all parts are user replaceable without any programming. I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Use op-amp integrators and pay careful attention to leakage. Because of the long time constant involved, tuning it will be arduous. If noise is a problem, it might be worth using a discrete FET differential amplifier input stage. The phase detector should probably be disconnected when GPS lock is lost to prevent integrator windup. A fast time constant mode would make for a faster lock. I think a dual phase/frequency detector could be used to indicate when a lock has been achieved. What's the input impedance of a VCXO or Rb unit? I assume we will need an op-amp to buffer the filter. I would probably drive it directly from an op-amp integrator output. The ugly problem in this area is that time constant to filter out phase detector noise overlaps the time constant needed to let environmental changes through. That doesn't matter if the filter is analog or digital. In a state variable filter you can adjust the filter cutoff by adjusting the integrator gain. I did something like this in a low noise chopper stabilized amplifier that I designed where I adjusted the integrator time constant via the gain for lowest output noise and amazingly enough, it ended up matching the bipolar amplifier noise corner frequency very closely. When set too high, the broadband noise from the chopper stabilized amplifier rose and when set too low, the 1/f noise from the bipolar amplifier rose. The whole thing worked well enough that I could measure the resistance of a piece of wire from its Johnson noise. If the osc is stable (Rb) filter time constants of 1000s of seconds might make sense. That might help take care of some of the hanging bridges. For those who aren't familiar with this trick, it's easy to make a low pass filter in software: X = X*(1-k) + k*new or X = X -k*X + k*new where k is less than one. Smaller k makes a slower filter. If you pick k as a (negative) power of 2, the multiplies can be done with a shift so there is nothing complicated with making filters with a very long time constant. (You may have to use multi-precision arithmetic, but that's not a big deal.) Would you measure the differential phase and then update the filter and output every second? ___ 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] Thunderbolt? (re simple gpsdo.)
On Sat, Dec 31, 2011 at 5:56 PM, Hal Murray hmur...@megapathdsl.net wrote: As soon as you say Software the device is no longer simple.Even a microprocessor is a very complex device and so is its development system. The software inside the uP is not simple either if you count the number of possible paths through the code (2 raided to the power of the number of branches.) Yes and no... Software doesn't have to be big, bloated, ugly, and complicated. (But I agree that it often is.) If you have eight if statements you have 2^8 = 256 possible paths through the code. For a hobby application I goes you'd not bother to write up and run 256 test cases. This looks like fun to me, but I like writing that sort of code. Note that it doesn't need an OS or even any libraries. The context for simple wasn't well specified. Does simple refer to design or construction? I think simple means you can explain how it works in a few sentences. And if software is used you have to explain every calculation and decision point. With software design and construction is the same thing if you only build one unit. How good does the GPSDO have to be? (After all, this is time nuts.) What sort of adev at what sort of time scale? I think the main problem in this area is building a low pass filter with a long time constant. The time constant of the filter has to be: long relative to the noise from the phase detector short relative to aging of the oscillator short relative to environmental changes (so the osc can track temperature and voltage those changes may be in the PLL system rather than the osc) If we are starting with PPS (rather than 10KHz), the filter time constant needs to be 10s or 100s of seconds. How do I build an analog filter with a time constant that long? Time constant is just R*C. If you have a 1000uF cap and a 1K resistor you have 1 second. In theory you could build 100s just by using a 100K resistor but I think real world components are not perfect enough. What's the input impedance of a VCXO or Rb unit? I assume we will need an op-amp to buffer the filter. I suspect you are right. The ugly problem in this area is that time constant to filter out phase detector noise overlaps the time constant needed to let environmental changes through. That doesn't matter if the filter is analog or digital. If the osc is stable (Rb) filter time constants of 1000s of seconds might make sense. That might help take care of some of the hanging bridges. The new $38 Rb units can only be adjust by RS-232 commands. So you need a digital controller. No choice there. The best oscillator for an analog controller would have to be a high quality ovenized crystal. About the time constants. If you are doing this in software then you can track performance inside the controller and adjust. Seems you shouod be able to tell the controller the tau you need and it should be able to optimize. Once you have a uP then more features are easy to do, like maybe using multiple GPS receivers or maybe fault detection and switching to holdover mode For those who aren't familiar with this trick, it's easy to make a low pass filter in software: X = X*(1-k) + k*new Designing filters seems like an art. What is the frequency response of the above for different values of k? I tend to like FIR filters because I think I understand them better. I think yours is an IIR. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
How can you tell that your GPSDO consistently beats the TBolt? On Fri, Dec 30, 2011 at 5:58 AM, Mark Spencer mspencer12...@yahoo.cawrote: Yes that is correct. I have one of the units made by James Miller G3RUH. I had hoped to build some something along these lines on my own, but the Jupiter gps modules I acquired didn't actually have a 10 kHz output. Also my comment re the adev is for the 10 MHz output. I've never looked at the one pps output. Sent from my iPad On 2011-12-29, at 8:45 PM, Richard W. Solomon w1...@earthlink.net wrote: I think you are talking about the G3RUH/N1JEZ design. I have built three of them and they work very well. 73 es HNY, Dick, W1KSZ -Original Message- From: Mark Spencer mspencer12...@yahoo.ca Sent: Dec 29, 2011 9:24 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. My first gpsdo was a manufactured version of this concept and it consistently beats my thunder bolt from an adev perspective and there is nothing to tweak (: Sent from my iPad On 2011-12-29, at 6:35 PM, Chris Albertson albertson.ch...@gmail.com wrote: The era of cheap Thunderbolts appears to be history. What is the simplest GPSDO you can build? There are many designs around but when the T-Bolts came out I think people lost interesting building. I think something very simple could work. If your local oscillator is at all decent it will not loose or gain full cycle in one second. So I think you only need to compare the phase of the oscillator and the PPS. Would an analog controller work? I do software all day every day at work so it would be fun to build an analog computer for a change. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
Do not forget that the thunderbolt was not designed to be the best GPSDO ever, it was designed to meet a set of requirements that include a certain stability in and out of holdover over a certain temperature range and it does that quite well. If you do not need holdover stability, you can come up with a simpler device with equivalent performance. I am not sure you can do that for what a Thunderbolt costs on eBay if you have to buy all the parts. On the other hand, you are likely to learn quite a bit more making your own. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Mark Spencer mspencer12...@yahoo.ca Sender: time-nuts-boun...@febo.com Date: Thu, 29 Dec 2011 20:24:34 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. My first gpsdo was a manufactured version of this concept and it consistently beats my thunder bolt from an adev perspective and there is nothing to tweak (: Sent from my iPad On 2011-12-29, at 6:35 PM, Chris Albertson albertson.ch...@gmail.com wrote: The era of cheap Thunderbolts appears to be history. What is the simplest GPSDO you can build? There are many designs around but when the T-Bolts came out I think people lost interesting building. I think something very simple could work. If your local oscillator is at all decent it will not loose or gain full cycle in one second. So I think you only need to compare the phase of the oscillator and the PPS. Would an analog controller work? I do software all day every day at work so it would be fun to build an analog computer for a change. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
On Thu, Dec 29, 2011 at 8:24 PM, Mark Spencer mspencer12...@yahoo.ca wrote: One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. I just finished reading about that one. It requires no longer available GPS reciever. Maybe I should r-phrase the question: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Half of the reason for the question is academic. Then if a simple enough design presented itself it would be fun to try it. The simplest design I can think of now is based on a flip-flop. The PPS sets' the FF and the next raising edge of the local oscillator resets it. (The local oscillator might need to be divided down or a slower 1Mhz oscillator used so the FF remains on for a reasonable time.) Next the FF gates a current source to a capacitor. The voltage in the cap is amplified and controls the local oscillator frequency via a low pas filter. Likely the low pass filter would be an active device that we call an integrator You need to discharge the cap for the next cycle. One could rig a one-shoot timer to discharge the cap. Actually there are about four states that need to be cycled every second. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
I currently use an HP5370B with a gpib interface to compare the 10 Mhz output of each unit to another reference, and process the time interval data to produce adev plots. My current reference is an fts 1050 and I'm confident it is beating it's typical adev spec of 1e-12 at 100 seconds. Regards Mark S -- On Fri, 30 Dec, 2011 6:11 AM EST Azelio Boriani wrote: How can you tell that your GPSDO consistently beats the TBolt? On Fri, Dec 30, 2011 at 5:58 AM, Mark Spencer mspencer12...@yahoo.cawrote: Yes that is correct. I have one of the units made by James Miller G3RUH. I had hoped to build some something along these lines on my own, but the Jupiter gps modules I acquired didn't actually have a 10 kHz output. Also my comment re the adev is for the 10 MHz output. I've never looked at the one pps output. Sent from my iPad On 2011-12-29, at 8:45 PM, Richard W. Solomon w1...@earthlink.net wrote: I think you are talking about the G3RUH/N1JEZ design. I have built three of them and they work very well. 73 es HNY, Dick, W1KSZ -Original Message- From: Mark Spencer mspencer12...@yahoo.ca Sent: Dec 29, 2011 9:24 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. My first gpsdo was a manufactured version of this concept and it consistently beats my thunder bolt from an adev perspective and there is nothing to tweak (: Sent from my iPad On 2011-12-29, at 6:35 PM, Chris Albertson albertson.ch...@gmail.com wrote: The era of cheap Thunderbolts appears to be history. What is the simplest GPSDO you can build? There are many designs around but when the T-Bolts came out I think people lost interesting building. I think something very simple could work. If your local oscillator is at all decent it will not loose or gain full cycle in one second. So I think you only need to compare the phase of the oscillator and the PPS. Would an analog controller work? I do software all day every day at work so it would be fun to build an analog computer for a change. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
Yes, it can be done based on a PPS only timing. You must design a PI (maybe PID) regulator: the EFC must stay steady when the phase difference between the two PPSes is zero (integral action). Then you must move the EFC (when there is a difference) proportionally with the difference itself and only a small part of the difference drives the integrator to increment/decrement the new steady EFC level. When the difference is again zero the proportinal part is gone and remains the small amount of correction for the integral part. There is a gain for the integral action (samll) and a gain for the porportional action (should be large, but to be evaluated). On Fri, Dec 30, 2011 at 6:26 PM, Chris Albertson albertson.ch...@gmail.comwrote: On Thu, Dec 29, 2011 at 8:24 PM, Mark Spencer mspencer12...@yahoo.ca wrote: One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. I just finished reading about that one. It requires no longer available GPS reciever. Maybe I should r-phrase the question: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Half of the reason for the question is academic. Then if a simple enough design presented itself it would be fun to try it. The simplest design I can think of now is based on a flip-flop. The PPS sets' the FF and the next raising edge of the local oscillator resets it. (The local oscillator might need to be divided down or a slower 1Mhz oscillator used so the FF remains on for a reasonable time.) Next the FF gates a current source to a capacitor. The voltage in the cap is amplified and controls the local oscillator frequency via a low pas filter. Likely the low pass filter would be an active device that we call an integrator You need to discharge the cap for the next cycle. One could rig a one-shoot timer to discharge the cap. Actually there are about four states that need to be cycled every second. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
There is no reason you can not do that. It is tricky because the low comparison frequency limits the loop bandwidth like any sampled data system and the analog requirements for the low frequency design become an issue do to leakage and the impedance levels needed. The long time constants involved could make tuning the loop response tricky. I wonder though how much of a problem jitter in the GPS 1pps signal would be. I understand that some receivers are useless for this type of application because of excessive jitter. Would something like a Garmin 16x or 18x work? On Fri, 30 Dec 2011 09:26:52 -0800, Chris Albertson albertson.ch...@gmail.com wrote: On Thu, Dec 29, 2011 at 8:24 PM, Mark Spencer mspencer12...@yahoo.ca wrote: One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. I just finished reading about that one. It requires no longer available GPS reciever. Maybe I should r-phrase the question: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Half of the reason for the question is academic. Then if a simple enough design presented itself it would be fun to try it. The simplest design I can think of now is based on a flip-flop. The PPS sets' the FF and the next raising edge of the local oscillator resets it. (The local oscillator might need to be divided down or a slower 1Mhz oscillator used so the FF remains on for a reasonable time.) Next the FF gates a current source to a capacitor. The voltage in the cap is amplified and controls the local oscillator frequency via a low pas filter. Likely the low pass filter would be an active device that we call an integrator You need to discharge the cap for the next cycle. One could rig a one-shoot timer to discharge the cap. Actually there are about four states that need to be cycled every second. ___ 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] Thunderbolt? (re simple gpsdo.)
What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Some sort of oscillator with a voltage control. CPU with a timer/counter that can capture the PPS. DAC. Software. Drive the CPU from the osc so you can count cycles between PPS pulses. Use the DAC to adjust the frequency. Build a low pass filter in software. The DAC may be the tricky part. You would like lots of bits, but it also has to be stable. With a given DAC, you can get finer control by trading off range. -- These are my opinions, not necessarily my employer's. 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] Thunderbolt? (re simple gpsdo.)
On a related note is anyone aware of PC controlled (Ie. RS232 or maybe GPIB ?) DAC's that would be suitable for this type of application ? I've also contemplated simply using the DAC of a TBolt but it would seem to be waste of a Tbolt. I'm thinking along the lines of something that might acquired used on an auction site. --- On Fri, 12/30/11, Hal Murray hmur...@megapathdsl.net wrote: From: Hal Murray hmur...@megapathdsl.net Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) To: Discussion of precise time and frequency measurement time-nuts@febo.com Received: Friday, December 30, 2011, 1:16 PM What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Some sort of oscillator with a voltage control. CPU with a timer/counter that can capture the PPS. DAC. Software. Drive the CPU from the osc so you can count cycles between PPS pulses. Use the DAC to adjust the frequency. Build a low pass filter in software. The DAC may be the tricky part. You would like lots of bits, but it also has to be stable. With a given DAC, you can get finer control by trading off range. -- These are my opinions, not necessarily my employer's. 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] Thunderbolt? (re simple gpsdo.)
How about USB to an FT232 that talks SPI to a low-cost DAC or digital pot? Would need a stable reference, though. See http://www.sparkfun.com/news/386 and http://www.chinwah-engineering.com/USB_SPI_Interface_Software.html for the methodology. Could also use a parallel DAC via FT232 bit-banging, see www.dlpdesign.com/images/bit-bang-usb.pdf From: Mark Spencer mspencer12...@yahoo.ca To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Fri, December 30, 2011 2:13:41 PM Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) On a related note is anyone aware of PC controlled (Ie. RS232 or maybe GPIB ?) DAC's that would be suitable for this type of application ? I've also contemplated simply using the DAC of a TBolt but it would seem to be waste of a Tbolt. I'm thinking along the lines of something that might acquired used on an auction site. ___ 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] Thunderbolt? (re simple gpsdo.)
Hi Chris, I just finished reading about that one. It requires no longer available GPS reciever. Maybe I should r-phrase the question: Most of us get (re)used stuff... Ebay #300437642776 has some Rockwell era receivers. Many time-nuts find HP5065A rubidiums and 5370 counters available and interesting, even though they have not been manufactured in decades. Then there are many receivers besides the Jupiter receivers that have faster-than-1Hz-pulse outputs. Some Oncores have 100PPS. Lots of high end L1 OEM-receivers can program the 1PPS output to higher frequencies. A prime example of a very modern receiver is the Ublox 6T receiver, that have two outputs - one classic 1PPS, and a second programmable frequency output. See link below: http://www.u-blox.com/images/downloads/Product_Docs/Timing_AppNote_%28GPS.G6-X-11007%29.pdf Good luck with your GPSDO buildproject! -- Björn ___ 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] Thunderbolt? (re simple gpsdo.)
What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Some sort of oscillator with a voltage control. CPU with a timer/counter that can capture the PPS. DAC. Software. How about MSC1200 : http://www.ti.com/lit/ds/symlink/msc1200y3.pdf Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
IF the 1pps is accurate and stable, one could measure the time between the GPS's 1pps and the 5680a 1pps and issue appropriate frequency offset commands. That's a big assumption or two, a Tbolt might still be cheaper. There's always WWVB. On 12/30/2011 11:39 AM, Robert LaJeunesse wrote: How about USB to an FT232 that talks SPI to a low-cost DAC or digital pot? Would need a stable reference, though. See http://www.sparkfun.com/news/386 and http://www.chinwah-engineering.com/USB_SPI_Interface_Software.html for the methodology. Could also use a parallel DAC via FT232 bit-banging, see www.dlpdesign.com/images/bit-bang-usb.pdf From: Mark Spencermspencer12...@yahoo.ca To: Discussion of precise time and frequency measurementtime-nuts@febo.com Sent: Fri, December 30, 2011 2:13:41 PM Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) On a related note is anyone aware of PC controlled (Ie. RS232 or maybe GPIB ?) DAC's that would be suitable for this type of application ? I've also contemplated simply using the DAC of a TBolt but it would seem to be waste of a Tbolt. I'm thinking along the lines of something that might acquired used on an auction site. ___ 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. -- Chuck Forsberg WA7KGX N2469R c...@omen.com www.omen.com Developer of Industrial ZMODEM(Tm) for Embedded Applications Omen Technology Inc The High Reliability Software 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 ___ 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] Thunderbolt? (re simple gpsdo.)
May I suggest use of small controllers such as the Picaxe series? I find them very useful around the lab for small tasks such as this. Easily programmed, very reliable, and the software application can be as simple or complex as needed, for example the suggested PID controller. No soldering, no fuss, just change the program and get on with it. 8 bit precision? not necessarily, capacitors are continuous... I use 1$ (yes!) 1st generation NES controllers (essentially 8 PB switches) for input, usually, and there are little I/O assemblies available from such vendors a sSparkfun. If you need them, 16-bit a/d and d/a's are there. There's also a forum with, by now, lots of examples. If things get more complex, the Arduino or the Propeller are available, and, in the near future, a $35 Linux unit called Raspberry Pi. I know, these things do not defy the laws of either physics or Murphy. But for just messing around, they've replaced a whole cabinet of flipflops,gates, amplifiers, and the like for me. Happy New Year to all! Don Azelio Boriani Yes, it can be done based on a PPS only timing. You must design a PI (maybe PID) regulator: the EFC must stay steady when the phase difference between the two PPSes is zero (integral action). Then you must move the EFC (when there is a difference) proportionally with the difference itself and only a small part of the difference drives the integrator to increment/decrement the new steady EFC level. When the difference is again zero the proportinal part is gone and remains the small amount of correction for the integral part. There is a gain for the integral action (samll) and a gain for the porportional action (should be large, but to be evaluated). On Fri, Dec 30, 2011 at 6:26 PM, Chris Albertson albertson.ch...@gmail.comwrote: On Thu, Dec 29, 2011 at 8:24 PM, Mark Spencer mspencer12...@yahoo.ca wrote: One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. I just finished reading about that one. It requires no longer available GPS reciever. Maybe I should r-phrase the question: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Half of the reason for the question is academic. Then if a simple enough design presented itself it would be fun to try it. The simplest design I can think of now is based on a flip-flop. The PPS sets' the FF and the next raising edge of the local oscillator resets it. (The local oscillator might need to be divided down or a slower 1Mhz oscillator used so the FF remains on for a reasonable time.) Next the FF gates a current source to a capacitor. The voltage in the cap is amplified and controls the local oscillator frequency via a low pas filter. Likely the low pass filter would be an active device that we call an integrator You need to discharge the cap for the next cycle. One could rig a one-shoot timer to discharge the cap. Actually there are about four states that need to be cycled every second. Chris Albertson Redondo Beach, California ___ 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. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ 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] Thunderbolt? (re simple gpsdo.)
I believe those Rockwells have a 10 KHz output. Not a bad price. 73 es HNY, Dick, W1KSZ -Original Message- From: b...@lysator.liu.se Sent: Dec 30, 2011 12:42 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) Hi Chris, I just finished reading about that one. It requires no longer available GPS reciever. Maybe I should r-phrase the question: Most of us get (re)used stuff... Ebay #300437642776 has some Rockwell era receivers. Many time-nuts find HP5065A rubidiums and 5370 counters available and interesting, even though they have not been manufactured in decades. Then there are many receivers besides the Jupiter receivers that have faster-than-1Hz-pulse outputs. Some Oncores have 100PPS. Lots of high end L1 OEM-receivers can program the 1PPS output to higher frequencies. A prime example of a very modern receiver is the Ublox 6T receiver, that have two outputs - one classic 1PPS, and a second programmable frequency output. See link below: http://www.u-blox.com/images/downloads/Product_Docs/Timing_AppNote_%28GPS.G6-X-11007%29.pdf Good luck with your GPSDO buildproject! -- Björn ___ 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] Thunderbolt? (re simple gpsdo.)
Usually timing grade GPS receivers have better PPS outputs than navigation GPS receivers and timing grade receivers support the so called position hold mode that provides a valid PPS output even if only 1 bird is being received. Yes, it is better to implement the PPS synchronization in the digital world: easier to implement very low low pass filters. On Fri, Dec 30, 2011 at 9:29 PM, Richard W. Solomon w1...@earthlink.netwrote: I believe those Rockwells have a 10 KHz output. Not a bad price. 73 es HNY, Dick, W1KSZ -Original Message- From: b...@lysator.liu.se Sent: Dec 30, 2011 12:42 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) Hi Chris, I just finished reading about that one. It requires no longer available GPS reciever. Maybe I should r-phrase the question: Most of us get (re)used stuff... Ebay #300437642776 has some Rockwell era receivers. Many time-nuts find HP5065A rubidiums and 5370 counters available and interesting, even though they have not been manufactured in decades. Then there are many receivers besides the Jupiter receivers that have faster-than-1Hz-pulse outputs. Some Oncores have 100PPS. Lots of high end L1 OEM-receivers can program the 1PPS output to higher frequencies. A prime example of a very modern receiver is the Ublox 6T receiver, that have two outputs - one classic 1PPS, and a second programmable frequency output. See link below: http://www.u-blox.com/images/downloads/Product_Docs/Timing_AppNote_%28GPS.G6-X-11007%29.pdf Good luck with your GPSDO buildproject! -- Björn ___ 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] Thunderbolt? (re simple gpsdo.)
The DAC and it's voltage reference looks to be the weak link in the digital control and the simple goal. The CPU I mentioned before on closer look doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure you can find it in the same package as the CPU. The cheap Rb standards with digital control would not need a DAC and maybe this points to a simpler GPSDO that doesn't control the XO with analog but corrects it with a DDS but again finding them both in one chip is the problem. I have seen OCXO and DAC in the same package and even the DDS and OCXO combined but they didn't fit the simple goal. Not even sure how good they were. I know they are hard to find. Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
On 12/30/11 11:39 AM, Robert LaJeunesse wrote: How about USB to an FT232 that talks SPI to a low-cost DAC or digital pot? Would need a stable reference, though. There's a bunch of eval boards from LTC, etc. which use this strategy. Looks like a serial port to the computer, simple ASCII protocol to set DAC values. We used one for an octal DAC to set I/Q voltages for vector mods. ___ 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] Thunderbolt? (re simple gpsdo.)
Yes, the DAC+reference is challenging and one way to go may be the coarse+fine approach to avoid large (18bit and beyond) DAC. My last GPSDO has an 18bit DAC but now I'm thinking to try the 8bit digital pot + 16bit DAC op-amp combined. The reference can't be overlooked anyway. On Fri, Dec 30, 2011 at 10:24 PM, Stanley timen...@n4iqt.com wrote: The DAC and it's voltage reference looks to be the weak link in the digital control and the simple goal. The CPU I mentioned before on closer look doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure you can find it in the same package as the CPU. The cheap Rb standards with digital control would not need a DAC and maybe this points to a simpler GPSDO that doesn't control the XO with analog but corrects it with a DDS but again finding them both in one chip is the problem. I have seen OCXO and DAC in the same package and even the DDS and OCXO combined but they didn't fit the simple goal. Not even sure how good they were. I know they are hard to find. Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
Yes, the DAC+reference is challenging and one way to go may be the coarse+fine approach to avoid large (18bit and beyond) DAC. My last GPSDO has an 18bit DAC but now I'm thinking to try the 8bit digital pot + 16bit DAC op-amp combined. The reference can't be overlooked anyway. Be careful, there is no free lunch. If you use a pair of DACs, the stability of the coarse DAC needs to be evaluated relative to the bottom bits of the fine DAC. -- These are my opinions, not necessarily my employer's. 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] Thunderbolt? (re simple gpsdo.)
Over the last two years along with two list members that may want to pipe in, I have spend a large amount of time on D/A's and we went as far as developing a test board using the LTC 2440 and testing numerous D/A's taking in to consideration performance, solderability, cost, availability and the winner is LTC 1655 by a long shot, is even available in a DIP with 16 bits more than you need for any Rb and if you want 20 bits, dithering is an option. My testing consistently shows with OCXO's aging that will in most cases allow operation of an OCXO for 3 years with out intervention. To top it off the LTC1655 cost less than $ 10. Testing the old AD 1861 was an eye opener but considering what its purpose was and its time the best choice. Bert In a message dated 12/30/2011 4:24:37 P.M. Eastern Standard Time, timen...@n4iqt.com writes: The DAC and it's voltage reference looks to be the weak link in the digital control and the simple goal. The CPU I mentioned before on closer look doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure you can find it in the same package as the CPU. The cheap Rb standards with digital control would not need a DAC and maybe this points to a simpler GPSDO that doesn't control the XO with analog but corrects it with a DDS but again finding them both in one chip is the problem. I have seen OCXO and DAC in the same package and even the DDS and OCXO combined but they didn't fit the simple goal. Not even sure how good they were. I know they are hard to find. Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
No free lunch, of course, but I want to avoid dithering DACs. The 18bit DAC (AD5680) is a 16bit+dithering, I think to use the AD5660 + AD5241 (already available) the pot has a tempco of 30ppm/degree and a noise of 14nV/sqr(Hz). Maybe I have to find something better but to make the first try is available. On Fri, Dec 30, 2011 at 11:48 PM, ewkeh...@aol.com wrote: Over the last two years along with two list members that may want to pipe in, I have spend a large amount of time on D/A's and we went as far as developing a test board using the LTC 2440 and testing numerous D/A's taking in to consideration performance, solderability, cost, availability and the winner is LTC 1655 by a long shot, is even available in a DIP with 16 bits more than you need for any Rb and if you want 20 bits, dithering is an option. My testing consistently shows with OCXO's aging that will in most cases allow operation of an OCXO for 3 years with out intervention. To top it off the LTC1655 cost less than $ 10. Testing the old AD 1861 was an eye opener but considering what its purpose was and its time the best choice. Bert In a message dated 12/30/2011 4:24:37 P.M. Eastern Standard Time, timen...@n4iqt.com writes: The DAC and it's voltage reference looks to be the weak link in the digital control and the simple goal. The CPU I mentioned before on closer look doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure you can find it in the same package as the CPU. The cheap Rb standards with digital control would not need a DAC and maybe this points to a simpler GPSDO that doesn't control the XO with analog but corrects it with a DDS but again finding them both in one chip is the problem. I have seen OCXO and DAC in the same package and even the DDS and OCXO combined but they didn't fit the simple goal. Not even sure how good they were. I know they are hard to find. Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
It has occurred to me that using 3/4 of a quad 256-step digital pot (like the AD5263, only 6$) set up as a Kelvin-Varley divider might be an alternative to a DAC. Use 2 sections both voltage driven but set 2 values apart, such that the wiper arms are just a fraction of the reference apart. That's a coarse adjust, effectively 8-bit. Use a 3rd section between the wiper arms of the first 2 for a fine adjust, now effectively 7 bits since the coarse are 2 steps apart. Generally monotonic since all the divider resistors are integrated on one chip, and with about 30 ppm resolution. Seems a 5 ppm/C reference would be a good match, the LTC6652 is also about $6. (Possibly even use the last digipot section with a filter amplifier to trim the result +/- 50 ppm or so.) With the AD5263 you get 5 ppm/C stability, so only 6C temp swing eats up one LSB. I'd think about using only 25 ppm/C or better resistors and putting the whole thing in an oven... Then again, a small micro with two 10-bit PWM outputs is a lot cheaper, and they can be combined and filtered to effect a 16-bit converter with only a few parts. From: Hal Murray hmur...@megapathdsl.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Fri, December 30, 2011 5:35:56 PM Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) Yes, the DAC+reference is challenging and one way to go may be the coarse+fine approach to avoid large (18bit and beyond) DAC. My last GPSDO has an 18bit DAC but now I'm thinking to try the 8bit digital pot + 16bit DAC op-amp combined. The reference can't be overlooked anyway. Be careful, there is no free lunch. If you use a pair of DACs, the stability of the coarse DAC needs to be evaluated relative to the bottom bits of the fine DAC. ___ 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] Thunderbolt? (re simple gpsdo.)
Bert, Would you have time to generate a brief report of your DAC testing? I for one am very interested. I could publish it on my web site if you want. Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: ewkeh...@aol.com Sender: time-nuts-boun...@febo.com Date: Fri, 30 Dec 2011 17:48:24 To: time-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) Over the last two years along with two list members that may want to pipe in, I have spend a large amount of time on D/A's and we went as far as developing a test board using the LTC 2440 and testing numerous D/A's taking in to consideration performance, solderability, cost, availability and the winner is LTC 1655 by a long shot, is even available in a DIP with 16 bits more than you need for any Rb and if you want 20 bits, dithering is an option. My testing consistently shows with OCXO's aging that will in most cases allow operation of an OCXO for 3 years with out intervention. To top it off the LTC1655 cost less than $ 10. Testing the old AD 1861 was an eye opener but considering what its purpose was and its time the best choice. Bert In a message dated 12/30/2011 4:24:37 P.M. Eastern Standard Time, timen...@n4iqt.com writes: The DAC and it's voltage reference looks to be the weak link in the digital control and the simple goal. The CPU I mentioned before on closer look doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure you can find it in the same package as the CPU. The cheap Rb standards with digital control would not need a DAC and maybe this points to a simpler GPSDO that doesn't control the XO with analog but corrects it with a DDS but again finding them both in one chip is the problem. I have seen OCXO and DAC in the same package and even the DDS and OCXO combined but they didn't fit the simple goal. Not even sure how good they were. I know they are hard to find. Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
I was thinking ... starting with a 5680a and a GPS with accurate 1pps but no 10 MHz ... Feed both 1pps signals to a 74ls123 to stretch the pulses to something longer. A 74ls74 is strobed by one of the one-shots, its D input being the other one-shot. Connect both one-shots and the 74 to an Arduino's inputs. An Arduino serial output connects to the 5680a. The Arduino watches the one-shots to obtain rough lock, then pays attention to the 74 output for fine lock. Between the jitter on the 1pps and the very long time constant(s) used to control the 5680a it just might work. Attached: Phase plot of two Thunderbolts using same antenna but different GPSDO parameters. Plenty of jitter/noise/whatever. -- Chuck Forsberg WA7KGX N2469R c...@omen.com www.omen.com Developer of Industrial ZMODEM(Tm) for Embedded Applications Omen Technology Inc The High Reliability Software 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 attachment: 2tbolt2.gif___ 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] Thunderbolt? (re simple gpsdo.)
Did you test the LTC1655 INL? The data sheet says plus or minus 20 counts maximum. I suspect Linear Technology designed those low DNL high INL parts for just this sort of application where only monotonic behavior really matters. Their equivalent current output DAC costs about twice as much not including a precision transimpedance amplifier but has an INL specification of plus or minus 1 count. Every couple years I consider the design of a digitally adjusted oscillator and do a search for likely parts. I wonder if it would be more cost effective to use an instrumentation ADC to correct a less expensive DAC design like one based on a PWM. On Fri, 30 Dec 2011 17:48:24 -0500 (EST), ewkeh...@aol.com wrote: Over the last two years along with two list members that may want to pipe in, I have spend a large amount of time on D/A's and we went as far as developing a test board using the LTC 2440 and testing numerous D/A's taking in to consideration performance, solderability, cost, availability and the winner is LTC 1655 by a long shot, is even available in a DIP with 16 bits more than you need for any Rb and if you want 20 bits, dithering is an option. My testing consistently shows with OCXO's aging that will in most cases allow operation of an OCXO for 3 years with out intervention. To top it off the LTC1655 cost less than $ 10. Testing the old AD 1861 was an eye opener but considering what its purpose was and its time the best choice. Bert In a message dated 12/30/2011 4:24:37 P.M. Eastern Standard Time, timen...@n4iqt.com writes: The DAC and it's voltage reference looks to be the weak link in the digital control and the simple goal. The CPU I mentioned before on closer look doesn't have a good DAC. The 20 bit TI DAC1220 looks better but not sure you can find it in the same package as the CPU. The cheap Rb standards with digital control would not need a DAC and maybe this points to a simpler GPSDO that doesn't control the XO with analog but corrects it with a DDS but again finding them both in one chip is the problem. I have seen OCXO and DAC in the same package and even the DDS and OCXO combined but they didn't fit the simple goal. Not even sure how good they were. I know they are hard to find. Stanley ___ 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] Thunderbolt? (re simple gpsdo.)
Don't need to stretch, use the two hardware interrupt pins... Don Chuck Forsberg WA7KGX N2469R I was thinking ... starting with a 5680a and a GPS with accurate 1pps but no 10 MHz ... Feed both 1pps signals to a 74ls123 to stretch the pulses to something longer. A 74ls74 is strobed by one of the one-shots, its D input being the other one-shot. Connect both one-shots and the 74 to an Arduino's inputs. An Arduino serial output connects to the 5680a. The Arduino watches the one-shots to obtain rough lock, then pays attention to the 74 output for fine lock. Between the jitter on the 1pps and the very long time constant(s) used to control the 5680a it just might work. Attached: Phase plot of two Thunderbolts using same antenna but different GPSDO parameters. Plenty of jitter/noise/whatever. -- Chuck Forsberg WA7KGX N2469R c...@omen.com www.omen.com Developer of Industrial ZMODEM(Tm) for Embedded Applications Omen Technology Inc The High Reliability Software 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 ___ 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. -- Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind. R. Bacon If you don't know what it is, don't poke it. Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ 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] Thunderbolt? (re simple gpsdo.)
On Fri, Dec 30, 2011 at 10:16 AM, Hal Murray hmur...@megapathdsl.net wrote: What is the simplest design for a GPSDO that uses only the PPS signal from a modern GPS? Some sort of oscillator with a voltage control. CPU with a timer/counter that can capture the PPS. DAC. Software. As soon as you say Software the device is no longer simple.Even a microprocessor is a very complex device and so is its development system. The software inside the uP is not simple either if you count the number of possible paths through the code (2 raided to the power of the number of branches.) I have nothing against software, that is what I do for a living, every day. But you can't count a uP with software indise as simple. And the point of this exercise is to find the simplest thing that can still work. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. My first gpsdo was a manufactured version of this concept and it consistently beats my thunder bolt from an adev perspective and there is nothing to tweak (: Sent from my iPad On 2011-12-29, at 6:35 PM, Chris Albertson albertson.ch...@gmail.com wrote: The era of cheap Thunderbolts appears to be history. What is the simplest GPSDO you can build? There are many designs around but when the T-Bolts came out I think people lost interesting building. I think something very simple could work. If your local oscillator is at all decent it will not loose or gain full cycle in one second. So I think you only need to compare the phase of the oscillator and the PPS. Would an analog controller work? I do software all day every day at work so it would be fun to build an analog computer for a change. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
I think you are talking about the G3RUH/N1JEZ design. I have built three of them and they work very well. 73 es HNY, Dick, W1KSZ -Original Message- From: Mark Spencer mspencer12...@yahoo.ca Sent: Dec 29, 2011 9:24 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. My first gpsdo was a manufactured version of this concept and it consistently beats my thunder bolt from an adev perspective and there is nothing to tweak (: Sent from my iPad On 2011-12-29, at 6:35 PM, Chris Albertson albertson.ch...@gmail.com wrote: The era of cheap Thunderbolts appears to be history. What is the simplest GPSDO you can build? There are many designs around but when the T-Bolts came out I think people lost interesting building. I think something very simple could work. If your local oscillator is at all decent it will not loose or gain full cycle in one second. So I think you only need to compare the phase of the oscillator and the PPS. Would an analog controller work? I do software all day every day at work so it would be fun to build an analog computer for a change. Chris Albertson Redondo Beach, California ___ 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] Thunderbolt? (re simple gpsdo.)
Yes that is correct. I have one of the units made by James Miller G3RUH. I had hoped to build some something along these lines on my own, but the Jupiter gps modules I acquired didn't actually have a 10 kHz output. Also my comment re the adev is for the 10 MHz output. I've never looked at the one pps output. Sent from my iPad On 2011-12-29, at 8:45 PM, Richard W. Solomon w1...@earthlink.net wrote: I think you are talking about the G3RUH/N1JEZ design. I have built three of them and they work very well. 73 es HNY, Dick, W1KSZ -Original Message- From: Mark Spencer mspencer12...@yahoo.ca Sent: Dec 29, 2011 9:24 PM To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt? (re simple gpsdo.) One of the designs using the 10 kHz output from a Jupiter gps engine and a simple PLL to discipline an ocxo might be good starting point if suitable gps engines are still available. There won't be much to tweak but the performance could be quite good. My first gpsdo was a manufactured version of this concept and it consistently beats my thunder bolt from an adev perspective and there is nothing to tweak (: Sent from my iPad On 2011-12-29, at 6:35 PM, Chris Albertson albertson.ch...@gmail.com wrote: The era of cheap Thunderbolts appears to be history. What is the simplest GPSDO you can build? There are many designs around but when the T-Bolts came out I think people lost interesting building. I think something very simple could work. If your local oscillator is at all decent it will not loose or gain full cycle in one second. So I think you only need to compare the phase of the oscillator and the PPS. Would an analog controller work? I do software all day every day at work so it would be fun to build an analog computer for a change. Chris Albertson Redondo Beach, California ___ 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.
