Re: General query about disciplining circuitry
Hi
With a moving platform, you get into the acceleration sensitivity of your oscillator.
That could be as high as 2x10^-9 / g. You might find a part down around 5x10^-10 / g.
Anything much past that gets you into an acceleration compensated device. Those
typically are a bit expensive and not an eBay sort of item.
If the motion is on a typical platform, you will need vibration compensation to get to your
1x10^-11 range. This is one step up from acceleration compensation. Price goes up
yet again and surplus availability goes to near zero.
One approach for time is to simply use the time pulse out of the GPS module. If you don’t
care about the PPS edge staying aligned with the (say) 10 MHz output it’s a valid solution
to the problem. Accuracy wise, it’s going to win every time. Jitter wise … not so much.
Bob
On Feb 3, 2023, at 12:37 PM, AC0XU (Jim) James.Schatzman@ac0xu.com wrote:
1W is the notional power budget for the discipliner.
I am interested in optimizing designs for precision time, precision frequency, and precision time and frequency (three cases). I am o.k. with the idea of not adjusting the oscillator phase to perfectly match GNSS but to instead record and track the offset without actually tweaking the oscillator for time/phase. That might be the best, and maybe that approach reduces the distinction between precision time and precision frequency.
The goal for the loosest case is 1e-11 adev over 0.1 to 1000 sec, but I am interested in doing as well as the oscillator will support. In a future design I will be using an oscillator with 1e-12 adev @ 1 sec, but the current one is good for maybe 1e-11 @ 1 sec at best. The receiver platform is moving, and no radio mfr publishes performance specs for this case.
Thank you for reminding me about the sawtooth. I will need to study the sawtooth behavior of the radio. One I am looking at now is the OEM7 series.
Again, given that there are many possible approaches to precision phase measurement, and being pretty sure that I want to do more than implement a frequency counter, I am looking for advice.
Thanks!
At 09:31 AM 2/3/2023, Bob Camp wrote:
Hi
I would back up a bit first
.
What sort of oscillator is being disciplined? If the 1W is the total power budget, that rules out
most OCXOâs. Why ask? The stability of the oscillator does get into this pretty quickly.
What is the end goal? Are you after precision time or precision frequency? While they are
connected, the approach to optimize one is not quite the same at the approach for the other.
What are the stability goals either for time or frequency?
Is this a mobile / portable application? If so that also impacts a lot of this and gets into a whole
other set of questions.
To at least partly answer the question you asked:
The PPS comes out of the GPS at the same time as the sawtooth correction information. In
most cases, you want to marry those two up immediately. That way the correction does apply
to the data you took. Does this matter in your case? Thus the long list of questions above.
Bpb
On Feb 3, 2023, at 10:16 AM, AC0XU (Jim) via time-nuts time-nuts@lists.febo.com wrote:
I can image all sorts of disciplining circuits for controlling a digitally-controlled oscillator against GPS. Presumably, I will measure oscillator phase at the 1 PPS times and run those values into a Kalman Filter. I think my question is about how best to measure the oscillator phase, given the constraint of low electrical power (<1W). There are zillions of commercial devices that do this but the mfrs generally do not advertize the details. I plan to use either an MCU or an FPGA, depending on which is more advantageous.
I looked at
https://hackaday.io/project/6872-gps-disciplined-xcxo/detailshttps://hackaday.io/project/6872-gps-disciplined-xcxo/details
and that seems interesting. I don't have to worry about VCO control because my oscillator has a digital control.
What about measuring the phase of a large divider PLL locked to the reference? With I-Q outputs the phase can be measured with a very slow ADC applied to a sample-and-hold triggered by the 1 PPS.
Thanks!
Jim
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
It’s not going to be budget friendly, but the symmetricom (now Microsemi) chip scale atomic clocks might get you there or close at least. You’d probably have to ask someone about what the loop time constants are. If they are something like 128 Hz, in theory the onboard quartz would be disciplined by the atomic transition as fast as the frequency was shifting…IF the loop filter once lock is achieved has the same bandwidth as when it’s unlocked.
I’m struggling with why you’d need the equivalent of hertz per 100GHz stability on that sort of power budget. A moving phase coherent receiver suggests whatever you’re trying to transmit or receive should be designed with a more forgiving frequency tracking loop. A carrier phase GNSS can probably cover most of the other use cases I can think of, and for the ones it can’t, you’re talking about things so big a bigger power budget isn’t a problem.
Get Outlook for iOShttps://aka.ms/o0ukef
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Friday, February 3, 2023 12:12:17 PM
To: AC0XU (Jim) James.Schatzman@ac0xu.com
Cc: Discussion of precise time and frequency measurement time-nuts@lists.febo.com; Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: General query about disciplining circuitry
Hi
With a moving platform, you get into the acceleration sensitivity of your oscillator.
That could be as high as 2x10^-9 / g. You might find a part down around 5x10^-10 / g.
Anything much past that gets you into an acceleration compensated device. Those
typically are a bit expensive and not an eBay sort of item.
If the motion is on a typical platform, you will need vibration compensation to get to your
1x10^-11 range. This is one step up from acceleration compensation. Price goes up
yet again and surplus availability goes to near zero.
One approach for time is to simply use the time pulse out of the GPS module. If you don’t
care about the PPS edge staying aligned with the (say) 10 MHz output it’s a valid solution
to the problem. Accuracy wise, it’s going to win every time. Jitter wise … not so much.
Bob
On Feb 3, 2023, at 12:37 PM, AC0XU (Jim) James.Schatzman@ac0xu.com wrote:
1W is the notional power budget for the discipliner.
I am interested in optimizing designs for precision time, precision frequency, and precision time and frequency (three cases). I am o.k. with the idea of not adjusting the oscillator phase to perfectly match GNSS but to instead record and track the offset without actually tweaking the oscillator for time/phase. That might be the best, and maybe that approach reduces the distinction between precision time and precision frequency.
The goal for the loosest case is 1e-11 adev over 0.1 to 1000 sec, but I am interested in doing as well as the oscillator will support. In a future design I will be using an oscillator with 1e-12 adev @ 1 sec, but the current one is good for maybe 1e-11 @ 1 sec at best. The receiver platform is moving, and no radio mfr publishes performance specs for this case.
Thank you for reminding me about the sawtooth. I will need to study the sawtooth behavior of the radio. One I am looking at now is the OEM7 series.
Again, given that there are many possible approaches to precision phase measurement, and being pretty sure that I want to do more than implement a frequency counter, I am looking for advice.
Thanks!
At 09:31 AM 2/3/2023, Bob Camp wrote:
Hi
I would back up a bit first
.
What sort of oscillator is being disciplined? If the 1W is the total power budget, that rules out
most OCXO’s. Why ask? The stability of the oscillator does get into this pretty quickly.
What is the end goal? Are you after precision time or precision frequency? While they are
connected, the approach to optimize one is not quite the same at the approach for the other.
What are the stability goals either for time or frequency?
Is this a mobile / portable application? If so that also impacts a lot of this and gets into a whole
other set of questions.
To at least partly answer the question you asked:
The PPS comes out of the GPS at the same time as the sawtooth correction information. In
most cases, you want to marry those two up immediately. That way the correction does apply
to the data you took. Does this matter in your case? Thus the long list of questions above.
Bpb
On Feb 3, 2023, at 10:16 AM, AC0XU (Jim) via time-nuts time-nuts@lists.febo.com wrote:
I can image all sorts of disciplining circuits for controlling a digitally-controlled oscillator against GPS. Presumably, I will measure oscillator phase at the 1 PPS times and run those values into a Kalman Filter. I think my question is about how best to measure the oscillator phase, given the constraint of low electrical power (<1W). There are zillions of commercial devices that do this but the mfrs generally do not advertize the details. I plan to use either an MCU or an FPGA, depending on which is more advantageous.
I looked at
https://hackaday.io/project/6872-gps-disciplined-xcxo/detailshttps://hackaday.io/project/6872-gps-disciplined-xcxo/details
and that seems interesting. I don't have to worry about VCO control because my oscillator has a digital control.
What about measuring the phase of a large divider PLL locked to the reference? With I-Q outputs the phase can be measured with a very slow ADC applied to a sample-and-hold triggered by the 1 PPS.
Thanks!
Jim
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi
There indeed are applications out there that get into the 1 to 5 x10^-11 per G vibration compensation
empire. There aren’t a lot of them but they most certainly do exist. Just exactly what those folks are
doing often is unclear. Pure acceleration compensation without vibration compensation is a very rare item.
What are the “best wild guess” numbers? Vibe comp might make up 0.1% of the OCXO production
in the US. Pure acceleration comp (with no vibe spec) probably is no more than a hundredth of that number.
Bob
On Feb 9, 2023, at 8:36 AM, Ed Marciniak ed@nb0m.org wrote:
It’s not going to be budget friendly, but the symmetricom (now Microsemi) chip scale atomic clocks might get you there or close at least. You’d probably have to ask someone about what the loop time constants are. If they are something like 128 Hz, in theory the onboard quartz would be disciplined by the atomic transition as fast as the frequency was shifting…IF the loop filter once lock is achieved has the same bandwidth as when it’s unlocked.
I’m struggling with why you’d need the equivalent of hertz per 100GHz stability on that sort of power budget. A moving phase coherent receiver suggests whatever you’re trying to transmit or receive should be designed with a more forgiving frequency tracking loop. A carrier phase GNSS can probably cover most of the other use cases I can think of, and for the ones it can’t, you’re talking about things so big a bigger power budget isn’t a problem.
Get Outlook for iOS https://aka.ms/o0ukef
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Friday, February 3, 2023 12:12:17 PM
To: AC0XU (Jim) James.Schatzman@ac0xu.com
Cc: Discussion of precise time and frequency measurement time-nuts@lists.febo.com; Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: General query about disciplining circuitry
Hi
With a moving platform, you get into the acceleration sensitivity of your oscillator.
That could be as high as 2x10^-9 / g. You might find a part down around 5x10^-10 / g.
Anything much past that gets you into an acceleration compensated device. Those
typically are a bit expensive and not an eBay sort of item.
If the motion is on a typical platform, you will need vibration compensation to get to your
1x10^-11 range. This is one step up from acceleration compensation. Price goes up
yet again and surplus availability goes to near zero.
One approach for time is to simply use the time pulse out of the GPS module. If you don’t
care about the PPS edge staying aligned with the (say) 10 MHz output it’s a valid solution
to the problem. Accuracy wise, it’s going to win every time. Jitter wise … not so much.
Bob
On Feb 3, 2023, at 12:37 PM, AC0XU (Jim) James.Schatzman@ac0xu.com wrote:
1W is the notional power budget for the discipliner.
I am interested in optimizing designs for precision time, precision frequency, and precision time and frequency (three cases). I am o.k. with the idea of not adjusting the oscillator phase to perfectly match GNSS but to instead record and track the offset without actually tweaking the oscillator for time/phase. That might be the best, and maybe that approach reduces the distinction between precision time and precision frequency.
The goal for the loosest case is 1e-11 adev over 0.1 to 1000 sec, but I am interested in doing as well as the oscillator will support. In a future design I will be using an oscillator with 1e-12 adev @ 1 sec, but the current one is good for maybe 1e-11 @ 1 sec at best. The receiver platform is moving, and no radio mfr publishes performance specs for this case.
Thank you for reminding me about the sawtooth. I will need to study the sawtooth behavior of the radio. One I am looking at now is the OEM7 series.
Again, given that there are many possible approaches to precision phase measurement, and being pretty sure that I want to do more than implement a frequency counter, I am looking for advice.
Thanks!
At 09:31 AM 2/3/2023, Bob Camp wrote:
Hi
I would back up a bit first
.
What sort of oscillator is being disciplined? If the 1W is the total power budget, that rules out
most OCXO’s. Why ask? The stability of the oscillator does get into this pretty quickly.
What is the end goal? Are you after precision time or precision frequency? While they are
connected, the approach to optimize one is not quite the same at the approach for the other.
What are the stability goals either for time or frequency?
Is this a mobile / portable application? If so that also impacts a lot of this and gets into a whole
other set of questions.
To at least partly answer the question you asked:
The PPS comes out of the GPS at the same time as the sawtooth correction information. In
most cases, you want to marry those two up immediately. That way the correction does apply
to the data you took. Does this matter in your case? Thus the long list of questions above.
Bpb
On Feb 3, 2023, at 10:16 AM, AC0XU (Jim) via time-nuts time-nuts@lists.febo.com wrote:
I can image all sorts of disciplining circuits for controlling a digitally-controlled oscillator against GPS. Presumably, I will measure oscillator phase at the 1 PPS times and run those values into a Kalman Filter. I think my question is about how best to measure the oscillator phase, given the constraint of low electrical power (<1W). There are zillions of commercial devices that do this but the mfrs generally do not advertize the details. I plan to use either an MCU or an FPGA, depending on which is more advantageous.
I looked at
https://hackaday.io/project/6872-gps-disciplined-xcxo/detailshttps://hackaday.io/project/6872-gps-disciplined-xcxo/details
and that seems interesting. I don't have to worry about VCO control because my oscillator has a digital control.
What about measuring the phase of a large divider PLL locked to the reference? With I-Q outputs the phase can be measured with a very slow ADC applied to a sample-and-hold triggered by the 1 PPS.
Thanks!
Jim
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Thanks to all for the various comments.
My question was really about how to make accurate phase measurements of an oscillator at the 1 PPS time tag output from a GNSS radio. There are some methods I can think of, but I am not finding one that has clear advantages of accuracy, immunity to all forms of noise on the oscillator output, and low complexity and power. I was hoping that someone out there had the perfect solution...
Thanks!
Jim
At 06:36 AM 2/9/2023, Ed Marciniak wrote:
Its not going to be budget friendly, but the symmetricom (now Microsemi) chip scale atomic clocks might get you there or close at least. Youd probably have to ask someone about what the loop time constants are. If they are something like 128 Hz, in theory the onboard quartz would be disciplined by the atomic transition as fast as the frequency was shifting IF the loop filter once lock is achieved has the same bandwidth as when its unlocked.
Im struggling with why youd need the equivalent of hertz per 100GHz stability on that sort of power budget. A moving phase coherent receiver suggests whatever youre trying to transmit or receive should be designed with a more forgiving frequency tracking loop. A carrier phase GNSS can probably cover most of the other use cases I can think of, and for the ones it cant, youre talking about things so big a bigger power budget isnt a problem.
Get https://aka.ms/o0ukefOutlook for iOS
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Friday, February 3, 2023 12:12:17 PM
To: AC0XU (Jim) James.Schatzman@ac0xu.com
Cc: Discussion of precise time and frequency measurement time-nuts@lists.febo.com; Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: General query about disciplining circuitry
Hi
With a moving platform, you get into the acceleration sensitivity of your oscillator.
That could be as high as 2x10^-9 / g. You might find a part down around 5x10^-10 / g.
Anything much past that gets you into an acceleration compensated device. Those
typically are a bit expensive and not an eBay sort of item.
If the motion is on a typical platform, you will need vibration compensation to get to your
1x10^-11 range. This is one step up from acceleration compensation. Price goes up
yet again and surplus availability goes to near zero.
One approach for time is to simply use the time pulse out of the GPS module. If you dont
care about the PPS edge staying aligned with the (say) 10 MHz output its a valid solution
to the problem. Accuracy wise, its going to win every time. Jitter wise
not so much.
Bob
On Feb 3, 2023, at 12:37 PM, AC0XU (Jim) James.Schatzman@ac0xu.com wrote:
1W is the notional power budget for the discipliner.
I am interested in optimizing designs for precision time, precision frequency, and precision time and frequency (three cases). I am o.k. with the idea of not adjusting the oscillator phase to perfectly match GNSS but to instead record and track the offset without actually tweaking the oscillator for time/phase. That might be the best, and maybe that approach reduces the distinction between precision time and precision frequency.
The goal for the loosest case is 1e-11 adev over 0.1 to 1000 sec, but I am interested in doing as well as the oscillator will support. In a future design I will be using an oscillator with 1e-12 adev @ 1 sec, but the current one is good for maybe 1e-11 @ 1 sec at best. The receiver platform is moving, and no radio mfr publishes performance specs for this case.
Thank you for reminding me about the sawtooth. I will need to study the sawtooth behavior of the radio. One I am looking at now is the OEM7 series.
Again, given that there are many possible approaches to precision phase measurement, and being pretty sure that I want to do more than implement a frequency counter, I am looking for advice.
Thanks!
At 09:31 AM 2/3/2023, Bob Camp wrote:
Hi
I would back up a bit first
.
What sort of oscillator is being disciplined? If the 1W is the total power budget, that rules out
most OCXOâs. Why ask? The stability of the oscillator does get into this pretty quickly.
What is the end goal? Are you after precision time or precision frequency? While they are
connected, the approach to optimize one is not quite the same at the approach for the other.
What are the stability goals either for time or frequency?
Is this a mobile / portable application? If so that also impacts a lot of this and gets into a whole
other set of questions.
To at least partly answer the question you asked:
The PPS comes out of the GPS at the same time as the sawtooth correction information. In
most cases, you want to marry those two up immediately. That way the correction does apply
to the data you took. Does this matter in your case? Thus the long list of questions above.
Bpb
On Feb 3, 2023, at 10:16 AM, AC0XU (Jim) via time-nuts time-nuts@lists.febo.com wrote:
I can image all sorts of disciplining circuits for controlling a digitally-controlled oscillator against GPS. Presumably, I will measure oscillator phase at the 1 PPS times and run those values into a Kalman Filter. I think my question is about how best to measure the oscillator phase, given the constraint of low electrical power (<1W). There are zillions of commercial devices that do this but the mfrs generally do not advertize the details. I plan to use either an MCU or an FPGA, depending on which is more advantageous.
I looked at
<https://hackaday.io/project/6872-gps-disciplined-xcxo/detailshttps://hackaday.io/project/6872-gps-disciplined-xcxo/details>https://hackaday.io/project/6872-gps-disciplined-xcxo/details
and that seems interesting. I don't have to worry about VCO control because my oscillator has a digital control.
What about measuring the phase of a large divider PLL locked to the reference? With I-Q outputs the phase can be measured with a very slow ADC applied to a sample-and-hold triggered by the 1 PPS.
Thanks!
Jim
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi,
You may take a look on the website https://www.axtal.com/English/Products/CrystalOscillators/VibrationInsensitiveOscillators/ , which shows crystal oscillators which low g-sensitivity down to 0.25 ppb/g
And oscillators with vibration isolation, where the g-sensitivity depends on the vibration frequency in a low-pass manner, going down to 1E-12 per g, as can be seen in the attached chart (blue dotted line).
At the end it may be a budget issue...
BTW: AXTAL is no longer owned by me, but acquired by Q-Tech USA since 01/01/2023. Therefore, this information is purely technical and is not intended to be commercially driven.
Bernd DK1AG
Bob Camp via time-nuts time-nuts@lists.febo.com, 9. Februar 2023 15:48 wrote:
There indeed are applications out there that get into the 1 to 5 x10^-11 per G vibration compensation empire. There aren’t a lot of them but they most certainly do exist. Just exactly what those folks are doing
often is unclear. Pure acceleration compensation without vibration compensation is a very rare item.
What are the “best wild guess” numbers? Vibe comp might make up 0.1% of the OCXO production in the US. Pure acceleration comp (with no vibe spec) probably is no more than a hundredth of that number.
On Feb 9, 2023, at 8:36 AM, Ed Marciniak ed@nb0m.org wrote:
It’s not going to be budget friendly, but the symmetricom (now Microsemi) chip scale atomic clocks might get you there or close at least. You’d probably have to ask someone about what the loop time constants are. If they are something like 128 Hz, in theory the onboard quartz would be disciplined by the atomic transition as fast as the frequency was shifting…IF the loop filter once lock is achieved has the same bandwidth as when it’s unlocked.
I’m struggling with why you’d need the equivalent of hertz per 100GHz stability on that sort of power budget. A moving phase coherent receiver suggests whatever you’re trying to transmit or receive should be designed with a more forgiving frequency tracking loop. A carrier phase GNSS can probably cover most of the other use cases I can think of, and for the ones it can’t, you’re talking about things so big a bigger power budget isn’t a problem.
Get Outlook for iOS https://aka.ms/o0ukef
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Friday, February 3, 2023 12:12:17 PM
To: AC0XU (Jim) James.Schatzman@ac0xu.com
Cc: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com; Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: General query about disciplining circuitry
Hi
With a moving platform, you get into the acceleration sensitivity of your oscillator.
That could be as high as 2x10^-9 / g. You might find a part down around 5x10^-10 / g.
Anything much past that gets you into an acceleration compensated
device. Those typically are a bit expensive and not an eBay sort of item.
If the motion is on a typical platform, you will need vibration
compensation to get to your
1x10^-11 range. This is one step up from acceleration compensation.
Price goes up yet again and surplus availability goes to near zero.
One approach for time is to simply use the time pulse out of the GPS
module. If you don’t care about the PPS edge staying aligned with the
(say) 10 MHz output it’s a valid solution to the problem. Accuracy wise, it’s going to win every time. Jitter wise … not so much.
Bob
On Feb 3, 2023, at 12:37 PM, AC0XU (Jim) James.Schatzman@ac0xu.com wrote:
1W is the notional power budget for the discipliner.
I am interested in optimizing designs for precision time, precision frequency, and precision time and frequency (three cases). I am o.k. with the idea of not adjusting the oscillator phase to perfectly match GNSS but to instead record and track the offset without actually tweaking the oscillator for time/phase. That might be the best, and maybe that approach reduces the distinction between precision time and precision frequency.
The goal for the loosest case is 1e-11 adev over 0.1 to 1000 sec, but I am interested in doing as well as the oscillator will support. In a future design I will be using an oscillator with 1e-12 adev @ 1 sec, but the current one is good for maybe 1e-11 @ 1 sec at best. The receiver platform is moving, and no radio mfr publishes performance specs for this case.
Thank you for reminding me about the sawtooth. I will need to study the sawtooth behavior of the radio. One I am looking at now is the OEM7 series.
Again, given that there are many possible approaches to precision phase measurement, and being pretty sure that I want to do more than implement a frequency counter, I am looking for advice.
Thanks!
At 09:31 AM 2/3/2023, Bob Camp wrote:
Hi
I would back up a bit first
.
What sort of oscillator is being disciplined? If the 1W is the
total power budget, that rules out most OCXO’s. Why ask? The stability of the oscillator does get into this pretty quickly.
What is the end goal? Are you after precision time or precision
frequency? While they are connected, the approach to optimize one is not quite the same at the approach for the other.
What are the stability goals either for time or frequency?
Is this a mobile / portable application? If so that also impacts a
lot of this and gets into a whole other set of questions.
To at least partly answer the question you asked:
The PPS comes out of the GPS at the same time as the sawtooth
correction information. In most cases, you want to marry those two
up immediately. That way the correction does apply to the data you took. Does this matter in your case? Thus the long list of questions above.
Bpb
On Feb 3, 2023, at 10:16 AM, AC0XU (Jim) via time-nuts time-nuts@lists.febo.com wrote:
I can image all sorts of disciplining circuits for controlling a digitally-controlled oscillator against GPS. Presumably, I will measure oscillator phase at the 1 PPS times and run those values into a Kalman Filter. I think my question is about how best to measure the oscillator phase, given the constraint of low electrical power (<1W). There are zillions of commercial devices that do this but the mfrs generally do not advertize the details. I plan to use either an MCU or an FPGA, depending on which is more advantageous.
I looked at
https://hackaday.io/project/6872-gps-disciplined-xcxo/detailshtt
ps://hackaday.io/project/6872-gps-disciplined-xcxo/details
and that seems interesting. I don't have to worry about VCO control because my oscillator has a digital control.
What about measuring the phase of a large divider PLL locked to the reference? With I-Q outputs the phase can be measured with a very slow ADC applied to a sample-and-hold triggered by the 1 PPS.
Thanks!
Jim
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe
send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send
an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-leave@lists.febo.com
Hi Jim,
there are a bunch of fairly low-complexity designs on EEVblog. Just to
name a few:
https://www.eevblog.com/forum/projects/lars-diy-gpsdo-with-arduino-and-1ns-resolution-tic/
https://www.eevblog.com/forum/projects/diy-gpsdo-project-w-stm32-tdc7200/
https://www.eevblog.com/forum/projects/yet-another-diy-gpsdo-yes-another-one/
https://www.eevblog.com/forum/projects/gpsdognssdo-stm32g4-u-blox-zed-f9t-tdc7200/
(disclaimer: my personal, currently stalled project)
Depending on your desired time tagging resolution, using an MCU timer
capture (with the timer driven by your oscillator) may already suffice.
Various STM32 advertise <10 ns capture resolution. If you require higher
resolution I'd suggest to use a TDC7200. For that extra effort to
amortize, I believe you need to rely on a dedicated timing GNSS receiver
and to implement time pulse quantization (sawtooth) correction.
Best regards,
Carsten
On 10.02.23 03:57, AC0XU (Jim) via time-nuts wrote:
Thanks to all for the various comments.
My question was really about how to make accurate phase measurements of an oscillator at the 1 PPS time tag output from a GNSS radio. There are some methods I can think of, but I am not finding one that has clear advantages of accuracy, immunity to all forms of noise on the oscillator output, and low complexity and power. I was hoping that someone out there had the perfect solution...
Thanks!
Jim
Hi Jim,
If I understand your question, you want a low cost precise method of
measuring 1pps phase relative to an independent oscillator?
If that is the case, then I would propose creating a linear ramp with at
least 10 samples in the linear region of the ramp from the pps and sampling
the ramp with a good ADC such as ADC3561 (10MHz assumed..). Least squares
fitting a line through the samples, and calculating the intersection with
the horizontal line preceding the ramp (in sim shown green is PPS in blue
is linear ramp). This is a cheap single supply version using a pfet
(ignore bss138, it was a bss84) to hold an integrator in reset until the
PPS arrives. On a dual supply version using a JFET, and a sampling rate
around 50MHz, a PPS arrival time measurement uncertainty of less than 20ps
has been achieved. There is a 3541 version of the TI ADC I referred to
which might be interfacable to a microcontroller with QSPI. I always use
FPGAs for this so...
Good luck. --mike
[image: image.png]
On Fri, Feb 10, 2023 at 9:09 AM AC0XU (Jim) via time-nuts <
time-nuts@lists.febo.com> wrote:
Thanks to all for the various comments.
My question was really about how to make accurate phase measurements of an
oscillator at the 1 PPS time tag output from a GNSS radio. There are some
methods I can think of, but I am not finding one that has clear advantages
of accuracy, immunity to all forms of noise on the oscillator output, and
low complexity and power. I was hoping that someone out there had the
perfect solution...
Thanks!
Jim
At 06:36 AM 2/9/2023, Ed Marciniak wrote:
It’s not going to be budget friendly, but the symmetricom (now Microsemi)
chip scale atomic clocks might get you there or close at least. You’d
probably have to ask someone about what the loop time constants are. If
they are something like 128 Hz, in theory the onboard quartz would be
disciplined by the atomic transition as fast as the frequency was
shifting…IF the loop filter once lock is achieved has the same bandwidth as
when it’s unlocked.
I’m struggling with why you’d need the equivalent of hertz per 100GHz
stability on that sort of power budget. A moving phase coherent receiver
suggests whatever you’re trying to transmit or receive should be designed
with a more forgiving frequency tracking loop. A carrier phase GNSS can
probably cover most of the other use cases I can think of, and for the ones
it can’t, you’re talking about things so big a bigger power budget isn’t a
problem.
Get https://aka.ms/o0ukefOutlook for iOS
From: Bob Camp via time-nuts time-nuts@lists.febo.com
Sent: Friday, February 3, 2023 12:12:17 PM
To: AC0XU (Jim) James.Schatzman@ac0xu.com
Cc: Discussion of precise time and frequency measurement <
time-nuts@lists.febo.com>; Bob Camp kb8tq@n1k.org
Subject: [time-nuts] Re: General query about disciplining circuitry
Hi
With a moving platform, you get into the acceleration sensitivity of your
oscillator.
That could be as high as 2x10^-9 / g. You might find a part down around
5x10^-10 / g.
Anything much past that gets you into an acceleration compensated device.
Those
typically are a bit expensive and not an eBay sort of item.
If the motion is on a typical platform, you will need vibration
compensation to get to your
1x10^-11 range. This is one step up from acceleration compensation. Price
goes up
yet again and surplus availability goes to near zero.
One approach for time is to simply use the time pulse out of the GPS
module. If you don’t
care about the PPS edge staying aligned with the (say) 10 MHz output it’s
a valid solution
to the problem. Accuracy wise, it’s going to win every time. Jitter wise
… not so much.
wrote:
1W is the notional power budget for the discipliner.
I am interested in optimizing designs for precision time, precision
frequency, and precision time and frequency (three cases). I am o.k. with
the idea of not adjusting the oscillator phase to perfectly match GNSS but
to instead record and track the offset without actually tweaking the
oscillator for time/phase. That might be the best, and maybe that approach
reduces the distinction between precision time and precision frequency.
The goal for the loosest case is 1e-11 adev over 0.1 to 1000 sec, but I
am interested in doing as well as the oscillator will support. In a future
design I will be using an oscillator with 1e-12 adev @ 1 sec, but the
current one is good for maybe 1e-11 @ 1 sec at best. The receiver platform
is moving, and no radio mfr publishes performance specs for this case.
Thank you for reminding me about the sawtooth. I will need to study the
sawtooth behavior of the radio. One I am looking at now is the OEM7 series.
Again, given that there are many possible approaches to precision phase
measurement, and being pretty sure that I want to do more than implement a
frequency counter, I am looking for advice.
Thanks!
At 09:31 AM 2/3/2023, Bob Camp wrote:
Hi
I would back up a bit first
.
What sort of oscillator is being disciplined? If the 1W is the total
power budget, that rules out
most OCXO’s. Why ask? The stability of the oscillator does get into
this pretty quickly.
What is the end goal? Are you after precision time or precision
frequency? While they are
connected, the approach to optimize one is not quite the same at the
approach for the other.
What are the stability goals either for time or frequency?
Is this a mobile / portable application? If so that also impacts a lot
of this and gets into a whole
other set of questions.
To at least partly answer the question you asked:
The PPS comes out of the GPS at the same time as the sawtooth
correction information. In
most cases, you want to marry those two up immediately. That way the
correction does apply
to the data you took. Does this matter in your case? Thus the long
list of questions above.
Bpb
On Feb 3, 2023, at 10:16 AM, AC0XU (Jim) via time-nuts <
time-nuts@lists.febo.com> wrote:
I can image all sorts of disciplining circuits for controlling a
digitally-controlled oscillator against GPS. Presumably, I will measure
oscillator phase at the 1 PPS times and run those values into a Kalman
Filter. I think my question is about how best to measure the oscillator
phase, given the constraint of low electrical power (<1W). There are
zillions of commercial devices that do this but the mfrs generally do not
advertize the details. I plan to use either an MCU or an FPGA, depending on
which is more advantageous.
https://hackaday.io/project/6872-gps-disciplined-xcxo/details>
https://hackaday.io/project/6872-gps-disciplined-xcxo/details
and that seems interesting. I don't have to worry about VCO control
because my oscillator has a digital control.
What about measuring the phase of a large divider PLL locked to the
reference? With I-Q outputs the phase can be measured with a very slow ADC
applied to a sample-and-hold triggered by the 1 PPS.
Thanks!
Jim
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
