Re: [time-nuts] Fw: New to list and GPSDO questions
As you drive down the road it is important that you do not over correct errors and look ahead and start turning before the car reaches the turn, your corrections have a delay in taking effect as well as a delay in knowing where on the road you are. You know where the car was but more important is where it will be when your correction takes effect. Stanley - Original Message - From: "Chris Howard" To: ; "Discussion of precise time and frequency measurement" Sent: Thursday, June 13, 2013 8:58 PM Subject: Re: [time-nuts] Fw: New to list and GPSDO questions I'm with Bob in that I don't really understand this description. And what are we trying to be in phase with? the 1PPS? Is it possible to reproduce the actual phase of the clock in the GPS birds once it has been through my GPS and come out as 1PPS? I picture the EFC steering the car straight down the road. And you want to adjust not just the drift to the right but steer back to the center of the lane. I think I get that part. I don't get who is setting the lane and why I should care. Do the statistics (ADEV, etc.) show that this is an improvement? If I'm doing my slow zigzag down the center line or the right shoulder, again, do I care? Chris w0ep On 6/13/2013 5:51 PM, Richard H McCorkle wrote: Hi Bob, The VE2ZAZ controller is a frequency locked loop that keeps the source on frequency but over time the phase drifts, as past corrections are not compensated for. When the system is stable every 16 seconds the 16-bit counter rolls over 2441 times with an extra 26624 counts (6800 HEX). The previous count is subtracted from the current count, the difference from 6800 HEX is used to update the EFC to correct the frequency, and the current count is stored as the previous count for the next sample. When the current difference is not exactly 6800 HEX then a phase shift of 6.25ns has occurred over the sample period for each count of the difference from 6800 HEX. The EFC corrects the frequency to give the proper 6800 HEX over the following samples, but the phase shift from the previous error during the correction period remains. If you add a little code to provide a correction history you can add phase correction to the VE2ZAZ controller as well. Once lock is established store the sample count as a phase reference count. Add 6800 HEX to the reference count every update and store the result as the next reference value. Use the difference between the current and previous samples from 6800 HEX to coarse correct the frequency as currently done, but add the difference between the current count and reference count to the EFC correction as a fine phase correction. If hold or unlock occurs disable the phase correction routine until lock is re-established. Then store a new reference and restart the phase correction process. By updating the reference every update it provides a phase history so the accumulated count error over time can be removed and the phase of the source can be stabilized. Richard Atilla, Isn't the VE2ZAZ circuit functionally equivalent to your example 3? Granted, he's not picking the 10 millionth transition and checking its phase difference to the reference, but I've only got a 1PPS reference with a 1uS or so jitter from pulse to pulse. Bert is averaging over 16 seconds, and creating a PWM signal to drive an integrator (simulating a DAC), which will drive a Trimble 34310-T. And like I mentioned earlier, I just like the way Bert did it. It has a kind of elegance that appeals to my inner hacker. =) Bob - AE6RV - Original Message - From: Attila Kinali To: Bob Stewart ; Discussion of precise time and frequency measurement Cc: Sent: Thursday, June 13, 2013 3:39 PM Subject: Re: [time-nuts] New to list and GPSDO questions snip [3] Describes how to use a clock synchronizer to build a GPSDO. Probably not the easiest and not the cheapest way, but definitly one with a very low parts count. snip [3] The AD9548 as a GPS Disciplined Stratum 2 Clock, by Gentile, 2009 http://www.analog.com/static/imported-files/application_notes/AN-1002.pdf ___ 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] Fw: New to list and GPSDO questions
Chris, I think I've figured it out. Here is the key phrase, I think: "The EFC corrects the frequency to give the proper 6800 HEX over the following samples, but the phase shift from the previous error during the correction period remains." Let's say that the frequency drifts off less than one cycle per second. Let's further say that it is a phase angle of 30 degrees. If we correct the frequency so that subsequently the frequency is spot on, the phase of our clock is still 30 degrees off. Let's say that that happens 11 more times. We are now a total of 360 degrees off in phase, but our frequency is exactly correct, and has been within our error tolerance through all 12 total error cycles. Without a phase correction our clock will wander around in phase, and thus in frequency, over the long term, though it will stay within tolerance over the short and medium term. If our clock was slightly fast this cycle, then we need to slow it down by just that much, i.e. that phase angle, on the next timing cycle. At least that's how I understand it. I need to think on it some more. Bob - Original Message - > From: Chris Howard > To: mccor...@ptialaska.net; Discussion of precise time and frequency > measurement > Cc: Bob Stewart > Sent: Thursday, June 13, 2013 8:58 PM > Subject: Re: [time-nuts] Fw: New to list and GPSDO questions > > > I'm with Bob in that I don't really understand this description. > > And what are we trying to be in phase with? the 1PPS? > Is it possible to reproduce the actual phase of the > clock in the GPS birds once it has been through my GPS > and come out as 1PPS? > > I picture the EFC steering the car straight down the road. > And you want to adjust not just the drift to the right but > steer back to the center of the lane. I think I get > that part. I don't get who is setting the lane > and why I should care. > > Do the statistics (ADEV, etc.) show that this is an improvement? > If I'm doing my slow zigzag down the center line or the > right shoulder, again, do I care? > > Chris > w0ep > > > > > > On 6/13/2013 5:51 PM, Richard H McCorkle wrote: >> Hi Bob, >> >> The VE2ZAZ controller is a frequency locked loop that keeps the source >> on frequency but over time the phase drifts, as past corrections are >> not compensated for. When the system is stable every 16 seconds the >> 16-bit counter rolls over 2441 times with an extra 26624 counts (6800 >> HEX). The previous count is subtracted from the current count, the >> difference from 6800 HEX is used to update the EFC to correct the >> frequency, and the current count is stored as the previous count for >> the next sample. When the current difference is not exactly 6800 HEX >> then a phase shift of 6.25ns has occurred over the sample period for >> each count of the difference from 6800 HEX. The EFC corrects the >> frequency to give the proper 6800 HEX over the following samples, but >> the phase shift from the previous error during the correction period >> remains. >> If you add a little code to provide a correction history you can >> add phase correction to the VE2ZAZ controller as well. Once lock is >> established store the sample count as a phase reference count. Add >> 6800 HEX to the reference count every update and store the result as >> the next reference value. Use the difference between the current and >> previous samples from 6800 HEX to coarse correct the frequency as >> currently done, but add the difference between the current count and >> reference count to the EFC correction as a fine phase correction. If >> hold or unlock occurs disable the phase correction routine until lock >> is re-established. Then store a new reference and restart the phase >> correction process. By updating the reference every update it provides >> a phase history so the accumulated count error over time can be >> removed and the phase of the source can be stabilized. >> >> Richard >> >>> >>> >>> Atilla, >>> >>> Isn't the VE2ZAZ circuit functionally equivalent to your example > 3? Granted, he's >>> not picking the 10 millionth transition and checking its phase >>> difference to the reference, but I've only got a 1PPS reference > with a >>> 1uS or so jitter from pulse to pulse. Bert is averaging over 16 >>> seconds, and creating a PWM signal to drive an integrator (simulating a > DAC), which >>> will drive a Trimble 34310-T. And like I mentioned >>> earlier, I just like the way Bert did it. It has
Re: [time-nuts] Fw: New to list and GPSDO questions
I'm with Bob in that I don't really understand this description. And what are we trying to be in phase with? the 1PPS? Is it possible to reproduce the actual phase of the clock in the GPS birds once it has been through my GPS and come out as 1PPS? I picture the EFC steering the car straight down the road. And you want to adjust not just the drift to the right but steer back to the center of the lane. I think I get that part. I don't get who is setting the lane and why I should care. Do the statistics (ADEV, etc.) show that this is an improvement? If I'm doing my slow zigzag down the center line or the right shoulder, again, do I care? Chris w0ep On 6/13/2013 5:51 PM, Richard H McCorkle wrote: > Hi Bob, > > The VE2ZAZ controller is a frequency locked loop that keeps the source > on frequency but over time the phase drifts, as past corrections are > not compensated for. When the system is stable every 16 seconds the > 16-bit counter rolls over 2441 times with an extra 26624 counts (6800 > HEX). The previous count is subtracted from the current count, the > difference from 6800 HEX is used to update the EFC to correct the > frequency, and the current count is stored as the previous count for > the next sample. When the current difference is not exactly 6800 HEX > then a phase shift of 6.25ns has occurred over the sample period for > each count of the difference from 6800 HEX. The EFC corrects the > frequency to give the proper 6800 HEX over the following samples, but > the phase shift from the previous error during the correction period > remains. > If you add a little code to provide a correction history you can > add phase correction to the VE2ZAZ controller as well. Once lock is > established store the sample count as a phase reference count. Add > 6800 HEX to the reference count every update and store the result as > the next reference value. Use the difference between the current and > previous samples from 6800 HEX to coarse correct the frequency as > currently done, but add the difference between the current count and > reference count to the EFC correction as a fine phase correction. If > hold or unlock occurs disable the phase correction routine until lock > is re-established. Then store a new reference and restart the phase > correction process. By updating the reference every update it provides > a phase history so the accumulated count error over time can be > removed and the phase of the source can be stabilized. > > Richard > >> >> >> Atilla, >> >> Isn't the VE2ZAZ circuit functionally equivalent to your example 3? >> Granted, he's >> not picking the 10 millionth transition and checking its phase >> difference to the reference, but I've only got a 1PPS reference with a >> 1uS or so jitter from pulse to pulse. Bert is averaging over 16 >> seconds, and creating a PWM signal to drive an integrator (simulating a >> DAC), which >> will drive a Trimble 34310-T. And like I mentioned >> earlier, I just like the way Bert did it. It has a kind of elegance >> that appeals to my inner hacker. =) >> >> >> Bob - AE6RV >> >> >> >> - Original Message - >>> From: Attila Kinali >>> To: Bob Stewart ; Discussion of precise time and frequency >>> measurement >>> Cc: >>> Sent: Thursday, June 13, 2013 3:39 PM >>> Subject: Re: [time-nuts] New to list and GPSDO questions >> snip >>> [3] Describes how to use a clock >> synchronizer to build a GPSDO. Probably >>> not the easiest and not the cheapest way, but definitly one with a very >>> low parts count. >> snip >>> [3] The AD9548 as a GPS Disciplined Stratum 2 Clock, by Gentile, 2009 >>> http://www.analog.com/static/imported-files/application_notes/AN-1002.pdf >> ___ >> 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] Fw: New to list and GPSDO questions
OK, I believe you. I can see I have a lot to learn. Bob - Original Message - > From: Richard H McCorkle > To: Bob Stewart ; Discussion of precise time and frequency > measurement > Cc: > Sent: Thursday, June 13, 2013 7:04 PM > Subject: Re: [time-nuts] Fw: New to list and GPSDO questions > > Hi Bob, > Any user of a Brooks Shera controller will tell you that phase errors > can be recovered using a jittery 1PPS reference. While the 1PPS may > jitter (+/- 42ns in a UT+ GPS) the jitter averages out to zero error > over time. The Shera controller uses the phase difference between the > 1PPS and divided by 16 source to drive the EFC to maintain a constant > phase difference. The Shera design updates every 30 seconds and in > mode 1 the phase error from setpoint is sent directly to a DAC to > correct the frequency. Shera adds a selectable filter before the DAC > to reduce the EFC noise and increase the correction stability. More > samples averaged over a longer period increases the stability, but > smaller corrections are applied over a longer period to make the > phase (frequency) correction. > > Richard > > > >> Hi Richard, >> >> As time goes by, I'll reread your post until I understand it. I'm > a newbie, but >> It's hard to believe that there is enough information in a jittery 1PPS > reference >> pulse to be able to recover phase errors. >> >> Bob >> >> >> >> - Original Message - >>> From: Richard H McCorkle >>> To: Bob Stewart ; Discussion of precise time and > frequency >>> measurement >>> Cc: >>> Sent: Thursday, June 13, 2013 5:51 PM >>> Subject: Re: [time-nuts] Fw: New to list and GPSDO questions >>> >>> Hi Bob, >>> >>> The VE2ZAZ controller is a frequency locked loop that keeps the source >>> on frequency but over time the phase drifts, as past corrections are >>> not compensated for. >> ___ >> 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] Fw: New to list and GPSDO questions
Hi Bob, Any user of a Brooks Shera controller will tell you that phase errors can be recovered using a jittery 1PPS reference. While the 1PPS may jitter (+/- 42ns in a UT+ GPS) the jitter averages out to zero error over time. The Shera controller uses the phase difference between the 1PPS and divided by 16 source to drive the EFC to maintain a constant phase difference. The Shera design updates every 30 seconds and in mode 1 the phase error from setpoint is sent directly to a DAC to correct the frequency. Shera adds a selectable filter before the DAC to reduce the EFC noise and increase the correction stability. More samples averaged over a longer period increases the stability, but smaller corrections are applied over a longer period to make the phase (frequency) correction. Richard > Hi Richard, > > As time goes by, I'll reread your post until I understand it. I'm a newbie, > but > It's hard to believe that there is enough information in a jittery 1PPS > reference > pulse to be able to recover phase errors. > > Bob > > > > - Original Message - >> From: Richard H McCorkle >> To: Bob Stewart ; Discussion of precise time and frequency >> measurement >> Cc: >> Sent: Thursday, June 13, 2013 5:51 PM >> Subject: Re: [time-nuts] Fw: New to list and GPSDO questions >> >> Hi Bob, >> >> The VE2ZAZ controller is a frequency locked loop that keeps the source >> on frequency but over time the phase drifts, as past corrections are >> not compensated for. > ___ > 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] Fw: New to list and GPSDO questions
Hi Bob, The VE2ZAZ controller is a frequency locked loop that keeps the source on frequency but over time the phase drifts, as past corrections are not compensated for. When the system is stable every 16 seconds the 16-bit counter rolls over 2441 times with an extra 26624 counts (6800 HEX). The previous count is subtracted from the current count, the difference from 6800 HEX is used to update the EFC to correct the frequency, and the current count is stored as the previous count for the next sample. When the current difference is not exactly 6800 HEX then a phase shift of 6.25ns has occurred over the sample period for each count of the difference from 6800 HEX. The EFC corrects the frequency to give the proper 6800 HEX over the following samples, but the phase shift from the previous error during the correction period remains. If you add a little code to provide a correction history you can add phase correction to the VE2ZAZ controller as well. Once lock is established store the sample count as a phase reference count. Add 6800 HEX to the reference count every update and store the result as the next reference value. Use the difference between the current and previous samples from 6800 HEX to coarse correct the frequency as currently done, but add the difference between the current count and reference count to the EFC correction as a fine phase correction. If hold or unlock occurs disable the phase correction routine until lock is re-established. Then store a new reference and restart the phase correction process. By updating the reference every update it provides a phase history so the accumulated count error over time can be removed and the phase of the source can be stabilized. Richard > > > Atilla, > > Isn't the VE2ZAZ circuit functionally equivalent to your example 3? Granted, > he's > not picking the 10 millionth transition and checking its phase > difference to the reference, but I've only got a 1PPS reference with a > 1uS or so jitter from pulse to pulse. Bert is averaging over 16 > seconds, and creating a PWM signal to drive an integrator (simulating a DAC), > which > will drive a Trimble 34310-T. And like I mentioned > earlier, I just like the way Bert did it. It has a kind of elegance > that appeals to my inner hacker. =) > > > Bob - AE6RV > > > > - Original Message - >> From: Attila Kinali >> To: Bob Stewart ; Discussion of precise time and frequency >> measurement >> Cc: >> Sent: Thursday, June 13, 2013 3:39 PM >> Subject: Re: [time-nuts] New to list and GPSDO questions > snip >> [3] Describes how to use a clock > synchronizer to build a GPSDO. Probably >> not the easiest and not the cheapest way, but definitly one with a very >> low parts count. > snip >> [3] The AD9548 as a GPS Disciplined Stratum 2 Clock, by Gentile, 2009 >> http://www.analog.com/static/imported-files/application_notes/AN-1002.pdf > ___ > 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] Fw: New to list and GPSDO questions
Hi Richard, As time goes by, I'll reread your post until I understand it. I'm a newbie, but It's hard to believe that there is enough information in a jittery 1PPS reference pulse to be able to recover phase errors. Bob - Original Message - > From: Richard H McCorkle > To: Bob Stewart ; Discussion of precise time and frequency > measurement > Cc: > Sent: Thursday, June 13, 2013 5:51 PM > Subject: Re: [time-nuts] Fw: New to list and GPSDO questions > > Hi Bob, > > The VE2ZAZ controller is a frequency locked loop that keeps the source > on frequency but over time the phase drifts, as past corrections are > not compensated for. ___ 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] Fw: New to list and GPSDO questions
Atilla, Isn't the VE2ZAZ circuit functionally equivalent to your example 3? Granted, he's not picking the 10 millionth transition and checking its phase difference to the reference, but I've only got a 1PPS reference with a 1uS or so jitter from pulse to pulse. Bert is averaging over 16 seconds, and creating a PWM signal to drive an integrator (simulating a DAC), which will drive a Trimble 34310-T. And like I mentioned earlier, I just like the way Bert did it. It has a kind of elegance that appeals to my inner hacker. =) Bob - AE6RV - Original Message - > From: Attila Kinali > To: Bob Stewart ; Discussion of precise time and frequency > measurement > Cc: > Sent: Thursday, June 13, 2013 3:39 PM > Subject: Re: [time-nuts] New to list and GPSDO questions snip > [3] Describes how to use a clock synchronizer to build a GPSDO. Probably > not the easiest and not the cheapest way, but definitly one with a very > low parts count. snip > [3] The AD9548 as a GPS Disciplined Stratum 2 Clock, by Gentile, 2009 > http://www.analog.com/static/imported-files/application_notes/AN-1002.pdf ___ 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.
