JS
Javier Serrano
Fri, Feb 6, 2015 9:21 AM
Dear all,
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
Thanks!
Javier
[1] http://www.ohwr.org/projects/white-rabbit/wiki
Dear all,
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
Thanks!
Javier
[1] http://www.ohwr.org/projects/white-rabbit/wiki
TS
Tim Shoppa
Fri, Feb 6, 2015 11:56 AM
The state of the art 20 years ago is described here:
http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf
They understood their OCXO very very well. And you can find EFC trends on
the web for hundreds of different Z3801A's (and similar) if you want to see
how the EFC trends (and occasionally jumps). It is very intuitive to watch
the smoothed EFC graphs build over time.
They were specifically meeting a telco spec for 24 hour holdover. Your 3
second requirement is, um, a bit different! I have no idea what your local
clock is, or what you are locking to, if 3 seconds is a long time.
Tim N3QE
On Fri, Feb 6, 2015 at 4:21 AM, Javier Serrano <
javier.serrano.pareja@gmail.com> wrote:
Dear all,
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
Thanks!
Javier
[1] http://www.ohwr.org/projects/white-rabbit/wiki
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.
The state of the art 20 years ago is described here:
http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf
They understood their OCXO very very well. And you can find EFC trends on
the web for hundreds of different Z3801A's (and similar) if you want to see
how the EFC trends (and occasionally jumps). It is very intuitive to watch
the smoothed EFC graphs build over time.
They were specifically meeting a telco spec for 24 hour holdover. Your 3
second requirement is, um, a bit different! I have no idea what your local
clock is, or what you are locking to, if 3 seconds is a long time.
Tim N3QE
On Fri, Feb 6, 2015 at 4:21 AM, Javier Serrano <
javier.serrano.pareja@gmail.com> wrote:
> Dear all,
>
> We would like to start working on holdover performance for White
> Rabbit [1]. This is a new domain for us. Our main use case is a WR
> switch losing its reference because someone disconnects a fiber. We
> can have redundancy, but it will take some time for a switch to change
> over to another reference. During this time, the oscillator in that
> switch will be free-running. We want to minimize the phase drift
> during that interval, which we think should be a couple of seconds
> maximum. We have never worked on holdover, and I am wondering if we
> can do something smarter than the obvious feeding of some constant
> voltage to the VCXO, based on averaging during the locked state. Does
> anybody know of any good references on holdover?
>
> Thanks!
>
> Javier
>
> [1] http://www.ohwr.org/projects/white-rabbit/wiki
> _______________________________________________
> 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.
>
JL
Jim Lux
Fri, Feb 6, 2015 12:55 PM
On 2/6/15 1:21 AM, Javier Serrano wrote:
Dear all,
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
The only thing that might be better is if you have a control loop that
forms a model and generates corrections based on that, so that while you
holdover, it's not just a constant tuning voltage, but perhaps a slow ramp.
For instance, if your control loop has estimated the aging rate (and you
have an oscillator that ages really, really fast), you could do that.
or if your control loop ingests the temperature and has calculated the
temperature/frequency transfer function.
But it seems that you have a fairly short holdover time requirement
(seconds, maybe a few minutes?) I'm not sure the environment changes all
that much in that time span. A simple "hold the control voltage" might
be as good as it gets.
I've looked into more complex schemes for situations where you are
tracking out something that changes fairly rapidly (Doppler shift for an
orbiter) and in a way that isn't a nice linear slope (which could be
done nicely by a PID kind of loop).
On 2/6/15 1:21 AM, Javier Serrano wrote:
> Dear all,
>
> We would like to start working on holdover performance for White
> Rabbit [1]. This is a new domain for us. Our main use case is a WR
> switch losing its reference because someone disconnects a fiber. We
> can have redundancy, but it will take some time for a switch to change
> over to another reference. During this time, the oscillator in that
> switch will be free-running. We want to minimize the phase drift
> during that interval, which we think should be a couple of seconds
> maximum. We have never worked on holdover, and I am wondering if we
> can do something smarter than the obvious feeding of some constant
> voltage to the VCXO, based on averaging during the locked state. Does
> anybody know of any good references on holdover?
>
The only thing that might be better is if you have a control loop that
forms a model and generates corrections based on that, so that while you
holdover, it's not just a constant tuning voltage, but perhaps a slow ramp.
For instance, if your control loop has estimated the aging rate (and you
have an oscillator that ages really, really fast), you could do that.
or if your control loop ingests the temperature and has calculated the
temperature/frequency transfer function.
But it seems that you have a fairly short holdover time requirement
(seconds, maybe a few minutes?) I'm not sure the environment changes all
that much in that time span. A simple "hold the control voltage" might
be as good as it gets.
I've looked into more complex schemes for situations where you are
tracking out something that changes fairly rapidly (Doppler shift for an
orbiter) and in a way that isn't a nice linear slope (which could be
done nicely by a PID kind of loop).
AK
Attila Kinali
Fri, Feb 6, 2015 1:58 PM
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
I think you are looking for something like [1]. I think [2] could be also
of help, although it's not as good as the Nicholls paper. Zhou's paper [3]
seems to be very similar to what Nicholls did (i have not fully read it yet).
HTH
Attila Kinali
[1] "Adaptive OXCO Drift Correction Algorithm", by Nicholls and Carlton, 2004
http://dx.doi.org/10.1109/FREQ.2004.1418510
[2] "A Frequency Model for OCXO for Holdover Mode of DP-PLL",
by Hwang, Shin, Han, Kim, 2000
http://dx.doi.org/10.1109/SICE.2000.889649
[3] "Adaptive Correction Method for an OCXO and Investagion of Analytical
Cummulative Time Eror Upperbound", by Zhou, Kunz, Schwartz, 2011
http://www.sce.carleton.ca/faculty/schwartz/abstracts/HuiPaperschwartz.pdf
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
On Fri, 6 Feb 2015 10:21:08 +0100
Javier Serrano <javier.serrano.pareja@gmail.com> wrote:
> We would like to start working on holdover performance for White
> Rabbit [1]. This is a new domain for us. Our main use case is a WR
> switch losing its reference because someone disconnects a fiber. We
> can have redundancy, but it will take some time for a switch to change
> over to another reference. During this time, the oscillator in that
> switch will be free-running. We want to minimize the phase drift
> during that interval, which we think should be a couple of seconds
> maximum. We have never worked on holdover, and I am wondering if we
> can do something smarter than the obvious feeding of some constant
> voltage to the VCXO, based on averaging during the locked state. Does
> anybody know of any good references on holdover?
I think you are looking for something like [1]. I think [2] could be also
of help, although it's not as good as the Nicholls paper. Zhou's paper [3]
seems to be very similar to what Nicholls did (i have not fully read it yet).
HTH
Attila Kinali
[1] "Adaptive OXCO Drift Correction Algorithm", by Nicholls and Carlton, 2004
http://dx.doi.org/10.1109/FREQ.2004.1418510
[2] "A Frequency Model for OCXO for Holdover Mode of DP-PLL",
by Hwang, Shin, Han, Kim, 2000
http://dx.doi.org/10.1109/SICE.2000.889649
[3] "Adaptive Correction Method for an OCXO and Investagion of Analytical
Cummulative Time Eror Upperbound", by Zhou, Kunz, Schwartz, 2011
http://www.sce.carleton.ca/faculty/schwartz/abstracts/HuiPaperschwartz.pdf
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
MD
Magnus Danielson
Fri, Feb 6, 2015 6:13 PM
Javier,
If you are aim to do hold-over as you switch between two sources, you
are looking at reasonably short times, then just keep a fixed voltage to
the oscillator suffice.
Even if you need a little longer times, say 10-20 s, it suffice.
Temperature changes and oscillator drift may be the main problems for
longer times.
Cheers,
Magnus
On 02/06/2015 10:21 AM, Javier Serrano wrote:
Dear all,
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
Thanks!
Javier
[1] http://www.ohwr.org/projects/white-rabbit/wiki
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.
Javier,
If you are aim to do hold-over as you switch between two sources, you
are looking at reasonably short times, then just keep a fixed voltage to
the oscillator suffice.
Even if you need a little longer times, say 10-20 s, it suffice.
Temperature changes and oscillator drift may be the main problems for
longer times.
Cheers,
Magnus
On 02/06/2015 10:21 AM, Javier Serrano wrote:
> Dear all,
>
> We would like to start working on holdover performance for White
> Rabbit [1]. This is a new domain for us. Our main use case is a WR
> switch losing its reference because someone disconnects a fiber. We
> can have redundancy, but it will take some time for a switch to change
> over to another reference. During this time, the oscillator in that
> switch will be free-running. We want to minimize the phase drift
> during that interval, which we think should be a couple of seconds
> maximum. We have never worked on holdover, and I am wondering if we
> can do something smarter than the obvious feeding of some constant
> voltage to the VCXO, based on averaging during the locked state. Does
> anybody know of any good references on holdover?
>
> Thanks!
>
> Javier
>
> [1] http://www.ohwr.org/projects/white-rabbit/wiki
> _______________________________________________
> 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.
>
JS
Javier Serrano
Mon, Feb 9, 2015 12:50 PM
This is a great list. Thanks everyone! Much of the material relates to
cases where good holdover needs to be maintained for several hours,
but there's a lot of insight to be gained from the reading, and I am
sure those techniques will come in handy for other projects. Thanks
again!
Javier
On Fri, Feb 6, 2015 at 2:58 PM, Attila Kinali attila@kinali.ch wrote:
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
I think you are looking for something like [1]. I think [2] could be also
of help, although it's not as good as the Nicholls paper. Zhou's paper [3]
seems to be very similar to what Nicholls did (i have not fully read it yet).
HTH
Attila Kinali
[1] "Adaptive OXCO Drift Correction Algorithm", by Nicholls and Carlton, 2004
http://dx.doi.org/10.1109/FREQ.2004.1418510
[2] "A Frequency Model for OCXO for Holdover Mode of DP-PLL",
by Hwang, Shin, Han, Kim, 2000
http://dx.doi.org/10.1109/SICE.2000.889649
[3] "Adaptive Correction Method for an OCXO and Investagion of Analytical
Cummulative Time Eror Upperbound", by Zhou, Kunz, Schwartz, 2011
http://www.sce.carleton.ca/faculty/schwartz/abstracts/HuiPaperschwartz.pdf
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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.
This is a great list. Thanks everyone! Much of the material relates to
cases where good holdover needs to be maintained for several hours,
but there's a lot of insight to be gained from the reading, and I am
sure those techniques will come in handy for other projects. Thanks
again!
Javier
On Fri, Feb 6, 2015 at 2:58 PM, Attila Kinali <attila@kinali.ch> wrote:
> On Fri, 6 Feb 2015 10:21:08 +0100
> Javier Serrano <javier.serrano.pareja@gmail.com> wrote:
>
>> We would like to start working on holdover performance for White
>> Rabbit [1]. This is a new domain for us. Our main use case is a WR
>> switch losing its reference because someone disconnects a fiber. We
>> can have redundancy, but it will take some time for a switch to change
>> over to another reference. During this time, the oscillator in that
>> switch will be free-running. We want to minimize the phase drift
>> during that interval, which we think should be a couple of seconds
>> maximum. We have never worked on holdover, and I am wondering if we
>> can do something smarter than the obvious feeding of some constant
>> voltage to the VCXO, based on averaging during the locked state. Does
>> anybody know of any good references on holdover?
>
> I think you are looking for something like [1]. I think [2] could be also
> of help, although it's not as good as the Nicholls paper. Zhou's paper [3]
> seems to be very similar to what Nicholls did (i have not fully read it yet).
>
> HTH
>
> Attila Kinali
>
>
>
> [1] "Adaptive OXCO Drift Correction Algorithm", by Nicholls and Carlton, 2004
> http://dx.doi.org/10.1109/FREQ.2004.1418510
>
> [2] "A Frequency Model for OCXO for Holdover Mode of DP-PLL",
> by Hwang, Shin, Han, Kim, 2000
> http://dx.doi.org/10.1109/SICE.2000.889649
>
> [3] "Adaptive Correction Method for an OCXO and Investagion of Analytical
> Cummulative Time Eror Upperbound", by Zhou, Kunz, Schwartz, 2011
> http://www.sce.carleton.ca/faculty/schwartz/abstracts/HuiPaperschwartz.pdf
>
> --
> It is upon moral qualities that a society is ultimately founded. All
> the prosperity and technological sophistication in the world is of no
> use without that foundation.
> -- Miss Matheson, The Diamond Age, Neil Stephenson
> _______________________________________________
> 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.
PA
pablo alvarez
Thu, Apr 2, 2015 10:35 AM
Hi Javier,
As far as I understand in WR both references are synchronous. Why don't you
try to track both references (or N references) simultanously? If you take
care of the design, your performance should increase while locked and the
transition from one reference to the other if you ever miss one should be
smoother.
Cheers,
Pablo
On Fri, Feb 6, 2015 at 10:21 AM, Javier Serrano <
javier.serrano.pareja@gmail.com> wrote:
Dear all,
We would like to start working on holdover performance for White
Rabbit [1]. This is a new domain for us. Our main use case is a WR
switch losing its reference because someone disconnects a fiber. We
can have redundancy, but it will take some time for a switch to change
over to another reference. During this time, the oscillator in that
switch will be free-running. We want to minimize the phase drift
during that interval, which we think should be a couple of seconds
maximum. We have never worked on holdover, and I am wondering if we
can do something smarter than the obvious feeding of some constant
voltage to the VCXO, based on averaging during the locked state. Does
anybody know of any good references on holdover?
Thanks!
Javier
[1] http://www.ohwr.org/projects/white-rabbit/wiki
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.
Hi Javier,
As far as I understand in WR both references are synchronous. Why don't you
try to track both references (or N references) simultanously? If you take
care of the design, your performance should increase while locked and the
transition from one reference to the other if you ever miss one should be
smoother.
Cheers,
Pablo
On Fri, Feb 6, 2015 at 10:21 AM, Javier Serrano <
javier.serrano.pareja@gmail.com> wrote:
> Dear all,
>
> We would like to start working on holdover performance for White
> Rabbit [1]. This is a new domain for us. Our main use case is a WR
> switch losing its reference because someone disconnects a fiber. We
> can have redundancy, but it will take some time for a switch to change
> over to another reference. During this time, the oscillator in that
> switch will be free-running. We want to minimize the phase drift
> during that interval, which we think should be a couple of seconds
> maximum. We have never worked on holdover, and I am wondering if we
> can do something smarter than the obvious feeding of some constant
> voltage to the VCXO, based on averaging during the locked state. Does
> anybody know of any good references on holdover?
>
> Thanks!
>
> Javier
>
> [1] http://www.ohwr.org/projects/white-rabbit/wiki
> _______________________________________________
> 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.
>
