From: Bob Camp <kb8tq@n1k.org>

   From: Scott Stobbe <scott.j.stobbe@gmail.com>

Hi Thermocouples in test leads are nasty because they operate on the temperature delta rather than the absolute temperature. It’s the gradient you have to worry about. Until you have run out a few dozen sensors around your bench (or test chamber) and monitored them for a few days … you won’t believe just how little “point A” has in common with “point B”. Bob > On Nov 7, 2016, at 1:44 PM, Bob Stewart <bob@evoria.net> wrote: > > -accidentally omitted timenuts from my reply to bob- > Hi Bob, > The data is at the 10uV level. As to whether I've plotted "data" or data, I can only report what I have. It seems to be consistent over the long run. I would expect to see something else if it were just noise. If the 4 attachments were strongly thermocoupled, wouldn't the data have a stronger correlation to temperature, rather than just to temperature transients? > > Bob ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net> > Cc: Discussion of Precise Time and Frequency Measurement <time-nuts@febo.com> > Sent: Monday, November 7, 2016 11:54 AM > Subject: Re: [time-nuts] Thermal impact on OCXO > > Hi > > I would suggest you read the papers on the subject. They are out there. Even over a few days > OCXO aging is likely to be non-linear ( => curved, not straight line). On an OCXO that is > warming up, your are dealing with retrace rather than aging. This can have an impact for a > few months after turn on. I have one unit in the basement that took 9 months to come out > of retrace after being in storage for “a while”. It was an eBay item so no idea just how long > the power off time was. > > Bob > > >> On Nov 7, 2016, at 12:47 PM, Bob Stewart <bob@evoria.net> wrote: >> >> Hi Bob, >> >> When you say that OCXOs don't age in a linear fashion, what does that mean? IOW, is this a case where it's almost linear over a week, and the non-linearity is only detectable when you consider the longer term? If that's the case, then it seems reasonable to use the past 3 or so days of data collection to project the near-term behavior; where near-term is less than 3 days into the future. >> >> Bob >> >> ----------------------------------------------------------------- >> AE6RV.com >> >> GFS GPSDO list: >> groups.yahoo.com/neo/groups/GFS-GPSDOs/info >> >> >> From: Bob Camp <kb8tq@n1k.org> >> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> >> Cc: Scott Stobbe <scott.j.stobbe@gmail.com> >> Sent: Monday, November 7, 2016 6:08 AM >> Subject: Re: [time-nuts] Thermal impact on OCXO >> >> Hi >> >> >>> On Nov 5, 2016, at 10:43 PM, Bob Stewart <bob@evoria.net> wrote: >>> >>> Hi Scott, >>> D'oh. Thanks for the correction! Like I said, I don't do these calculations often. >>> >>> If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit stumped. I do have an op-amp in the EFC string with a voltage divider for gain. The resistors are Panasonic ERA-6AEDxxxV resistors. Mouser says they're temperature stable to 25PPM/C, but of course they don't mention an aging rate. I don't really see anything else, other than the OCXO, that is likely to be prone to a linear type of aging. >> >> OCXO’s don’t age in a linear fashion. At least 90% of them don’t. If you dig into the FCS papers there are various >> curves proposed as models. Mil-O-55310 has one of them as the “official” approach. All of them have the basic >> issue of mistakenly fitting to to short a time constraint. >> >> Bob >> >>> The aging rate appears to be stable from unit to unit, so naturally I considered the OCXO first. >>> >>> There is one other bit in the EFC string that might be controversial, but I don't see that it would be a candidate for the symptoms of aging. >>> >>> Bob >>> ----------------------------------------------------------------- >>> AE6RV.com >>> >>> GFS GPSDO list: >>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info >>> >>> From: Scott Stobbe <scott.j.stobbe@gmail.com> >>> To: Bob Stewart <bob@evoria.net> >>> Cc: Discussion of Precise Time and Frequency Measurement <time-nuts@febo.com> >>> Sent: Saturday, November 5, 2016 9:19 PM >>> Subject: Re: [time-nuts] Thermal impact on OCXO >>> >>> If your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the EFC range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1 LSB is ~1PPT. So, if everything else is stable the DAC code reflects changes solely due to the OCXO, which would be an aging of 24 PPT/day. >>> On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <bob@evoria.net> wrote: >>> >>> Hi Scott, >>> The 20 bits span about 6 volts. The EFC range spans about 8Hz (+/-4Hz). I don't do these calculations every day, but that's about 4.5PPT? >>> Bob ------------------------------ ------------------------------ ----- >>> AE6RV.com >>> >>> GFS GPSDO list: >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info >>> >>> >>> >>> From: Scott Stobbe <scott.j.stobbe@gmail.com> >>> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> >>> Sent: Saturday, November 5, 2016 8:38 PM >>> Subject: Re: [time-nuts] Thermal impact on OCXO >>> >>> I think that's a nice plot, it looks like you have stepped 160 LSB over 7 days or roughly 1 LSB per hour. With a 20bit dac you are trimming maybe 1 ppt/LSB to 4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB, solely due to drift, you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the case of 4ppt/hour your at 1E-12 at 1280 s. Seems reasonable. >>> On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <bob@evoria.net> wrote: >>> >>> Oh dear. I attached the wrong file. Here's the correct one. >>> ----------------------------- ------------------------------ ------ >>> AE6RV.com >>> >>> GFS GPSDO list: >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info >>> >>> >>> >>> ______________________________ _________________ >>> 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.

  From: Bob Camp <kb8tq@n1k.org>

Hi Bob, OK, given that, what is your view of the plot I presented?  Let's remember that I plotted this because I was trying to discover whether the EFC circuitry has a time-related drift, or  whether the DAC value drift I plotted with the GPSDO locked to the GPS was caused by the OCXO. In one of your posts today, you talked about a long-term retrace lasting some months.  I've been using the term "aging".  Has my choice of terms caused the discussion to take a turn that it wouldn't have taken if I had used the term "retrace"?  The fact is that I don't know whether it's aging or retrace.  I'm not really clear on how to tell the difference.  I'm especially handicapped by not having the mfg specs for the OCXOs I use.  It could be that I simply haven't had the test unit under power for long enough to let the OCXO settle out.  And for sure when I added the test lead to the EFC (breaking a trace in the process) there was enough off time to thoroughly insult the OCXO. Bob ----------------------------------------------------------------- AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Bob Camp <kb8tq@n1k.org> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Monday, November 7, 2016 1:01 PM Subject: Re: [time-nuts] Thermal impact on OCXO Hi Thermocouples in test leads are nasty because they operate on the temperature delta rather than the absolute temperature. It’s the gradient you have to worry about. Until you have run out a few dozen sensors around your bench (or test chamber) and monitored them for a few days … you won’t believe just how little “point A” has in common with “point B”. Bob > On Nov 7, 2016, at 1:44 PM, Bob Stewart <bob@evoria.net> wrote: > > -accidentally omitted timenuts from my reply to bob- > Hi Bob, > The data is at the 10uV level.  As to whether I've plotted "data" or data, I can only report what I have.  It seems to be consistent over the long run.  I would expect to see something else if it were just noise.  If the 4 attachments were strongly thermocoupled, wouldn't the data have a stronger correlation to temperature, rather than just to temperature transients? > > Bob ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > >      From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net> > Cc: Discussion of Precise Time and Frequency Measurement <time-nuts@febo.com> > Sent: Monday, November 7, 2016 11:54 AM > Subject: Re: [time-nuts] Thermal impact on OCXO > > Hi > > I would suggest you read the papers on the subject. They are out there. Even over a few days > OCXO aging is likely to be non-linear ( => curved, not straight line). On an OCXO that is > warming up, your are dealing with retrace rather than aging. This can have an impact for a > few months after turn on. I have one unit in the basement that took 9 months to come out > of retrace after being in storage for “a while”. It was an eBay item so no idea just how long > the power off time was. > > Bob > > >> On Nov 7, 2016, at 12:47 PM, Bob Stewart <bob@evoria.net> wrote: >> >> Hi Bob, >> >> When you say that OCXOs don't age in a linear fashion, what does that mean?  IOW, is this a case where it's almost linear over a week, and the non-linearity is only detectable when you consider the longer term?  If that's the case, then it seems reasonable to use the past 3 or so days of data collection to project the near-term behavior; where near-term is less than 3 days into the future. >> >> Bob >>  >> ----------------------------------------------------------------- >> AE6RV.com >> >> GFS GPSDO list: >> groups.yahoo.com/neo/groups/GFS-GPSDOs/info >> >> >> From: Bob Camp <kb8tq@n1k.org> >> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> >> Cc: Scott Stobbe <scott.j.stobbe@gmail.com> >> Sent: Monday, November 7, 2016 6:08 AM >> Subject: Re: [time-nuts] Thermal impact on OCXO >> >> Hi >> >> >>> On Nov 5, 2016, at 10:43 PM, Bob Stewart <bob@evoria.net> wrote: >>> >>> Hi Scott, >>> D'oh.  Thanks for the correction!  Like I said, I don't do these calculations often.  >>> >>> If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit stumped.  I do have an op-amp in the EFC string with  a voltage divider for gain.  The resistors are Panasonic ERA-6AEDxxxV resistors.  Mouser says they're temperature stable to 25PPM/C, but of course they don't mention an aging rate.  I don't really see anything else, other than the OCXO, that is likely to be prone to a linear type of aging. >> >> OCXO’s don’t age in a linear fashion. At least 90% of them don’t. If you dig into the FCS papers there are various >> curves proposed as models. Mil-O-55310 has one of them as the “official” approach. All of them have the basic >> issue of mistakenly fitting to to short a time constraint. >> >> Bob >> >>>  The aging rate appears to be stable from unit to unit, so naturally I considered the OCXO first.  >>> >>> There is one other bit in the EFC string that might be controversial, but I don't see that it would be a candidate for the symptoms of aging. >>> >>> Bob >>>  ----------------------------------------------------------------- >>> AE6RV.com >>> >>> GFS GPSDO list: >>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info >>> >>>      From: Scott Stobbe <scott.j.stobbe@gmail.com> >>> To: Bob Stewart <bob@evoria.net> >>> Cc: Discussion of Precise Time and Frequency Measurement <time-nuts@febo.com> >>> Sent: Saturday, November 5, 2016 9:19 PM >>> Subject: Re: [time-nuts] Thermal impact on OCXO >>> >>> If your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the EFC range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1 LSB is ~1PPT. So, if everything else is stable the DAC code reflects changes solely due to the OCXO, which would be an aging of 24 PPT/day. >>> On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <bob@evoria.net> wrote: >>> >>> Hi Scott, >>> The 20 bits span about 6 volts.  The EFC range spans about 8Hz (+/-4Hz).  I don't do these calculations every day, but that's about 4.5PPT? >>> Bob  ------------------------------ ------------------------------ ----- >>> AE6RV.com >>> >>> GFS GPSDO list: >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info >>> >>> >>> >>> From: Scott Stobbe <scott.j.stobbe@gmail.com> >>> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> >>> Sent: Saturday, November 5, 2016 8:38 PM >>> Subject: Re: [time-nuts] Thermal impact on OCXO >>> >>> I think that's a nice plot, it looks like you have stepped 160 LSB over 7 days or roughly 1 LSB per hour. With a 20bit dac you are trimming maybe 1 ppt/LSB to 4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB, solely due to drift, you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the case of 4ppt/hour your at 1E-12 at 1280 s. Seems reasonable. >>> On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <bob@evoria.net> wrote: >>> >>> Oh dear.  I attached the wrong file.  Here's the correct one. >>>  ----------------------------- ------------------------------ ------ >>> AE6RV.com >>> >>> GFS GPSDO list: >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info >>> >>> >>>    >>> ______________________________ _________________ >>> 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.

		Attila Kinali

On Mon, 7 Nov 2016 17:20:58 +0000 (UTC) Bob Stewart <bob@evoria.net> wrote: > There's something interesting on the far right hand side where the > temperature goes low and stays there.  The DVM value follows it down, but > then recovers while the temperature stays down.  I'm not sure what to make > of this.  Either then OCXO is making up for the temperature change by > increasing the temperature, or the 3456 is compensating for it after the > fact.  In either case, the EFC seems to only follow the transient > temperature changes, and doesn't actually track the temperature on the board. These are most likely caused by temperature gradients due to temperature changes. Once the temperature is (almost) constant, these differences equalize and the effect goes away. Where that gradient is and what part of the circuit it affects is not clear. It could be your circuit, or it could be the measurement. At least the measurment looks like that temperature dependence is low enough that it shouldn't be much of an issue. Attila Kinali -- Malek's Law: Any simple idea will be worded in the most complicated way.

		Attila Kinali

On Mon, 7 Nov 2016 17:47:19 +0000 (UTC) Bob Stewart <bob@evoria.net> wrote: > When you say that OCXOs don't age in a linear fashion, what does that mean?  > IOW, is this a case where it's almost linear over a week, and the non- > linearity is only detectable when you consider the longer term?  If that's > the case, then it seems reasonable to use the past 3 or so days of data > collection to project the near-term behavior; where near-term is less than 3 > days into the future Have a look at John Vig's tutorial. There are 2-3 slides on aging and retrace with references to papers for details. Attila Kinali -- Malek's Law: Any simple idea will be worded in the most complicated way.

  From: Bob Camp <kb8tq@n1k.org>

  From: Scott Stobbe <scott.j.stobbe@gmail.com>

Hi This is your design, and under your control. Looking at one plot here or there and trying to guess what is going on is not a really good way to do this. The whole sub-thread we are on is simply a result of a “if it’s not crystal aging it can’t be anything else” comment way way back. My point here is that it *can* be something else and the list of things it *can* be is actually quite long. The voltage measurement stuff is simply one example out of at least a dozen and probably closer to a hundred possibles. Digging through all of those possible things is a lot of work. It’s work that can only be done “hands on” with a set of units and test gear. My first step would be to toss the setup into an environmental chamber and do some 48 hour temperature sweeps. Aging is a “long term” drift. It goes on for years. Warmup is a very short term effect. It goes on for hours or days. Retrace is the process of re-settilitg to the previous long term aging line. It can take days / weeks / months depending on the oscillator. If you were buying the OCXO’s as an OEM, the specs you bought them to would be a function of what you asked for and how much you were willing to pay. It is unlikely that as an OEM you would have requirements on retrace and warmup, and aging. If you did have a spec it would be under fairly specific conditions (on power for three months, measure frequency, off power at XX C for 24 hours, on power again for 24 hours at YY C, measure delta frequency. That would cover warmup, but really says nothing about aging or retrace. Regardless of if an OCXO is spec’d for this or that issue or not, it experiences it. There are a lot of other things that OCXO’s do that many or may not be spec’d. When using one and digging into it, you have to deal with all the issues, regardless of if there is a spec or not. That assumes you want to dig in at this level. A *very* reasonable question is - what level do you want to dig into? That is why I bring up the good old “what is the goal?” question on a regular basis. Without a goal in mind, you will keep digging ever deeper. The number of issues you need to look into grows exponentially as you dig deeper. The time, learning, equipment, experiments, and number of test units each go up rapidly. It is work, equipment, and experiments that only apply to your design. It is not a piggyback process as you go deeper. Yes, that’s a bit of a long winded reply … sorry about that. Bob > On Nov 7, 2016, at 2:23 PM, Bob Stewart <bob@evoria.net> wrote: > > Hi Bob, > > OK, given that, what is your view of the plot I presented? Let's remember that I plotted this because I was trying to discover whether the EFC circuitry has a time-related drift, or whether the DAC value drift I plotted with the GPSDO locked to the GPS was caused by the OCXO. > > In one of your posts today, you talked about a long-term retrace lasting some months. I've been using the term "aging". Has my choice of terms caused the discussion to take a turn that it wouldn't have taken if I had used the term "retrace"? The fact is that I don't know whether it's aging or retrace. I'm not really clear on how to tell the difference. I'm especially handicapped by not having the mfg specs for the OCXOs I use. It could be that I simply haven't had the test unit under power for long enough to let the OCXO settle out. And for sure when I added the test lead to the EFC (breaking a trace in the process) there was enough off time to thoroughly insult the OCXO. > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > From: Bob Camp <kb8tq@n1k.org> > To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Monday, November 7, 2016 1:01 PM > Subject: Re: [time-nuts] Thermal impact on OCXO > > Hi > > Thermocouples in test leads are nasty because they operate on the temperature > delta rather than the absolute temperature. It’s the gradient you have to worry about. > Until you have run out a few dozen sensors around your bench (or test chamber) and > monitored them for a few days … you won’t believe just how little “point A” has in common > with “point B”. > > Bob > > > On Nov 7, 2016, at 1:44 PM, Bob Stewart <bob@evoria.net> wrote: > > > > -accidentally omitted timenuts from my reply to bob- > > Hi Bob, > > The data is at the 10uV level. As to whether I've plotted "data" or data, I can only report what I have. It seems to be consistent over the long run. I would expect to see something else if it were just noise. If the 4 attachments were strongly thermocoupled, wouldn't the data have a stronger correlation to temperature, rather than just to temperature transients? > > > > Bob ----------------------------------------------------------------- > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > > From: Bob Camp <kb8tq@n1k.org> > > To: Bob Stewart <bob@evoria.net> > > Cc: Discussion of Precise Time and Frequency Measurement <time-nuts@febo.com> > > Sent: Monday, November 7, 2016 11:54 AM > > Subject: Re: [time-nuts] Thermal impact on OCXO > > > > Hi > > > > I would suggest you read the papers on the subject. They are out there. Even over a few days > > OCXO aging is likely to be non-linear ( => curved, not straight line). On an OCXO that is > > warming up, your are dealing with retrace rather than aging. This can have an impact for a > > few months after turn on. I have one unit in the basement that took 9 months to come out > > of retrace after being in storage for “a while”. It was an eBay item so no idea just how long > > the power off time was. > > > > Bob > > > > > >> On Nov 7, 2016, at 12:47 PM, Bob Stewart <bob@evoria.net> wrote: > >> > >> Hi Bob, > >> > >> When you say that OCXOs don't age in a linear fashion, what does that mean? IOW, is this a case where it's almost linear over a week, and the non-linearity is only detectable when you consider the longer term? If that's the case, then it seems reasonable to use the past 3 or so days of data collection to project the near-term behavior; where near-term is less than 3 days into the future. > >> > >> Bob > >> > >> ----------------------------------------------------------------- > >> AE6RV.com > >> > >> GFS GPSDO list: > >> groups.yahoo.com/neo/groups/GFS-GPSDOs/info > >> > >> > >> From: Bob Camp <kb8tq@n1k.org> > >> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > >> Cc: Scott Stobbe <scott.j.stobbe@gmail.com> > >> Sent: Monday, November 7, 2016 6:08 AM > >> Subject: Re: [time-nuts] Thermal impact on OCXO > >> > >> Hi > >> > >> > >>> On Nov 5, 2016, at 10:43 PM, Bob Stewart <bob@evoria.net> wrote: > >>> > >>> Hi Scott, > >>> D'oh. Thanks for the correction! Like I said, I don't do these calculations often. > >>> > >>> If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit stumped. I do have an op-amp in the EFC string with a voltage divider for gain. The resistors are Panasonic ERA-6AEDxxxV resistors. Mouser says they're temperature stable to 25PPM/C, but of course they don't mention an aging rate. I don't really see anything else, other than the OCXO, that is likely to be prone to a linear type of aging. > >> > >> OCXO’s don’t age in a linear fashion. At least 90% of them don’t. If you dig into the FCS papers there are various > >> curves proposed as models. Mil-O-55310 has one of them as the “official” approach. All of them have the basic > >> issue of mistakenly fitting to to short a time constraint. > >> > >> Bob > >> > >>> The aging rate appears to be stable from unit to unit, so naturally I considered the OCXO first. > >>> > >>> There is one other bit in the EFC string that might be controversial, but I don't see that it would be a candidate for the symptoms of aging. > >>> > >>> Bob > >>> ----------------------------------------------------------------- > >>> AE6RV.com > >>> > >>> GFS GPSDO list: > >>> groups.yahoo.com/neo/groups/GFS-GPSDOs/info > >>> > >>> From: Scott Stobbe <scott.j.stobbe@gmail.com> > >>> To: Bob Stewart <bob@evoria.net> > >>> Cc: Discussion of Precise Time and Frequency Measurement <time-nuts@febo.com> > >>> Sent: Saturday, November 5, 2016 9:19 PM > >>> Subject: Re: [time-nuts] Thermal impact on OCXO > >>> > >>> If your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the EFC range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1 LSB is ~1PPT. So, if everything else is stable the DAC code reflects changes solely due to the OCXO, which would be an aging of 24 PPT/day. > >>> On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <bob@evoria.net> wrote: > >>> > >>> Hi Scott, > >>> The 20 bits span about 6 volts. The EFC range spans about 8Hz (+/-4Hz). I don't do these calculations every day, but that's about 4.5PPT? > >>> Bob ------------------------------ ------------------------------ ----- > >>> AE6RV.com > >>> > >>> GFS GPSDO list: > >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > >>> > >>> > >>> > >>> From: Scott Stobbe <scott.j.stobbe@gmail.com> > >>> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> > >>> Sent: Saturday, November 5, 2016 8:38 PM > >>> Subject: Re: [time-nuts] Thermal impact on OCXO > >>> > >>> I think that's a nice plot, it looks like you have stepped 160 LSB over 7 days or roughly 1 LSB per hour. With a 20bit dac you are trimming maybe 1 ppt/LSB to 4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB, solely due to drift, you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the case of 4ppt/hour your at 1E-12 at 1280 s. Seems reasonable. > >>> On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <bob@evoria.net> wrote: > >>> > >>> Oh dear. I attached the wrong file. Here's the correct one. > >>> ----------------------------- ------------------------------ ------ > >>> AE6RV.com > >>> > >>> GFS GPSDO list: > >>> groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > >>> > >>> > >>> > >>> ______________________________ _________________ > >>> 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. > >

Another nice plot! It looks like after 2am you see temperature swings of 1.5 degF roughly every 30 minutes? Correspondingly, the EFC line which is nominally ~2.8vdc sees swings of +-50 uV? On Monday, 7 November 2016, Bob Stewart <bob@evoria.net> wrote: > Hi guys, > First of all, thanks for the additional responses. I was a bit angry and > rude yesterday, and I figured this thread was over. Thanks for staying > with me. > I haven't had time to look over the data etc in your responses. I'll do > that and get back to the list if appropriate. > > I spoke to Attila and Azelio offline last nite and from their input, I > decided to hook up the 3456A and collect some data, which is in the plot > attached. As usual, I've modified one of my standard plot scripts, so > there is some extraneous data that wasn't removed. > > First for our purposes is the thin red line, which is the DAC value locked > at 0x734B0. The orange trace is the temperature adjusted so that each step > of 10 on the right hand Y tics is one degree F. The dark blue trace is the > EFC value read by the 3456A. It has been multiplied by 100,000 and then > had 282600 subtracted. This leaves just the LSD scaled at 1:1 on the right > hand Y tics. > There's something interesting on the far right hand side where the > temperature goes low and stays there. The DVM value follows it down, but > then recovers while the temperature stays down. I'm not sure what to make > of this. Either then OCXO is making up for the temperature change by > increasing the temperature, or the 3456 is compensating for it after the > fact. In either case, the EFC seems to only follow the transient > temperature changes, and doesn't actually track the temperature on the > board. > > So, to my eye, after 14 hours, there is only a dependency on thermal > transients. I'll leave it running for some time yet, but the EFC doesn't > seem to be drifting in any meaningful way at this point, other than in > relation to temperature changes. > > Note: I used a shielded twisted-pair with the usual clips attached to > ground and EFC in my GPSDO. On the 3456, the two leads go to the > appropriate volts inputs, and the shield goes to the ground input. The > "guard" switch is out, which is the off position. There is no shield > connector on the DUT side. > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > >

  From: Scott Stobbe <scott.j.stobbe@gmail.com>

Hi Scott, The EFC is a nominal 2.826 volts, which I removed and plotted the last 2 decimal places.  I'd have to do a lot of fiddling to find the range, but 50uV looks about right from the plot.  I'm going to let this bake for another day or two to see if there's a time-related element to it after the thermal stuff averages out.  After that, I plan to take the software out of hold mode and see what the EFC plot looks like as the DAC voltage changes over time.  Bob ----------------------------------------------------------------- AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Scott Stobbe <scott.j.stobbe@gmail.com> To: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <time-nuts@febo.com> Sent: Monday, November 7, 2016 2:48 PM Subject: Re: [time-nuts] Thermal impact on OCXO Another nice plot! It looks like after 2am you see temperature swings of 1.5 degF roughly every 30 minutes? Correspondingly, the EFC line which is nominally ~2.8vdc sees swings of +-50 uV?

      Year   Aging [PPM]  dF/dt [PPT/Day]
         1       180.51       63.884
         2       196.65        31.93
         5          218       12.769
         9       231.69       7.0934
        10       234.15        6.384
        25        255.5       2.5535

  From: Scott Stobbe <scott.j.stobbe@gmail.com

Deeper into the rabbit hole :) I'm not sure what specific pic you are you using but most of them have at least one timer that will run fully asynchronously and its timer input is usually shared with one of the 32k osc pins. Which you can then use to wake the prossesor from one of its sleep states. Do you end up hitting a clock sync with the pwm block? Good old 74 series to the rescue. On Monday, 7 November 2016, Bob Stewart <bob@evoria.net> wrote: > Hi Scott, > > I wish I had some long term data, but I don't. I had initially set out to > build an accurate GPS frequency reference type of GPSDO. So, aging wasn't > an issue. It's either on and locked or it's not. So, I didn't worry about > leaving a unit running for months and collecting aging data. > > But then I had this crackpot idea of using the latches in a 7474 to > stabilize the 1PPS from the receiver to the OCXO. Tom had a bit of a > misunderstanding about what I was doing and we had a bit of a discussion > until he caught on to what I was doing and its limitations. > > But, somewhere along the line, I realized that the idea was sound but my > implementation was poor. The basic problem with using a timer in the > dsPIC33 is that they use a PLL to generate the internal clock - even if you > supply a clock. That gives you a 1-count jitter in any output pulse you > try to create. So, I realized that I could use the latches in a 7474 to > latch the OCXO to the output of a timer on the PIC. With the PIC running > at 40MHz, I have plenty of room for the jitter without the worry of a phase > slip. I think I've proved that that works, so now I have the possibility > of using my system as a time server. And that means I now have to deal > with such arcane matters as holdover, aging, and generating the time from > the OCXO. The learning curve has been a bit steep. > > Bob > > ----------------------------------------------------------------- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > > ------------------------------ > *From:* Scott Stobbe <scott.j.stobbe@gmail.com > <javascript:_e(%7B%7D,'cvml','scott.j.stobbe@gmail.com');>> > *To:* Bob Camp <kb8tq@n1k.org > <javascript:_e(%7B%7D,'cvml','kb8tq@n1k.org');>> > *Cc:* Bob Stewart <bob@evoria.net > <javascript:_e(%7B%7D,'cvml','bob@evoria.net');>>; Discussion of precise > time and frequency measurement <time-nuts@febo.com > <javascript:_e(%7B%7D,'cvml','time-nuts@febo.com');>> > *Sent:* Monday, November 7, 2016 9:34 AM > *Subject:* Re: [time-nuts] Thermal impact on OCXO > > Here is a sample data point taken from http://tycho.usno.navy.mil/ > ptti/1987papers/Vol%2019_16.pdf; the first that showed up on a google > search. > > Year Aging [PPM] dF/dt [PPT/Day] > 1 180.51 63.884 > 2 196.65 31.93 > 5 218 12.769 > 9 231.69 7.0934 > 10 234.15 6.384 > 25 255.5 2.5535 > > If you have a set of coefficients you believe to be representative of your > OCXO, we can give those a go. > > On Mon, Nov 7, 2016 at 7:08 AM, Bob Camp <kb8tq@n1k.org > <javascript:_e(%7B%7D,'cvml','kb8tq@n1k.org');>> wrote: > > Hi > > > > On Nov 5, 2016, at 10:43 PM, Bob Stewart <bob@evoria.net > <javascript:_e(%7B%7D,'cvml','bob@evoria.net');>> wrote: > > > > Hi Scott, > > D'oh. Thanks for the correction! Like I said, I don't do these > calculations often. > > > > If as Bob Camp implies, the aging isn't from the OXCO, then I'm a bit > stumped. I do have an op-amp in the EFC string with a voltage divider for > gain. The resistors are Panasonic ERA-6AEDxxxV resistors. Mouser says > they're temperature stable to 25PPM/C, but of course they don't mention an > aging rate. I don't really see anything else, other than the OCXO, that is > likely to be prone to a linear type of aging. > > OCXO’s don’t age in a linear fashion. At least 90% of them don’t. If you > dig into the FCS papers there are various > curves proposed as models. Mil-O-55310 has one of them as the “official” > approach. All of them have the basic > issue of mistakenly fitting to to short a time constraint. > > Bob > > > The aging rate appears to be stable from unit to unit, so naturally I > considered the OCXO first. > > > > There is one other bit in the EFC string that might be controversial, > but I don't see that it would be a candidate for the symptoms of aging. > > > > Bob > > ------------------------------ ------------------------------ ----- > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > <http://groups.yahoo.com/neo/groups/GFS-GPSDOs/info?soc_src=mail&soc_trk=ma> > > > > From: Scott Stobbe <scott.j.stobbe@gmail.com > <javascript:_e(%7B%7D,'cvml','scott.j.stobbe@gmail.com');>> > > To: Bob Stewart <bob@evoria.net > <javascript:_e(%7B%7D,'cvml','bob@evoria.net');>> > > Cc: Discussion of Precise Time and Frequency Measurement < > time-nuts@febo.com <javascript:_e(%7B%7D,'cvml','time-nuts@febo.com');>> > > Sent: Saturday, November 5, 2016 9:19 PM > > Subject: Re: [time-nuts] Thermal impact on OCXO > > > > If your DAC spans the full EFC range than 1LSB is 1/2^20 ~ 1 PPM of the > EFC range, and the EFC tuning range is 8/10E6 ~ 1 PPM full scale, so 1 LSB > is ~1PPT. So, if everything else is stable the DAC code reflects changes > solely due to the OCXO, which would be an aging of 24 PPT/day. > > On Sat, Nov 5, 2016 at 9:57 PM, Bob Stewart <bob@evoria.net > <javascript:_e(%7B%7D,'cvml','bob@evoria.net');>> wrote: > > > > Hi Scott, > > The 20 bits span about 6 volts. The EFC range spans about 8Hz > (+/-4Hz). I don't do these calculations every day, but that's about 4.5PPT? > > Bob ------------------------------ ------------------------------ > ----- > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/ > <http://groups.yahoo.com/neo/groups/?soc_src=mail&soc_trk=ma> > GFS-GPSDOs/info > > > > > > > > From: Scott Stobbe <scott.j.stobbe@gmail.com > <javascript:_e(%7B%7D,'cvml','scott.j.stobbe@gmail.com');>> > > To: Bob Stewart <bob@evoria.net > <javascript:_e(%7B%7D,'cvml','bob@evoria.net');>>; Discussion of precise > time and frequency measurement <time-nuts@febo.com > <javascript:_e(%7B%7D,'cvml','time-nuts@febo.com');>> > > Sent: Saturday, November 5, 2016 8:38 PM > > Subject: Re: [time-nuts] Thermal impact on OCXO > > > > I think that's a nice plot, it looks like you have stepped 160 LSB over > 7 days or roughly 1 LSB per hour. With a 20bit dac you are trimming maybe 1 > ppt/LSB to 4 ppt/LSB? In allan devation terms, the case of 1ppt/LSB, solely > due to drift, you're at 1E-12 at 3600*sqrt(2) = 5000 s, in the case of > 4ppt/hour your at 1E-12 at 1280 s. Seems reasonable. > > On Sat, Nov 5, 2016 at 2:47 PM, Bob Stewart <bob@evoria.net > <javascript:_e(%7B%7D,'cvml','bob@evoria.net');>> wrote: > > > > Oh dear. I attached the wrong file. Here's the correct one. > > ----------------------------- ------------------------------ ------ > > AE6RV.com > > > > GFS GPSDO list: > > groups.yahoo.com/neo/groups/ > <http://groups.yahoo.com/neo/groups/?soc_src=mail&soc_trk=ma> > GFS-GPSDOs/info > > > > > > > > ______________________________ _________________ > > time-nuts mailing list -- time-nuts@febo.com > <javascript:_e(%7B%7D,'cvml','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 > <javascript:_e(%7B%7D,'cvml','time-nuts@febo.com');> > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > <https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > > and follow the instructions there. > > > > >

      Year   Aging [PPB]  dF/dt [PPT/Day]
         1       180.51       63.884
         2       196.65        31.93
         5          218       12.769
         9       231.69       7.0934
        10       234.15        6.384
        25        255.5       2.5535

 Fdot = (A1*A2)/(A2*x +1)

 Fdotdot = -(A1*A2^2)/(A2*x +1)^2

 Fdot ~= A1/x

 Fdotdot ~= -A1/x^2

 T1(x, xo) = A3 + A1*ln(A2*xo + 1) +  (A1*A2)(x - xo)/(A2*xo +1) + O(

 Fdot(365) =  63.796 PPT/day, alternatively the approximate derivative

 |R(366)| =  0.087339 PPT (more than likely, this is no where near 1

 |R(372)| = 4.282 PPT (So on the 7th day, a 1st order model starts to

On Mon, Nov 7, 2016 at 10:34 AM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > Here is a sample data point taken from http://tycho.usno.navy.mil/ptt > i/1987papers/Vol%2019_16.pdf; the first that showed up on a google search. > > Year Aging [PPB] dF/dt [PPT/Day] > 1 180.51 63.884 > 2 196.65 31.93 > 5 218 12.769 > 9 231.69 7.0934 > 10 234.15 6.384 > 25 255.5 2.5535 > > If you have a set of coefficients you believe to be representative of your > OCXO, we can give those a go. > > I thought I would come back to this sample data point and see what the impact of using a 1st order estimate for the log function would entail. The coefficients supplied in the paper are the following: A1 = 0.0233; A2 = 4.4583; A3 = 0.0082; F = A1*ln( A2*x +1 ) + A3; where x is time in days Fdot = (A1*A2)/(A2*x +1) Fdotdot = -(A1*A2^2)/(A2*x +1)^2 When x is large, the derivatives are approximately: Fdot ~= A1/x Fdotdot ~= -A1/x^2 It's worth noting that, just as it is visually apparent from the graph, the aging becomes more linear as time progresses, the second, third, ..., derivatives drop off faster than the first. A first order taylor series of the aging would be, T1(x, xo) = A3 + A1*ln(A2*xo + 1) + (A1*A2)(x - xo)/(A2*xo +1) + O( (x-xo)^2 ) The remainder (error) term for a 1st order taylor series of F would be: R(x) = Fdotdot(c) * ((x-xo)^2)/(2!); where c is some value between x and xo. So, take for example, forward projecting the drift one day after the 365th day using a first order model, xo = 365 Fdot(365) = 63.796 PPT/day, alternatively the approximate derivative is: 63.836 PPT/day |R(366)| = 0.087339 PPT (more than likely, this is no where near 1 DAC LSB on the EFC line) More than likely you wouldn't try to project 7 days out, but considering only the generalized effects of aging, the error would be: |R(372)| = 4.282 PPT (So on the 7th day, a 1st order model starts to degrade into a few DAC LSB) In the case of forward projecting aging for one day, using a 1st order model versus the full logarithmic model, would likely be a discrepancy of less than one dac LSB.

     Year   Aging [PPB]  dF/dt [PPT/Day]
        1       180.51       63.884
        2       196.65        31.93
        5          218       12.769
        9       231.69       7.0934
       10       234.15        6.384
       25        255.5       2.5535

 Fdot = (A1*A2)/(A2*x +1)

 Fdotdot = -(A1*A2^2)/(A2*x +1)^2

 Fdot ~= A1/x

 Fdotdot ~= -A1/x^2

 T1(x, xo) = A3 + A1*ln(A2*xo + 1) +  (A1*A2)(x - xo)/(A2*xo +1) + O(

 Fdot(365) =  63.796 PPT/day, alternatively the approximate derivative

 |R(366)| =  0.087339 PPT (more than likely, this is no where near 1

 |R(372)| = 4.282 PPT (So on the 7th day, a 1st order model starts to

Hi If you already *have* data over a year (or multiple years) the fit is fairly easy. If you try to do this with data from a few days or less, the whole fit process is a bit crazy. You also have *multiple* time constants involved on most OCXO’s. The result is that an earlier fit will have a shorter time constant (and will ultimately die out). You may not be able to separate the 25 year curve from the 3 month curve with only 3 months of data. Bob > On Nov 13, 2016, at 10:59 PM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > > On Mon, Nov 7, 2016 at 10:34 AM, Scott Stobbe <scott.j.stobbe@gmail.com> > wrote: > >> Here is a sample data point taken from http://tycho.usno.navy.mil/ptt >> i/1987papers/Vol%2019_16.pdf; the first that showed up on a google search. >> >> Year Aging [PPB] dF/dt [PPT/Day] >> 1 180.51 63.884 >> 2 196.65 31.93 >> 5 218 12.769 >> 9 231.69 7.0934 >> 10 234.15 6.384 >> 25 255.5 2.5535 >> >> If you have a set of coefficients you believe to be representative of your >> OCXO, we can give those a go. >> >> > I thought I would come back to this sample data point and see what the > impact of using a 1st order estimate for the log function would entail. > > The coefficients supplied in the paper are the following: > A1 = 0.0233; > A2 = 4.4583; > A3 = 0.0082; > > F = A1*ln( A2*x +1 ) + A3; where x is time in days > > Fdot = (A1*A2)/(A2*x +1) > > Fdotdot = -(A1*A2^2)/(A2*x +1)^2 > > When x is large, the derivatives are approximately: > > Fdot ~= A1/x > > Fdotdot ~= -A1/x^2 > > It's worth noting that, just as it is visually apparent from the graph, the > aging becomes more linear as time progresses, the second, third, ..., > derivatives drop off faster than the first. > > A first order taylor series of the aging would be, > > T1(x, xo) = A3 + A1*ln(A2*xo + 1) + (A1*A2)(x - xo)/(A2*xo +1) + O( > (x-xo)^2 ) > > The remainder (error) term for a 1st order taylor series of F would be: > R(x) = Fdotdot(c) * ((x-xo)^2)/(2!); where c is some value between x > and xo. > > So, take for example, forward projecting the drift one day after the 365th > day using a first order model, > xo = 365 > > Fdot(365) = 63.796 PPT/day, alternatively the approximate derivative > is: 63.836 PPT/day > > |R(366)| = 0.087339 PPT (more than likely, this is no where near 1 > DAC LSB on the EFC line) > > More than likely you wouldn't try to project 7 days out, but considering > only the generalized effects of aging, the error would be: > > |R(372)| = 4.282 PPT (So on the 7th day, a 1st order model starts to > degrade into a few DAC LSB) > > In the case of forward projecting aging for one day, using a 1st order > model versus the full logarithmic model, would likely be a discrepancy of > less than one dac LSB. > _______________________________________________ > 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.