SS
Scott Stobbe
Mon, Nov 7, 2016 3:47 PM
Typo, "Aging [PPM]" should read "Aging [PPB]".
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/
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 wrote:
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
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 <
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 ------------------------------ ------------------------------
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.
mailman/listinfo/time-nuts
ailman/listinfo/time-nuts
and follow the instructions there.
Typo, "Aging [PPM]" should read "Aging [PPB]".
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/
> 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> wrote:
>
>> 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/m
>> ailman/listinfo/time-nuts
>> > and follow the instructions there.
>>
>>
>
BS
Bob Stewart
Mon, Nov 7, 2016 5:20 PM
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
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
BS
Bob Stewart
Mon, Nov 7, 2016 5:38 PM
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>
To: Bob Camp kb8tq@n1k.org
Cc: Bob Stewart bob@evoria.net; Discussion of precise time and frequency measurement 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 wrote:
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.
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>
To: Bob Camp <kb8tq@n1k.org>
Cc: Bob Stewart <bob@evoria.net>; Discussion of precise time and frequency measurement <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> wrote:
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.
CC
Chris Caudle
Mon, Nov 7, 2016 5:41 PM
On Mon, November 7, 2016 11:20 am, Bob Stewart wrote:
Either then OCXO is making up for the temperature change
by increasing the temperature
Isn't that the entire point of an OCXO?
--
Chris Caudle
On Mon, November 7, 2016 11:20 am, Bob Stewart wrote:
> Either then OCXO is making up for the temperature change
> by increasing the temperature
Isn't that the entire point of an OCXO?
--
Chris Caudle
CC
Chris Caudle
Mon, Nov 7, 2016 5:45 PM
On Mon, November 7, 2016 11:41 am, Chris Caudle wrote:
On Mon, November 7, 2016 11:20 am, Bob Stewart wrote:
Either then OCXO is making up for the temperature change
by increasing the temperature
Isn't that the entire point of an OCXO?
Actually, that is not very precise language on my part. The OCXO does not
increase the temperature, it increases the heat input to the oven to
counteract the decrease in ambient temperature, i.e. attempts to keep the
internal oven temperature constant.
--
Chris Caudle
On Mon, November 7, 2016 11:41 am, Chris Caudle wrote:
> On Mon, November 7, 2016 11:20 am, Bob Stewart wrote:
>> Either then OCXO is making up for the temperature change
>> by increasing the temperature
>
> Isn't that the entire point of an OCXO?
Actually, that is not very precise language on my part. The OCXO does not
increase the temperature, it increases the heat input to the oven to
counteract the decrease in ambient temperature, i.e. attempts to keep the
internal oven temperature constant.
--
Chris Caudle
BS
Bob Stewart
Mon, Nov 7, 2016 5:47 PM
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.
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.
BC
Bob Camp
Mon, Nov 7, 2016 5:49 PM
Hi
Ok, You have a thermocouple junction at the + post on the DVM. You have one at the - post on the DVM.
You have a junction at the + connection to the board. You have a junction at the - connection to the board.
There are indeed more than that, but those four are pretty much a sure thing. The ones near the hot OCXO
are also worth looking at.
The metals involved are unknown, so we have to guess a bit. You can get some alarming junctions with
very normal test lead materials. Getting low thermal EMF connections requires special attention.
If your junctions have a 1 mV / K coefficient, then you need temperature data that is good to 0.001C at each
junction to work out what is going on at the junctions. That assumes you are after 1 uV on your “data” plot.
It’s not terribly hard to get a contact at one (or more than one) junction that messes you up.
Bob
On Nov 7, 2016, at 12:20 PM, 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
<PLL.png>_______________________________________________
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
Ok, You have a thermocouple junction at the + post on the DVM. You have one at the - post on the DVM.
You have a junction at the + connection to the board. You have a junction at the - connection to the board.
There are indeed more than that, but those four are pretty much a sure thing. The ones near the hot OCXO
are also worth looking at.
The metals involved are unknown, so we have to guess a bit. You *can* get some alarming junctions with
very normal test lead materials. Getting low thermal EMF connections requires special attention.
If your junctions have a 1 mV / K coefficient, then you need temperature data that is good to 0.001C at each
junction to work out what is going on at the junctions. That assumes you are after 1 uV on your “data” plot.
It’s not terribly hard to get a contact at one (or more than one) junction that messes you up.
Bob
> On Nov 7, 2016, at 12:20 PM, 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
>
>
>
> <PLL.png>_______________________________________________
> 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.
BC
Bob Camp
Mon, Nov 7, 2016 5:51 PM
On Nov 7, 2016, at 12:45 PM, Chris Caudle chris@chriscaudle.org wrote:
On Mon, November 7, 2016 11:41 am, Chris Caudle wrote:
On Mon, November 7, 2016 11:20 am, Bob Stewart wrote:
Either then OCXO is making up for the temperature change
by increasing the temperature
Isn't that the entire point of an OCXO?
Actually, that is not very precise language on my part. The OCXO does not
increase the temperature, it increases the heat input to the oven to
counteract the decrease in ambient temperature, i.e. attempts to keep the
internal oven temperature constant.
…. and as it does so, it pulls more current (or less) which changes the voltage
on the ground pin which hits the EFC reference which impacts things to a
greater or lesser extent depending on the board layout.
Bob
Hi
> On Nov 7, 2016, at 12:45 PM, Chris Caudle <chris@chriscaudle.org> wrote:
>
> On Mon, November 7, 2016 11:41 am, Chris Caudle wrote:
>> On Mon, November 7, 2016 11:20 am, Bob Stewart wrote:
>>> Either then OCXO is making up for the temperature change
>>> by increasing the temperature
>>
>> Isn't that the entire point of an OCXO?
>
> Actually, that is not very precise language on my part. The OCXO does not
> increase the temperature, it increases the heat input to the oven to
> counteract the decrease in ambient temperature, i.e. attempts to keep the
> internal oven temperature constant.
…. and as it does so, it pulls more current (or less) which changes the voltage
on the ground pin which hits the EFC reference which impacts things to a
greater or lesser extent depending on the board layout.
Bob
>
> --
> Chris Caudle
>
>
> _______________________________________________
> 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.
BC
Bob Camp
Mon, Nov 7, 2016 5:54 PM
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.
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.
>
>
BS
Bob Stewart
Mon, Nov 7, 2016 6:44 PM
-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.
-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.
>
>
