[time-nuts] Thermal impact on OCXO

[Scott Stobbe]

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 at n1k.org> wrote:

> Hi
>
>
> > On Nov 5, 2016, at 10:43 PM, Bob Stewart <bob at 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 at gmail.com>
> > To: Bob Stewart <bob at evoria.net>
> > Cc: Discussion of Precise Time and Frequency Measurement <
> time-nuts at 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 at 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 at gmail.com>
> > To: Bob Stewart <bob at evoria.net>; Discussion of precise time and
> frequency measurement <time-nuts at 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 at 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 at 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 at febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> > and follow the instructions there.
>
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: MIL-0-55310_Sample.png
Type: image/png
Size: 36322 bytes
Desc: not available
URL: <http://www.febo.com/pipermail/time-nuts/attachments/20161107/7ff3b6e9/attachment-0001.png>