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Discussion of precise time and frequency measurement

GPSDO uncertainties

donald collie

Mon, Oct 8, 2018 1:59 AM

I have a GPSDO which has a Trimble receiver, and Trimble OCXO inside.[I
think it runs Lady Heather] What I would like to know is what uncertainty
the 10MHz output will be with a 10 second count.This presumes that the
GPSDO is receiving satellite signals, and the OCXO is being suitably
diciplined. Should I expect 1 part in 10E12?, 1 part in 10E10?. This device
gives superior performance to an OCXO barefoot - but how much better? Would
somebody in the group who knows the answer, please wax elequently.
Thankyou,.................................................................................................Donald
B. COLLIE

I have a GPSDO which has a Trimble receiver, and Trimble OCXO inside.[I think it runs Lady Heather] What I would like to know is what uncertainty the 10MHz output will be with a 10 second count.This presumes that the GPSDO is receiving satellite signals, and the OCXO is being suitably diciplined. Should I expect 1 part in 10E12?, 1 part in 10E10?. This device gives superior performance to an OCXO barefoot - but how much better? Would somebody in the group who knows the answer, please wax elequently. Thankyou,.................................................................................................Donald B. COLLIE

Bob kb8tq

Mon, Oct 8, 2018 3:11 PM

The question becomes very much, what confidence level are you after? Is 99%
good enough? Are you after 99.9999%? Obviously the stability gets worse as
you crank on more nines.

Next layer to the onion is - how long have things been running and under what
conditions are they running? A few days is probably the minimum for any sort of
reasonable performance. A month or more will indeed help a bit. A stable temperature
environment is also going to have a direct impact on performance.

Things like survey position and antenna location ( number of sats viewed at all times)
will have a more subtle impact on frequency. Solar storms and ionospheric stability (sun
spot cycle) eventually get into the picture if you put in enough nines.

So simple answer: better than 2x10^-9 with any practical number of nines involved. Better
than 2x10^-10 with rational numbers (99.9 or 99.99). Maybe 2x10^-11 at the 99% level, but
probably not.

Since this is a very non-standard measure your numbers may not match my numbers. ADEV
was invented primarily because this sort of measure has so many issues. One of the issues
is that you need a lot of data to even begin to estimate the confidence levels and they are
very dependent on data set size. A typical spec tends to have weird stuff like “99.9%
based on 4 out of 5 runs of 100 hours”. Statements like that tend to make a statistics guy
groan ….(or throw something at you).

Bob

On Oct 7, 2018, at 9:59 PM, donald collie donaldbcollie@gmail.com wrote:

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Hi The question becomes very much, what confidence level are you after? Is 99% good enough? Are you after 99.9999%? Obviously the stability gets worse as you crank on more nines. Next layer to the onion is - how long have things been running and under what conditions are they running? A few days is probably the minimum for any sort of reasonable performance. A month or more will indeed help a bit. A stable temperature environment is also going to have a direct impact on performance. Things like survey position and antenna location ( number of sats viewed at all times) will have a more subtle impact on frequency. Solar storms and ionospheric stability (sun spot cycle) eventually get into the picture if you put in enough nines. So simple answer: better than 2x10^-9 with any practical number of nines involved. Better than 2x10^-10 with rational numbers (99.9 or 99.99). Maybe 2x10^-11 at the 99% level, but probably not. Since this is a very non-standard measure your numbers may not match my numbers. ADEV was invented primarily because this sort of measure has so many issues. One of the issues is that you need a *lot* of data to even begin to estimate the confidence levels and they are very dependent on data set size. A typical spec tends to have weird stuff like “99.9% based on 4 out of 5 runs of 100 hours”. Statements like that tend to make a statistics guy groan ….(or throw something at you). Bob > On Oct 7, 2018, at 9:59 PM, donald collie <donaldbcollie@gmail.com> wrote: > > I have a GPSDO which has a Trimble receiver, and Trimble OCXO inside.[I > think it runs Lady Heather] What I would like to know is what uncertainty > the 10MHz output will be with a 10 second count.This presumes that the > GPSDO is receiving satellite signals, and the OCXO is being suitably > diciplined. Should I expect 1 part in 10E12?, 1 part in 10E10?. This device > gives superior performance to an OCXO barefoot - but how much better? Would > somebody in the group who knows the answer, please wax elequently. > Thankyou,.................................................................................................Donald > B. COLLIE > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there.