Hi Since the network is being measured, I suspect that using it as the time reference would present a basic problem.
Bob On Feb 20, 2012, at 2:07 PM, Jim Lux <[email protected]> wrote: > On 2/20/12 10:31 AM, Bob Camp wrote: >> Hi >> >> Simple answer: >> >> A rack mount cesium standard is as good as you can get. Figure on 15 ns per >> day of drift. That gets you to 15 us in 1000 days. You may or may not get >> one that drifts that little, a lot depends on little details. For> 3 >> years, consider an ensemble of cesiums. At $50K each cost can go up pretty >> fast. >> >> There is nothing out there that will do better stand alone for less money. >> Either you get a sky view or you change the budget.... >> >> Bob >> >> > > > But he *does* have the ability to have an external network connection.. So > the real question is whether one could come up with a better-than-NTP scheme > to get the 100 (or 10) microseconds. > > I suspect that with sufficiently controlled network paths (which might be > doable in a widescale deployment) and a tweaking of the NTP stuff, you might > be able to get it to work. > > 100 microseconds out of a day is 1E-10, which is actually a fairly liberal > drift spec for an OCXO or even a TCXO. (which are things like ppb/day) > > Maybe there's a particular time of day (or day of week) when network > uncertainties are minimal, or can be bounded. So what you really need is a > onboard oscillator that is good at "carry over" between periodic calibration > checks. > > > One question about the 100 microsecond spec.. is that a worst case at any > instant, or is it an average spec over a day (so a consistent diurnal > variation would cancel out) > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
