Hi > On Nov 21, 2018, at 12:12 PM, Tom Van Baak <[email protected]> wrote: > > Donald E. Pauly, WB0KVV wrote: >> Ft Collins is at 5,003 ft and clocks there run fast by 1.663·10^-13. >> (g/c^2)/meter) compared to sea level. How did you correct for >> altitude on yours? I presume that frequency is defined at sea level >> but I don't know that. > > Yes. Standard time & frequency is defined at sea level. > > But in the context of a WWV/WWVB thread it's best not to say that the clocks > in Ft Collins "run fast". The clocks at the transmitter site are set and > maintained to keep standard time. They don't run fast or slow; they tick SI > seconds and they report UTC time. They are more like "UTC-disciplined > oscillators" than stand-alone cesium clocks. > > What you may be thinking of is that if you built a cesium clock and turned it > on in Ft Collins it would run fast, faster than a similar clock running at > sea level. That is true. But it wouldn't be UTC then. That's why all the > national timing labs coordinate their clocks so they tick the same rate, in > spite of the actual elevation of the lab.
Gravity is not the only thing you need to “standardize” if you are building a Cs clock from scratch in your basement. Magnetic field also quickly gets its nasty fingers into things as well. There are other environmental impacts, even on a Cs standard. For “best” performance you do indeed need to sweat what seem like really minor details. This ultimately gets back to a never ending debate about depending on one design for all of your standards. Even if a *really* good job was done - how can you be sure? Having multiple this and that in your comparison “pool” is the answer to that concern. Bob > > >> Sea level clocks at the North or South Poles >> run fast relative to those at equator sea level by 1.192·10^-12. > > No. Clocks at sea level all tick at the same rate. > > You might be thinking that because the earth spins, clocks on the equator run > slower due to SR. But remember the earth is not a sphere, but an oblate > spheroid. So clocks on the equator are also farther from the center of the > earth and thus run faster due to GR. The two effects neatly cancel each other > (not by accident). In fact that is one definition of sea level -- the point > where all clocks run the same, minimum rate. > > See also my reply to N8ZM earlier. Clocks run faster both as you go below or > as you go above the surface. So altitude is the key factor, not latitude or > longitude. I can go into this in more detail if you want. > > /tvb > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
