[time-nuts] WWV Doppler Shift

[Bob kb8tq]

Hi

> On Nov 21, 2018, at 12:12 PM, Tom Van Baak <tvb at leapsecond.com> 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
> 
> 
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