[time-nuts] GSP clock stabilitiy, Rb vs Cs

Tom Van Baak (lab) tvb at leapsecond.com
Sat May 4 15:36:20 EDT 2013

Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term.

For GPS clocks the long-term doesn't matter that much since each space clock is monitored and updated against the GPS master clock(s) on the ground. 

/tvb (iPhone4)

On May 4, 2013, at 11:40 AM, Attila Kinali <attila at kinali.ch> wrote:

> Hi,
> Bruce recently mentioned [1], where Fig. 2 shows that the Cs clocks
> of the old II and IIA birds are less stable than the Rb clocks of the
> newer birds. This struck me as odd and i tried to find out why 
> a Cs beam had worse stability than a Rb vabor cell. The only paper comparing
> both clocks that i found was [2] which shows in Fig. 2 that the Cs clocks
> are less stable even at very small taus. But the only mention of a property
> that is worse for the Cs than for the Rb mentioned is that the Rb's are
> temperature stabilized while the Cs is not. But i would expect the temperature
> effect to be significant from a couple 100s upward, not down to 1s.
> Can anyone shed some light on why the GPS Cs beams have a worse stability
> than the Rb vapor clocks?
>            Attila Kinali
> [1] "GPS clocks in space: Current performance and plans for the future",
> by Dass, Freed, Petzinger, Rajan, 2002
> http://tycho.usno.navy.mil/ptti/ptti2002/paper18.pdf
> [2] "Atomic frequency standards for the GPS IIF satelites", 
> by Emmer, Watts, 1997
> http://www.pttimeeting.org/archivemeetings/1997papers/Vol%2029_19.pdf
> -- 
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