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

[Attila Kinali]

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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