[time-nuts] How Rubidiums make their frequency

[Normand Martel]

Hi..
In his message, Paul-Henning Kamp writes that a
drift-free standard has not been yet designed... 

But Isn't Cesium drift-free? Since the SI second is
standardized as de duration of 9192631770 oscillation
of the hyperfine transition of the atom 133Cs?

If Cesium drifts, theren should be a more formal
definition of the second (Such as density, maximum
C-field or level of purity). Does anyone here has it?

And also, something else i don't understand: Why do
the newer GPS satellites rely on Rb standards rather
than Cs standards? Since Rubidium is known as less
precise than cesium? Is there a reliability issue
there (Rb clocks are more reliable / longer MTBF tha
Cesium clocks). I don't know...

73 de Normand Martel VE2UM

(A PLL based 9192631770 synthesizer i once
imagined...)

10 MHz ---(/250)--40000PPS-,
OCXO                       |
                           |
 ,-------------<-----------'
 |
 `-(/)---[Filter]---(VCO)--*--829.08 MHz--,
    |                      |              |
    `---(/20727)-----------'              |
                                          |
 ,---<-41454 PPS--<--(/20000)-------<-----'
 |
 `--(/)---[Filter]---(VCO)--*--1838.526354 MHz--,
     |                      |                   |
     `---(/44351)-----------'                   |
                                                |
 ,----<--------------<--------------<-----------'
 |
 `-(*5 SRD)--9192631770 Hz (to physics)

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