Bob
Some isothermal radiation (thermal) shields between the blanket and the
top of the Rubidium source may also be required.
Unless you have a hydrogen maser you will need to use 3 rubidium sources
each with its own engine block in order to determine AVAR (using the 3
cornered hat technique).
FEI claim that their rubidium sources are actually quieter than typical
caesium sources so using a caesium reference isn't as effective for
measuring the short term (< 1day) stability.
Bruce
Bob Camp wrote:
Hi
I agree that if you simply bolt the rubidium to an old engine block and toss a blanket
over it, you might get some pretty good thermal stability in the "hour to couple
hours" time period. That's certainly a better approach than putting some kind of DC
heater (and it's varying magnetic field) near the rubidium.
I'm still wondering if they do indeed hit 1x10-13 (as in almost 1x10-14) or
not. I suspect not. I'm sure that they do indeed get into the 1x10-13's, just
not sure they get to the bottom of that region.
Bob
On Dec 22, 2009, at 8:26 PM, Bruce Griffiths wrote:
Bob Camp wrote:
Hi
If I randomly pick up a FE 5680A data sheet, I find that it's short term
stability is 1.4/sqrt(Tau) x 10-11. Since I never doubt anything I see on a
data sheet, this immediately tells me I should get 1.4x10-12 at 100 seconds,
and I only have to wait for 10,000 seconds to get to 1.4x10-13.
Since the temperature performance is at the 1x10-12 / C level, I would need a
room that's stable to *much* better than 0.1 C over a 3 hour period to get
there. I suspect that 0.01C might not be good enough ...
So here's the question:
Has anybody run any of the cheap rubidiums (FE or Efratom) in a *very* stable
temperature environment to see how close they get / what the floor is? I've
run through a lot of data on the web, but I haven't really found what I'm
looking for.
Thanks!
Bob
Figure 7 on the FE5680 page (also on the data sheet) indicates that you may
need somewhat less than 3hours to achieve ADEV ~1E-13.
0.01C stability should be adequate.however its not necessary to control the
room temperature to this stability if the FE5680 is in an enclosure with a
sufficiently high time constant whilst having a sufficiently low thermal
resistance so as to avoid overheating the FE5680.
Bruce
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