[time-nuts] Cheap Rubidium

[Bob Camp]

Hi

Water might work. It would take quite a bit of it.

Here's my "wild guess" level math:

1) The basement moves 0.1 to 1 C short term / over a day. 

2) I want to get to < 0.01 

That takes the time constant out to >= 10X the time I'm interested in.

3) The time period of interest is 3 to 30 hours. 

That gets to a time constant of at least 10 days. 

At the same time you have >10 watts coming out of the gizmo. You can't put the thermal mass inside a vacuum  bottle. 

I suspect that some combination of thermal mass and active stabilization will be needed.

So much fun ....

Bob


On Dec 23, 2009, at 2:18 AM, Don Latham wrote:

> sheesh! How about a right-sized water jug?
> Don
> 
> ----- Original Message ----- From: "Bob Camp" <lists at cq.nu>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Sent: Tuesday, December 22, 2009 8:23 PM
> Subject: Re: [time-nuts] Cheap Rubidium
> 
> 
>> 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
>>> 
>>> 
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>> 
>> 
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>