Bob, I don't know why you would want 4 Rb's running, not to mention 8 or ten of them. I don't see the need for a follow up OCXO either. If you had such a good OCXO, it would not make much sense to also have the Rb.
You could put an oil bath together for a better thermal mass. Use a mineral oil much like Johnson&Johnson Baby oil. You would probably want at least two gallons (if not more) per Rb and make sure you have a heat sink on the Rb to help spread the heat in to the oil. If you have a big enough tube then you could have all four in the same pot. You would want to stir the oil constantly at a slow rate. A small 2 1/2 or 3 " 12 volt computer fan, suspended in the oil, would be good for that. You can adjust it's speed by varying the voltage to the fan. The Johnson&Johnson Baby type mineral Oil would not hurt the electronics, but it would be messy in some respects. Bill....WB6BNQ Bob Camp wrote: > 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" <li...@cq.nu> > > To: "Discussion of precise time and frequency measurement" > > <time-nuts@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@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@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@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@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@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.