************** I meant to say TUB not tube in the third paragraph.
************** WB6BNQ wrote: > 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. _______________________________________________ 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.