Hi Ummm ….. errrr ….. multiple GPSDO’s …. L1/L2 GPSDO(s) …. Cs standard (s) … Maser(s) …. Ensembles of all of the above ….
There’s *lots* of steps still to take …. Bob > On Nov 20, 2017, at 6:31 PM, Jerry Hancock <je...@hanler.com> wrote: > > One step at a time. > > 2yrs ago when the time-bug hit, I had a crystal oscillator. 6 months later, > DOCXO then GPSDO then Rubidium soon to be with GPSDO and there aren’t too > many steps after that… > > I also gave my brother the bug the other day… > > > >> On Nov 20, 2017, at 3:05 PM, Bob kb8tq <kb...@n1k.org> wrote: >> >> Hi >> >> It’s very much a “somewhere near that number” sort of thing with an Rb. The >> “thing” you are looking at is quantum mechanical in nature. Unfortunately >> that >> by its self does not make it perfect. A beam tube (as opposed to a gas cell) >> isolates things better. >> >> A 5061 is a beam tube device. A 5065 is gas cell based. It is very important >> to note that >> accuracy and stability are two different things …. The beam tube is more >> accurate. >> The gas cell is more stable (over some range of tau). >> >> A normal Rb standard has a bit of this and that in the bulb. These other >> gasses >> help in various ways. They each also add a bit of “pull” to the frequency >> one way >> or the other. They get you away from your “magic number” but the benefits >> they >> deliver are worth the trouble. The exact gas mix gets into the “secret >> sauce” of >> the Rb manufacturer. They each optimize things a bit differently. The walls >> of the bulb get into the act …. >> >> Beam standards are actually a bit old these days. The more modern approach >> would be a fountain (toss the ion straight up and let it fall back to you). >> An even >> more modern approach would be a trapped ion standard. The amount of money >> involved goes up dramatically with each of those steps. You get rid of this >> and >> that subtle effect with each improvement. Accuracy gets better and better. >> >> Lots of choices !!! >> >> Bob >> >>> On Nov 20, 2017, at 3:28 PM, Jerry Hancock <je...@hanler.com> wrote: >>> >>> Bob, I was referring to the rubidium standard of 6834682610.904 Hz. For >>> some reason I thought it was closer to 9Ghz. >>> >>> I assume then rubidium standards oscillate (if that is the correct term) >>> somewhere around that number but not exact or is it in the detection where >>> things fall down? >>> >>> >>> >>>> On Nov 20, 2017, at 11:40 AM, Bob kb8tq <kb...@n1k.org> wrote: >>>> >>>> Hi >>>> >>>> There is no direct relation for an Rb to 10 MYz. Cs beam tubes are what >>>> have a direct relation. >>>> Even then, the qualifier is “under standard conditions”. They are >>>> sensitive to magnetic field. Rb’s >>>> also are sensitive to magnetic field. Both can be tuned by varying the >>>> field. In the case of an Rb >>>> that also takes care of a multitude of other issues. >>>> >>>> In the case of Rb, there is a distribution of cells coming out of the >>>> manufacturing process. Some >>>> are pretty close to the “right” frequency. Others are way off (as in 100’s >>>> of KHz or more). All of them >>>> are capable of meeting the required specs. DDS techniques allow those >>>> cells to be used in a >>>> production part. That increases the yield and thus drops the production >>>> cost. >>>> >>>> Since you now magically have a DDS in the Rb, you can do all sorts of >>>> interesting things. If you >>>> suddenly need a 9.99900 MHz standard …. here it is … If you need to do >>>> temperature compensation >>>> via a lookup table … it just takes a bit of testing and some code to make >>>> it happen. Indeed, the DDS >>>> does also give you some issues. Without some sort of cleanup oscillator, >>>> you will have spurs and >>>> phase noise on the output. >>>> >>>> Lots of fun …. >>>> >>>> Bob >>>> >>>> >>>>> On Nov 20, 2017, at 1:34 PM, Jerry Hancock <je...@hanler.com> wrote: >>>>> >>>>> I know this is going to sound dumb as I know many GPSDOs had rubidium >>>>> oscillators in them. I can see why, in that during holdover, they would >>>>> tend to be more stable vs others, but given that there is a direct >>>>> mathematical relationship between the rubidium frequency and potentially >>>>> the 10Mhz desired output frequency, why do they have to be disciplined or >>>>> better yet, what advantage does it bring? Also, I can see how you >>>>> discipline a DOCXO with the external voltage, how do you discipline a >>>>> rubidium? Pulse stretching? >>>>> >>>>> I guess I don’t understand how the technology works, but it seems like an >>>>> RF signal is swept that would be used to detect a dip at a pretty well >>>>> defined frequency. This dip can be used to discipline the oscillator to >>>>> something like 9Ghz or a factor of what, 900+ times better than 10Mhz. >>>>> So wouldn’t that be able to get your desired 10Mhz to 10,000,000.001 or >>>>> pretty much my level of measurement? Or does is the dip not quite that >>>>> precise? If you can point me to a write-up on this I’ll go away. >>>>> >>>>> Thanks to Gilbert for providing me with at least one rubidium oscillator >>>>> that is working out of 5 though 2 others seems to stay locked for a few >>>>> hours during my testing. >>>>> >>>>> Jerry >>>>> _______________________________________________ >>>>> 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.
