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.
