Hi Most GPSDO’s run the GPS signal only on one “band” (L1). If you want to eliminate the errors in the ionosphere correction process you go to.a double band (L1 and L2) GPS receiver. Since there are fewer potential errors in the GPS signal, you may have fewer net errors in your GPSDO.
For the Cs - the issue is a stand alone reference. How can you be sure that GPS is not lying to you? The only way to check something like that is with a stand alone reference. That’s somewhere between priceless and worthless depending on which half of the family you happen to ask. You can (or course) do a GPS disciplined Cs standard. That’s not easy to do, but some are attempting it …. Lots to do… Bob > On Nov 20, 2017, at 7:14 PM, Jerry Hancock <je...@hanler.com> wrote: > > Not to junk up the mailboxes, but I have the multiple GPSDOs. Don’t know > what you mean by L1/L2 GPSDO, is that a quality statement? > > Also, what would the next step cost me for a Cesium Beam? Roughly? And what > order of magnitude improvement would that be for the cost? Have to do a > cost/benefit analysis for the wife... > > >> On Nov 20, 2017, at 4:09 PM, Bob kb8tq <kb...@n1k.org> wrote: >> >> 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. > > _______________________________________________ > 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.
