And even without problems like external magnetic fields, Rb oscillators do drift with age. Over a period of several years they may drift as much as ~1E-9, which is a *huge* error for serious time nuts.
In my pre-retirement job I rode herd on an active Hydrogen maser system, and even that has a clear drift tendency. Generally a couple or three times per year I had to make a frequency adjustment in the neighborhood of 3E-14. And still being privy to its performance, I was amused to note that its drift tendency was interrupted by the hurricane Maria. On the day of eye passage over the site the frequency suddenly decreased by a few parts in 10^14, held about constant for roughly a week, then resumed almost its original value and drift rate thereafter. If anybody in this group can explain* that* behavior (that is, held for a week before resuming old habits), I'd love to learn about it. Dana On Mon, Nov 20, 2017 at 1:40 PM, 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.