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.
