Hi Rubiola is looking at resonators he can buy off the shelf. They are constrained by the commonly available packages. The Q x F product does not suddenly stop going up at 5 MHz. There is good documentation that it keeps on going as the frequency goes down. Is Q everything - of course not. However *if* you wanted a much higher Q crystal than the 5 MHz, it could be built if you had the time and the money.
Bob On Nov 3, 2013, at 7:58 AM, [email protected] wrote: > Hi Bob > > I've seen this topic discussed here before and it does seem to raise some > quite strong emotions and there does seem to be some confusion. > > I can remember quite clearly, historically at least, 5MHz being commonly > promoted as the optimum frequency for crystal oscillators on the basis that > 5MHz crystals had this "sweet spot", presumably when it came to temperature > stability. > An online search today hasn't been very forthcoming and unfortunately most > of my reference library remains in storage, so I can't provide instant > references, but I know I've also seen this in print and can still envisage > the > graphs used to demonstrate it. > > The nearest to a current reference I've found is this comment from Enrico > Rubiola on page 156 of "Phase Noise and Frequency Stability in > Oscillators"......... > "The process described relies on the ability to estimate the resonator's > quality factor. Experience indicates that the product voQ is a technical > constant for piezoelectric quartz resonators, in the range from 1 x 10^11 to > 2 > x 10^13. As a matter of fact, the highest values are found in 5MHz > resonators. ............." > > I have no axe to grind on this, aside from willingly admitting to being > one of the confused:-), but if this is a misconception is it possible to > address why such a situation might have arisen? > > Regards > > Nigel > GM8PZR > > > > In a message dated 03/11/2013 01:46:01 GMT Standard Time, [email protected] > writes: > > Hi > > I believe that you are talking to two very different groups, one who > actually design the crystals and the other who use the products that are > designed. One is talking about what they can buy, the other is talking about > what > could / could not be done and why. > > Bob > > On Nov 2, 2013, at 8:22 PM, Tom Knox <[email protected]> wrote: > >> From reading your past posts I must respect your opinion. Your are > obviously extremely educated on the subject. So why is there some > disagreement > in two very knowledgeable groups? >> >> Thomas Knox >> >> >> >>> From: [email protected] >>> Date: Sat, 2 Nov 2013 18:44:18 -0400 >>> To: [email protected] >>> Subject: Re: [time-nuts] The 5MHz Sweet Spot >>> >>> Hi >>> >>> The only thing that the 5 MHz 3rd crystal is “optimum” for is a holder > that will accept a 0.55” max diameter blank. >>> >>> Bpb >>> >>> On Nov 2, 2013, at 6:06 PM, Tom Knox <[email protected]> wrote: >>> >>>> Mike I think we must be talking to the same smart people. I think 5MHz > was adopted over 3MHz simply because 5MHz multiplies to other commonly > used frequencies with greater ease. I think the top frequency standards have > evolved to 5MHz Third Overtone SC cut crystals for a reason. The evolution > has gone on from the days of Tesla and improved greatly during the glory > days of Quartz in the years leading up to atomic standards with countless > hours of experimentation and research. Those lessons learned are constantly > examined through the lens of the latest science. I may be wrong, but I > have > not heard of any extreme design prototype quartz oscillator with superior > Phase Noise and Stability. Our house standard F1 a cesium fountain is used > roughly one month every few months to characterize roughly 12 5071A cesium > standards steering about 5 MHM 2010 cleaned up with a number of 8607 option > 08 oscillator. (The equipment choices are not a recommendation or > endorsement, and there are po >>>> ssibly m >>>> any product that could meet or exceed the performance of these fine > products.) But the oscillators selected are 5MHz third Overtone SC cut. >>>> >>>> Thomas Knox >>>> >>>> >>>> >>>>> From: [email protected] >>>>> To: [email protected]; [email protected] >>>>> Date: Sat, 2 Nov 2013 09:50:50 -0400 >>>>> Subject: Re: [time-nuts] The 5MHz Sweet Spot >>>>> >>>>> Exactly - I mentioned this on here about 3 years ago and all of the >>>>> self-proclaimed geniuses poo-pooded it. I was told early in my > engineering >>>>> career in the early 70's, by a very smart man, when I thought I had > all of >>>>> the answers, that considering all of the trade-offs regarding > performance, >>>>> around 3 MHz for a crystal is best, operating in the 3rd overtone > mode, >>>>> hence the slow progression from the 1 and 5 MHz standards to 10 MHz. > Now, >>>>> getting close to 70, I just see what I can learn from all the "smart" > people >>>>> on here, and keep quiet most of the time. Regards - Mike >>>>> >>>>> Mike B. Feher, EOZ Inc. >>>>> 89 Arnold Blvd. >>>>> Howell, NJ, 07731 >>>>> 732-886-5960 office >>>>> 908-902-3831 cell >>>>> >>>>> -----Original Message----- >>>>> From: [email protected] [mailto:[email protected]] > On >>>>> Behalf Of David McGaw >>>>> Sent: Saturday, November 02, 2013 1:30 AM >>>>> To: Discussion of precise time and frequency measurement >>>>> Subject: Re: [time-nuts] The 5MHz Sweet Spot >>>>> >>>>> This all seems to be forgetting that the crystals are usually > operated at >>>>> 3rd or 5th harmonic. The crystal in a 10811A is 10 MHz/3rd overtone. > A >>>>> high quality 5 MHz/5th overtone crystal is really a 1 MHz > fundamental, a >>>>> large piece of quartz. Running at a harmonic greatly reduces the > influence >>>>> of the package. >>>>> >>>>> David >>>>> >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- [email protected] >>>>> To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
