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.
