Hi A “modern” 5 MHz 5th overtone AT cut resonator *should* be able to hit a Q of 5 million. Indeed one has to do everything right to hit that number. More or less it is the design that “defines” the Q of a bar of quartz. (Yes, there’s more to it …..).
Since that part uses a blank that is about 15 mm in diameter you *could* scale from there. This is never going to be the whole story some things get messy. Freq MHz diameter mm 5 15 2.5 30 1 75 0.5 150 0.1 750 The obvious point here being that a 3/4 M diameter resonator blank just isn’t going to work. Things like the Essen Ring are a way to get around some of this. Yes, there are trade off’s. That’s what keeps crystal design guru’s employed. Bob > On Apr 5, 2021, at 5:40 PM, Alan Melia via time-nuts > <[email protected]> wrote: > > Bob somewhere buried in my collection of interesting bits I have a rather > battered demo sample of what the British GPO Research crystal labs refered to > as an Essen Ring. It is indeed around 3 inches in outer diameter and almost > an inch thick and wide. this would have been cut from natural quartz. I > suspect this specimen is a 'failed' sample. The ring is suspended in a couple > of silk threads.I also have what I think is a higher frequency ring which is > mouned in a 1.5inch diameter evacuated glass holder. > I was told that if the large ring was tapped gently with a pencil it would > 'ring' for 5 minutes (that there may be some exageration there) I believe Qs > of 5E^6 were mentioned. More reliable info would be found in the reports :-)) > This was around 60 years ago. > > Alan > G3NYK > > ----- Original Message ----- From: "Bob kb8tq" <[email protected]> > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Sent: Monday, April 05, 2021 9:43 PM > Subject: [time-nuts] Re: Crystal sweet-spot (was: Best frequency to start for > GHz synth ?) > > >> Hi >> >> Back it the “old days” ( so 1960’s in this case ) glass packages >> were very commonly used for precision crystals. They were available >> in large diameters ( think of transmitting sized vacuum tubes). This allowed >> use of larger diameter blanks than what fit in today’s much smaller packages. >> >> The result was that things like 2.5 MHz fifth overtone parts could be made. >> Cute things like silk thread supports for the blank were not uncommon. Yields >> simply due to the “thread tweaking” process often ran in the 10 to 15% range >> (as in 8 or 9 out of ten failed …) . >> >> Since there was no way to re-do the process once the part was under >> vacuum ( and no way to test it before that) this was indeed black magic. >> Occasionally somebody would do a batch and 25% would work. They >> would then talk about that event for at least the next 20 years …. >> >> One would *not* want to go back and do it the “good old way”. >> >> Bob >> >>> On Apr 5, 2021, at 4:02 PM, Attila Kinali <[email protected]> wrote: >>> >>> On Wed, 31 Mar 2021 16:44:40 +0000 >>> "Poul-Henning Kamp" <[email protected]> wrote: >>> >>>> It used to be that 5MHz was the "hot spot" for crystals on the >>>> parameters we care about as time-nuts. >>> >>> Depends on what kind of time-nut you are ;-) >>> >>> If you are going for high frequencies beyond 1GHz, then a mesa >>> type high frequency BAW is the best you can do (given you don't >>> want to use frequency comb to divide down a cryogenic silicon >>> cavity). >>> >>> As Bob wrote, for low-frequency, high stability applications, >>> the lower the frequency of the crystal the better. Or rather, >>> the thicker the crystal the better. I.e. you want to use an >>> as low frequency crystal with an as high as possible overtone. >>> Unfortunately, to make full use of the properties of low >>> frequency crystals, you need to scale the diameter with the >>> frequency. Otherwise, the energy loss due to the edges of the >>> crytal will limit the Q. >>> >>> For historical reasons, 3rd overtone 5MHz turned out to be the >>> lowest that could be done economically with the avaible tools >>> and methods and still fit the size constraints. >>> >>> Today we could probaly go lower, but the market demands for >>> large crystal units is shrinking steadily and, as Bob wrote >>> a few times in the past, nobody has the tooling to do so. >>> >>> Attila Kinali >>> -- >>> The driving force behind research is the question: "Why?" >>> There are things we don't understand and things we always >>> wonder about. And that's why we do research. >>> -- Kobayashi Makoto >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] -- To unsubscribe send >>> an email to [email protected] >>> To unsubscribe, go to and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- [email protected] -- To unsubscribe send an >> email to [email protected] >> To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
