[time-nuts] Re: Crystal sweet-spot (was: Best frequency to start for GHz synth ?)
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 MHzdiameter 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 > 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" > To: "Discussion of precise time and frequency measurement" > > 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 wrote: >>> >>> On Wed, 31 Mar 2021 16:44:40 + >>> "Poul-Henning Kamp" 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 >>> -- >
[time-nuts] Re: Crystal sweet-spot (was: Best frequency to start for GHz synth ?)
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" To: "Discussion of precise time and frequency measurement" 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 wrote: On Wed, 31 Mar 2021 16:44:40 + "Poul-Henning Kamp" 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 -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[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 wrote: > > On Wed, 31 Mar 2021 16:44:40 + > "Poul-Henning Kamp" 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 -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
