Hi > On Feb 29, 2020, at 3:07 PM, Attila Kinali <[email protected]> wrote: > > On Sat, 29 Feb 2020 13:44:59 -0500 > Bob kb8tq <[email protected]> wrote: > >> One wonders what the result would be of doing a large blank (> 50mm) >> 2.5 MHz 5th OT using modern design, packaging and mounting techniques. > > If we use the venerable Sulzer as guide (see e.g. [1]) and going > by what the FE-405 achieves, I would say sub-1e-13 around 10-100s > should be possible. As far as I can tell, from the paper's I've > read, the major contributors to instability between 1s and 1000s > seem to be temperature and absorption/desorption of material on the blank. > We know how to do temperature control these days (see E1938 [2]). > But, there is not much we can do about absorption/desorption. > The best strategy is to polish the surface as much as possible > and use an as thick blank as possible. And then, backe the whole > thing in high vacuum for as long as possible at as high temperature > as possible (which isn't that high, due to twining). > > The diameter of the blank has to be scaled with its thickness, in > order not to compromise the f*Q product. Which in turn makes it > a bit problematic in terms of packaging, but nothing unsolvable. > > I am not sure, how much an advantage it is to go BVA. It helps in > terms of Q (seems to be 30-50% higher), but I'm not sure whether > the ab/desorption rate is much lower if there are no metal > electrodes on the crystal. The specs of the HSO-14 are awfully > close to the 8607, even though Rakkon places the electrodes > on the blank itself. But I have not seen any actual measurements > of an HS0-14 yet, so I don't know how it actually performs, > especially at tau >1000. > > BTW: this is another advantage of SC cut: an AT cut is ~1.6 MHz*mm > an SC cut is ~1.8 MHz*mm, ie you get about 10% more thicknes at the > same frequency for an SC cut than for an AT cut. > >> Given that it would take a rather large pile of nickels to >> find out (like > $50M worth), I very much doubt we ever will know the >> answer. > > Why would it cost so much? There are enough companies that make > crystal blanks for various purposes, getting one to make large > ones shouldn't be too difficult. And the FE-405 is very close > to what you are asking for, being a 5th OT 5MHz SC cut.
The FE-405 crystal is in a package that is already a bit “tight” for a 3rd overtone at 5 MHz. You can *force* just about anything. The point is to make it at a thickness to diameter ratio that is more on the order of what is used at 10 MHz. That makes it a *very* large diameter blank (at least out of high performance quartz). Bob > > > Attila Kinali > > > [1] https://febo.com/for_sale/sulzer/index.html > > [2] "The Theory of Zero-Gradient Crystal Ovens", 1997 > by Karlquist, Cutler, Ingman, Johnson and Parisek > http://www.karlquist.com/oven.pdf > > -- > <JaberWorky> The bad part of Zurich is where the degenerates > throw DARK chocolate at you. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
