Hi Here’s the gotcha with what they are talking about. The SC when done as a *fundamental* crystal has a higher Q than the AT. You don’t use fundamental mode SC’s in a normal OCXO.
The issue with Q relates very specifically to the sort of HC-40 package AT resonators you *would* use for maximum Q in a 5 or 10 MHz OCXO. Practical package size for the resonators is as much a part of it as anything else. ( = that’s about as big a package as anybody is tooled to do an OCXO crystal in ) Bob > On Jul 12, 2019, at 4:24 AM, Leo Bodnar <l...@leobodnar.com> wrote: > > From: Bob kb8tq <kb...@n1k.org> >>>>> - high-Q crystals require SC-cut >>>> ... An SC has a lower Q than an AT of similar size >>>> and design up to the point acoustic Q losses completely take over. >>>> If you are talking about sub 20 MHz OCXO?s with ?doable? crystal >>>> package sizes, the AT will have the higher Q by a significant margin. >>> >>> Could you please back up this claim with verifiable facts? >> >> Order up a few 5 MHz 3rd overtones in HC-40 packages and see what you get. >> You also could send in an RFQ for a batch of each to any of the people who >> make them >> and see what comes back. >> Bob > > Here is a random selection of links to back my point of view that, if you > have noticed, contradicts Bob's. > If anybody is interested they will find information themselves without much > effort. I suggest printed books if you don't trust Internet at large. > > http://www.crovencrystals.com/croven_pdf/Old%20Spec%20Sheets/croven_catalogue.pdf > (Croven Crystals is Wenzel company) > The main advantages of these resonators, and in particular the SC-cut type > are: > higher Q-factor (typically 10 - 15% better than equivalent AT-cut resonators) > > https://www.tfc.co.uk/pdfs/SC_cut_crystals_article_TFC.pdf > SC cut family of quartz crystals: > Other key characteristics include Higher Q factor > > https://www.rfwireless-world.com/Terminology/AT-cut-vs-SC-cut-quartz-crystal.html > Specification:Q factor > AT cut: lower > SC cut: higher (it will achieve low phase noise) > > http://members.femto-st.fr/sites/femto-st.fr.patrice-salzenstein/files/content/Peer-review-journal/smdo160017.pdf > SC-cut > It has faster higher Q, warm-up speed and better phase noise close to the > carrier. > > http://www.resonal.com/Downloads/John%20R.%20Vig%20-%20tutorial%20on%20Quartz%20Crystals%20and%20Oscillators.pdf > Advantages of the SC-cut: > Higher Q for fundamental mode resonators of similar geometry > > http://www.mtronpti.com/sites/default/files/files/crystal-resonator-terminology.pdf > A typical 10 MHz, 3rdovertone SC may have a Q of 1.0 to 1.3 million; > a 100 MHz, 5th overtone AT may have a Q of 80 to 100 thousand, > while a 100 MHz AT fundamental would be much lower, in the range of 20 to 50 > thousand. > > https://www.eetimes.com/document.asp?doc_id=1290592# (MptronPTI) > Since SC-cuts have a much higher Q-factor than AT-cuts, SC-based OCXOs offer > better noise performance from 1-Hz offset to 1,000-Hz offset. > > Worryingly, I have started receiving unpleasant personal emails from list > members suggesting that I do not question factual correctness of other's > opinions. > This will explain why I am going off the list for the sake of everyone's good. > > Leo Bodnar > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.