Hi By most modern definitions, “high stability” starts around 1x10^-12 (1 ppt) at a tau of 1 second to 10 seconds. There are $20 eBay OCXO’s that run at that level. With a fundamental crystal you aren’t going to get to that point.
How much EFC range are you after? How good a CNC setup do you have? What kind of temperature test setup do you have? Simply put, the design approach is a “test over temperature / collect data -> optimize” loop. Without good frequency vs temperature data, you are flying totally blind. Even on a production design, this is how it’s done. The parts you fiddle are likely to be odd shaped chunks of metal that fit here or there. Bob > On Mar 15, 2017, at 3:36 PM, Gilles Clement <clemg...@club-internet.fr> wrote: > > Hi, > I have a bunch of 5.184Mhz crystals. Large metallic tanks: HC33U case > Maybe not OCXO grade, but I build a simple oscillator with a 4060 chip > placed in a double oven, and reached 10E-9 short term stability up to 10sec > tau. > Not bad, so wondering if I can get better with a more advanced design. > Gilles. > > >> Le 15 mars 2017 à 12:45, Bob Camp <kb...@n1k.org> a écrit : >> >> Hi >> >> Where do you plan on getting an OCXO grade crystal at an odd frequency like >> that? Much of the performance of a good OCXO is in the crystal. Doing a >> proper >> design on one is a lot of work. You *might* think that having a design for >> 5.000000 >> MHz would give you a good design for 5.000050 MHz. I have empirical evidence >> that >> this isn’t the case. Many years later, I’m still utterly amazed that this is >> the way things >> work in the crystal business ….( = it’s not just a design issue, it’s also a >> business decision) >> >> More or less the crystal needs to be: >> >> 1) Cut specifically to have a turn at a temperature that makes sense for >> your application. >> 2) A “large blank” design (for it’s frequency) >> 3) In a cold weld package (most of the normal crystals are resistance weld) >> 4) Run through a high vacuum / high temperature process >> 5) Be plated with gold rather than something like silver or aluminum (unless >> it’s at VHF). >> 6) Have a motional capacitance that makes sense for your EFC range ( >> normally = minimize) >> 7) Preferably be an SC or modified SC cut. >> >> This is for a high stability part. The list does keep going on for a while, >> but that should >> give you a pretty good idea. >> >> Bob >> >>> On Mar 15, 2017, at 3:11 AM, Gilles Clement <clemg...@club-internet.fr> >>> wrote: >>> >>> Hi, >>> So what is the « best » design for DIY a high stability OCVXO ? >>> I am looking after one, needed for an exotic frequency : 5184kHZ >>> Thx, >>> Gilles. >>> >>> >>>> Le 14 mars 2017 à 18:02, Richard (Rick) Karlquist <rich...@karlquist.com> >>>> a écrit : >>>> >>>> >>>> >>>> On 3/14/2017 4:03 AM, Bruce Griffiths wrote: >>>> >>>>> >>>>> Looking at oscillator circuits like the HP10811A will give some idea of >>>>> some of the additional complexity required for a overtone operation. >>>>> Dissecting a few ocxos may also be helpful. Some start with a 10MHz >>>>> crystal and a Colpitts sustaining stage and use a 74HC74 or similar to >>>>> divide the 10Mhz by 2 and drive the output pin. Even when a sinewave >>>>> output is required often a CMOS inverter drives the output pin via an LC >>>>> filter. >>>>> >>>>> Bruce >>>>> >>>> >>>> I don't agree here. The 10811 is not a good tutorial for general >>>> oscillator design. Because it is SC cut, it has a complicated >>>> mode suppression network across the base emitter junction to >>>> suppress mode B as well as the fundamental. >>>> >>>> The E1983A oscillator uses the same crystal (in a low profile >>>> package). You can read my paper about it and see that I >>>> used a very simple bridged tee oscillator circuit. That is >>>> all you need to select the right overtone and mode. >>>> >>>> This is the same circuit that I used at Zeta Labs 40 years >>>> ago to design hundreds of custom VCXO's, up to the 9th >>>> overtone. It simply worked every time, unlike various other >>>> designs that were in use at Zeta. >>>> >>>> Around 1985, I got a consulting gig at Equatorial Communications >>>> to redesign their 5th overtone VCXO. Only about half of the >>>> crystals would work in their circuit. They had thousands >>>> of "reject" crystals. I just used my old Zeta circuit and >>>> all the crystals started working again. >>>> >>>> Equatorial owned the 10 meter dish that you used to see on >>>> your right going south on 237 just before passing over >>>> Central Expressway in Mountain View. >>>> >>>> Rick N6RK >>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
