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.