[time-nuts] Bye-Bye Crystals

[Bruce Griffiths]

Most likely AT cut fundamental (although there are other possibilities.) designed for operation around room temperature.

Do you have the manufacturer's specs for these?

What is the change in frequency between room temperature and oven temperature?

What is the operating temperature of the inner oven?

Bruce

> 
>     On 16 March 2017 at 08:36 Gilles Clement <clemgill at 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 <kb8tq at 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 <clemgill at 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 <richard at 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
> > > > 
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> > > >             > > > 
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> > >         > > 
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> >     > 
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