[time-nuts] Bye-Bye Crystals

[Bruce Griffiths]

Gilles

What is the required tuning range for the OCVXO?

Bruce

> 
>     On 15 March 2017 at 20:11 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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> >     >