[time-nuts] Bye-Bye Crystals
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Wed Mar 15 07:53:13 UTC 2017
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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> > >
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