[time-nuts] Bye-Bye Crystals
michael.cook at sfr.fr
Wed Mar 15 12:16:22 EDT 2017
> Le 15 mars 2017 à 08:11, Gilles Clement <clemgill at club-internet.fr> a écrit :
> So what is the « best » design for DIY a high stability OCVXO ?
> I am looking after one, needed for an exotic frequency : 5184kHZ
Crystals have existed for this frequency. A quick scan of the bay threw up item 252813375636 which is an old radio crystal. If you can figure what you need to drive it, it could be installed into a home-brew oven. How stable you can get it would be the subject of a nice project.
>> 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.
>> 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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