[time-nuts] Bye-Bye Crystals

Wed Mar 15 22:51:25 UTC 2017

Hi

Ok, I missed that. 

Unless there is also a trimmer cap, the EFC will be >> 0.01Hz if it needs to be 
on frequency for any rational amount of time. If the crystals are the typical old fundamentals, 
they may age 5 to 10 ppm / year when heated to OCXO temperatures. That’s +/- 25 to +/-
50 Hz just for the first year. 

Bob

> On Mar 15, 2017, at 6:11 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
> 
> Bob
> 
> He stated 0.01Hz EFC tuning range was adequate.
> Gave no spec as to how close to nominal frequency is required though.
> 
> Bruce
>> On 16 March 2017 at 10:53 Bob Camp <kb8tq at n1k.org> wrote:
>> 
>> 
>> Hi
>> 
>> By most modern definitions, “high stability” starts around 1x10^-12 (1 ppt)  at a tau of 1 second to 
>> 10 seconds. There are $20 eBay OCXO’s that run at that level.  With a fundamental crystal you 
>> aren’t going to get to that point. 
>> 
>> How much EFC range are you after? 
>> 
>> How good a CNC setup do you have?
>> 
>> What kind of temperature test setup do you have? 
>> 
>> Simply put, the design approach is a “test over temperature / collect data -> optimize” loop. 
>> Without good frequency vs temperature data, you are flying totally blind. Even on a production
>> design, this is how it’s done. The parts you fiddle are likely to be odd shaped chunks of metal 
>> that fit here or there. 
>> 
>> Bob
>> 
>>> On Mar 15, 2017, at 3:36 PM, 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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