[time-nuts] looking for SMT oscillator SC cut, with no oven

[Jim Lux]

On 8/27/15 4:46 PM, Bob Camp wrote:
> Hi
>
>> On Aug 27, 2015, at 3:58 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>>
>>
>> kb8tq at n1k.org said:
>>>> Is there anything fundamental about SC that forces the turn over
>> temperature
>>>> to be high?
>>
>>> Simple answer yes. More complicated answer : that depends.
>>
>>> The crystal curve on an AT or an IT centers roughly at room temperature.
>>> When you fiddle the  angles to get a stress compensated blank, that center
>>> point moves up to the 90 to 100 C range.
>>
>> Thanks.  I guess I thought there was an extra degree of freedom so you could
>> pick the turn over temperature.
>
> Life would be so much simpler if that was true ….
>
> There are indeed a range of cuts you could make. Working out the in’s and outs
> of any one of them is a megabuck sort of endeavor. You can predict that this or that
> will happen. That only gets you just so far. There are a lot of fine details that
> you can only find out by experiment.
>
>>
>> The graph at the bottom of this URL
>>   http://www.4timing.com/techcrystal.htm
>> shows that there are actually 3 turn over temperatures.
>
> The Beckman graph at the bottom of that page shows a number of curves that
> have no turnover (those below 0 angle) . For the ones that do have a turnover, each
> one has an upper turn and a lower turn. The magic point in the middle that they all
> go through is generally called the inflection temperature.
>
> Lots of make your head hurt info at:
>
> http://www.ieee-uffc.org/frequency-control/learning/fc_conqtz2.html
>
> I don’t see anything on a quick Google search that actually give
> the Beckman constants.
>


there's some C code out there that models AT (and also other cuts).. 
I'll see if I can find it. I found it in a PhD dissertation on designing 
temperature compensation neworks, as I recall.

It's not necessarily reality, but it's a model that you could probably 
use to predict a range of variations.