[time-nuts] Re: Is SC the most stable cut for lowest phase noise?

[Bob kb8tq]

Hi

> On Jun 10, 2022, at 2:38 PM, Lux, Jim via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> On 6/10/22 1:57 PM, Dr. David Kirkby wrote:
>> On Fri, 10 Jun 2022 at 17:39, Lux, Jim via time-nuts <time-nuts at lists.febo.com> wrote:
>> 
>>    On the subject of rapid warm up. I suppose if you had a need, one
>>    could
>>    dump as much power as you need into the heater. Turn on oscillator,
>>    lights in room dim for a few moments.
>> 
>> 
>> Is that not likely to damage a crystal? Different parts of the crystal and likely to be at significantly different temperatures at the same time, putting a lot of stress on the crystal due to a thermal gradient. It's probably a bit academic, as nobody is going to make an oven that heats up in fractions of a second, but if one did, I suspect it might not do the crystal a lot of good. This is only an educated guess - I don't have anything to back it up.
> Oh, it would be disastrous, although quartz is pretty strong, all the rest of the mounting components might not be.

Indeed, breaking a quartz blank via thermal stress would be very hard to do.
The “rest of the parts” actually are pretty durable as well. Most of it is metal and
it is quite able to handle thermal issues. 

The big issue in a fast warm up AT turned out to be designing the heater and the 
mount to get the energy to the blank quickly….. If you use a small enough package
and blank, the amount of power turns out to be surprisingly small. 

If you want to go bonkers, you mount the heaters *inside* the crystal package. This
does indeed create some issues in various areas. 

Bob

>> 
>> At the other extreme,  would there be any advantage in actually heating the crystal very slowly, over the course of an hour/day/week, so the temperature gradient across the crystal is very small? Of course, if an oven took ages to reach the correct temperature, it would be inconvenient for most applications, but for some applications, the advantages might outweigh the disadvantages. Of course, if one does this, I suspect one would have to cool the crystal slowly too to prevent a significant thermal gradient across the crystal.
>> 
>> I know it's a bit different, but I have a 600 mm f4 Nikon camera lens. I was told that Nikon cools the front element over a period of 6 months to reduce stresses in the glass.
> 
> Big glass mirrors for telescopes do the same.
> 
> 
> 
>> 
>> Dave
> 
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