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

[Bob kb8tq]

Hi

Tear into some of your SC cut based OCXO’s. Take a look at the crystal package. For 
bonus points, open up the crystal package. If you have the gear to test it, take a look 
at what the gas *is* inside the package. ( Good luck with that :) :) :) )

If you had the gear and the willingness to scrap out OCXO’s you would find that a number
of fast warmup OCXO’s have a *tiny* amount of He in the package. Measuring this would 
be tough ( it’s that small). Go through the thermal modeling and it’s *way* more conductive 
(thermal wise) than a *perfect* vacuum ……

Bob

> On Jun 12, 2022, at 9:18 AM, Ross P via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> I have seen that manufacturers seal their crystals in a vacuum, maybe air interaction affects Q. The point that vacuum inhibits heat flow is something I have never considered in ovenized units. My ovenized crystals take about an hour to settle. I have some WW2 surplus crystals in non-sealed packages that I have not tested... something to do.rp
> 
>    On Sunday, June 12, 2022 at 07:26:19 AM PDT, Louis Taber via time-nuts <time-nuts at lists.febo.com> wrote:  
> 
> I have been of the impression for years now that most "better" crystals are
> in a vacuum.  And the electrical and mechanical connections to the quartz
> itself place as little mechanical load on the crystal as possible.
> Thermal conductivity from the oven to the crystal itself would be both
> hard to model and hard to speed up.
> 
> IR transmission of energy to the crystal also seems problematic considering
> the IR transmission of quartz and the IR reflectivity of gold
> contact plating.
> 
> Is any of this an issue?
> 
>   - Louis
> 
> On Fri, Jun 10, 2022 at 9:53 PM Bob kb8tq via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>> 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
>>> 
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>> To unsubscribe send an email to time-nuts-leave at lists.febo.com
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe send an email to time-nuts-leave at lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com  
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com