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

[Magnus Danielson]

Hi,

So, one of my hydrogen masers have a tiny leak. The outer vacuum does 
not pump down as it should, and it has consumed the ion pump. This have 
massive effect on the thermal balance and causes heat to leak out much 
faster from the outer heaters to surrounding wall. This prohibits its 
controllers of reaching the temperature but also prohibits next layer to 
achieve it and finally inside that the actual resonator temperature 
stabilization. That is in itself 5 temperature control-loops in 3 
layers. There is also passive heat-shields in it. So, it is crazy 
efficient heat transfer. It is so efficient method, that it's the basis 
for pressure gauges, such as the Pirani gauge.

Now, while it is annoying it does not work, I can say that it has 
significantly increased my knowledge about temperature stabilitzation of 
hydrogen masers and workings of vacuum systems. Not to say I am fully 
skilled, but at least not as ignorant as before, so there is a good 
start. I also learned how to write some Python to log the serial port, 
toss it into a InfluxDB and plots it with Graphana.

So the effect is real, very real.

We are looking into bringing a masspectrometer over, pump it down and 
then do helium leakage tests to see if we can locate the joint that is 
leaking. While there is many possible joints in the vacuum system, my 
testing have helped to narrow it down to three. Of those, in particular 
one could be suspect as it could potentially take more hit than the 
others upon transport. Yes, I need a turbopump setup and spare parts.

Cheers,
Magnus

On 2022-06-13 03:30, Bob kb8tq via time-nuts wrote:
> 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
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