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

[Bob kb8tq]

Hi

Like it or not, modern crystal packages are mad of metal ( as opposed to glass).
The gotcha with metal is that getting rid of *all* of the He is darn hard. That makes
a “perfect vacuum” more than a bit tough.

Bob

> On Jun 12, 2022, at 7:38 PM, Lux, Jim via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> On 6/12/22 6:30 PM, 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
> 
> 
> And the worst thing is that if your vacuum sealed widget is in an atmosphere with more He around (like waiting for a launch, in a place that does more He leak tests, etc.), the He will diffuse into your package and it doesn't work like expected.
> 
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