In message 299B45118C9248498D7B4F3AFE72231E@pc52, "Tom Van Baak" writes:

Whispering gallery sapphire resonators at cryogenic temperatures
is a thing for phase-noise, but those are dielectric (microwave)
resonators, not piezoelectric resonators.

Yes it will reduce your thermal noise as a source of PN, and
dramatically so.

But I doubt short and long term performance will improve.

Even if you can find a zero-turnover cut at a convenient temperature,
I don't think anybody know how to produce mK temperature stability
at cryogenic temperatures ?

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Is the thermal noise generated in the loss in a quartz resonator a
significant part
of the overall phase noise picture?  I would have not thought so.  I'd
think that a
greater benefit ought to be derived from chilling the other parts in the
oscillator,
such as the active devices.  Unless, of course, chilling the quartz
actually improves
the Q significantly, which I don't know about.

If cooling (whatever) by just a modest amount helps much, then one could
consider using Peltier cooling.  It doesn't really get things very cold,
but is a
lot more convenient than either dry ice or LN2.  But then you don't get the
fun
that you do when playing with LN2, either.

Dana

On Mon, Apr 2, 2018 at 2:46 PM, Tom Van Baak tvb@leapsecond.com wrote:

You also run in to mechanical vibration issues from the cooling system. At
the temperatures involved you are looking at something like a Stirling
cycle cooler.

Here is a good article;

https://arxiv.org/pdf/1309.5445.pdf

Maintaining a very stable temperature probably has a much greater impact.

Tisha Hayes, AA4HA

Ms. Tisha Hayes

On Mon, Apr 2, 2018 at 2:58 PM, Poul-Henning Kamp phk@phk.freebsd.dk
wrote:

Hi Tom:

Put the dry ice in acetone to the lowest temp.

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-------- Original Message --------

Tom: I sense a nice experiment!  Dry ice temps can be attained with
modest Dewars and thermoelectric fridge devices. PID controller and
bob's your uncle.  Type K thermocouple modules on epay.  With that
apparat, a nice set of adev vs temperature possible?  Dry ice/acetone or
ethyl alcohol (everclear) slurry is often used as a calibration point
BTW. Liquid N2 may be too cold, or is it He I'm thinking of???
Don
On 2018-04-02 13:46, Tom Van Baak wrote:

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Dr. Don Latham
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Hi

If you dig back in the FCS archives, you will find papers on “cold” OCXO’s. You also
will find papers on cryo cooled quartz. The bottom line appears to be that if you are
going to all the trouble of cooling things, sapphire (or other exotic materials) are a
better bet.

Quick simple answer: not enough improvement in ADEV, aging, or phase noise to
make it wroth it. As PHK mentioned, coming up with a “ideal” cut for your arbitrary
temperature  cryo setup is non-trivially difficult ( = plan on spending a few million
dollars and a lot of years).

Bob

On Mon, 2 Apr 2018 12:46:26 -0700
"Tom Van Baak" tvb@LeapSecond.com wrote:

Yes, it has been done. Down to liquid helium tempratures even.
The main benefit is that the Q of the crystal increses with
decreasing temperatures, but the effect is not as large as with
dielectric resonators (aka whispering galery mode CSO).

Of course thermal noise decreases as well, but usually quartz
oscillators are limited by their amplifiers and the 50 Ohm system
for termal noise. I do not remember reading anything about flicker
noise, but my guess would be that it decreases as well.

I am sure I have some paper on this somewhere in my collection,
if you want I can dig it out.

			Attila Kinali

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<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.

Hi

The gotcha there is that the 1/F noise of the resonator is already below
the oscillator “result” at room temperature. Reducing it further is great,
but it doesn’t translate directly to an improved signal source.

Unless you have a “flat” crystal temperature wise and good temperature
controll (like micro degree level) improving ADEV …. not so much.

Bob