Discussion:
quartz / liquid nitrogen
(too old to reply)
Tom Van Baak
2018-04-02 19:46:26 UTC
Permalink
Has anyone tried running a quartz oscillator at liquid nitrogen temperatures: -196 C (-321F, 77K)? It's probably impractical commercially, but maybe something of value to a time nut. Would that dramatically lower temperature improve phase noise & short-term performance? Is there a crystal cut that could be optimized for 77 K instead of ~25 C (room) or 60 C (oven)?

If not Nitrogen, how about dry ice (-109F -78C)?

/tvb

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Poul-Henning Kamp
2018-04-02 19:58:50 UTC
Permalink
--------
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen
temperatures: -196 C (-321F, 77K)? It's probably impractical
commercially, but maybe something of value to a time nut.
Whispering gallery sapphire resonators at cryogenic temperatures
is a thing for phase-noise, but those are dielectric (microwave)
resonators, not piezoelectric resonators.
Post by Tom Van Baak
Would that dramatically lower temperature improve phase noise &
short-term performance?
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 ?
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
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Never attribute to malice what can adequately be explained by incompetence.
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Tisha Hayes
2018-04-02 20:47:02 UTC
Permalink
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*
Post by Poul-Henning Kamp
--------
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen
temperatures: -196 C (-321F, 77K)? It's probably impractical
commercially, but maybe something of value to a time nut.
Whispering gallery sapphire resonators at cryogenic temperatures
is a thing for phase-noise, but those are dielectric (microwave)
resonators, not piezoelectric resonators.
Post by Tom Van Baak
Would that dramatically lower temperature improve phase noise &
short-term performance?
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 ?
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Dana Whitlow
2018-04-02 20:30:39 UTC
Permalink
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
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen
temperatures: -196 C (-321F, 77K)? It's probably impractical commercially,
but maybe something of value to a time nut. Would that dramatically lower
temperature improve phase noise & short-term performance? Is there a
crystal cut that could be optimized for 77 K instead of ~25 C (room) or 60
C (oven)?
If not Nitrogen, how about dry ice (-109F -78C)?
/tvb
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Brooke Clarke
2018-04-02 21:11:18 UTC
Permalink
Hi Tom:

Put the dry ice in acetone to the lowest temp.
--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

-------- Original Message --------
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen temperatures: -196 C (-321F, 77K)? It's probably impractical commercially, but maybe something of value to a time nut. Would that dramatically lower temperature improve phase noise & short-term performance? Is there a crystal cut that could be optimized for 77 K instead of ~25 C (room) or 60 C (oven)?
If not Nitrogen, how about dry ice (-109F -78C)?
/tvb
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djl
2018-04-02 21:15:14 UTC
Permalink
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
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen
temperatures: -196 C (-321F, 77K)? It's probably impractical
commercially, but maybe something of value to a time nut. Would that
dramatically lower temperature improve phase noise & short-term
performance? Is there a crystal cut that could be optimized for 77 K
instead of ~25 C (room) or 60 C (oven)?
If not Nitrogen, how about dry ice (-109F -78C)?
/tvb
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Bob kb8tq
2018-04-02 21:23:43 UTC
Permalink
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
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen temperatures: -196 C (-321F, 77K)? It's probably impractical commercially, but maybe something of value to a time nut. Would that dramatically lower temperature improve phase noise & short-term performance? Is there a crystal cut that could be optimized for 77 K instead of ~25 C (room) or 60 C (oven)?
If not Nitrogen, how about dry ice (-109F -78C)?
/tvb
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Attila Kinali
2018-04-02 21:38:39 UTC
Permalink
On Mon, 2 Apr 2018 12:46:26 -0700
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen
temperatures: -196 C (-321F, 77K)? It's probably impractical commercially,
but maybe something of value to a time nut. Would that dramatically lower
temperature improve phase noise & short-term performance? Is there a crystal
cut that could be optimized for 77 K instead of ~25 C (room) or 60 C (oven)?
If not Nitrogen, how about dry ice (-109F -78C)?
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
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Bob kb8tq
2018-04-02 23:36:15 UTC
Permalink
Hi
Post by Attila Kinali
On Mon, 2 Apr 2018 12:46:26 -0700
Post by Tom Van Baak
Has anyone tried running a quartz oscillator at liquid nitrogen
temperatures: -196 C (-321F, 77K)? It's probably impractical commercially,
but maybe something of value to a time nut. Would that dramatically lower
temperature improve phase noise & short-term performance? Is there a crystal
cut that could be optimized for 77 K instead of ~25 C (room) or 60 C (oven)?
If not Nitrogen, how about dry ice (-109F -78C)?
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.
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
Post by Attila Kinali
I am sure I have some paper on this somewhere in my collection,
if you want I can dig it out.
Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Alexander Pummer
2018-04-03 03:11:14 UTC
Permalink
at low temperatures bipolar devices will have reduced gain

73

KJ6UHN

Alex



-------- Forwarded Message --------
Subject: [time-nuts] quartz / liquid nitrogen
Date: Mon, 2 Apr 2018 12:46:26 -0700
From: Tom Van Baak <***@LeapSecond.com>
Reply-To: Tom Van Baak <***@leapsecond.com>, Discussion of precise time
and frequency measurement <time-***@febo.com>
Organization: LeapSecond.com
To: Discussion of precise time and frequency measurement
<time-***@febo.com>



Has anyone tried running a quartz oscillator at liquid nitrogen temperatures: -196 C (-321F, 77K)? It's probably impractical commercially, but maybe something of value to a time nut. Would that dramatically lower temperature improve phase noise & short-term performance? Is there a crystal cut that could be optimized for 77 K instead of ~25 C (room) or 60 C (oven)?

If not Nitrogen, how about dry ice (-109F -78C)?

/tvb

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