Re: [time-nuts] quartz / liquid nitrogen

[Dr. Ulrich L. Rohde via time-nuts]

Very true 

Sent from my iPhone

> On Apr 3, 2018, at 7:51 PM, Bob kb8tq  wrote:
> 
> Hi
> 
> If the objective is great phase noise far removed from carrier, there’s a 
> gotcha.
> 
> Let’s say you have a 10 dbm source at room and it’s broadband is at KTB of 
> -174 + 1db. 
> That gives you -183 dbc. You cool your oscillator to whatever and KTB goes 
> down
> to -194. You do a bang up job at that temperature and get within a db there 
> was well.
> You now have a 10 dbm source with -203 dbc. 
> 
> Run the super cooled signal through a coax out to the room environment. Pass 
> it through 
> a 50 ohm gizmo and …. KTB is back at -174. Your source is at -184 dbc. To 
> *use* the
> signal, you likely need to cool whatever it’s driving as well.
> 
> While one might say …. that pretty weird. Well, similar things do happen. 
> Many an ultra 
> low phase noise OCXO gets sold, only to find that the “next stage” isn’t as 
> quiet as the
> system guys hand hoped. Hmmm …. e ….oops !!
> 
> Bob
> 
>> On Apr 3, 2018, at 5:29 AM, Dana Whitlow  wrote:
>> 
>> Many years ago, circa 1977, I was moved to try some crude tests on a few
>> semiconductor devices at LN2 temperature (77K).
>> 
>> These tests were very crude, involving dunking the parts into the LN2 bath,
>> and
>> many failed outright.  Most of the devices tested were in plastic packages.
>> 
>> Here are the results as I remember them, applicable only for the survivors:
>> 
>> Silicon bipolar transistors:   The DC beta fell to very low values.
>> Junction
>> forward voltages rose considerably.
>> 
>> Silicon JFETs:  Seemed to continue working reasonably well.
>> 
>> Silicon MOSFETs:  Same as JFETs
>> 
>> Red LEDs:   The junction forward voltages rose considerably, to about  5V as
>> I recall.   The light output per unit current rose truly spectacularly.
>> 
>> My first experiences with seriously-cryogenic RF amplifiers were at the
>> Arecibo Observatory beginning about 11 years ago.  These were all either
>> GaAs- or InP-based and we cooled them to ~15K, generally leading to
>> input-referred amplifier noise temperatures of ~3K.  Many of the devices
>> needed continuous exposure to light to work properly when cold, and the
>> metal block amplifier packages had holes in the lid directly over the active
>> device chips. Small red LEDs in ordinary plastic packages were inserted
>> in the holes and were driven at a few mA, generally in a series string.
>> Since cool-down was fairly gradual over a span of at least a couple hours,
>> there was little problem with thermal shock and almost all LEDs survived
>> cooldown and warmup for the several cycles they experienced during
>> my 10 years at the observatory.
>> 
>> RF amplifier biasing was invariably done with opamp circuits to maintain
>> set drain currents and drain voltages, with said bias control circuits
>> outside
>> the dewar at room ambient temperature.   Failures were not too uncommon,
>> largely attributed to connector misbehavior at low temperature.  Formation
>> of "ice" (really frozen air) inside the dewars was suspected because fine
>> wires
>> inside the dewar were often found to have fairly sharp bends at improbable
>> locations upon warmup for diagnostic purposes (or due to cooling system
>> failure).
>> 
>> Cooling was done with a closed-cycle gaseous He system, using the
>> Gifford-McMahon cycle.  Note that He does not liquefy (at reasonable
>> pressures) until around 4K.  All dewars for this kind of work depend on
>> high vacuum inside for thermal insulation, with black body radiation
>> and direct conduction through wires and mounting structures being
>> the principal remaining heat leaks.
>> 
>> At these temperatures, maintenance of high vacuum inside the dewar was
>> essentially automatic because all components of the inward-leaking air
>> were known to freeze out.  This could lead to a hazard because over time,
>> months or years, enough air could freeze out to result in dangerously high
>> internal pressures upon "thawing" when the dewar was warmed for any
>> reason.  For this reason, all dewars were equipped with blowout plugs
>> to avoid high pressure's damaging the dewars themselves.
>> 
>> Dana
>> 
>> 
>>> On Tue, Apr 3, 2018 at 12:26 AM, Mark Sims  wrote:
>>> 
>>> And you want your semiconductors to be in ceramic/lided packages with the
>>> bond wires flapping in free air.   Bond wires embedded in epoxy like to
>>> break...  don't ask how I found this out  ;-)   ... it brings back bad
>>> memories... and makes bad memories...  Quantum chips have very
>>> elaborate/specialized bonding to survive liquid helium... even with that,
>>> thermal cycling still breaks them.
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>>> mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>> 
>> 

Re: [time-nuts] quartz / liquid nitrogen

[Bob kb8tq]

Hi

If the objective is great phase noise far removed from carrier, there’s a 
gotcha.

Let’s say you have a 10 dbm source at room and it’s broadband is at KTB of -174 
+ 1db. 
That gives you -183 dbc. You cool your oscillator to whatever and KTB goes down
to -194. You do a bang up job at that temperature and get within a db there was 
well.
You now have a 10 dbm source with -203 dbc. 

Run the super cooled signal through a coax out to the room environment. Pass it 
through 
a 50 ohm gizmo and …. KTB is back at -174. Your source is at -184 dbc. To *use* 
the
signal, you likely need to cool whatever it’s driving as well.

While one might say …. that pretty weird. Well, similar things do happen. Many 
an ultra 
low phase noise OCXO gets sold, only to find that the “next stage” isn’t as 
quiet as the
system guys hand hoped. Hmmm …. e ….oops !!

Bob

> On Apr 3, 2018, at 5:29 AM, Dana Whitlow  wrote:
> 
> Many years ago, circa 1977, I was moved to try some crude tests on a few
> semiconductor devices at LN2 temperature (77K).
> 
> These tests were very crude, involving dunking the parts into the LN2 bath,
> and
> many failed outright.  Most of the devices tested were in plastic packages.
> 
> Here are the results as I remember them, applicable only for the survivors:
> 
> Silicon bipolar transistors:   The DC beta fell to very low values.
> Junction
> forward voltages rose considerably.
> 
> Silicon JFETs:  Seemed to continue working reasonably well.
> 
> Silicon MOSFETs:  Same as JFETs
> 
> Red LEDs:   The junction forward voltages rose considerably, to about  5V as
> I recall.   The light output per unit current rose truly spectacularly.
> 
> My first experiences with seriously-cryogenic RF amplifiers were at the
> Arecibo Observatory beginning about 11 years ago.  These were all either
> GaAs- or InP-based and we cooled them to ~15K, generally leading to
> input-referred amplifier noise temperatures of ~3K.  Many of the devices
> needed continuous exposure to light to work properly when cold, and the
> metal block amplifier packages had holes in the lid directly over the active
> device chips. Small red LEDs in ordinary plastic packages were inserted
> in the holes and were driven at a few mA, generally in a series string.
> Since cool-down was fairly gradual over a span of at least a couple hours,
> there was little problem with thermal shock and almost all LEDs survived
> cooldown and warmup for the several cycles they experienced during
> my 10 years at the observatory.
> 
> RF amplifier biasing was invariably done with opamp circuits to maintain
> set drain currents and drain voltages, with said bias control circuits
> outside
> the dewar at room ambient temperature.   Failures were not too uncommon,
> largely attributed to connector misbehavior at low temperature.  Formation
> of "ice" (really frozen air) inside the dewars was suspected because fine
> wires
> inside the dewar were often found to have fairly sharp bends at improbable
> locations upon warmup for diagnostic purposes (or due to cooling system
> failure).
> 
> Cooling was done with a closed-cycle gaseous He system, using the
> Gifford-McMahon cycle.  Note that He does not liquefy (at reasonable
> pressures) until around 4K.  All dewars for this kind of work depend on
> high vacuum inside for thermal insulation, with black body radiation
> and direct conduction through wires and mounting structures being
> the principal remaining heat leaks.
> 
> At these temperatures, maintenance of high vacuum inside the dewar was
> essentially automatic because all components of the inward-leaking air
> were known to freeze out.  This could lead to a hazard because over time,
> months or years, enough air could freeze out to result in dangerously high
> internal pressures upon "thawing" when the dewar was warmed for any
> reason.  For this reason, all dewars were equipped with blowout plugs
> to avoid high pressure's damaging the dewars themselves.
> 
> Dana
> 
> 
> On Tue, Apr 3, 2018 at 12:26 AM, Mark Sims  wrote:
> 
>> And you want your semiconductors to be in ceramic/lided packages with the
>> bond wires flapping in free air.   Bond wires embedded in epoxy like to
>> break...  don't ask how I found this out  ;-)   ... it brings back bad
>> memories... and makes bad memories...  Quantum chips have very
>> elaborate/specialized bonding to survive liquid helium... even with that,
>> thermal cycling still breaks them.
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
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Re: [time-nuts] quartz / liquid nitrogen

[Brooke Clarke]

Hi Mark:

When Aetech started to make their own Tunnel Diodes there was a problem with 
the neck breaking.
Note they were made by alloying a ball of metal onto a highly doped chip, bonding from the lip of the ceramic package to 
the ball then on to the opposite lip, then etching the chip away leaving something that in cross section looked like a 
mushroom.  The neck was a few microns wide and often broke.  The fix was to epoxy a glass rod on either side of the 
chip, between the metal bottom of the ceramic pill package and the bonding wire.  The glass was chosen to have a CTE 
that matched the die.  That solved the broken neck problem.

http://prc68.com/I/Aertech.shtml#Prod

--
Have Fun,

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

 Original Message 

And you want your semiconductors to be in ceramic/lided packages with the bond 
wires flapping in free air.   Bond wires embedded in epoxy like to break...  
don't ask how I found this out  ;-)   ... it brings back bad memories... and 
makes bad memories...  Quantum chips have very elaborate/specialized bonding to 
survive liquid helium... even with that, thermal cycling still breaks them.
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Re: [time-nuts] quartz / liquid nitrogen

[Dana Whitlow]

Many years ago, circa 1977, I was moved to try some crude tests on a few
semiconductor devices at LN2 temperature (77K).

These tests were very crude, involving dunking the parts into the LN2 bath,
and
many failed outright.  Most of the devices tested were in plastic packages.

Here are the results as I remember them, applicable only for the survivors:

Silicon bipolar transistors:   The DC beta fell to very low values.
Junction
forward voltages rose considerably.

Silicon JFETs:  Seemed to continue working reasonably well.

Silicon MOSFETs:  Same as JFETs

Red LEDs:   The junction forward voltages rose considerably, to about  5V as
I recall.   The light output per unit current rose truly spectacularly.

My first experiences with seriously-cryogenic RF amplifiers were at the
Arecibo Observatory beginning about 11 years ago.  These were all either
GaAs- or InP-based and we cooled them to ~15K, generally leading to
input-referred amplifier noise temperatures of ~3K.  Many of the devices
needed continuous exposure to light to work properly when cold, and the
metal block amplifier packages had holes in the lid directly over the active
device chips. Small red LEDs in ordinary plastic packages were inserted
in the holes and were driven at a few mA, generally in a series string.
Since cool-down was fairly gradual over a span of at least a couple hours,
there was little problem with thermal shock and almost all LEDs survived
cooldown and warmup for the several cycles they experienced during
my 10 years at the observatory.

RF amplifier biasing was invariably done with opamp circuits to maintain
set drain currents and drain voltages, with said bias control circuits
outside
the dewar at room ambient temperature.   Failures were not too uncommon,
largely attributed to connector misbehavior at low temperature.  Formation
of "ice" (really frozen air) inside the dewars was suspected because fine
wires
inside the dewar were often found to have fairly sharp bends at improbable
locations upon warmup for diagnostic purposes (or due to cooling system
failure).

Cooling was done with a closed-cycle gaseous He system, using the
Gifford-McMahon cycle.  Note that He does not liquefy (at reasonable
pressures) until around 4K.  All dewars for this kind of work depend on
high vacuum inside for thermal insulation, with black body radiation
and direct conduction through wires and mounting structures being
the principal remaining heat leaks.

At these temperatures, maintenance of high vacuum inside the dewar was
essentially automatic because all components of the inward-leaking air
were known to freeze out.  This could lead to a hazard because over time,
months or years, enough air could freeze out to result in dangerously high
internal pressures upon "thawing" when the dewar was warmed for any
reason.  For this reason, all dewars were equipped with blowout plugs
to avoid high pressure's damaging the dewars themselves.

Dana


On Tue, Apr 3, 2018 at 12:26 AM, Mark Sims  wrote:

> And you want your semiconductors to be in ceramic/lided packages with the
> bond wires flapping in free air.   Bond wires embedded in epoxy like to
> break...  don't ask how I found this out  ;-)   ... it brings back bad
> memories... and makes bad memories...  Quantum chips have very
> elaborate/specialized bonding to survive liquid helium... even with that,
> thermal cycling still breaks them.
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] quartz / liquid nitrogen

[Bob kb8tq]

Hi

> On Apr 2, 2018, at 11:18 PM, jimlux  wrote:
> 
> On 4/2/18 1:39 PM, Hal Murray wrote:
>>> If not Nitrogen, how about dry ice (-109F -78C)?
>> Dry ice is relatively easy to get.  It wouldn't be hard to try a quick
>> experiment.
> 
> 
> CTE mismatch in packages will be a significant problem - you might find that 
> your ICs don't work because bond wires have been ripped off the die. Parts 
> might have popped off the board too.
> 
> But if you have one, and it's sacrificable, give it a try - a cooler with 
> some dry ice, and put the circuit above the dry ice, and it will cool slowly


The first level solution is to forget about things like die coat and (gulp) die 
attach epoxy …. yes, this makes building things a bit insane.

Bob


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[time-nuts] quartz / liquid nitrogen

[Mark Sims]

And you want your semiconductors to be in ceramic/lided packages with the bond 
wires flapping in free air.   Bond wires embedded in epoxy like to break...  
don't ask how I found this out  ;-)   ... it brings back bad memories... and 
makes bad memories...  Quantum chips have very elaborate/specialized bonding to 
survive liquid helium... even with that, thermal cycling still breaks them.
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Re: [time-nuts] quartz / liquid nitrogen

[jimlux]

On 4/2/18 1:39 PM, Hal Murray wrote:

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


Dry ice is relatively easy to get.  It wouldn't be hard to try a quick
experiment.





CTE mismatch in packages will be a significant problem - you might find 
that your ICs don't work because bond wires have been ripped off the 
die. Parts might have popped off the board too.


But if you have one, and it's sacrificable, give it a try - a cooler 
with some dry ice, and put the circuit above the dry ice, and it will 
cool slowly

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Re: [time-nuts] quartz / liquid nitrogen

[Bob kb8tq]

Hi



> On Apr 2, 2018, at 5:38 PM, Attila Kinali  wrote:
> 
> On Mon, 2 Apr 2018 12:46:26 -0700
> "Tom Van Baak"  wrote:
> 
>> 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


> 
> I am sure I have some paper on this somewhere in my collection,
> if you want I can dig it out.
> 
>   Attila Kinali
> 
> 
> -- 
>   The bad part of Zurich is where the degenerates
>throw DARK chocolate at you.
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Re: [time-nuts] quartz / liquid nitrogen

[Attila Kinali]

On Mon, 2 Apr 2018 12:46:26 -0700
"Tom Van Baak"  wrote:

> 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


-- 
The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Re: [time-nuts] quartz / liquid nitrogen

[Bob kb8tq]

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 Apr 2, 2018, at 3:46 PM, Tom Van Baak  wrote:
> 
> 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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Re: [time-nuts] quartz / liquid nitrogen

[djl]

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:

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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PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304

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Re: [time-nuts] quartz / liquid nitrogen

[Brooke Clarke]

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 

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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Re: [time-nuts] quartz / liquid nitrogen

[Tisha Hayes]

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 
wrote:

> 
> In message <299B45118C9248498D7B4F3AFE72231E@pc52>, "Tom Van Baak" writes:
>
> >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.
>
> > 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
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
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Re: [time-nuts] quartz / liquid nitrogen

[Hal Murray]

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

Dry ice is relatively easy to get.  It wouldn't be hard to try a quick 
experiment.


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] quartz / liquid nitrogen

[Dana Whitlow]

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  wrote:

> 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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Re: [time-nuts] quartz / liquid nitrogen

[Poul-Henning Kamp]

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

>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.

> 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
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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[time-nuts] quartz / liquid nitrogen

[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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