[time-nuts] quartz / liquid nitrogen

Bob kb8tq kb8tq at n1k.org
Mon Apr 2 19:36:15 EDT 2018


Hi



> On Apr 2, 2018, at 5:38 PM, Attila Kinali <attila at kinali.ch> wrote:
> 
> On Mon, 2 Apr 2018 12:46:26 -0700
> "Tom Van Baak" <tvb at LeapSecond.com> 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
> 
> 
> -- 
> <JaberWorky>	The bad part of Zurich is where the degenerates
>                throw DARK chocolate at you.
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