[time-nuts] quartz / liquid nitrogen

Attila Kinali attila at kinali.ch
Mon Apr 2 17:38:39 EDT 2018


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.

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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