[time-nuts] Quartz crystall and beyond

[Richard (Rick) Karlquist]

On 2/29/2020 1:58 PM, Attila Kinali wrote:

> Different concept. Quartz oscillators are mechanical resonators.
> Cryogenic sapphire oscillators are electro-magnetic resonators.
> The problem with those is, that they are large and need liquid He
> for cooling. Not only is He expensive, but it also needs a cryostat
> that will mechanically shake the CSO. But they get down to a few parts
> in 10^-15 between 1s and ~1000s, I've even seen papers with a few parts
> in 10^-16 in the same range(e.g. [1]) . There have been attempts to get
> them to liquid nitrogen temperatures [2]. But they only got down to 1e-13
> (i.e. where good crystal oscillators are). And not much happend since,
> beside an attempt to get them working at room temperature [3]
> 

Agilent (now Keysight) attempted for years to put a whispering
gallery oscillator in an instrument.  It wasn't cyrogenic.
They actually heated/cooled it to lock it to a 10811.  The real thing 
that stymied them was microphonics.  I retired in 2014 and don't know 
whatever became of this effort.  The two biggest experts on WGO's went 
with Agilent during the Keysight spinoff, which might have finally 
killed it completely.  A cryogenic WGO would face the same microphonic
issues.

Rick N6RK