[time-nuts] Is there anything better than a crystal oscillator?

[Tom Van Baak]

> Over the years, better and better long-term accuracy has been 
> achieved with various "atomic" references, but if I understand 
> correctly, the actual oscillating element is still a quartz crystal, 
> albeit in a tightly controlled loop.  None-the-less, from discussions 
> in this group I believe that the short-term noise and stability is 
> still mainly that of the quartz crystal, and its associated 
> electronics.  Is there anything better than quartz?  Did I hear 
> something about sapphire?
> 
> Regards,
> 
> Peter Vince  (London, England)

Yes, it's true that almost all atomic frequency standards are
actually a form of "disciplined" quartz oscillator. A "physics
package" resonator is used to close a VCOCXO loop.

Exceptions are active masers, which generate their own
oscillations.

Correct, there is an exotic oscillator made from sapphire
that operates at liquid nitrogen (or cooler) temperatures and
frequencies in the many GHz. Here's a few links, or google
for words like Cryogenic Sapphire Oscillator, or CSO.

http://horology.jpl.nasa.gov/quantum/sapphireoscillator.html
http://www.psi.com.au/Pages/Library.html
http://www.psi.com.au/Pages/LibraryPublished/FCS2004_-_Review_of_Sapphire_Oscillators.pdf

/tvb