[time-nuts] Improving the stability of crystal oscillators

Brooke Clarke brooke at pacific.net
Wed Oct 10 13:52:26 EDT 2007

Hi Tom:

That's a cleaver improvement to a non ovenized crystal.  Usually crystals are 
ground to have a temp vs freq turnover point occur at a specified temperature. 
  The common one is to be on frequency at room temperature.  So if a room 
temperature crystal is heated it's no longer operating at the turnover 
temperature and so there is a steep delta frequency vs. temperature slope.  Did 
  you get a crystal cut for your heater temperature or somehow match the 
heaters temperature to a turnover point on your crystal?

I spent many many hours adjusting the oven temperature of a Gibbs frequency 
standard to get it right on the turnover point.

Since the improvement in frequency stability depends on minimizing the 
temperature excursions it's good to have as much gain as possible in the heater 
feedback circuitry.  This was done for the HP E1938 10 MHz oscillator, see:
and the paper: The Theory Of Zero Gradient Crystal Ovens, R.K. Karlquist, L.S. 
Cutler, E.M. Ingman, J.L. Johnson, T. Parisek

Have Fun,

Brooke Clarke, N6GCE
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam

Tom Clifton wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+brooke=pacific.net at febo.com RETRY
> While the website is not explicitly about frequency
> measurement, there is an interesting bit on improving 
> the stability of crystal oscillators with external
> heater controllers.  While it may not be suitable for
> long term high stability control it might be suitable
> for many other purposes.
> http://www.qrss.thersgb.net/Crystal-Ovens.html
> The main page is also a good read:
> http://www.qrss.thersgb.net/Receiving-QRSS.html#Introduction
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