[Elecraft] crystal oven question

[Ron D'Eau Claire]

The oven simply keeps the crystal at a stable temperature. The frequency of
a crystal is based on its physical size. The crystal mechanically vibrate at
the RF frequency. The "piezo-electric" effect causes it. That effect says
that when the crystal is mechanically 'deformed' it will produce a voltage
across electrodes attached to it, and when a voltage is applied to those
electrodes, it will mechanically deform the crystal. So by applying small
pulses of noise to the crystal electrodes, it can be made to "ring" like a
tiny bell at a specific frequency based on its size. As it rings, the
pieze-electric effect produces an a-c voltage across the leads equal at its
"resonant" frequency. But that resonant frequency depends upon the size of
the crystal, and the size of the crystal depends upon the ambient
temperature. 

The oven maintains the temperature of the crystal, hence its physical size,
precisely.

The most simple form of an "oven" is to button up a rig using a crystal and
let it operate for a good while. When the temperature inside the rig
stabilizes, the frequency of the crystal oscillators will also stabilize. 

By providing an accurate, repeatable temperature, the more sophisticated
ovens ensure that the crystal not only oscillates on one stable frequency,
but that it oscillates as close as possible to the SAME frequency every time
the rig is used.

Of course the stability of a crystal oscillator is dependent on other things
as well. The circuit elements in the oscillator outside of the crystal must
also be stable over time and temperature. In the most extreme cases, the
entire oscillator may be enclosed in a temperature-stable "oven".  

One could use a 'crystal cooler' too and get the same result. Something like
a tiny refrigerator. The point is to have it at a specific temperature
whenever it's used. It's just easier to heat the crystal than it is to cool
it. 

Ron AC7AC 

-----Original Message-----

Does anyone have a pic or quick description of a crystal oven.  I notice on
Elecraft site they sell them for the Transverters.  From my understanding
that makes the crystal more stable as it becomes heated so it does not
drift?  Is this right?

WT5Y