[time-nuts] Super stable BVA Quartz resonators... BVA??

[Bernd T-Online]

Hi all,

For explanation how the BVA works, please see the attached slide which 
shows schematically its internal construction. (The explaning text is in 
German, as it is from my periodically given crystal seminar.)
The key points which yield the BVA's improved aging are, that
- the whole resonator package is made from quartz, consisting of the 
resonationg quartz plate in the middle section and the two mounting & 
sealing plaates on top and bottem - you may call it a Hamburger style ;-)
- the resonating plate is held through quartz bridges rather than metal 
suspensions, thus reducing mounting stress.
- the BVA is "electrodeless", as the electrodes are evaporated on the 
inner side of the upper and lower mounting plates. Therefore no stress 
between the quartz surface and the metal eletrode.
- Therefore the energizing electrical field is applied through an 
airgap, which represents two small load capacitors in series to the 
resonator, thus making the resonator electrically "stiffer" and less 
sensitive to circuit influences.

On the other side you may imagine the main problems associated with such 
a construction:
- The difficulty to manufacture the convex and concave shaped parts with 
such a precision, that the curvature yields a constant and very small 
airgap.
- To realize the fine adjustment to frequency, because the unit cannot 
be tuned in the conventional way, i.e. by plating some metal on the 
electrode.
- The frequency accuracy to which the resonator has to manufactured, 
because the resonator frequency cannot be pulled with the external 
circuit elements by more than some hundred ppb.

It may be interesting to note, that there was a company "BVA 
Industries", which wanted to generate their income solely from making 
BVA - which failed. Maybe because of the cost could not be covered by 
the revenues from the rather limited market.

Bernd DK1AG
__________________
AXTAL GmbH & Co. KG
Facility MOS
Wasemweg 5
D-74821 Mosbach / Germany
fon: +49 (6261) 939834
fax: +49 (6261) 939836
www.axtal.com



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