On 08/30/2012 11:10 PM, Rick Karlquist wrote:
Azelio Boriani wrote:
Interesting this third overtone/fundamental*3 idea but what makes the
third
overtone not equal to the fundamental*3? Is the crystal operated in series
or parallel resonance?
That is where the special SC cut crystal comes into play.
It's not so much that the 3rd OT is on a different frequency, but
rather that it has a different and known tempco relative to the
fundamental, so it can be used as a thermometer. It would be
interesting to take a crystal out of a random 10811 and compare the
frequencies of the fundamental and 3rd OT vs temperature to see
if that crystal would accidentally make a good thermometer.
All the different modes have different temperature dependencies. Being
able to maintain dual oscillation on both over the range seems like a
reasonable challenge.
Cheers,
Magnus
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