[time-nuts] OCXO Voltage Input? (Bob Camp)

[Bob Camp]

Hi

Simple answer = crystals are never perfect.

Longer winded, but very incomplete answer =

A spurious response in a crystal normally refers to a mode that is not one of the “identified” modes of the crystal. An AT has a set of identified modes, an SC has a more complex set of modes. In the case of the AT it would be the fundamental and the odd overtones. In the case of the SC you have the A, B, C modes and their odd overtones. None of those are considered spurious. 

A spur can come from a lot of different places.  One common one is higher order vibrations in a longer dimension face of the resonator. The 183rd overtone of the width of the blank is still a legitimate resonant mode. Another source are modes other than shear (like flex). Deriving a full catalog of all the modes of an arbitrary blank design is a major project. There are only a handful of people out there who are into that sort of thing (as opposed to simply cranking through some formulas).  

Practical answer = Don’t worry about it. Unless you are building a wide pull VCXO or a wide deviation VCXO (often the same thing) you will never notice them. 

Bob

On Sep 6, 2014, at 9:13 PM, Hal Murray <hmurray at megapathdsl.net> wrote:

> 
> kb8tq at n1k.org said:
>> The biggest problem comes from crystal spurs rather than crystal Q. 
> 
> What's the mechanism for making spurs with a crystal?
> 
> -- 
> These are my opinions.  I hate spam.
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