[time-nuts] How far can I push a crystal?

[Bob Camp]

Hi

Just to complete the thread:

You can take the inductor that resonates out C0 one more step. If you break (or tap) the inductor it can act as a transformer. The impedance transformation lets you swing the oscillator further with a specific amount of variap change in capacitance. 

Resonating out C0 does indeed let you swing above the "anti resonant" point on the crystal. It also eliminates the linearity issues associated with C0. 

All that said, The stability / jitter / phase noise / ADEV of a wide band VCXO is not going to be TimeNuts compatible.

Bob

On Jan 17, 2013, at 11:50 PM, "Rick Karlquist" <richard at karlquist.com> wrote:

> Bernd Neubig wrote:
> 
>> A parallel inductor for compensation of the static capacitance C0 does not
>> help much at 10 MHz, because such a coil, which resonates out a 6 pF
>> capacitance has an internal winding capacitance, which is larger than 6
>> pF.
>> So you would need a coil which has a self-resonance of slightly above 10
>> MHz.
> 
> Actually, a parallel inductor helps a lot and is essential for getting
> a large pulling range.  Modern surface mount coils have a self capacitance
> of a fraction of a pF, not 6 pF, and in any event, you can always find
> an inductor that is resonant when combined with the crystal.  The
> nominal value of this inductor may be considerably less than the
> calculated value, but there is always some value of inductor that works.
> This was true even in the through hole era.
> 
> Rick Karlquist N6RK
> 
> 
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