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

Don Latham djl at montana.com
Fri Jan 18 21:46:04 UTC 2013


About $4 on epay will get you a DDS knurdle with crystal reference
that'll deliver...
Rick Karlquist
> Ed Breya wrote:
>> Maybe I should clarify what I meant by pushing the crystal frequency.
>> I
>> meant only using various topologies and electronic components in the
>> associated circuitry, that would detune it from its natural resonance
>> far enough to reach the new frequency, and still have it be sort of a
>> narrow-bandwidth crystal oscillator - not doing any mechanical changes
>> to the crystal element itself.
>>
>> Since the ceramic resonators seem to work well, and can be pushed (or
>> pulled?) fairly far away by proper selection of the associated
>> component
>> values, I was wondering how far quartz crystals can reasonably go. I
>
> Since you asked:
>
> You can get something like a range of 0.1% by resonating out the
> holder capacitance with a shunt inductor.  You then put this
> assembly in series with an inductor and varactor.  If you want to
> get into the lunatic fringe, you use a high Q inductor wound on
> Fair-Rite 61 or 67.  Now you can seriously pull the crystal below
> its resonant frequency.  How far you can go depends on the Q of
> the inductor.  I am not sure if you can also pull it above,
> but even if you could, there are spurious resonances up there that
> could get you.  The lunatic fringe might get you .2 or .3%, still
> not .6%.  You'll definitely take a hit in temperature stability
> and phase noise with high pulling.  If you don't have experience
> with VCXO's, you will find the circuit design quite challenging.
>
> It wasn't clear if you needed a 10.05944 MHz VCXO, or just a
> source at that frequency.  There a lots of one chip synthesizers
> that could generate that frequency as I'm sure you know.
>
> Rick Karlquist N6RK
>
>
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-- 
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
De Erroribus Medicorum, R. Bacon, 13th century.
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com





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