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

Bob Camp lists at rtty.us
Fri Jan 18 00:54:20 UTC 2013


Hi

Mouser shows 16 items tighter than +/- 20 ppm accuracy. Six of them are in stock and less than $1 in single piece quantities. The cheapest is 39 cents. 

Bob

On Jan 17, 2013, at 7:38 PM, WB6BNQ <wb6bnq at cox.net> wrote:

> Hi Ed,
> 
> I seriously doubt you will be able to pull the 10 MHz crystal tht far off.
> International Crystal Manufacturering (ICM)
> 
> http://www.icmfg.com/
> 
> still makes crystals for a reasonable amount (about $25) cut to order.  That may
> be far easier than all the time you would spend bending and pushing things around
> trying stretch components.
> 
> Bill....WB6BNQ
> 
> 
> Ed Breya wrote:
> 
>> I've got to make a very clean 10.05944444... MHz VCXO for a redo of one
>> of my old circuits. I previously used a 10 MHz ceramic resonator, which
>> was easy enough to push around in frequency. Of course, I have a couple
>> dozen of those somewhere, but can't find them now that I need them
>> again. I figured I'd just pull the ones out of the old circuit, but
>> since I did find a whole bunch of 10 MHz quartz crystals, I'd like to
>> revisit whether I can push one of those that far with decent results. As
>> I recall, the results of my previous experiments in doing this were less
>> than satisfactory, which is why I went with the ceramics.
>> 
>> This would be a change of 60 kHz out of 10 MHz, or 0.6 percent - a
>> helluva lot for a crystal. The frequency will be exactly phase locked to
>> a reference. It doesn't need to have extremely high in-circuit Q or
>> long-term stability - just tunable to that magic number - the PLL will
>> do the rest. A conventional varicap circuit will provide the VCO-ness,
>> while the tuning range just needs to be enough to accommodate drift and
>> the initial setting. The power gain element will be a 74HC04 or 74HC86
>> section. The PLL reference will be 59.44444...  kHz - way above the
>> necessary loop BW.
>> 
>> Has anyone successfully pushed a quartz crystal that far off, with
>> reliable (still sort of a sharp resonance) operation and no spurious
>> modes? Any ideas? If this isn't practical, I'll just go back to the
>> ceramic resonator (which worked just fine), but I'd like to settle it
>> once and for all.
>> 
>> Ed
>> 
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> 
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