[time-nuts] How to get unknown frequency quartz crystals oscillating

Bob Camp kb8tq at n1k.org
Sat Jun 4 08:29:17 EDT 2016


Simple approach is to assume that you have a crystal resistance in the range of 100K ohms. If you guess to 
high, the oscillator will just work to well :)

Multiple JFETS in cascade for the higher frequency stuff should work. For anything below 20 KHz, an op-amp
is likely your best bet.

A spectrum analyzer with a tracking generator will give you some idea of their impedance and *if* they still have 
any activity at all. 


> On Jun 4, 2016, at 4:46 AM, Mike Cook <michael.cook at sfr.fr> wrote:
> Hi,
> I have a number of crystals either in glass, bakelite, ceramic or metal housings that I would like to get resonating . They are of three basic types.
> Square, or rectangular flat   
> Round flat 
> Bar  square section
> Sizes range from 2-10cm or more in the longest face.
> Some have frequency markings. ranging from IKHz 5MHz. 
> Others have none.
> Some are of  Military origin, probably radios and as they have markings I can probably find a schematic from the radios to see how to proceed.  There may be dedicated testers still around. I am not so interested in this bunch at the moment. 
> Others have no known origin so I have no idea what oscillator circuits were used with them. 
> In terms of vintage, I would guess pre 1940  to late 50s 
> I have built a little Pierce circuit an tried a few. Some of the later 1-5MHz crystals will oscillate but there are a lot of parasitic signals as well as the supposed fundamental. I cannot make any of the low frequency / big crystals to react.
> So my question:
> If you had a crystal with unknown frequency and drive requirements that you wanted to investigate. How would you go about it?
> If I can get them going I will share the Adevs. I don’t have a spectrum analyser so I can’t do phase noise.
> Regards
> "The power of accurate observation is commonly called cynicism by those who have not got it. »
> George Bernard Shaw
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