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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jun 4 05:52:25 EDT 2016

Some idea of the crystal equivalent circuit at the oscillation frequency would help considerably. Usually lower frequency crystals have a considerably higher series resistance than those operated at 1MHz or above.
At frequencies below 100kHz or so a Meacham bridge using something likke a wideband FET opamp may be feasible.

    On Saturday, 4 June 2016 9:01 PM, Mike Cook <michael.cook at sfr.fr> wrote:


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.


"The power of accurate observation is commonly called cynicism by those who have not got it. »
George Bernard Shaw

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