On reflection, building a jig to measure the crystal transmission as a function
of frequency may be much easier than attempting to build an oscillator for an
unknown crystal. However a suitable signal generator and detector are required.
Once the crystal parameters are known its much easier to design a suitable
oscillator circuit. Measuring the location of spurious resonances may also be
useful.
Bruce
On Saturday, 4 June 2016 9:52 PM, Bruce Griffiths
<[email protected]> wrote:
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.
Bruce
On Saturday, 4 June 2016 9:01 PM, Mike Cook <[email protected]> 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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