A vector voltmeter can be replaced by a spectrum analyser or even a 14 bit
scope with or without a preamp. In lieu of phase information one can measure
the 3dB bandwidth to elicit the Q, combined with measurement of the low
frequency shunt capacitance and the attenuation at resonance, the crystal
parameters can be extracted without knowledge of the phase shift.
Bruce
On Saturday, 4 June 2016 11:01 PM, Bruce Griffiths
<[email protected]> wrote:
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
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
