My response got lost in the Internet, so I repeat the info.
If you have access to a Network Analyzer, either Scalar or Vector, you
can measure the crystal parameters. You need a test fixture (it could be
homemade) to convert the 50 Ohm analyzer impedance to 12.5 Ohm and you
very slowly sweep the crystal to obtain its serial resonance (frequency
and attenuation) the and the -3dB points frequencies. From these
measurements there are simple formulas to obtain the motional
resistance, inductance and capacitance, and the crystal Q.
Some professional Network Analyzers seems not to be very adequate to do
this because they cannot sweep slowly enough, but some low cost hobby
type analyzers have a mode for measuring crystals with these
calculations integrated. One example being the Poor Ham Scalar Network
Analyzer which has a function for specifically measuring crystals using
a step rate of 1 Hz and the nanoVNA, that can measure the resonance
point and you do the calculations. A program with the measurements and
calculations integrated is under development at this time.
This an example of the PHSNA output:
Crystal Id: 8 Mhz #3
Peak Frec. (Hz): 7996356
Bandwidth (Hz): 354,5
Rs (Ohm): 24,3
Lm (mH): 22,13353409
Cm (pF): 0,01789803
Q: 45763
Regards,
Ignacio EB4APL
El 01/03/2021 a las 0:35, Dan Kemppainen escribió:
Hi All,
I've picked up a couple of old crystals. Mostly because they look
neat. They are 1Mhz, in a glass tube. The quartz is ~25mm dia, at
about 1 mm thick. Was able to get them to oscillate using a Colpitts
circuit. They will oscillate at 2.851Mhz (probably some strange mode)
if given the chance.
I've been scouring my reference books here, and haven't had much luck
finding any details on how one would even guess at the parameters of a
quartz like this.
There area few numbers on them, 33 stamped on the side, 1000 (KHz???)
on the top, 87 on the top, and hand written 501 (probably a SN).
Digging on line, I'd guess an AT cut based on thickness. I'm guessing
the 33 is capacitance in pF. 87, might be year.
If any of you have any suggestions on where to find information on how
to get something like this to oscillate properly, guess at correct
parameters, or even measure any of the parameters I would really
appreciate it.
I'm sure these are really nothing special, but it would be neat to
give them a fighting chance to show what they can or can't do without
breaking them!
Thanks,
Dan
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