[time-nuts] Old Crystal.

[EB4APL]

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:Â  8 Mhz #3
Peak Frec. (Hz):Â Â Â Â Â  7996356
Bandwidth (Hz):Â  354,5
Rs (Ohm):Â Â Â Â Â Â Â Â Â Â Â Â Â  24,3
Lm (mH):Â Â Â Â Â Â Â Â  22,13353409
Cm (pF):Â Â Â Â Â Â Â Â  0,01789803
Q:Â Â Â Â Â Â Â Â Â Â Â Â Â Â  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)Â  
> 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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