[time-nuts] Old Crystal.

[Bob kb8tq]

Hi

You don’t necessarily  need to convert to a 12.5 ohm system. A lot depends on 
just what your objectives are. 

It a bit like needing a fancy Fluke Hart Chub thermometer if you are only after
a couple of degree accuracy. The tools vary depending on the job.

Bob

> On Mar 1, 2021, at 3:23 PM, EB4APL <eb4apl at gmail.com> wrote:
> 
> 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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