[vna] measurement of quartz crystal

[Tom McDermott]

Hi Koji:

	The TAPR VNA can be calibrated against an external reference
oscillator for good frequency accuracy. However in order to determine
accurately the 4 motional parameters (Ls, Rs, Cs, Cp) of the crystal
requires extreme precision of the fixture stray reactances. I am not an
expert in crystal filters, but I think the 4-parameter model is used pretty
extensively in filter modeling. 100 Hz frequency accuracy is not a problem,
but stray reactances are a problem.

	I think Agilent has a software package to extract the motional
parameters from swept S parameters. The TAPR unit does not have this
software, but it perhaps could be an interesting exercise; certainly for
those who enjoy working on software.

	Key to measurement is that the fixture parallel measurement will be
contaminated by fixture parallel capacitance. This will rotate the series
resonance frequency away from R + j Zero X and must be compensated. The
parallel anti-resonance will have the same issue. S-parameters will show the
crystal resistance as compared to 50 ohms but the fixture will rotate the
phase angle. The fixture perhaps can be calibrated out of the measurement if
the crystal is replaced with a 50 ohm resistor, but I have never tried it.

	-- Tom, N5EG






> -----Original Message-----
> From: vna-bounces at lists.tapr.org 
> [mailto:vna-bounces at lists.tapr.org] On Behalf Of Koji Terai
> Sent: Saturday, December 03, 2005 9:14 AM
> To: vna at lists.tapr.org
> Subject: [vna] measurement of quartz crystal
> 
> 
> Hi, everyone! I would like to know if the VNA is able to 
> determine resonant frq. and antiresonant frq. of a quartz 
> crystal in accuracy of 100 Hz. I plan to construct Cohn type 
> crystal filters, and I tried to measure crystals but I was 
> not able to measure these two frequencies definitely, 
> especially ant frequency measurement was very critical. I am 
> looking forward to a good solution for this.
> 
>  Koji
> 
> 
> 
> _______________________________________________
> vna mailing list
> vna at lists.tapr.org https://lists.tapr.org/cgi-bin/mailman/listinfo/vna
>