Quartz crystal motional parameters, and how to measure them 

+rapsod1911 You're correct, the inductance should read 62.949mH; see my reply to Dennis Lubert. Thanks!

+SLEAGD I’ve uploaded a few pictures here: analogzoo.com/xtal_pics/. The markings on the crystal are: “5128K 8607 94”. The 5128K is the frequency (5.128MHz) and I presume 8607 is a date code. There is also what appears to be a logo stamped on it that I haven’t been able to identify. If it helps, this is the eBay seller I bought it from: www.ebay.com/usr/bird_sr71a. I’d love to hear about any info you might find on it!

+devttys0 Manufacturer is identifiable from the logo. Oddly enough, they are still in business: www.morion.com.ru A few interesting examples of USSR-made quartz crystal resonators in the glass envelop could be found here 155la3.ru/quartz_glass.htm There are lots of other interesting soviet electronics related stuff there. Package type and resonant frequency range of your crystal matches resonator type РК-187 (RK-187). According to general databook this is rather high spec. part. It operates at 7-th harmonic, 4.6-5.3MHz crystals of this type were available, tuning precision is +-(0.4..2.0)10^{-6}, temp. coefficient +-0.05ppm/K (incredible performance, can you please confirm it for your crystal?) rated Q>1.5x10^6

+SLEAGD Very cool, thanks for tracking all that down! Those specs are very impressive, it sounds like I'll have to do a follow-up video on just this crystal.

I've never worked with them, but being piezoelectric like quartz I would expect the equivalent circuit to be the same. It's a bit old, but this handbook seems to have quite a bit of information on the subject of transducer analysis and equivalent circuits: www.dtic.mil/dtic/tr/fulltext/u2/a082503.pdf

When you depress the "Ct" switch, yes, the variable capacitance is placed in parallel with the crystal and the total capacitance is measured. You can then just subtract the known variable capacitance value from the total to get the Co capacitance.

How does one know the variable capacitance value when the knob has no calibration?

If you press the Ct switch with no crystal in place, the displayed capacitance will be only that of the variable capacitor.

You can see an example of this at 5:08 in the video

Yes, I see. The display implies 0.01pF resolution though I doubt that the last digit is stable over time. I would label the knob PARALLEL not SERIAL capacitance.

+Susan Donovan I was wondering if someone would notice those. :)

Pfft... little floppies. 8" or bust!

+hpux735 It is called "quality" (hence Q) of resonator. You can think of it as a number of oscillations in which amplitude will decay by e-fold if oscillator will be left alone. It is also related to narrowness of frequency response (delta f /f ~ 1/Q)

+hpux735 "Q" (or quality factor) is a unit-less quantity that is simply the ratio of stored energy (reactance) to dissipated energy (resistance). Ideal components such as inductors, capacitors, and crystals would be purely reactive with no resistive losses, and hence have an infinite Q. In the real world of course this is not possible, so limiting the resistive losses (and therefore increasing the Q) is a major design/manufacturing goal. You're absolutely correct, the Q does effect frequency response / stability. A higher Q (less resistive loss) would mean a sharper filter response or less oscillator phase noise. Inductors in particular are difficult in this respect because a coil of wire has some unavoidable inherent resistance; this is exacerbated at RF frequencies by the skin effect and can make realizing sharp filters with low passband losses difficult or impossible. The relatively low resistive losses of a quartz crystal then makes it preferable to an LC circuit in situations where high performance is required.

+devttys0 +SLEAGD Thanks! I'm used to hearing about Q of inductors, etc, but didn't know how it mapped to crystals. This was a very cool video, thanks!