Mike, XTALs does work in air, or better: dry gases (i.e. nitrogen) too, but OK; quality exemplares are (for better, spurious free, oscillating) in vacuum...
Karl <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virenfrei. www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DDB4FAA8-2DD7-40BB-A1B8-4E2AA1F9FDF2> 2016-06-04 19:41 GMT+02:00 Mike Cook <michael.c...@sfr.fr>: > Thanks all for your advice, hints, tips and links. Lots to read , do and > some hardware to check. I don’t have a frequency generator so I’ll have to > go another route. > > Oh. One last Q. Has anyone tried repairing the « spring » wire electric > connections on large quartz plates. In one large unit I have they had > corroded and dropped the plate, luckily no damage. I have done one, but I > have no Idea what the original wire composition was so have certainly > induced some stray capacitance/resistance. It is possible that it was a > filter rather than a frequency source as it was not in a vacuum. > > Have a good one. > > > Le 4 juin 2016 à 18:49, Bernd Neubig <bneu...@t-online.de> a écrit : > > > > > > Tim Shoppa wrote: > >> The Pierce logic-gate-biased-active oscillator is pretty reliable to > start and will oscillate somewhere with most crystals from kHz to MHz. > >> As you found out, it will often come up on one of many overtones. > >> To reduce chance of coming at an overtone, a series resistor from logic > gate output to the crystal is often enough. If not, a RC low-pass will cut > down even further (although of course adding phase shift.) > > > > This is certainly the easiest and fastest way for a go/no-go test and to > find the approximate resonance frequency. > > In the attached circuit diagram make CX1 and CX2 about 10 pF and RGK > several MegOhms. > > The inverter gate should be preferably an unbuffered HCMOS or other fast > inverter. > > For crystals in the MHz range you can replace RV by a short, for kHz > crystals make it a few kOhms. If testing small watch crystals @ 32768 kHz > or around, RV should be 100 kOhm at least. RV reduces the crystal drive > level (RF current) to an acceptable level to avoid overloading or even > damaging of the crystal. For low frequency crystals the RV-CX2 lowpass also > avoids start-up at the overtone. > > It is recommended to add a second inverter gate at the output to isolate > your oscilloscope or counter input from the oscillator stage. Add some >330 > ohm in series to the output of the 2nd inverter, if you connect a coaxial > cable. Then terminate the coax at the oscilloscope or frequency counter end > with 50 Ohms, so the square wave form will be roughly maintained. > > > > In this circuit the crystal will not operate at its series resonance, > but at a load resonance with load capacitance of something between 8 pF and > 10 pF (depending on the inverter input and output capacitance plus the > stray capacitances of your test fixture). > > If you want to operate the oscillator at a (low) overtone, such as 3rd > (or maybe 5th), you must add a series combination of 10 nF plus an inductor > in parallel to CX2. The 10 nF is to avoid DC short-circuiting of the > output. The inductor together with CX2 must have a resonance frequency mid > between fundamental mode and 3rd overtone (not at one of them). So the > tuned circuit acts like a capacitor at the 3rd OT and is inductive at > fundamental mode (thus the phase condition for oscillation is not fulfilled > at the fundamental mode) > > Have fun > > > > Bernd > > DK1AG > > <Pierce_Logic_Gate.gif>_______________________________________________ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > "The power of accurate observation is commonly called cynicism by those > who have not got it. » > George Bernard Shaw > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.