Hi, Even if my VNA steps in 1 Hz if I ask it kindly, it can be a bit teadious work to find it.
Cheers, Magnus On 2020-02-27 14:35, Bob kb8tq wrote: > Hi > > Ok, so just to run the math: > > 5 MHz / 2.9 = 1.724 MHz > > If the Q at the fundamental is 500K (a wild guess) then 1.724 MHz / 500,000 = > 3.4 Hz > > In a world where a synthesized sweeper *might* be stepping in 10Hz steps, > that’s an > easy one to miss. > > Bob > > >> On Feb 26, 2020, at 11:40 PM, Bernd Neubig <[email protected]> wrote: >> >> Hi Gerhard, >> I am rather sure that it is a 5 MHz 3rd overtone crystal. >> the resistance should be in the 80 to 110 Ohm range and Q about 1.5 million. >> You can see the resonance without ringing in a span of 100 Hz or smaller >> with a sweep time of 10 sec minimum. >> See attached the response of a 5 MHz SC3 crystal in HC-40/U package. >> Indeed the 5.45 MHz is the B-mode which has a temperature coefficient of -30 >> ppm/K >> Because the crystal blank has a plano-convex shape. The overtones are >> quite far away from 3 times or 5 times the fundamental mode. 3rd overtone is >> about (rough guess) 2.9 time of fundamental mode. >> To find them you must really carefully sweep around a few 10 to 100 kHz span >> with slow sweep time a narrow bandwidth >> >> Regards >> Bernd >> DK1AG >> >> -----Ursprüngliche Nachricht----- >> Von: time-nuts [mailto:[email protected]] Im Auftrag von >> Gerhard Hoffmann via time-nuts >> Gesendet: Mittwoch, 26. Februar 2020 01:42 >> >> To get a first impression, I soldered the crystal to an SMA plug and put it >> on an >> R&S ZVB-8 network analyzer and measured S11. I could see the 5 MHz resonance >> as a 15 dB dip. There was also a resonance at 5.45 and a smaller one >> another 90 KHz >> higher. the +10% suggest that it is an SC cut. >> But I could not see anything at 1 or 1.6666 MHz, so it should be a >> fundamental crystal? >> Is that common? >> I made most measurements at room temperature. I can turn the hot air solder >> station down to 91°C which is not far away from the crystal's 87.7°C >> inflection point, and I could see some variation on the 5.45 MHz resonance >> vs. temp. >> I must build a fixture for the hot air because the sweep time at 1 Hz >> bandwidth >> is close to eternal. >> Is the un-harmonicity (???) between fundamental and overtones stronger with >> SC-cuts >> than normal AT? I also could not see anything at 15 MHz. Next I'll make a >> board >> for the PI fixture as described by Bernd Neubig in his crystal cookbook. >> BTW I could see some more dips with >= 10 Hz resolution. I hope that does >> not mean >> that the ZVB needs service. >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> <5MC5735H.jpg>_______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
