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.
