Hi Unfortunately not all TCXO’s are created equal. It depends a bit on the original intended use. I’d bet it also depends a bit on the original target price. Perturbations (frequency jumps) over temperature are one “feature” that might be present. Hysteresis at half the temperature spec is another “feature”.
Even within the same batch or same test run, some will be much better than others. You stop the compensation process when they get “good enough”. That will mean that a few are right at whatever the production target is and others exceed the target by quite a bit. While crystal curves are indeed cubic, there are higher order terms in the curve. The “why” is something people get to write papers on.If you are trying to compensate to tight specs, you will see all sorts of stuff. It is not at all uncommon to see >9th order curves residual curves. Indeed some of that is from residuals in the compensation circuit as well as from the crystal. Why all this yack? A lot of people come from a background using OCXO’s. An OCXO generally has a low order temperature characteristic. It also is rare to see things like frequency perturbations in an OCXO. Moving from one to the other can be a bit interesting. Bob > On Oct 31, 2017, at 10:42 PM, jimlux <[email protected]> wrote: > > On 10/31/17 1:47 PM, Bob kb8tq wrote: >> HI >> TCXO is a very loosely defined term. A part that does +/- 5 ppm -40 to +85C >> is a TCXO. A part that does +/- 5x10^-9 over 0 to 50C may also be a TCXO. >> Dividing the total deviation of either one by the temperature range to come >> up with a “delta frequency per degree” number would be a mistake. You >> would get a number that is much better than the real part exhibits. >> Working all this back into a holdover spec in an unknown temperature >> environment is not at all easy. > > Very much so - most of the TCXO curves I've seen tend to be "much" better > than the spec over the central part of the frequency range (which makes > sense, the underlying crystal is a cubic with temp, most likely) > > Retrace and hysteresis might be your dominant uncertainty. > I've attached a typical TCXO data plot for your viewing pleasure.. > (that's an expensive oscillator, because it's for space, but I don't think > space or not changes the underlying performance) > > >> Bob > <TCXODataVectron 47.pdf>_______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
