Hi Indeed, you would probably do better with a simple XO than with a TCXO. A proper OCXO is temperature tested and the gain and set point of the oven are adjusted to optimize the temperature performance.
Bob > On May 14, 2016, at 5:52 PM, David <davidwh...@gmail.com> wrote: > > As you pointed out earlier, with a TCXO, any inflection points of the > crystal itself will be unavailable because the temperature coefficient > at any one point will be the product of the crystal and the > temperature compensation circuitry. > > I am left to wonder if this will work better with a TCXO or just an > XO. The later would allow for a better optimized voltage control but > at that point, I will have just reinvented the ovenized crystal > oscillator using AT cut crystals and operating at room temperature. > > Do OCXOs use internal temperature compensation other than that > provided by the oven itself? > >> Bottom line: A $10 eBay OCXO is likely to beat an ovenized or cooled TCXO. > > Designing something which relies on the availability of often > questionable Ebay items just bugs me. > > On Sat, 14 May 2016 08:54:36 -0400, you wrote: > >> Hi >> >> If the crystal has a most stable point it will be a point that the slope >> goes >> from positive to negative (or vice versa). These points are symmetrical >> about >> the center of the crystal curve. For an AT cut, your center will be just a >> bit above >> 25C. How far above depends on the geometry of the blank and a few other >> things. >> For simplicity you see 25 used a lot. >> >> If you look at the curves on the link posted earlier they follow a pattern. >> Anything >> below zero angle never goes through a slope change The zero angle goes flat >> at the center. The useful part of the curves have a turn at 25 +/- X where >> X can >> be anything from 5 to 100C in normal crystal. >> >> You need to dig into the actual math to take a look at the slopes near turn. >> Obviously >> the turn at 50C is a better bet for your OCXO than the one at 125C. >> >> The enemy of any temperature stabilization system is waste heat. On an OCXO >> with a normal heater, there is some (small) current in the circuit even when >> the heater >> is turned off. With a TEC, there is a *lot* of waste heat when cooling. The >> systems >> I have seen using them get into stacked devices and water cooling pretty >> quickly. >> >> Bob > _______________________________________________ > 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.