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.
