[time-nuts] poor-man's oven
kb8tq at n1k.org
Sun Jun 4 10:07:43 EDT 2017
There is no way to know how every outfit makes their products. My guess is that
the temperature compensation “stuff” is pretty stable. At least it has been on all
the product I’ve designed :) I’d bet that the crystals in the TCXO’s are the culprit.
In some of the factories I’ve visited, they package their own crystals. They bring in the
blanks pre-sorted and take it from there. The aging pretty much all comes from the
plating / packaging process. It would not surprise me to find that long term aging is
not a major focus on parts headed for sort lifespan consumer electronics ...
> On Jun 4, 2017, at 9:45 AM, Tim Shoppa <tshoppa at gmail.com> wrote:
> Bob, at the same time, look at all the guys here who absolutely insist that
> the only way to use a double-oven OCXO is to put it in a tightly
> temperature controlled environment. "Nuts", yes, but that's why we're here!
> I myself have been extremely disappointed with the aging characteristics of
> low-end TCXO's. They seem to age even worse than plain old crystal
> oscillators, My theory, is this is because the temperature compensation
> components are themselves aging more than an AT cut crystal does by itself,
> but I've never ripped into one (they're way too tiny to rip into anyway!).
> Tim N3QE
> On Sun, Jun 4, 2017 at 9:36 AM, Bob kb8tq <kb8tq at n1k.org> wrote:
>> The gotcha is that you have multiple systems working against each other.
>> The crystal in the TCXO has
>> one temperature characteristic. The compensation in the TCXO has a
>> temperature characteristic. They
>> cancel each other out to a limited degree. The residual slope may (or may
>> not) be as shallow as you
>> might think. Your PTC is at an arbitrary point on the residual curve. A
>> somewhat more subtle issue is
>> the gradient between your PTC, the crystal, and the compensation as it
>> If the TCXO really isn’t a full TCXO, then some of this goes away. A +/- 2
>> ppm 0-50C “TCXO" may not have
>> any compensation in it at all. Some 0 to 70C parts are done as 2 ppm 0 to
>> 50 and only compensated at the
>> hot end. They actually may be worse with the PTC than at room...
>> Yes this all assumes an AT cut in the TCXO. That’s a pretty good bet ….
>>> On Jun 4, 2017, at 8:13 AM, jimlux <jimlux at earthlink.net> wrote:
>>> I recall some years ago folks were talking about putting a PTC
>> thermistor on the TCXO of a FlexRadio SDR1000 to stabilize the frequency as
>> a sort of poor-man's OCXO.
>>> It's also referenced at
>>> where he says "order of magnitude improvement" with no numbers (from 1%
>> to 0.1% or from 1 ppb to 0.1 ppb?)
>>> I wonder how well that actually works.
>>> Say you bought an inexpensive (perhaps non TC) XO and an equally
>> inexpensive thermistor, glued on on the other, hooked em both up to 3.3 or
>>> Yeah, there's issues with room air blowing on it, and tolerances in both
>> the XO and thermistor, so your absolute frequency accuracy may not be so
>> hot. But what sort of medium to long term performance can one expect.
>>> I did some searches, because I'm sure we've discussed this before, but I
>> couldn't find it. There was some stuff from Oct 2007, but that was in the
>> context of a more complex circuit, and the thermistor was the sensor.
>> (discussions of TE devices too)
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>>> and follow the instructions there.
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> and follow the instructions there.
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
More information about the time-nuts