[time-nuts] Designing an embedded precision GPS time
jimlux at earthlink.net
Tue Oct 31 22:42:54 EDT 2017
On 10/31/17 1:47 PM, Bob kb8tq wrote:
> 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)
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