On 1/1/12 8:38 AM, Rob Martin wrote:
> I am making delay lines using coaxial cables.
> How does the velocity factor of a cable change with temperature and over time?
> Does anybody have information about this?
For run of the mill coax the effect is small (tens of ppm per degree C).
You've got several factors working together:
1) The CTE of the coax longitudinally-> it gets longer as the
temperature goes up
2) The CTE of the dielectric -> it gets bigger in diameter, which
decreases the epsilon and changes the ratio of inner/outer diameter,
changing the capacitance per unit length, changing the propagation
speed. But.. again a few ppm/degree effect.
For some coax, there are charts on the mfr websites.
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