Originally posted by rueckwaertsflieger
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The coaxial cable's Velocity Factor is applicable to the circuit formed by inner surface of shield and core wire of coax with PE or FPE etc insulation completely filling the gap between core and shield.
In case of sleeve, the circuit condutors involved are the sleeve's inner surface and shield's outer surface. The insulation between these two conductors is composed of an air gap and the outer plastic covering of the coax. Since the sleeve is loosly fit, the air gap is much bigger than the thickness of coax's outer plastic cover. Hence effectively the velocity factor is close to 1, and in most cases safely ignored.
Translation from German to English (in red ink) added by me
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