On 1/2/2012 12:32 AM, Steve Hunt wrote:
> All that I've ever measured lie in the range 0.95 to 0.99.
> Did you notice that I said*COMMON-MODE* velocity factor? Signals
> flowing on the outside of the braid are Common-Mode signals - signals on
> the inside are Differential-Mode; they can have totally different
> velocity factors.
Yes, on all counts. A common mode signal can be thought of as using the
coax braid as a long wire antenna. Thus, the common mode VF for coax is
simply that which corresponds to an insulated wire having the diameter
of the shield. It is well known that using a fatter conductor moves the
resonant frequency down a few percent as compared to a small diameter
conductor, and so does adding insulation. How much it moves depends on
the diameter of the wire, the thickness of the insulation (the jacket),
and the dielectric constant of the insulation (the jacket). A thin wire
with no insulation would be close to 1.0 Vf.
73, Jim K9YC
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