One effect that is much discussed with wire and cable is skin effect.  The formula for skin effect on a copper wire is: Depth (inches) = 2.61/sq rt Frequency.  What this means is that, as frequencies get higher, the signal begins to migrate to the outside of the conductor.  Skin effect begins to be measurable at 5 kHz on a 12 AWG wire, where 91% of the wire is then...