Hal Rosser wrote:

This is interesting. Are the negative effects due to the fact that induced
magnetism will persist, and thus set up additional impedence on the line ?

Not if I understand you correctly. The effect I'm describing isn't an
impedance due to inductance, as you seem to imply. It's that the density
of an AC current decays exponentially from the surface downward into a
conductor, increasing the resistance of that conductor (known as skin
effect). The skin depth is a measure of how rapidly it decays and
therefore how resistive a conductor will be, and the skin depth is a
function of the frequency, the DC conductivity of the material, and its
permeability. I'm sorry I'm not able to explain why increased
permeability decreases the skin depth except that it's due to the
increased magnetic field opposing current into the conductor (which
might be what you tried to say). I'm sure you can find a lot about skin
effect on the web, as well as in any electromagnetics text.

and does this skin effect caused by the magnetism vary significantly with
frequency ?

I honestly don't know the answer to this. The permeability of
ferromagnetic materials does vary with frequency, in what appears to be
an unpredictable way. Whether this value or the DC permeability should
be used for calculation, I don't know. I suspect that the DC
permeability should be used, and the permeability change with frequency
regarded as a change in effective permeability -- but I don't know for
sure. I'd really appreciate it if anyone who does know would comment. Of
course, skin depth varies with frequency even if the permeability is
constant.

Roy Lewallen, W7EL