"David Eduardo" wrote in message
m...
I did a little more research on this, and the key issue is, of course,
conductivity. I am guilty of using the old adage of 1 kw at the bottom is
equal to 50 kw at the top... which is true on average conductivity paths
to
a great extent.


Another way of explaining the frequency dependence is to consider the
phenomenon of skin effect in conductors. The higher frequencies do not
penetrate a conductor (or the earth in the case of an AM band ground wave)
as deeply as do the lower frequencies. Try to visualize the signal being
conducted via a narrow conductor vs. a thicker one, which is essentially the
case.