Richard Harrison wrote:
Surely the signal follows the path of the turns on a coil.

Not entirely as adjacent turns do have an effect on
each other so there is a grain of truth in what W8JI
is saying. W8JI's error was in taking that grain of
truth and rationalizing that small grain into an
explanation that is off by at least a magnitude.

It looks like a reasonable rule of thumb is that the
velocity factor of a coil is approximately half what
it would be if the signal followed the wire entirely.
In other words, if one calculates the delay in the
length of wire used to wind the coil, the actual
delay through the coil is likely to be half of that
value.
--
73, Cecil http://www.w5dxp.com