I think you dropped a decimal point, there, Denny. How did you get
from 0.01mm skin depth at 10MHz to talking about 0.1mm? If you stay at
0.01mm, it would be about 0.4 mils. The rule of thumb I remember is
2.6 mils at 1MHz, so it would be 0.8 mils at 10MHz. That's for
_copper_ and as Roy wrote, steel will be much less.

Another rule of thumb: the RF resistance of copper wire is about 1
milliohm/foot * sqrt(freq. in MHz) / diameter in inches. For 14AWG
wire at 4MHz, that's about 31 milliohms per foot, which is pretty much
inconsequential for a 75M half-wave dipole with about 75 ohms feedpoint
radiation resistance.

The resistivity of nonmagnetic stainless steel is roughly 50 times that
of copper, so the loss would be about seven times as great at RF,
assuming that the permeability really is low at RF; that wouldn't be
bad. But high permeability would not be good, especially in a small
diameter wire..

Moderately wide bandwidth, high strength, low loss dipole: a center
support steel cable, surrounded by 4 or so small copper conductors in a
"cage" spaced out from the center support to make a conductor perhaps
1/200 of a wavelength effective diameter.

Cheers,
Tom


Denny wrote:
Roy,
As my cobwebby brain remembers, for conductive materials such as
aluminum through gold, the rough rule of thumb is that at 10 megacycles
the skin depth is .01MM (01 is 10 backwards, only reason I remember)
So 1mm is 0.0394" therefore a skin depth of 0.1mm is 0.00394", call it
4/1000 of an inch for round numbers... So, the other rough rule of
thumb I have always used in my wasted career in industrial electronics
is to have the conductive plating 5 times the skin depth... So, 0.020"
would suffice for 10 megacycles...
Now, that begs the question for steel, or zinc plated steel... Anyone
interested can google up answers with a bit of personal effort...

What has always intrigued me though, is the concept that a moving
charge at RF frequences, spreads over the surface and penetrates only
0.020" the majority of the charge ( @10 mc ) , while still having lines
of flux penetrating radially to the electrical center of the metal
object... Yet, by the same token, if the metal shape is a hollow tube,
no signal will be detected upon the inner skin of the tube...

denny