For those of us who have found the “Yellow Gold” in the ground at tower bases disappearing: Ron Nott of Nott LTD (the unipole folks) are experimenting with the use of #10 Copperweld for the radial wires of a ground system. They are checking out the potential pitfalls and benefits of installing a copper bonded steel wire instead of installing a wire which people want to steal!
I am looking forward to hearing of the eutectic (metal bonding) and corrosion resistance characteristics of this promising technology. Once the problems of connecting the wire to strap and assuring that the copper cladding stays continuous in the corrosive conditions of soil are understood, we just might be able to find a way to keep the ground system in the ground!
Copperweld wire has low resistance to RF currents because of skin effect. At low frequencies or DC current in a wire flows through the entire conductor. The conductivity of steel is 7 – 13 times higher than copper, so it makes a poor conductor for DC or AC power. At RF steel is even worse, because it is ferromagnetic. A ferromagnetic material increases the skin effect by the permittivity of the steel.
At Medium Wave frequencies the current in a #10 copper wire is squeezed into the outer few thousandths of an inch of the conductor by skin effect, and the amount of current that can be handled by a wire is much less than for DC. Steel wire has much more loss at RF because the skin effect is so much stronger, the conductivity is poorer, and there are other magnetic losses.
The trick with copperweld, is to replace the outside of the steel with copper bonding several thousandths of an inch thick. All the current goes through the thin layer of copper. The heat it causes is on the outside where it can be radiated and carried off by convection or conduction. A copperweld wire is able to handle nearly as much RF current as the same size solid wire, although its rating for DC is not much higher than what it can handle for RF. What is critical is that the copper layer is not damaged by friction during installation, heating during bonding or corrosion, since there is not that much copper. Breaks in the cladding could be disastrous.
Keep your eyes out here for developments.