Hams being innovative come up with a myriad of cheap alternatives for wire for antennas. One of those alternatives is common 0.91mm steel MIG wire.
Steel MIG wire is often coated with copper and is claimed by some online experts to “work real good”, particularly as a stealth antenna.
But is it the makings of a reasonably efficient antenna?
This article applies the model developed at A model of current distribution in copper clad steel conductors at RF to estimate the effective RF resistance of the wire at 3.5MHz.
Copper coated round steel conductor (MIG wire) – 0.91mm single core
In fact copper is an undesirable and restricted contaminant of steel welding wire, high grade MIG wire is not copper coated.
Copper content is held to less than 0.05% in the core, and less than 0.05% in the coating… which on my calcs says the coating of common 0.91mm MIG wire is less than 0.125µm…. basically it is a small diameter wire with low conductivity and high permeability.
The permeability contributes to higher inductance per metre of wire, and very small skin depth which contributes to higher resistance per metre of wire.
Analysis of the current distribution in the wire shows that almost all the current flows in the core, and that the RF resistance with and without the coating is almost the same. The copper plating can be ignored as significant, in fact the copper plating will usually fall off with a few weeks of exposure to weather as rust develops under the copper.
Lets model a 40m long centre fed dipole in free space, this would be a half wave dipole on 80m if using a copper conductor but we will use the MIG wire equivalent, a steel wire (σ=2.1e6, µ=800). We will use NEC-4.2 (NEC2 cannot natively model ferromagnetic wires.)
The current distribution is nothing like a half wave dipole, it is more like a three half waves dipole due to the magnetic effect of the wire.
Conductor loss is a staggering 91% whereas you might expect more like 3% for a copper dipole.
Ferromagnetic wire changes the tuning of the antenna, radically.
If the objective is a stealth antenna, this is doubly stealthy, not only can no one see it, no one can hear it!