80m half wave dipole made from galvanised fence wire

Hams being innovative come up with a myriad of cheap alternatives for wire for antennas. One of those alternatives is galvanised steel fence wire.

A small roll of galvanised tie wire can be purchased from Bunnings hardware for about $10 for 95m… so at $0.10/m it looks like an economical solution.

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.

Galvanised round steel conductor – 1.5mm single core

A sample of new unweathered wire was measured to determine the approximate zinc coating depth, it was 15µm. Note that zinc is a sacrificial coating and it will erode through life, so this study is an optimistic one of wire when new.

Above is a plot of the current density distribution in the surface region of the wire. Essentially the current flows in the zinc coating and negligible current flows in the steel core.

At 15µm, the cladding depth is just a quarter of the skin depth (60µm), so we might expect high effective RF resistance, it is not the zinc so much as that it is very thin.

The current distribution allows calculation of the effective RF resistance, it is 805mΩ/m, as against a 1.5mm copper conductor’s 0.106Ω.

Whilst you might anticipate the conductor loss in a 80m half wave dipole made from 1.5mm copper conductor to be around 3% (0.13dB), the galvanised wire above is likely to be more like 20% (1dB).

As mentioned earlier, as the zinc erodes with weathering, resistance goes up. When say half the zinc thickness has eroded, effective RF resistance will roughly double.

It is cheap, little risk of the wire being stolen, but it is low efficiency. As a half wave dipole, it would be more efficient on higher bands where the wire length is shorter.

We can reasonably assume that a multistrand wire that uses strands thinner than this wire will be worse.