Thick Tubing vs Wire in Verticals: Why Conductor Size Matters

When designing vertical antennas, the choice of conductor material and diameter directly impacts how efficiently your antenna radiates. A common trade-off exists between lightweight, flexible wire (like 1.5mm² copper or steel wire) and robust aluminum tubing (such as 35mm diameter). But beyond mechanical considerations, there's a critical electrical factor at play: radiation resistance and conductor loss.

Why Radiation Resistance Matters

Radiation resistance (Rr) represents the portion of an antenna's feedpoint resistance that actually contributes to radiating electromagnetic energy. The higher the Rr relative to loss resistance (Rl), the better your power is being used for radiation rather than being dissipated as heat.

In short: Efficiency ≈ Rr / (Rr + Rl)

Antenna conductors also have a loss resistance (due to skin effect and ohmic resistance), and thin wires inherently suffer higher loss per unit length due to their small surface area.

Aluminum Tubing = Lower Loss, Higher Efficiency

Using 35mm aluminum tubing improves the effective radiating surface dramatically. At HF frequencies, current flows mostly in the outer layer of the conductor (skin effect). A large diameter tube has far more surface area than a 1.5mm² wire, greatly reducing ohmic losses:

  • A 35mm aluminum tube has much lower Rl due to increased surface area
  • The effective Rr stays the same (geometry dependent), but overall efficiency increases
  • Tubing reduces the current taper effect due to lower RF resistance, allowing more current to flow in the upper portions of the antenna
  • On resonant verticals (like a 1/4-wave), tubing still reduces losses and increases bandwidth, but the gain is more modest compared to short verticals

Where It Makes the Biggest Difference

The improvement in radiating efficiency is most significant on lower HF bands, such as:

  • 160 meters: For a short vertical, Rr might be as low as 2 Ω. Loss resistance dominates unless large conductors are used
  • 80 meters: A 10m vertical has ~10 Ω Rr. Replacing wire with tubing can easily double the efficiency
  • 40 meters and above: The efficiency gap between tubing and wire narrows as verticals approach resonance and Rr increases

On resonant verticals (like a 10m tall 1/4-wave on 40m), the radiation resistance is already ~25–35 Ω. Here, tubing still improves performance (e.g. reducing Rl from ~2.5 Ω to <0.3 Ω), but efficiency goes from ~91% to ~98% — a worthwhile improvement, but not as dramatic.

What About Horizontal Antennas?

Horizontal antennas like dipoles or inverted-Vs are often near resonance and have radiation resistances in the 60–75 Ω range. In these cases, conductor loss is a much smaller fraction of the total resistance. Replacing a thin wire with a thick tube makes only a minor difference in efficiency — unless you’re working with very low bands (160m) or extremely long spans.

And Inverted-L Antennas?

Inverted-Ls are part vertical, part horizontal. Because the current is highest in the vertical section and drops rapidly in the horizontal, the losses mostly occur in the vertical part. Since the wire length is longer and the top section adds capacitive loading, the radiation resistance is higher than a purely vertical radiator of the same height. This reduces sensitivity to conductor loss somewhat — but the vertical part still benefits from using thicker conductors.

Mechanical Stability is a Bonus

Besides electrical performance, tubing structures are more rigid, wind-resistant, and easier to elevate without sag. They're ideal for permanent verticals, phased arrays, and DX-peditions where efficiency matters.

35mm aluminum tubing greatly improves efficiency in vertical antennas by reducing loss resistance—especially critical for 160m and 80m, with diminishing returns on resonant and horizontal systems.