Carbon-Fiber Antenna Elements (not masts) vs Stainless Steel

17 ft (5.18 m) telescoping radiator — modeling, assumptions, and QRO heating behavior

Scope & stance: We’re talking about a carbon-fiber element used as the radiator itself, not a CF mast that just supports a wire. Vendor claims are treated as marketing until verified. Below are our working assumptions—a realistic engineering baseline for lab validation.

What the manufacturer says vs what we assume

• Claim: “True woven carbon fabric in a mesh structure maintains continuous conductivity.” Reality: Woven plies help, but continuity depends on joint metallurgy and surface treatment. We assume plated or metallic collars at the overlaps, not raw carbon-on-carbon.
• Claim: “Conductive coating or fiber surface treatment.” Reality: If it’s true metal plating ≥ several skin depths thick, it behaves metal-like. If it’s graphite or conductive paint, resistivity can be 100× higher. We’ll test sheet resistance (Ω/□) to confirm.
• Claim: “Smooth conductivity across segments.” Reality: We assume ~0.2 Ω total contact resistance for the entire whip—reasonable for plated overlaps. If joints are bare carbon, expect higher loss and instability with use.
• Claim: “±0.4 mm manufacturing tolerance.” Reality: Fine mechanically, but we care about electrical details: plating type, wall thickness (vs skin depth), and surface resistance.

Our locked assumptions for modeling & testing

• Length = 17 ft (5.18 m); OD = 20 mm (0.79 in).
• Ground/counterpoise loss fixed at 5 Ω.
• Stainless: σ ≈ 1.4 × 10⁶ S/m; joints = 0.05 Ω total.
• Carbon-fiber “moderate”: σ ≈ 2 × 10⁴ S/m; joints = 0.20 Ω total.
• R_rad (monopole over ground): 40 m ≈ 7 Ω · 30 m ≈ 12 Ω · 20 m ≈ 36 Ω · 17 m ≈ 60 Ω · 15 m ≈ 75 Ω · 12 m ≈ 90 Ω · 10 m ≈ 1.5 kΩ.

Resonance: If both radiators share geometry, they’ll resonate the same. That confirms continuity, not necessarily low resistance or plating quality.

Power handling & QRO heating

The radiator’s heat dissipation follows I²R, but equivalently at resonance:

P_heat = P_in × R_cond / (R_rad + R_ground + R_cond)

That fraction is constant; heating scales linearly with applied power.

Estimated radiator heating (watts)

(Radiator only — not including ground or match losses. SSB ≈ 25 % duty; FT8/RTTY ≈ 100 %.)

Takeaways from these assumptions

• QRP–100 W: CF performs well 20–10 m; 30–40 m workable but warmer.
• QRO (1 kW continuous): CF marginal 30–40 m (tens–90 W in element base/joints). 20–10 m feasible if plating and joints stay ≤ 0.2 Ω.
• 10 m: Radiator heating tiny; watch voltage stress, not current heating.
• These are radiator-only watts; coils/matches can add more localized heat.

EZNEC / NEC modeling notes

• NEC’s “Wire Loss” assumes a uniform round metal conductor several skin depths thick — not accurate for CF laminates (often only 1–2 skin depths at HF).
• Use LD5 per-element conductivity (e.g., σ = 1×10⁴–5×10⁴ S/m) for the radiator, while keeping radials as copper/aluminum.
• Add small series-R loads (20–100 mΩ per joint) for contact resistance.
• Run Average Gain (loss-off) to confirm segmentation before trusting sub-dB differences.
• Bottom line: “Wire Loss only” gives an optimistic, lower-bound loss figure for CF.

“Is it QRO-capable?” — realistic verdict

• 20–10 m: Yes — plausibly QRO-capable with metal-plated joints and metal-like surface conductivity.
• 30–40 m: Borderline at 1 kW 100 % duty (FT8/RTTY). SSB/CW duty is fine; monitor base/joint temperature.
• Paint-like coatings: Expect higher resistance, more heat, and reduced headroom.

Why CF can still be viable at HF

• Across 40–10 m, CF averages only ~0.1–0.3 dB behind stainless; biggest hit on 40 m, negligible by 10 m.
• Stainless: tunable length, peak efficiency. CF: lighter, stiffer, fixed length (needs matching network).
• Bottom line: If low-R joints and metalized surfaces hold up, CF is excellent 20–10 m, acceptable 30–40 m. Stainless still dominates for maximum QRO safety margin.

Ω per square (Ω/□) — why we measure it

Sheet resistance (Ω/□) quantifies surface conductivity independent of size. Picture the coating as tiled into squares: three squares in series give 3 × (Ω/□) total R. Low Ω/□ (≤ 0.05) = true metal plating; high (≥ 0.5–5) = conductive paint. At RF, low Ω/□ plus thickness ≥ several skin depths behaves like real metal.

Our lab validation plan

• VNA A/B test: Same ground field, same OD elements (SS vs CF). Measure R at resonance and 2:1 SWR bandwidth on 40–10 m. Wider bandwidth ⇒ higher loss.
• Sheet-resistance check: Measure Ω/□ on outer surface or coupon to confirm metal plating vs paint.
• QRO stress test: Run 500–1000 W key-down 5–10 min on 40–20 m; monitor element and match temperatures and voltages.

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