What Recent Resistance Measurements Tell Us About the 20 m Carbon Whip
In short: the derived electrical behaviour indicates a better composite than expected — both mechanically and electrically.
Electrical Model for the 20 m Whip
From the measurements:
- Joint/contact contribution ≈ 8 Ω
- Carbon-path contribution ≈ 15 Ω per meter
Applying this to a 5.12 m whip:
- Carbon contribution ≈ 77 Ω
- Joints + base ≈ 8 Ω
Total DC ≈ 85 Ω end-to-end. But RF behaviour differs:
DC resistance is not RF resistance. Carbon behaves better at HF because current crowds near the base and flows through multiple micro-paths created by the fibre geometry.
Using our validated carbon-resistance mapping, this corresponds to:
- Optimistic: Rcond ≈ 2 Ω
- Realistic: Rcond ≈ 5 Ω
- High-loss: Rcond ≈ 10 Ω
These values align perfectly with known carbon-radiator behaviour on HF.
How Much Power Is Dissipated as Heat?
Pheat = Pin × (Rcond / (Rrad + Rground + Rcond))
with Rrad ≈ 36 Ω and Rground ≈ 5 Ω on 20 m.
| Scenario | 100 W | 500 W | 1500 W |
|---|---|---|---|
| Rcond = 2 Ω | ≈ 4.7 W | ≈ 23 W | ≈ 70 W |
| Rcond = 5 Ω | ≈ 11 W | ≈ 54 W | ≈ 163 W |
| Rcond = 10 Ω | ≈ 20 W | ≈ 98 W | ≈ 294 W |
These watts concentrate in the lower 20–40 cm where RF current peaks and where thermal stress accumulates.
Realistic TX Power Handling
Carbon radiators tolerate: - 10–20 W continuous heat comfortably - Above 50 W continuous, epoxy and joints begin to degrade!
- 100 W carrier
- 100 W digital
- Up to 400 W SSB PEP (≈100 W avg)
- 200–300 W SSB PEP during long overs
- 500 W+ SSB prolonged
- 1.5 kW under any mode
Conclusion: A Balanced View of 20 m Carbon Whips
Our measurements confirm what we has published before: Carbon whips are not miracle antennas — but neither are they the lossy “dummy loads” some believe.- Only ~1–1.5 dB behind stainless on 20 m
- Excellent for HF receive
- Light, stiff, easy to deploy
- Better-than-expected material quality
- Heat concentration near the base limits continuous TX power
- Not suited for high-duty-cycle QRO
- Thermal drift increases above 300–400 W PEP
Bottom line
Mini-FAQ
- Is carbon much less efficient than stainless? — No, typically only 1–1.5 dB on 20 m.
- Is 100 W digital safe? — Yes, heat stays within acceptable limits.
- Why not run 1.5 kW? — The lower segment overheats and degrades rapidly.
- Does loss matter for RX? — Almost not at all; HF noise floor dominates.
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