Carbon-Fibre vs Stainless HF Whips: What the Measurements Show

The source data support a narrow conclusion: two unidentified whips produced similar input impedances in one test installation. They do not support the published efficiency table, a universal carbon-versus-stainless loss figure, a “10 m” capacitor value, identical receive SNR, or a generic power limit. Those require identified samples, calibrated methods and a complete antenna system.

The “10 m” Data Were Taken Outside 10 m

The source compared equal-length samples at 33.6 MHz for carbon and 32.2 MHz for stainless. The amateur 10 m band is 28.0–29.7 MHz, so neither frequency is a 10 m operating point.

The arithmetic in the source for cancelling those two positive reactances was correct at those exact frequencies: about 249 pF for +j19 Ω at 33.6 MHz and 441 pF for +j11.2 Ω at 32.2 MHz. The application was not. A 249 pF series capacitor is not thereby a 10 m match.

An 89 in whip is 2.2606 m long. Its free-space quarter-wave frequency is about 33.15 MHz. By comparison, a free-space quarter wave is 2.68 m at 28.0 MHz and 2.52 m at 29.7 MHz. End effects, diameter, mount and the return system shorten the required physical element, but the correct 10 m reactance must still be measured in the installed system. If it is negative, a series inductor—not a capacitor—is needed; if it is positive, a series capacitor may be appropriate.

The 20 m Arithmetic Is Mostly Sound—with One Bad Phase

The source reported these same-installation values at 14.2 MHz:

The source’s approximately 0.2° reflection phase is inconsistent with its own complex impedances. The recomputed phases above use Γ = (Z − 50)/(Z + 50). The series-inductor values use L = |X|/(2πf). Neither component is necessary merely to protect a 50 Ω transmitter from an SWR near 1.46, but a matching decision should include feedline loss, bandwidth, component loss and the transmitter’s allowed load.

A 201.6 in element is 5.1206 m. Its free-space quarter-wave frequency is 14.64 MHz; an installed resonance in or near 20 m is plausible after end and environmental effects. The source reports SWR below 1.5 from 14.0 to 14.35 MHz, with minima near 14.3 MHz for carbon and 14.1 MHz for stainless. Without the raw calibrated sweeps, that full-band result and its uncertainty cannot be independently checked from the single 14.2 MHz rows.

Input Resistance Is Not Radiation Efficiency

At resonance, the measured input resistance contains several inseparable terms:

A value near 40–46 Ω can be an efficient quarter-wave monopole over a good radial system, or it can contain appreciable conductor, joint and ground loss. SWR and return loss only describe the input match at a reference plane. They do not divide accepted power into radiation and heat. This is why the source’s detailed efficiency percentages—based on assumed conductivity, a nominal 6 mm rod and assumed 2 Ω ground loss—have been removed.

The active IEEE 145-2025 maintains distinct antenna terms for impedance, efficiency, directivity and gain. To compare sub-decibel material losses, use identified samples and a method such as calibrated field-strength or gain comparison in a controlled geometry, a validated loss/efficiency measurement, or a model anchored by measured DC/RF tube and joint resistance. Include an uncertainty budget.

A wide dip can indicate loss—but does not prove it

Added series loss can lower Q and broaden a matched response. Element diameter, taper, joints, the radial system, feedline common-mode current, nearby objects and matching topology can also change bandwidth. Therefore a wider carbon trace is a clue to investigate, not a measurement of loss. Loaded Q also cannot be recovered as simply as 1/fractional bandwidth from an arbitrary 1.5:1 SWR span unless the applicable resonator model and coupling are established.

“Carbon Fibre” Is Not One Electrical Material

A manufacturer datasheet illustrates the scale without defining either tested whip. Toray T700S carbon fibre lists electric resistivity of 1.6 × 10⁻³ Ω·cm, or 1.6 × 10⁻⁵ Ω·m. The Outokumpu Core datasheet lists about 0.73 Ω·mm²/m, or 7.3 × 10⁻⁷ Ω·m, for its 304/304L austenitic stainless grades. On those bulk figures, the carbon fibre’s resistivity is about 22 times higher.

That comparison is illustrative only. A whip is a composite assembly, not an individual filament: fibre orientation, volume fraction, resin, weave or winding, coatings, wall thickness, telescoping overlaps and metal-to-composite terminations determine longitudinal and transverse resistance. The Toray sheet itself reports very different axial and 90° composite strengths, demonstrating why a laminate cannot be treated as isotropic. Directly measure resistance of the complete radiator and every joint instead of assigning a generic conductivity.

Current Product Figures Do Not Match the Old Weight Table

As checked on 29 August 2026, RF.Guru publishes:

The source’s 40–65 g carbon-whip and under-70 g system figures do not describe the current 5.12 m CF5200. They may refer to another, unidentified sample. Likewise, the source does not identify the supposed 5.2–10.35 m stainless sliders, their grade, diameter, wall, minimum overlap, mass or power rating. Do not apply either table to a purchase without the exact model datasheet.

The current CF5200’s 250 W ICAS and 100 W digital/CW limits are vendor claims, not universal carbon limits. The page does not publish an ICAS keying cycle, ambient temperature, thermal endpoint, joint-temperature data, RF resistance or withstand test. Operate within the exact product instructions and derate when contacts, SWR, duty, temperature or ventilation are worse than the rated test conditions.

Power Handling Is Usually a Joint-and-Temperature Problem

Using the reported 20 m resistance terms only as accepted-power examples, 100 W implies about 1.61 A RMS for the carbon sample and 1.54 A RMS for stainless. At 250 W they become about 2.54 A and 2.44 A RMS. A localized 0.10 Ω contact would dissipate about 0.26 W at 1.61 A and 0.65 W at 2.54 A. Several unstable contacts, smaller contact area or greater resistance can concentrate heat and cause a much worse result.

The radiator loss is I²R; the resin and adhesive temperature limits, heat flow, segment overlaps, base adapter and contact pressure decide whether that loss is harmless. The current CF5200 page warns that partial extension can cause binding, damage and RF arcing. Always fully extend and seat the sections as its instructions require, keep joints clean and dry, and stop if the match moves, a joint warms, crackles or discolours.

A capacitor voltage label is not an RF power rating

The source’s recommendation of “at least 100 V RF” for a 10 m series capacitor is incomplete and attached to an out-of-band measurement. A matching capacitor or inductor must be selected for peak voltage, RMS current, ESR/dissipation, dielectric and temperature at the actual frequency and load. C0G/NP0 or mica identifies a dielectric family, not adequate RF current or assembly clearance. A tuner or fixed match also has non-zero loss.

A Slider Changes Length; It Does Not Guarantee a Match

A 34 ft whip is 10.363 m, corresponding to a free-space quarter-wave frequency near 7.23 MHz. Shortening it can place its fundamental near 30, 20, 17, 15, 12 or 10 m. That makes a slider mechanically versatile, but “slide to resonance, no tuner” is conditional on the available adjustment range, minimum segment overlap, mount capacitance and inductance, and the return system.

A quarter-wave monopole over an ideal ground plane is not exactly 50 Ω. Real radial slope, number, length, soil loss and feedline current alter the input resistance and reactance. Resonance means zero input reactance; it does not mean 50 Ω or low system loss. Measure the complete deployment and use matching when the radio, feedline loss or bandwidth requires it.

Adding a top wire to make an inverted-L for 80 or 160 m changes the antenna into a new radiator. Its efficiency depends strongly on total electrical length, vertical height, top-wire route, base loading/match loss and the ground or radial system. A “small L-match” is not guaranteed, and a tuner cannot restore power already lost in a short radiator, coil or ground.

Receive SNR Depends on the Noise Budget

Antenna loss attenuates the wanted signal and external noise together while adding thermal noise; the receiver then adds its own noise. If atmospheric, galactic or local man-made noise remains far above the receiver contribution after antenna loss, a modest efficiency difference may have little effect on SNR. At a quiet site, with a low-gain antenna, narrow bandwidth or a less sensitive receiver, the same loss can matter.

The in-force ITU-R P.372-17 models atmospheric, man-made and galactic noise statistically rather than declaring 1–35 MHz universally noise-dominated. Replace “receive is basically identical” with a measurement: compare calibrated signal and noise power in the same bandwidth, time window and pointing/installation state.

Mechanical Choice Is Product-Specific Too

Carbon composites can provide high axial stiffness at low mass, but impact tolerance, transverse strength, splintering, fatigue and joint life depend on lay-up and construction. Stainless can yield or kink rather than fracture, while thin telescoping sections and contacts can still fatigue, seize or collapse. Neither “strong but brittle” nor “very durable” is a complete rating.

Compare exact products for wind rating, allowed unsupported length, guying, bend radius, overlap, cycle life, temperature, UV/moisture exposure, transport protection, base moment and replacement parts. At carbon-to-metal adapters, maintain designed contact pressure and sealing; contamination or corrosion changes both mechanical integrity and RF resistance.

A Defensible A/B Test

1. Identify both samples. Record manufacturer, model, revision, materials, dimensions, mass, sections, overlap and contacts.
2. Hold geometry constant. Use the same mount, calibrated reference plane, radial field, feedline/choke, height and surroundings; document weather and soil state.
3. Measure more than SWR. Save complex impedance sweeps, calibration method and uncertainty. Measure DC four-wire resistance and, where possible, RF tube and joint resistance.
4. Separate matching. Characterise match loss and component temperature independently at the intended frequency, power, waveform and duty cycle.
5. Test radiated performance. Compare calibrated field strength or gain with enough repeats to resolve the expected difference; do not infer sub-decibel efficiency from an analyzer trace.
6. Run thermal and mechanical checks. Record temperatures at the base and every joint to equilibrium, then inspect contact stability and damage after deployment cycles and wind loading.

Primary Sources Checked

• RF.Guru CF5200 current product page — dimensions, mass, construction and vendor power limits
• RF.Guru CFP2600 current product page — dimensions, mass and assembly instructions
• Toray T700S revision 4.22.2025 — fibre resistivity and directional composite properties
• Outokumpu Core range datasheet — austenitic stainless physical properties
• IEEE 145-2025 — Standard for Definitions of Terms for Antennas
• Recommendation ITU-R P.372-17 — radio-noise sources and system-analysis data
• ICNIRP 2020 — RF exposure guidelines, 100 kHz–300 GHz

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