Forget Trapped Radials

— Why Two Tuned Ones per Band Beat Every “Multi-Band Hack”

Traps in elevated radials aren’t crazy—they’re just an overcomplication of something simple. A radial is a tuned return path, and when you add L/C traps in series, you’re trying to fake multiple resonant lengths on one wire. That can work… but two plain quarter-wave radials per band will almost always outperform any trapped system in efficiency, bandwidth, and power handling.

Why Elevated Radials Are “Tuned”

An elevated radial behaves like an open-ended transmission line stub. Open stubs are low impedance at odd multiples of ¼-λ (¼, ¾, 5/4, …) and high impedance at even multiples. That’s why a ¼-wave radial works—it presents a low-Z path for return current—and why a ¾-wave wire can also “work” on a harmonic. That’s the same reason a 40 m dipole often resonates again on 15 m.

Example: a 40 m ¼-wave radial (~10.5 m) is nearly ¾-λ at 15 m (~3 × 3.5 m = 10.5 m). So yes—your 40 m radials can conduct on 15 m even without traps. (As N6LF modeled, elevated radials behave as open stubs with harmonic current peaks.)

What Traps Actually Do

A parallel-resonant trap in series with a radial behaves like this:

• At its resonant frequency, it looks like a high impedance and blocks current—so only the inner section radiates or returns current.
• Below resonance, it looks inductive; above resonance, it looks capacitive.

That means your 20 m trap blocks 14 MHz current, but on 15 m (21 MHz) it passes some current as a capacitive link. Depending on trap Q and position, your outer “40 m” section may still carry current on higher bands—or not at all. (W8JI’s measurements show that trap losses peak right at resonance.)

Why Two Tuned Radials per Band Are Better

• Less loss. Traps add resistive loss, especially near resonance. You’re inserting lossy hardware into your return path—never ideal at QRO.
• Higher power margin. Commercial trap-radial verticals (e.g., Diamond CP-5HS) are only rated a few hundred watts. The radiator isn’t the limit—the traps are.
• Predictable pattern. Elevated systems with few radials are very sensitive to imbalance. N6LF found 10–12 radials per band give stable current distribution—but that’s unmanageable if each has traps.
• Simple is smart. Two quarter-wave radials per band—ideally opposite each other—deliver excellent results. Harmonic sharing (e.g., 40 m radials doubling as 15 m) is free gain, no traps required.

Common Misconceptions

• “The power divides across all radials.” Not true. Current divides according to impedance; traps change that division unpredictably. You can end up with hot traps and cold wires.
• “Traps handle as much power as the antenna.” No. The highest voltage stress often appears at radial ends or trap junctions. Use high-Q components and proper spacing if you must use them.
• “More traps = more bands.” Technically yes, but practically no—the losses add up, and tuning interactions multiply.

Measurements Tell the Truth

Clamp-on RF ammeters or small current transformers near the feedpoint show which radials actually carry current per band. Sweep the feedpoint with a VNA, disconnect one branch at a time, and watch the resonance shift. That’s the only way to confirm whether a trapped radial “helps” or just looks busy.

Bottom Line

• Elevated radials are resonant stubs—odd harmonics already give you multi-band benefit without traps.
• Traps add loss, power limits, and unpredictability.
• Two simple tuned radials per band (with harmonic sharing) outperform any trap network in both efficiency and reliability.
• Add a common-mode choke at the feedpoint so your coax doesn’t become the “best radial.”

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