Nextgen Non-Resonant Traps: Engineering with Frequency Means
Last updated: August 22, 2025.
Non-resonant traps are changing multiband antenna design. Unlike LC resonant traps that block current, these elements shift current distribution to achieve broadband, efficient operation across multiple HF bands. The key is how you choose the mean frequency and place the trap.
The Secret Lies in the Mean Frequency
When covering two bands (80/40 m, 40/20 m), trap behavior is optimized by choosing the right mean frequency between them. Each mean has its niche:
| Mean Type | Formula | Best Use |
|---|---|---|
| Arithmetic | (f1+f2)/2 | Physical symmetry, e.g. two equal poles |
| Geometric | √(f1·f2) | Octave-spaced bands (80/40, 40/20) |
| Harmonic | 2/(1/f1+1/f2) | Impedance-sensitive, less common |
| Log midpoint | exp[(ln(f1)+ln(f2))/2] | Similar to geometric, for log spacing |
Octaves vs. Physical Symmetry
Most amateur pairs are near octaves: 160/80, 80/40, 40/20, 20/10. Here, the geometric mean centers current evenly. But if you want physical equality—like two equal 4.5 m poles in a vertical—the arithmetic mean maintains both electrical and mechanical balance.
Example: a non-resonant trap placed at 16.05 MHz (arithmetic mean of 3.6 and 28.5 MHz) splits a vertical symmetrically, optimizing performance from 80–10 m.
Why It Matters
- Controls current shift between bands
- Maintains symmetry in dipoles, loops, or verticals
- Keeps feedpoint impedance predictable
- Improves mechanical balance and durability
Applications That Benefit Most
- Dual/tri-band verticals with symmetrical sections
- Multiband delta loops or dipoles with shared elements
- Hybrid antennas (vertical + capacity hat + trap)
- Phased RX arrays using “soft load” traps
Conclusion
Nextgen non-resonant traps bring elegance and scalability to HF multiband design. The trick is choosing the right frequency mean for your symmetry goals. Do that, and your traps will “thank you” with cleaner patterns, wider bandwidth, and lower losses.
Mini-FAQ
- Do non-resonant traps block current? — No. They redirect current smoothly instead of isolating band segments.
- Which mean works for 40/20 m dipoles? — Geometric mean ensures symmetry across octave spacing.
- Which mean works for verticals? — Arithmetic mean when using equal physical sections.
- Why use non-resonant traps? — They yield symmetry, broadband performance, and avoid narrow Q losses of resonant traps.
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