Why the EFHW Inverted-L Works Without Radials
Should You Add Radials to an EFHW Inverted-L?
The short answer: usually no—not if you want to keep it behaving like an EFHW. A true EFHW Inverted-L is a high-impedance half-wave radiator matched by a 49–70:1 transformer and does not require a quarter-wave radial system. Adding “real” radials often morphs it into a mismatched Marconi-type vertical, shifting impedance, pattern, and losses.
Why EFHW Inverted-L Works Without Radials
End-fed half-wave systems “close the circuit” via displacement current and a small local reference (e.g., the coax shield, a short counterpoise, or mounting hardware). The feedpoint impedance is typically in the 2–3 kΩ range and is intentionally matched with a 49–70:1 transformer. No extensive radial mat is required.
Practical bonus: less dependency on soil conductivity compared to a quarter-wave vertical that lives and dies by its radials.
What Adding Radials Actually Does
- Lowers feedpoint impedance toward vertical-like values, detuning the 49–70:1 transformer and worsening SWR.
- Raises ground current and soil-loss sensitivity, eroding one of the EFHW-L’s key advantages.
- Alters the pattern and can invite common-mode issues unless you also redesign the choking and match.
• EFHW-L (end-fed dipole): high-Z (~2–3 kΩ) end, match via 49–70:1, minimal ground current by design.
• With long/elevated radials: system trends toward a Marconi vertical; feedpoint Z drops, transformer ratio becomes wrong, losses and SWR rise.
The Smart Stabilizer: Short Counterpoise + Proper Choking
To tame touchy SWR or “RF in the shack” without breaking the EFHW behavior, use:
- Short counterpoise ≈ 0.02–0.05 λ of the lowest band at the transformer ground.
- 1:1 current choke about 0.05–0.1 λ down the coax (add a second choke before shack entry if needed).
This provides a defined local reference while preserving the high-impedance end-feed match.
When Radials Do Make Sense
If your goal is a quarter-wave vertical with strong low-angle DX and known, repeatable efficiency, then embrace it: use elevated radials and match near 50 Ω (often with a different transformer or simple L-network). That’s an excellent antenna—but it’s not an EFHW Inverted-L anymore.
Mini-FAQ
- Do EFHW Inverted-L antennas need radials? — No. They rely on displacement current and a small local reference, not a radial field.
- Will adding radials improve efficiency? — Not for an EFHW-L. It typically detunes the transformer match and increases loss sensitivity.
- What should I add instead of radials? — A short counterpoise (0.02–0.05 λ) and a 1:1 current choke 0.05–0.1 λ down the coax.
Interested in more technical content? Subscribe to our updates for deep-dive RF articles and lab notes.
Questions or experiences to share? Feel free to contact RF.Guru.