Coiled Into Compromise: The Truth About Shortened End-Fed Antennas

Shortened end-fed antennas with loading coils are everywhere—especially in portable setups and small garden installations. You'll see compact wire antennas, sometimes only 16 to 23 meters long, with one or two loading coils placed somewhere along the wire. The promise? Multiband operation (80–10m) in a tiny footprint, and “full-sized performance” from a half-sized wire.

But as with many things in antenna design, there’s no free lunch. So the question is: How far can you go with loading coils before efficiency collapses? Are these electrically-lengthened wires a smart compromise—or are we just coiling ourselves into disappointment?

Electrically Long, Physically Short: The Core Idea

A full-sized half-wave on 40 meters is roughly 20 meters long. If you only have room for 16 to 23 meters of wire, you’re sitting well below a full quarter-wave for the lower bands—far from ideal. Enter the loading coil: it adds inductance to make the antenna electrically resonant at the desired frequency, even though the physical length remains much shorter.

So far, so good. But there’s a catch: resonance does not mean efficiency. (read more)

The Compromise Behind the Coil

When you insert a loading coil, you’re shifting the current distribution. In a full-length antenna, most of the current is centered, tapering off toward the ends. That center current is where most of the radiation comes from. But when you coil up the midsection—especially in antennas significantly shorter than 1/4 wavelength—the current has nowhere to go. You end up with low current at the coil and even lower current beyond it, reducing radiated power drastically.

And it gets worse: coils aren’t lossless. Any resistance—be it from wire thickness, poor Q-factor, or even heating—translates into power dissipation instead of radiation

The “One Coil Wonder” Myth

Many commercial and DIY antennas rely on a single loading coil placed somewhere around the 60–70% point on the wire. While this can “force” a match at the feedpoint (often using a 49:1 or 64:1 transformer), the reality is:

  • Efficiency drops steeply below about 0.15λ mechanical length.
  • A single coil creates a sharp impedance transition and standing wave on the wire.
  • Only a small part of the wire is actually contributing to radiation.

These antennas may appear to perform “okay” thanks to modern tuners and sensitive receivers—but they’re more noise collectors than signal throwers.

Why RF.Guru Does Not Use Coils to Electrically Lengthen EFHW Antennas

At RF.Guru, we take a meticulous approach to antenna design, ensuring that our products offer the best performance, efficiency, and reliability for amateur radio operators. While some EFHW antenna manufacturers incorporate loading coils to electrically lengthen the antenna, RF.Guru has consciously chosen not to do so.

Here’s why:

1. Efficiency First

Loading coils introduce resistive losses. Whether from the wire itself, dielectric losses in cores, or heating under high power, each coil becomes a small heater instead of a radiator. Our full-length EFHW designs avoid these compromises, ensuring more of your power makes it to the airwaves.

2. Wider Bandwidth, Fewer Hassles

Coil-loaded antennas often exhibit narrower usable bandwidths, particularly on lower bands. That’s a big drawback for multiband use. RF.Guru antennas retain broader bandwidths across all supported bands, reducing the need for constant re-tuning or matching tweaks.

3. No Reactance Games

Loading coils can introduce unexpected reactance and impedance bumps. These can complicate matching, reduce efficiency, and increase tuner dependency. Our designs maintain clean, predictable impedance profiles without relying on risky mid-wire inductance.

4. Reliable in All Weather

Outdoor coils are vulnerable—especially to moisture, UV degradation, corrosion, and mechanical stress. A failed coil means a failed antenna. By eliminating them, we increase durability, reduce failure points, and improve longevity.

5. True EFHW Behavior

An EFHW antenna derives its efficiency and signature radiation pattern from being a true half-wave. When you artificially shorten it with a coil, it no longer behaves like a half-wave antenna. Current distribution changes, lobes distort, and efficiency plummets. At RF.Guru, we preserve the integrity of the EFHW concept.

6. Simplified Construction and Deployment

No coils means no guesswork. Our antennas are easy to install, tune, and trust. Whether you’re at home or portable, you get a predictable result—without mid-wire inductors that need careful positioning or extra tuning.

7. Better Alternatives for Space-Constrained Ops

When space is tight, we offer better solutions than compromised coils:

  • Skywave and Delta loop antennas
  • Short ground-mounted multiband verticals
  • Resonant multi-element verticals
  • Our EFOC29 (80–10m) easily tunes 160m with a simple 40m counterpoise wire.

All these options outperform shortened coil-loaded EFHWs—while staying compact and easy to deploy.

8. Case Study: Dual-Band 160/80m and 80/40m EFHWs

Consider an EFHW antenna intended for dual-band 160m and 80m operation. Adding a loading coil to "trick" the antenna into resonance on 160m significantly distorts the current distribution and radiation pattern on 80m:

  • Vertical Radiation Increase: High-angle takeoff on 80m limits DX potential.
  • Pattern Distortion: Expect unpredictable lobes and nulls instead of a clean broadside pattern.
  • Efficiency Drop: Power lost in the coil rather than radiated.

The same effect shows up in 80/40m dual-band designs. The 40m pattern degrades into high-angle lobes—great for NVIS, terrible for DX. RF.Guru avoids these problems entirely by not introducing coils in the first place.

Conclusion

Loading coils can force resonance, but they can’t cheat the laws of physics. Efficiency, pattern integrity, bandwidth, and durability all suffer when a coil is added to a too-short antenna.

That’s why RF.Guru doesn’t do it.

We design antennas with full-length radiators, clean impedance characteristics, and no shortcuts—offering performance you can trust, whether you’re calling CQ from your backyard or chasing DX from a hilltop. No coils. No compromises.

Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.