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 (End-Fed Half-Wave) antenna manufacturers incorporate loading coils to electrically lengthen the antenna, RF.Guru has consciously chosen not to do so. Here’s why:

1. Efficiency Considerations

Loading coils introduce additional losses into the antenna system. Every coil acts as a resistive element due to the finite conductivity of the wire and the core material (if used). These losses can significantly reduce the radiation efficiency, making the antenna less effective in radiating RF energy.

2. Compromised Bandwidth

Antenna designs incorporating loading coils typically suffer from narrower bandwidths. This is especially problematic for EFHW antennas, which are often used for multi-band operation. By avoiding loading coils, RF.Guru antennas maintain broader bandwidths, allowing for more flexible tuning and operation across multiple bands.

3. Unwanted Reactance and Matching Issues

The introduction of a loading coil can create complex reactances that require additional tuning or matching elements. This can complicate installation and reduce the ability of the antenna to perform well across its intended frequency range. RF.Guru prioritizes designs that offer simple and effective impedance matching without unnecessary complications.

4. Physical Durability and Reliability

Coils, particularly those exposed to outdoor conditions, are susceptible to degradation over time. Corrosion, water ingress, and mechanical stress can alter the inductance value, causing unpredictable changes in performance. By eliminating coils from our EFHW designs, RF.Guru ensures long-term durability and reliability in real-world environments.

5. True Half-Wave Performance

An EFHW antenna derives its efficiency and radiation pattern from its full half-wave length. By artificially shortening it with a coil, the antenna no longer behaves as a true half-wave antenna, impacting the expected radiation pattern and overall performance. RF.Guru believes in maintaining the integrity of the EFHW concept by using full-length radiators.

6. Simplified Construction and Deployment

By keeping EFHW antennas free of loading coils, we ensure that our designs are straightforward to deploy and use. Operators benefit from a hassle-free setup process without needing to account for additional inductive components that could affect tuning and placement.

7. Alternative Solutions for Space Constraints

For operators with space limitations, RF.Guru offers alternative solutions such as Skywave and Delta loop antennas. Additionally, we provide short ground-mounted multiband verticals and resonant multi-element verticals, including quarter-wave and half-wave designs. Our EFOC29 design (80-10M, easy tunable) can also operate on 160M by adding a 40M counterpoise wire.

8. Impact of Coils on Dual-Band 160/80M and 80/40M Antennas

As an example, consider an EFHW antenna designed for dual-band operation on 160m and 80m. If a loading coil is used to electrically shorten the 160m portion, it significantly alters the radiation pattern of the antenna on 80m. Instead of maintaining a desirable broadside radiation pattern with effective low-angle takeoff, the introduction of the coil forces the current distribution to shift, leading to:

  • Increased Vertical Radiation: This change results in a higher takeoff angle on 80m, making the antenna less effective for long-distance (DX) communication and more suited for NVIS (Near-Vertical Incidence Skywave) operation.
  • Pattern Distortion: Instead of the expected symmetrical radiation pattern, the shortened antenna may develop unpredictable lobes and nulls, degrading performance.
  • Reduced Efficiency: The coil introduces losses, further reducing effective radiated power on 80m.

A similar issue arises with 80/40M dual-band antennas. When a loading coil is used to shorten the 80m portion, the 40m radiation pattern is also affected. Instead of achieving the expected broadside radiation with lower takeoff angles, the shorter electrical length distorts the pattern, creating higher angle lobes and reducing DX performance. Additionally, efficiency losses in the coil further reduce the antenna’s effective performance on 40m.

By avoiding such compromises, RF.Guru ensures that our antennas provide optimal performance on all intended bands without sacrificing efficiency or radiation characteristics.

Conclusion

RF.Guru’s decision to exclude loading coils in our EFHW designs is based on a commitment to efficiency, durability, and real-world performance. We prioritize delivering antennas that offer reliable and consistent results without introducing unnecessary compromises. For operators seeking a high-performance EFHW antenna, our full-length designs ensure optimal efficiency and ease of use across multiple bands.

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.