Why RF.Guru Pushes Dual-Band EFHW for High-Power (3kW-4kW)

At RF.Guru, we prioritize efficiency, reliability, and practical design choices when it comes to high-power End-Fed Half-Wave (EFHW) antennas. Through extensive research and real-world testing, we have concluded that dual-band EFHW designs are the superior choice for high-power applications (3kW-4kW) compared to traditional broadband EFHWs. Here’s why:

1. Better Core Efficiency and Material Optimization

Ferrite cores have frequency-dependent properties, and their efficiency varies across the HF spectrum.

  • Broadband EFHW transformers (160m-10m) require compromise, leading to core losses and heating at high power levels.
  • Dual-band EFHW transformers (e.g., 160m-80m, 80m-40m or 40m-20m) allow optimized core selection, minimizing losses and improving power handling.

By focusing on a narrower frequency range, the core material performs closer to its optimal efficiency, reducing unnecessary heating and saturation risks.

2. Improved Impedance Transformation and Matching

A broadband EFHW (160m-10m) struggles with impedance stability, often requiring complex matching networks and tuners.

  • Dual-band EFHWs ensure the transformer sees a more stable impedance, improving efficiency.
  • Lower SWR across the two target bands reduces tuner losses and RF heating in the feed system.
  • Optimized compensation capacitors can be fine-tuned more effectively for fewer bands, enhancing power transfer.

3. Reduced Core Heating at High Power (3kW-4kW)

In high-power applications, ferrite cores experience significant RF energy absorption, which leads to:

  • Increased core temperature
  • Higher resistive losses
  • Possible saturation and degradation of performance

Since broadband EFHW designs force the core to work across a wider frequency range, power dissipation is less controlled. A dual-band design spreads the RF load more efficiently across the core, reducing excessive heating and allowing the transformer to sustain higher power levels without failure.

4. Better Radiation Effectiveness per Wavelength (λ)

The radiation efficiency of an EFHW antenna is strongest when operating at λ/2 or λ on its resonant bands. A broadband EFHW may work across multiple bands, but as the frequency increases, it becomes 3λ/2, 5λ/2, or more, leading to suboptimal current distribution and inefficient radiation.

  • Dual-band EFHWs keep the radiation pattern predictable, ensuring consistent performance.
  • Broadband EFHWs suffer from unstable takeoff angles and high-angle lobes, leading to wasted radiation on certain bands.
  • For DX or NVIS work, dual-band EFHWs allow better control of the signal propagation.

5. Higher Reliability and Longevity in High-Power Use

For continuous-duty high-power operations (contest stations, digital modes, or AM transmission),

  • Ferrite longevity is critical—excessive heating from broadband operation can degrade ferrite over time.
  • Voltage stress at the feedpoint is reduced in a dual-band EFHW, preventing insulation breakdown.
  • Transformer efficiency is maximized, reducing the risk of SWR drift over time due to core temperature changes.

Final Verdict: Dual-Band EFHW is the Right Choice for High Power

At 3kW-4kW power levels, pushing a broadband EFHW (160m-10m) is not practical due to efficiency losses, core heating, and radiation instability. Instead, dual-band EFHW designs ( 160m-80m, 80m-40m or 40m-20m, etc.) provide the best combination of efficiency, impedance stability, and radiation effectiveness.

Key Takeaways:

  • Better core efficiency: Optimized material choice for the frequency range 
  • Lower heating and losses:Improved core longevity and high-power handling 
  • Stable impedance matching: Reduced SWR and better power transfer 
  • More effective radiation patterns: Consistent takeoff angles for DX and local contacts
  • Reliable long-term operation: Less stress on cores, insulation, and overall system longevity
  • By focusing on dual-band EFHW transformers, RF.Guru ensures that high-power stations achieve maximum efficiency, reliability, and real-world performance without compromise.

Need help selecting the right EFHW transformer for your high-power station? Contact RF.Guru today!

Article written by Joeri Van Dooren, ON6URE – RF engineer, antenna designer, and founder of RF.Guru. With extensive experience in active and passive antenna systems, high-power RF transformers, and custom RF solutions, Joeri shares insights into cutting-edge radio communication technologies.