The Role of a Ground Lug in EFHW Flat-Top, Inverted-L, Vertical Setups

The ground lug on an End-Fed Half-Wave (EFHW) transformer enclosure often sparks confusion among operators. While some regard it as a true RF ground, its actual purpose depends heavily on the antenna's physical deployment and feed configuration. Let’s break down how the ground lug behaves in different EFHW configurations and what best practices ensure clean operation.

1. The Ground Lug: What It Is (and Isn’t)
The lug is typically connected to the cold side of the transformer — that is, the side tied to the coax shield and, indirectly, to station ground via the transceiver. It serves as a reference point for the return currents and offers a location to attach an optional counterpoise. However, it is not a safety ground or a dedicated low-impedance RF ground.

2. Flat-Top and Sloper EFHWs
In a flat-top or sloping configuration, the EFHW is strung horizontally or with minimal vertical rise. These installations lack vertical radiation coupling to the earth, increasing the risk of return and common-mode currents on the coax. Here, the ground lug plays a more active role.

A short counterpoise (2–5 meters) connected to the ground lug can improve current balance and reduce coax radiation due to the skin effect. Additionally, a 1:1 choke placed at approximately 0.05 to 0.1 wavelength down the coax (e.g., 3–7 meters on 40 meters) is highly effective in stopping common-mode currents before they enter the shack.

Without such measures, RF feedback in TX and elevated noise can become noticeable on receive.

3. Inverted-L EFHWs with High-Impedance Stakes
When the EFHW is deployed as an inverted L (e.g., for 80m or 160m operation), the transformer feeds the wire at a 1.5–1.8 meter height, with a vertical rise followed by a horizontal segment. In this case, the vertical section contributes capacitive coupling to earth, and the transformer sees a more vertical current distribution.

For designs using 68:1 or 70:1 impedance ratios, the feedpoint is already at a very high impedance. Attaching the ground lug to an RVS stake or copper rod provides a controlled, high-impedance drain path for static and unbalanced current, without robbing power from the radiator. In such cases, the lug is not there to form a true counterpoise but acts as a safety drain and stabilizing point for the floating cold end.

4. Vertical EFHWs
When the EFHW is mounted as a vertical (e.g., full quarter-wave vertical wire up a tree or pole), the feedpoint is near the ground, and the antenna has strong capacitive coupling to earth via the vertical radiator.

In this configuration, common-mode currents are often less severe due to better vertical symmetry and more natural ground return. Nonetheless, a choke at 0.05 to 0.1 wavelength down the coax remains a good practice. The ground lug may be connected to a short radial or ground rod, but its role is less critical than in flat-top setups.

5. Summary of Best Practices

  • Always use a 1:1 current choke 0.05 to 0.1 wavelength from the transformer, regardless of antenna geometry
  • For flat-top or sloper setups, connect a short wire or counterpoise to the ground lug
  • For inverted Ls, the lug can be tied to an RVS stake as a high-impedance stabilization point
  • For verticals, the ground lug may be optional, but grounding or choking still helps keep RF off the feedline

Understanding the context and current paths around your EFHW is critical. The ground lug is not just a convenience terminal — it's a tool that, when properly used, improves performance, reduces RFI, and keeps your station quiet and safe.

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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.