Setting Up a Safe Station: Grounding and Lightning Protection

Earthing is the least exciting part of amateur radio and the one that most often gets skipped. It is also the part that decides whether your station is quiet, whether your equipment survives a nearby strike, and whether you are safe while operating.

There are three separate things that get called "ground" in a station, and confusing them is the source of most of the trouble. They are electrical safety earth, RF earth, and lightning earth. A proper installation bonds all three to a single reference, but they do different jobs.

The three earths

• Electrical safety earth carries fault current away from the chassis of mains equipment so a fault trips the breaker rather than energising the case.
• RF earth provides a low-impedance return for radio-frequency current, which stops the shield of your coax acting as an unintended antenna.
• Lightning earth gives surge current somewhere to go other than through your equipment, and it is the one that must handle the largest currents.

The critical rule is that these must be bonded together at a single point. Separate earths at different potentials are worse than no earth at all, because a potential difference between them will drive current through your equipment along whatever path happens to be available — usually the shield of a signal cable.

Building the earth system

A single rod is rarely enough. Soil resistance is high, and a 2.4 metre rod may measure 25 to 100 ohms. Multiple rods spaced at least their own length apart, bonded together with wide conductors, reduce the total resistance substantially — three well-spaced rods can achieve a third of the resistance of one.

Lightning protection

No amateur installation can survive a direct strike, and equipment sold as lightning protection does not change that. What protection can do is reduce the damage from a nearby strike or from static build-up, and that is worth having.

The approach is to intercept surge energy at the building entry, before it reaches the equipment. A coax arrestor mounted where the feedline enters, bonded to the station earth with the shortest possible conductor, diverts most of the surge. Mains protection at the distribution board does the same job for the power supply.

The checklist

• All equipment chassis bonded to a common earth bus with short, wide conductors.
• Coax arrestor at the building entry, not at the radio.
• Every rod bonded to the same system, never left separate.
• Antenna disconnected when a storm is forecast, not when it arrives.
• Mains protection fitted at the distribution board.
• Earth connections inspected annually and after any nearby strike.