lightning protection for large radio dishes
I asked ChatGPT about this and it’s response is reproduced below. However, I recommend reading the following from Bob Williams before reading the ChatGPT response. Bob is a long-time radio ham and disagrees with much of ChatGPT’s response.
CHATGPT SUGGESTED THE FOLLOWING:
Lightning protection for large satellite dishes is critical to prevent damage to both the dish and associated electronics. Here’s a practical and effective approach tailored for large radio astronomy dishes:
1. Grounding System
a. Ground Rods
- Install multiple copper-clad steel ground rods (at least 2.4 m or 8 ft long).
- Place them at least 3–6 m apart around the dish base and bond them together with heavy gauge copper wire (#6 AWG or thicker).
- Use exothermic welding (e.g. Cadweld) or bolted clamps for durable connections.
b. Equipotential Bonding
- Ensure the dish pedestal, mounting structure, motors, and any metal parts are bonded to the ground system using low-impedance paths.
- Use braided grounding straps where possible (better for high-frequency lightning impulses).
2. Lightning Rod / Air Terminal
Install a lightning rod (air terminal) above or on the highest point of the dish structure:
- Mount it centrally on the back frame of the dish or the elevation axle, ensuring it extends 1–2 m above the highest point.
- Connect this rod directly to the ground system with a straight, low-resistance down-conductor (preferably copper or copper-bonded aluminum).
⚠️ Do not rely on the coaxial cable or control wires for grounding. This invites damage.
3. Coax and Cable Entry Protection
a. Coaxial Surge Protection
Install gas discharge tube (GDT) surge arrestors or inline coaxial lightning arrestors (e.g., PolyPhaser or Huber+Suhner) on all RF cables where they enter the building or connect to equipment.
- Ground the arrestor body directly to the grounding system.
b. Ethernet/Data Line Protection
If your dish has motor control, encoders, or cameras:
- Use RJ45 surge protectors on all Ethernet/control lines.
- Use optical isolation where practical (e.g., replace Ethernet with fiber for long runs).
c. Power Line Protection
- Install AC power surge protectors at the breaker panel and at the dish control unit.
- If using 12V or 24V DC systems, install DC line surge arrestors near the dish.
4. Metal Enclosure Shielding
- Enclose sensitive electronics (e.g. LNA, SDR, motor control) in metal boxes or Faraday cages bonded to ground.
- Avoid ground loops — all ground paths should lead to a single ground reference.
5. Optional: Ground Ring
For large installations, consider a ground ring:
- Bury a bare copper wire (at least #2 AWG) in a ring around the dish foundation, bonded to all ground rods and structure points.
Maintenance Tips
- Inspect annually: Look for corrosion, loosened clamps, or rod exposure.
- After any nearby strike, test ground continuity and arrestor function.