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2 years ago in Material Science By Meera

For a mast-mounted LPDA covering 100–1000 MHz, how do I choose between aluminum and copper tubing, considering mechanical strength, weight, corrosion, and RF performance?

I'm constructing a large, high-power LPDA for field use. Copper has superior conductivity, but aluminum is lighter and cheaper. At HF/VHF/UHF frequencies, does the skin effect make the bulk conductivity difference negligible if I use tubing of the same outer diameter? Should I be more concerned about galvanic corrosion at joints, the strength-to-weight ratio for a long boom, or the RF loss difference over a decade bandwidth? What are the best practices for joints and connections with each material?

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By Vipin Mittal Answered 1 year ago

For HF/VHF, aluminum is the practical choice for large LPDAs. The RF loss difference is minimal because at 1 GHz, skin depth in Al is about 2.6 μm versus 2.1 μm in Cu—both are far smaller than typical tubing wall thickness (1-2 mm). The current flows entirely on the surface, so equal OD tubes perform nearly identically. Aluminum's superior strength-to-weight ratio is decisive for long booms, reducing load on the mast and rotator. The primary concern is galvanic corrosion. Use stainless steel hardware and apply antioxidant compound (e.g., Noalox) at all joints. For connections, use welded or brazed lugs instead of relying on clamps alone for long-term conductivity. Copper is better for small, permanent soldered arrays, but for a large, field-deployed LPDA, aluminum's weight savings and cost win.
 

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