Corrosion protection of antenna connections

Connections between components of an antenna system are prone to corrosion which increases electrical resistance and causes loss if the connections carry RF current.

Corrosion of components in the air takes place mainly due to galvanic corrosion when dissimilar metals are exposed to an electrolytic solution. Although galvanic corrosion is worst for metals that differ greatly in nobility, even apparently similar metals may be different enough in mobility to support a galvanic reaction.

Exclusion of oxygen and water from the interior surfaces of a connection denies the exposure to an electrolyte, and can be an effective preventative measure.

Materials such as petroleum jelly, mineral grease, silicon grease, lanolin have all been used successfully to coat the connection interfaces to exclude oxygen and water. Of these, marine grease is a low cost option that is quite weather resistance, and relatively easy to clean out of the joint when refurbishing. Note that none of these materials are conductors, and the joint still depends on adequate clamping forces between the metal components to ensure reliable metal to metal contact.

Purpose specific conductive pastes are available. They are typically a mineral based grease with finely ground zinc particles in suspension. Some forms use a silicon grease base for applications where mineral grease is incompatible with wire insulation, but they are more expensive.

The zinc particles act to ‘punch through’ the aluminium oxide when the parts are forced together to get initial low contact resistance, and the grease excludes oxygen and water which would sustain galvanic corrosion. Again, the joint depends on adequate clamping force.

Ideally, the connection interfaces should be scratched clean with a stainless steel brush, apply the paste and bolt them together. (A Dremel #530 stainless steel wheel brush is quite handy for getting inside tubes, like HF Yagis, trapped verticals etc.) Stainless steel is recommended because ordinary steel or steel wool, brass, etc embed the connector parts with metal particles that enhance corrosion, and non metallic abrasives like scotch pads, sandpaper, emery etc embed insulating material in the asperities of the joint.

Conductive joint pastes are widely used in the electric transmission and distribution industry, and should be readily available from electrical wholesalers. Marine grease should be available from most marine suppliers.

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