Synthetic fibre rope for antenna rigging

Fibre rope has applications in antenna rigging, typically for halyards and tails to support the ends of wire antennas such as dipoles. The use of fibre rope for guying applications has issues due to shrinkage when wet.

Much is made of the ‘best’ fibre rope for these applications, and the almost universal answer is black Dacron (Polyester) in small sizes from 2.5mmm to 6mm diameter. The smaller sizes are usually a braided construction, commonly known as venetian cord. Claims are that the Polyester rope is strong, UV proof and rot proof. Whilst Polyester rope is resistant to mild acids and alkalis, it is damaged by strong alkalis (such as might develop when an alkaline solution dries on the rope).

Another option that is readily available in Australia at lower cost is ‘Silver Rope’, it is a low cost synthetic fibre rope made from UV stabilised Polyethylene. It is manufactured using a special extrusion process which gives the rope superior strength and a distinctive hairy appearance. Silver Rope is strong and versatile, with excellent handling properties due to its surface characteristics. It is ideal for general and industrial applications, particularly in the marine industries where high resistance to abrasion is required.

Silver Rope is white in colour, normal three strand cable laid rope and at the time of writing, costs about A$0.25/m for 6mm rope in 100m lots. It is easy to splice and holds knots well. In my experience, it withstands exposure to sun very well, I have halyards that have been in the weather for over 10 years, and they are still quite flexible and show no signs of mildew, rot, hardening or cracking. Polyethylene ropes (eg Silver Rope) are highly resistant to acids and alkalis, more so than Polyester rope.

Both types have similar strength, the breaking strain of 6mm is about 4kN. Both types of rope are readily sourced through marine suppliers, though Silver Rope tends to be lower in cost.

If you are designing antenna spans, see my article Sufficient sag for wire antenna spans for wind survival.

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