14 August 2015

Insulated element support for ultralight VHF/UHF Yagi-Uda beams

Once upon a time, 10 years ago, I used to build VHF beams for high mountain contesting that could be carried in the backpack. My best result was a 5 element Yagi of DK7ZB design whose boom was a telescopic fiberglass fishing pole, elements attached with clothes pegs.

The system could not grow, though: longer poles have larger diameter, while there are no large clothes pegs.

I had built a 4 metre long aluminium square boom cut in two sections, that is OK for backpack transportation where there is no vegetation around. I broke it before the first contest.

Fast forward 6-7 years and I still haven't found a solution to the larger clothes pegs. But while hanging around "special offers" from Chinese online retailers I came across this product: Adhesive cable ties in packs of 6. I couldn't pass on them at the incredible price of 0.8€/pack, including shipping. Their original purpose is to keep cables (like USB) from falling off (behind) furniture.

But their base size matches my aluminium boom (6 or 8 mm per side) and the cable hole is perpendicular to the longest side: do you see a better, lightweight and cheap alternative to large clothes pegs?

The clip sitting on my old boom.

8 mm element into the clip.
The hole diameter is about 7.5 mm. An 8 mm dia. element fits perfectly with the right friction. A 6 mm dia. element needs to be embossed at the junction point with some rubber pipe.

While I could stick them to the fishing rod once fully extended, I will rebuild the Yagi beam with a square boom and element supports already in place.

Side view of the element inserted into the support.
Too bad I got only one color!