VDA 30m

I was interested to build a 30m VDA after I had read about the good result such an antenna provides. After I saw an article from Remco 7QNL (PA3FYM) in de magazine of DKARS, it was trigger to start experimenting and building a 30m VDA.
The main ingredients are a 18m Spiderbeam pole and a 4m boom. For the latter I ordered 4 pieces of 35mm 1.15m tubes from Spiderbeam. I first worked on the cross section clamps and constructed something with PE plate materials and drain pipe clamps, as it is easy to purchase from the DIY shop. On the top of the mast I constructed a small aluminum tube with plastic spreader for attaching the wires. At the base of the mast I also made a clamp where I could also attach the wires. Further two guy rings were made with the corresponding guy sets.
The instructions were to run the coax horizontal (along the boom) and gradually sloping down to avoid having the coax detuning and effecting the antenna. Therefor I made a feed point that fitted nicely in/on the end of the boom and let the coax run through the boom. I slided ferrite beats on the coax and remained inside the boom, in such a way that the weight of the beats was divided over each section of the boom.

Once all piece were put together and the wires of the driven element and reflector were strung between the top, boom and bottom of the mast, we could erect the antenna. With a 18m fiber pole, you need two sets of guying wires.
First I have used the theoretical dimension for the wires since they will be too long but it is easier to cut off pieces than to extend the wires by soldering in the field. Based on SWR measurements the wires were adjusted in order to get the antenna resonant on the desired low CW part.
The 30m VDA we used successfully on our C81G DXpedition. PA4WM has also build a 30m VDA based on the same dimension which worked out well. Obviously, performance and wire dimensions will vary, depending on soil conditions and VDA are most famous on beach locations.


Based on the experience of setting up and using the antenna during our C8X/C81G Dxpedition in February 2018, I wanted to make some improvements. The first thing was to have a better boom/mast cross section and a lighter boom. For the boom I selected two fishing rods, Lakeside-1 Travel 400cm from which I removed the top elements.

For the cross section I developed a new method and used a U-shape aluminum profile and put plastic u-shaped plastic on the rim in order to avoid slipping on the mast. The U-shape profile was tied with two tiewraps onto the mast. To attach the two boom sections, I use a piece of wooden stick available from any DIY shop. I drilled a hole in the aluminum profile so the stick fitted well. The diameter was a little bit too small for the boom sections and therefor placed heat shrink tubes over the stick and that provided exactly the needed diameter.
In the meantime I have seen many examples where the coax was running along the boom and at the mast, running down. This was easier and mechanically better, so I made a new spreader for the driven element to attach the coax via cable lugs to the spreader.
At the bottom I also made a small U-shape aluminum bracket where the wires could be terminated.
This modified version of the VDA30 is now part of the Swains2020 DXpedition setup.