Cobwebb antenna

I just put a cobweb antenna in my attic.

The Cobwebb is an antenna that has gained in popularity in recent years. The horizontally polarized omnidirectional antenna is suitable for the 10m, 12m, 15m, 17m and 20m band. All elements are fed through one single feed line. At only half wave length above the ground, it will outperform any vertical antenna. Measuring only 2. The elements are folded dipoles with open ends, usually made from figure 8 speaker wire.

Cobwebb antenna

Watts up? November EME listing 22 March. Yagis and SWR Jan The CobWebb is a five band 14 to 28MHz compact array of dipoles, bent into a square, almost omni-directional and with unity gain. There are also a number of copies available; some of them look rather cheap and cheerful. This is the route which I took. There are two versions of the Cobwebb and I chose to make the one which uses single wires for each band, with a current balun transforming the low loop impedance back to 50 ohms. I have supplied friends with a hardware kit which has formed the basis of their homebrew CobWebb antenna. The hardware kit comprised two aluminium plates, V bolts for mounting on a pole, Stauff clamps to hold the aluminium tube, three lengths of aluminium tube and all the necessary nuts and bolts. The builder will need to add either plastic or fibreglass tubes, wire for the dipoles, and the connection box and balun. If you are interested, please contact me via email. By the way, fibreglass can be used throughout if you prefer, without aluminium. The Stauff clamps are great for this because they have a large surface area for clamping — much better than U bolts which can crush the tube. With a bit of spare time early in I decided it was time to put one together myself.

Apart from this the antennas are the same, cobwebb antenna. I've designed and made adjustable gizmos that employ small hose clamps that can be loosened and moved along the length of the spreader.

JavaScript seems to be disabled in your browser. For the best experience on our site, be sure to turn on Javascript in your browser. In stock, shipped in 1 to 2 days. The Cobweb antenna operates on the five upper shortwave bands 20, 17, 15, 12 and 10m. The five folded dipoles are fed via a common balun, only one feed line is required.

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Cobwebb antenna

Without question, the most difficult part of building the cobwebb antenna is the metalwork, and if like me, your engineering skills could be better then a full kit of pre-drilled parts is available from Aerial Parts in Colchester for a reasonable price, this project was built using this very kit. Various articles with slightly differing designs can be found in plentiful supply online, the G3TXQ version of the cobwebb is the one my friend and I chose to construct — download the instructions. Some designs of the antenna require the use of twin core insulated wire for the elements, and when using this method, at a given length, the insulation has to be stripped and the cores shorted together to allow matching. Construction is fairly straightforward if following the instructions. The most complicated part of construction is the current balun, but is fully explained in the downloadable pdf mentioned above. Trim the four ends to form short pigtails.

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This was rebuilt on a secondhand commercial frame with fibreglass spreaders. He uses single wire as apposed to twin and a balun which by all accounts seems a much simpler and easier design to build. I can't find that information or the way to calculate measures. Finally with a bit more trimming completed, I climbed the ladder with antenna in hand and clamped it in to place. JavaScript seems to be disabled in your browser. Something I need to research. This was rebuilt on a second-hand commercial frame with fibreglass spreaders. I tend to feel that general purpose antennas like long wires and G5RVs do not often work well at the higher frequencies. The second conductor does not need to be cut, it passes underneath the board, is secured by hot melt glue. Let me know how you get on

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The tuner at the feedpoint of the Square Halo With some pieces of aluminum from my scrap metal collection, I made some brackets and mounted the tuner where normally the feedpoint would be mounted. Saturday morning I set to work and I did the full tuning with the MFJ which took an age as the G3TXQ definitely has much finer tuning points, it dips very quickly and the freq range is literally a few hundred kilohertz, a noticeable difference to the much wider freq of the G3TPW. Gain when installed 10m above ground. The extra bandwidth with folded dipoles is canceled out now by the tuner, so I presumed open dipoles would do fine and would reduce total weight. A quick wipe on a wet sponge cleans the iron and you can resolder without needing to clean all the glue from the joint. Some folk have had difficulty visualising the balun construction, so here are more details; click on the thumbnails for higher resolution photographs. The connection is a PL socket. Looking inside the box it is a remarkable simple system that is very easy to build and yet gives great results. If you want to get really technical, Vf depends on the wire you use, but this seems close enough for ordinary speaker or lamp cord. Then it was just a case of re waterproofing the box, sealing up and mounting back on the mast.