Cobwebb antenna

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I just put a cobweb antenna in my attic. My house is a wood frame so the attic is fairly electrically transparent. The height is approx m above ground. My cobweb is of the single-wire type with FT toroid. Since the attic provides four support points I didn't use any poles; just strung up some Dacron line in an "X" pattern and attached the wires to the line. I machined some plastic thumbscrew adjusters to slide along the line and hold the wires in place.

Cobwebb antenna

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. Exactly in the middle of the folded dipoles, the two parts of the dipole are interconnected. This shorting point creates a kind of T-match to bring the impedance to 50 ohms. The impedance is brought to 50 ohm by means of a balun. It uses closed-ended folded dipoles, also from figure 8 speaker wire.

Finally with a bit more trimming completed, I climbed the ladder with antenna in hand and clamped it in to place. I always recommend a resonant dipole as the easiest way to get good results from a single cobwebb antenna, if this antenna works similarly to a dipole on all bands then it should be worth having.

Read the PDF file. Maybe a Google will find it elsewhere. Cobwebb CB1. Before I finished my construction I looked at the web and found Steve's site. The PDF shows the 17m element as mm, I think this is a misprint, was intended. I do not think the pdf gives the element support dimensions very clearly.

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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. Lay the two coaxes alongside one another and connect centre-to centre and braid-to-braid at each end.

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Cobwebb CB1. I suggest mm more on the ends each element. I could trim to match the frequency of the G3TPW, but to be honest I couldn't be bothered to get it exactly the same. Well after much playing about with tuning and trimming, I finally got the G3TPW Cobweb back up on the mast yesterday evening. A couple of my wooden spreaders broke in the gales at the end of last year. Yes, my elements were all a bit longer than the ones in the pdf. Hardware kit for the CobWebb. For 10 or 12 meters they are a reasonable size and if you can get them up to about 20 foot high you'll have some fun! August This model still survives. Even on m band with 25 watts I was received in more places in FT8 than ever in the past with the 13m long vertical with auto tuner. Also when tuning for a good SWR, if the antenna can be raised to a minimum height of 6ft, tuning may well be easier. This reminds me of when I had a VK2ABQ break A two element, 5 band, built with 12ft wooden spreaders - similar but twice the size of a Cobwebb This was in the Jan storm, three of the spreaders broke but as the element wires were reasonably secure on them nothing actually fell down. Hi David, yes indeed the gaps will effect the SWR of the antenna, you need to follow the G3TXQ link to make sure you have the elements cut to the correct lengths, then each length gap will need a very slight adjustment by measuring the SWR using something like an MFJ or similar to get the accurate SWR.

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My cobweb is of the single-wire type with FT toroid. I guess it will be quite big for 40? Please note that the wire used was PVC insulated with an outside diameter of 2mm and a conductor diameter of 1mm; dimensions will vary slightly if you use different wire. A search on www. Our experts are there to help you in word and deed - independent of the frequency range and radio application. Bad weather stops play Yesterday I thought the HF bands seemed particularly quiet. G0MTD shortened his but mine needed lengthening, the 15m element was not long enough. We are happy to help! This does not look too good but I expect it to outlast a method that requires you to seal a box with a lid and over a dozen holes. The horizontally polarized omnidirectional antenna is suitable for the 10m, 12m, 15m, 17m and 20m band. My house is a wood frame so the attic is fairly electrically transparent.