Cobwebb antenna

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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.

Cobwebb antenna

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. It's very easy to adjust the elements into symmetry this way. Plus, it looks like a real spider web! I'm still evaluating the cobweb but am very happy with its performance on 20m compared to my outdoor endfed wire antenna approx 30m long and 10m high , which has been my main antenna over the past several years. A definite improvement. I use the WSPRNet low power beacon system to compare the antennas side by side over the course of several thousand "contacts", both transmitting and receiving.

Each loop is held by plastic ties so that it can be easily adjusted, cobwebb antenna. I have recently added a few notes on the web page.

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.

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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. Although not strictly necessary, I find it helps keep things neat if you slide a few narrow pieces of heat-shrink tubing over the coaxes to keep them together. You have now created a single transmission line with a Characteristic Impedance of 25 Ohms.

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Good luck in your build and please let me know how you get on. Page details. Amateur Radio G3TXQ - Cobweb Antenna During recent range testing of a hexbeam I needed a horizontally-polarised resonant antenna covering 20m thru 10m which could be assembled and disassembled quickly and easily. Up in the air, this time with all five bands, and no droop in the arms. 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. I will be connecting one end of the balun to an SO connector red to center, black to ground and the other connections to the two copper plates which then connect to each of the 5 element on each side of the enclosure via small bolts. Click on the photos on the right for enlarged pictures, and see the bottom of this page for more construction details. Note Peter's plot of the dipole takes account of the effect of ground reflections which which "fill in" the theoretical nulls off the end of a dipole. Anyway, as I shorten the wires, I intend to take up the slack by moving the gizmos until the shock cord tensions. 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.

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Once I start building I will take pictures and post them online. I agree with all of the points keep up the good work. Nevertheless, I am also going to test with the folded dipoles. At the moment I use a 30m vertical which works very well, but I always like to experiment and see if I can improve things. All other elements were all above 2. Now comes the usual tricky bit of tuning up the elements for each band, sometimes you get lucky and other times it becomes a real test of patience. I've no idea which way the tap needs to go. The silicon grease has done its job and kept the contacts all clean and rust free, I'm amazed there is no rust on the copper wire or the steel screws. Email This BlogThis! Placing the two antennas side by side it was interesting to see the physical difference. I'm in building cobweb m process. The photos below are probably self explanatory. I could not resist the temptation to extend the principle of the Cobwebb a little, and added an element for 6m. The most noticeable being the background noise but that cannot be helped as the attic naturally has bricks and mortar and electrical wiring.