Cobwebb antenna

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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.

Cobwebb antenna

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. I measured one, from the centre along each spreader , , , , mm. The feed point of the 10m element is mm from the centre. I think Steve's new site has got a lot of information about dimensions. G3TXQ says dimensions may depend, to a certain amount, on the dielectric properties of the wire insulation. I have adjusted tuning by altering the amount of end folded back. G3TPW, the designer, seems to infer the amount of foldback is critical. To me it just seems to alter the effective length of the elements, just as when adjusting any other wire to resonance. I suggest using slightly longer elements.

Now bind the two Chokes together - again, I used a couple of plastic tie-wraps. Use a couple of plastic cobwebb antenna to hold the coax to the core at each end. Can you tell me if the two antennas differ on performance?

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.

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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.

Synonyms for tremendous

A balun would be fine, but if built correctly, the coax is good and I have never had a problem. The only one which is pretty well spot on is the 20 meter band so obviously I now have to adjust the loops on each band element by lengthening or shortening to get the SWR readings to exactly where I want them. The rod for strengthening. This sounds an interesting project, I've thought about building a separate cobweb just for 30 and 40 meters but not all bands combined and I can certainly see the issue with the balun and I guess at some stage I would have worked out the harmonics but probably not till after build completion!! 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. Generally I start at with 28Mhz and work downwards, but it doesn't really matter naturally with new poles and slightly different lengths I knew I was going to have to re-tune. I'm in building cobweb m process. For example, resonance in the dry was set to February Performance:- Early days yet! I finally go round to a rebuild.

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To my relief, the analyser showed a match of right in the middle of the band at I can't find that information or the way to calculate measures. The solution is to tune each element separately for those bands, for example via the built-in tuner in your transceiver. Other bands I could not resist the temptation to extend the principle of the Cobwebb a little, and added an element for 6m. Skip to the end of the images gallery. At first I was at a loss as to what I had done and so eventually decided to do a total rebuild and took the main box apart to check that everything was in order and to clean out all the silicone which was causing a mess everywhere. Each loop is held by plastic ties so that it can be easily adjusted. Computer modelling of this arrangement shows that one result of bending the dipoles is that the antenna is close to being omnidirectional in azimuth, with a Free Space eccentricity of about 4dB; a less attractive result is that the feedpoint impedance drops to around 12 ohms at resonance. For example, resonance in the dry was set to The alternative arrangement I used was to combine the impedance transformation and balun functions into a Guanella current balun mounted in the terminal box. I did not like the Cobwebb feed I saw, the connector block had seriously corroded. 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.