MFJ (W) and H "Cobweb" (W) HF Antenna. Introduction: The horizontally polarized MFJ and MFJH Cobweb antennas cover G3TPW CobWebb Antenna for the 14, 18, 21, 24 and 28 MHz Bands All the other small multi-band commercial antennas that are available are less than. The antenna compliments my 40m dipole nicely and gives me the PDF quide so I drew-up the plans using my trusty Serif Draw application.
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COBWEB ANTENNA Introduction. Thank you for downloading the MFJ five band HF antenna. The antenna is omnidirectional enough to not require a. Loop Dipole Antenna, also published in the RSARS e-Library, a decision 5 - band Cobweb antenna, or for a compact Moxon beam Antenna. 5 Fundamentals of Radio Antennas 6 High-Frequency Dipole and Other Doublet Antennas 7 Vertically Polarized HF Antennas 8 Multiband and .
Dimensions The following details my own build and what worked for me — Each piece of PVC sticks out cm past the ali-tube, with mm inside the ali and held in place via a through-bolt.
The dimensions shown on the plan below are all in mm. The dimensions shown next to each wire are the distances from the outer-end of the PVC tube. The 10m wire is therefore around 40mm from the ali-tube and the 20m wire is only 20mm from the edges of each spreader.
When installing each set of wires for the first time — Secure them onto the PVC using velcro cable ties. This means that you can move the position of them quite easily if you need to make changes.
I have opted for the G3TXQ version in this case. Quite acceptable for the average transceiver.
You simply wind a total of 8-turns: 4 and then a cross-over and finally another 4. The ends are solded inner-to-inner and outer-to-outer.
Make 2 of these and link them together via 2 cable-ties — The ends of both are then soldered in the following way: End 1 is inner-to-inner and outer-to-outer ie: parallel. End 2 is inner-to-outer which leaves you with an inner and outer.
End 2 is the one you connect to the SO socket.
Once the balun has been trimmed and soldered in place, I pour casting resin into the box giving it a water-tight seal. The only drawback with the G3TXQ single-wire version is having to make-up the balun!
Thanks to my earlier test This is quite easily the best antenna I have used, it's small 8ft circumference omnidirectional and produces very little TVI.
If you decide to build a Cobweb do let me know how you get on and good luck! A bit of rust here and there on the metal tubes that hold the wooden poles, but perhaps through luck or my building capabilities it has managed to withstand all that has been thrown at it! The wooden poles and the box are covered in mildew and slightly bowed, but still sound, the cables are fairly loose which I suspect is the main reason my SWR has been out, especially on 20 meters which at the last reading was 2.
Since the main box is in such good condition I will do little except give the outside a good scrub and more importantly drill a couple of draining holes. 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.
Over the next few days I will tighten the cables and recheck the SWR and if needs be replace any that are suspect, luckily I have some spare cable that I got last summer from Maplins, our version of Radio Shack. Looking inside the box it is a remarkable simple system that is very easy to build and yet gives great results.
This is easily the best antenna I've ever built and quite honestly if I can build one anyone can. If you want further information look at the Cobweb Revealed website or alternatively please ask and I'll be happy to help where I can but I warn you now I don't understand the theory, hi hi.
Good Reads & Links
I will include as many picture as I can during the service process so you can see just how easy it is put together. Further work on Servicing the Cobweb Antenna The fibreglass poles have arrived for the Cobweb antenna, these I suspect are fibreglass fishing poles but ideal for what I want and more to the point once I had removed the plastic ends with copious amounts of boiling water fit the metal sleeves perfectly.
Their length is 7ft which provides the correct length for arranging the twin speaker cable. I have replaced the 20 meter cable, although I could find no fault.
I suspect the SWR was high either because of the element being too short or tapping point misaligned, so I have re-measured and added a few more cm for trimming, twisted and soldered the wire at the correct length for the tapping point. It's worth searching on the web to see what else is about, G3TXQ does a similar antenna but uses a balun and single wire which probably makes life a lot easier.February A couple of my wooden spreaders broke in the gales at the end of last year.
The useable SWR bandwidth covers a large part of each band. So I re-measured all the elements and added wire where necessary, once completed I re-attached them to the box and laid them back on the poles and took some readings, everything looked much better and in some cases the SWR was lower than the original build.
Antenna 1/2-wave, 5-Band HF Cobweb Antenna – MFJ-1835 Time Lapse Video
Make 2 of these and link them together via 2 cable-ties — The ends of both are then soldered in the following way: End 1 is inner-to-inner and outer-to-outer ie: parallel. The position of the wires along the rods are shown on the attached excel spreadsheet, as measured from Cobwebb centre.
For the rest of the weekend I will continue to trim up and hopefully by tomorrow afternoon I should be ready to think about mounting the antenna back up on the mast although there's no real hurry and I may just end up waiting till next weekend.