Cobwebb Antenna

Which antenna to use is the ultimate question for many. Look on any forum (that has ham radio on it obviously) and there’ll be someone asking a question about which antenna should I use and which one is better than that one. Equally there are a lot of questions about what to fit into which space.

Like many, I like to make some of my own stuff. Some things are more effective than others but I can say with a lot of confidence that the Cobwebb antenna has been one of the better things I’ve made. Not because its particularly stunning in its performance or that it is able to be used on all bands, with ruthless efficiency and will guarantee the best DX possible.

The truth is that its a great antenna, that’s more compact than a long wire, is Omni directional, is easy to build (although will take a bit longer than cutting a length of wire) and will give you 5 bands with reasonable performance. One of the more important factors, for me at least, is that it is XYL friendly.

If you’d like to read the technical information then I would suggest looking here. The original designer, Steven Webb, G3TPW has put together a comprehensive write up of how it works and why it works. I don’t intend in going over his work. Also Steve G0MTD, has a great series of step by step instructions on how to build this antenna and how to tune it. Steve has used a Cobwebb on DXpeditions with great success. I’m not so well travelled but can confirm it works well when Its been used at my mother in laws ;-)

The build

I followed others lead and bought a set of poles from an eBay trader called spratreader with a shop called AMTools  (Just a wild guess, but I think he’s a qrp fan). Who has other goodies that can be used which will be mentioned later. These fibreglass poles are used as supports for the cable that forms the antenna. A central plate to hold it all together was bought from Aerial parts at Colchester. I had to order this specially but John was able to produce something quickly and for a very reasonable price.

Cable is just twin speaker cable from Rapid and it came in a 50m reel for, again, a reasonable price.

If you follow the instructions on Steve’s pdf I will fairly certain that when you put an an analyser onto the antenna and start the tuning process (From 10m down) there will be minor discrepancies between what Steve saw, what I saw and what you’ll see. There are a number of factors that will affect the antenna but it’ll be nearly there so only minor chopping should do it. Take care and remember that a few cm of cable is quite a lot of KHz.

 

 

Here’s the layout in my garage. the white poles are bits of cheapo trunking from B&Q that were used to help with the layout. Then the centre I originally used and setting out the test antenna

IMG00061-20101002-1627Cobwebb-layed-outCobwebb-centre-detail

 

 

cobwebb

 

Performance

Simply put, as expected. If you think it’s going to out perform a monobander then you may be looking in the wrong place. I have had qrp contacts into Europe easily enough and managed to get to VK with a few more watts. Generally I wouldn’t expect to get that far with my vertical so what doe it tell you.

1. Its better than my vertical for long distance
2. Its quieter (but does that mean its less effective?)
3. It has worked well for me in a north west coastal area without being blown to bits.

 

Variants

Tuning the antenna isn’t as easy as it may be, especially if you’ve committed to joining the wires and made a minor error, which could lead you off into a place where your antenna isn’t quite as efficient as if could be. Step in the single wire Cobwebb. A similar sized antenna but with one major difference. It uses just a single wire per band and a particular type of balun ( Oddly enough available from spratreader as a kit) to match the impedance. Again all the hard work is done by someone else and I’m just copying. Look here for all the original details. Mine has been used in anger several times and was responsible for some good DX.

Here it is up on the decking during the summer months next to the Hustler 6-BTV which as served for many years and is showing its age

wpid-IMAG0127

Leave a Reply