Build your own Cobwebb Antenna
| I have a very small back garden and am limited with what type of antenna I can use. I have found a marvellous link ,the G6PJE web site, to build a folded dipole antenna. You can buy a commercial version from 'G3TPW'. I built my antenna in July 2004. If you are looking at this after speaking to me, you know it works. It is basically a 5 band antenna comprising of 5 full half wave dipoles for each band - between 10M & 20M. Each dipole leg is made from twin cable and fed with 50ohm coax. It is Omni directional and cost about £40.00 to build. |
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I got the 4 fibreglass poles from ebay from Amtools, they cost £18.00. I bought a roll of black & red cable from Maplin Electronics, their partnumber PH71N which is a 100m roll of 10A Figure 8, it cost £14.46 for the 100m roll. (you only use approx. 40m) The other bits and pieces were 'lurking' around in my shack. So far I am very pleased with its results. It is resonant on each band, I don't use an ATU, so nearly all power is radiated out. I found that tuning the antenna the most complex bit. In the end I used an MFJ-259B to help with the process - this proved invaluable Below are some pictures that may help anyone considering building an antenna of this type. You are more than welcome to email me if you want more info.
Here are some smaller pictures
of the assembly, followed by
some larger pictures of the antenna up & running. You can click
on the pictures to
enlarge.
You will notice a 6 turn RF balun at the junction box of the antenna.
Here some pictures with only 3 bands connected.
This is the antenna up around 15ft
This is my shack which the 33ft push up mast is attached to
These are where the folded dipoles connect to
Here is a closer picture
Another view of the antenna up around 15ft
| Band | Overall Loop (suggest you cut 15-20cm longer to allow for band adjustment.) | Each leg | Short point |
| 10M | 508cm | 254cm | 156cm |
| 12M | 586cm | 293cm | 179cm |
| 15M | 690cm | 345cm | 208cm |
| 17M | 812cm | 406cm | 222cm |
| 20M | 1030cm | 515cm | 272cm |
Each loop is made from figure 8 power cable. The middle point is found and one wire is cut. This single wire is then fed in to the junction box. Shorts are made at the appropriate distances per the table. The ends of each loop are folded back on themselves to adjust resonant frequency as well as providing an anchor point for the loop. The ends have been left approx. 3" apart from each other, but are joined together using cable ties. Have another look at the mini photos to clarify what I have just written. Click here for a handdrawn diagram with additional fine tuning info (approx 254kb). Click here for a parts list and tips for this project. If you do contemplate building this antenna I strongly suggest you visit Dave's site at G6PJE and read through the guest book comments, lots of useful information and construction tips are contained.
Here are some of the countries I have reached using this antenna mounted approx. 15ft high over a 6 week period (between July and mid September 2004) using about 50 watts power.
Unless otherwise stated the contents of this web site are © 2005 M0MRR
