CobWebb 5 band antenna

I have a very small back garden and am limited with what type of antenna I can use. I built my first 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. As an added bonus, the antenna is also resonant on 6M!! Each dipole leg is made from twin cable and fed with 50ohm coax. It is Omni directional and cost about £40.00 to build. I don't know how much power it will take except to say it comfortably handles 400 watts, although I usually only use 50 watts. I used an MFJ-259B to help tune the antenna - 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.

 

 

Antenna Construction tips

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

 

 

*(suggest you cut 15-20cm longer to allow for band adjustment.) Each loop is made from figure 8 speaker cable. 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. Click here for a handdrawn diagram with additional fine tuning info (approx 254kb). 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. When next I get the time I will update this image to 2005 stats.

 

 

**Update July 2005**

 

I rebuilt the antenna using white fibreglass poles, white twin speaker wire and a white junction box. A good friend of mine, Pete - 2E0PRP, welded up the quad bracket.

 

The result is a much neater looking antenna on top of my push up mast. The antenna is resonant on the bands it has been designed for, and to my delight I also find that it is resonant on 6m. The table below shows the SWR / bandwidth with the antenna about 15ft high. As you will see its' turned out quite well - but you have to decide what mode you want as the antenna has not got a wide bandwidth. The pictures below show the revised antenna.

 

Band Low Point SWR Mid Point SWR High Point SWR Bandwidth

20m

14.024 1:1.6 14.090 1:1.0 14.151 1:1.6 125Khz

17m

18.081 1:1.6 18.115 1:1.3 18.190 1:1.6 110Khz

15m

21.000 1:1.6 21.044 1:1.0 21.099 1:1.6 99Khz

12m

24.872 1:1.6 24.931 1:1.1 25.000 1:1.6 125Khz

10m

28.484 1:1.6 28.406 1:1.0 28.325 1:1.6 160Khz

6m

    50.110 1:1.5     approx 100Khz

 

 

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