I was missing antennas for 160/17/12/10m at my summer qth, so I tought I'd try to do something easy for the higher bands so I wouldn't need to have tons of coaxes running into the woods here.
My mind stuck on building a common fed antenna, I already have one for 20/15m where 20m is a vertical dipole, and 15m is a Inv-V with the same feedpoint.
Since I wanted three bands on this one (17/12/10) I figured I gotta do something different than that. Also, it would be a pain to mount an antenna with six independent wires..
I got the idea to build it just like a dipole, but space the wires by about 20cm.
Take four electrical pipes or something similiar. Cut them to about 42 centimetres.
drill one hole in the middle, a hole 1-2 cm from the end of each pipe. Also make two additional holes to mount guy wires in between the first thee holes. Feedpoints consists of a dogbone isolator. All dipoles are soldered to the same point, and a regular RG-58 coax wired one turn around the insulator, tightened with self amalgamating tape.
This is during the wire-cutting phase. I just loosely tightened the wires to the pipes using electrical tape. 17m is the middle dipole, and 10/12m is on the sides.
When finished, I added two wires between the electrical pipes in the centre of the antenna. They can be used to staighten the dipoles up, and keep them in place.
Here it is, cutting finished, but the support wires isn't added yet, just a temporary mounting for testing.
From another angle.
Results?
When I spoke to other hams, they told me I would gain top capacitance from the other wires, ending up with weird lengths of the wires, and that the result would not be as broad banded as regular dipoles. Also SWR could be a bit higher at the resonant frequency.
The result when all the cutting was done, is SWR less than 1.5:1 on 17m and 12m. On 10m I have about 1200kc with SWR <1.5:1, and 1800kc with SWR <2:1 (According to the IC-703). I'm very happy with this antenna. It's located 10 meters above the ground, and it performs very well. It's mounted like a half-sloper (see top picture) towards europe. It's being fed by approximately 25 meters of RG-58. I worked VR2 on 17m first day I tried it with 120 watts and got a good report back. I don't have any scientific measurings, but I doubt the losses compared to regular monoband dipoles is noticeable. About the cutting lengts and topcap, I'm not sure. I did cut on all bands at the same time for best performance, and it turned out very well. A warning not to cut too much, I accidentally did that on 10m & 12m wich is very sensitive, 2 centimeters can ruin the antenna at the end (moved resonant frequency about 300kc on 10m).
I'm sure I'm not the first one to come up with this construction. But I find it working very well, so I just wanted to share my experiences. Next try will be a fieldday/portable antenna constructed in the same way, for 20/17/15/12/10m :-)
SM6YOU/Rick - 2005-07-28
2005-08:
I made anotherone with 5 bands! It also seems to work very well, but it was quite a bit harder to manage to get everything straight on this one. Ten wires is quite much to keep track of! :-)
Here's some picture of it from the creation:
