I’ve been looking around for good ideas for a portable HF antenna and finally settled on Robert Johns’ (W3JIP) plan from a QST article (Aug 88). The antenna design is a vertical dipole (6M to 40M), using a loading coil at the base of the vertical with a tap and the other half the dipole is formed with a 1/2 wave length cut of wire. The coil is mounted on a 3/4″ PVC pipe which slips into a 6″ length of aluminum tubing. The tubing then slides into a bracket designed to hold a flag. Mounted on the bracket is a SO-239 with the center pin making contact with the bracket. The main element sitting on top of the coil is 8′, but you can lengthen it to 11′.
I spent the morning gathering the parts, had a hard time with some of the specific items, but ended up with a couple work-arounds. I put the coil together first, that went pretty easy. W3JIP’s plan calls for #8 aluminum ground wire for the coil – which no one has. I used copper instead. I wrapped the copper around a 4″ piece of PVC. The directions call for 12 turns, but I only purchased 12′ of copper (the directions didn’t say what length to get)… ended up getting 9 turns. I mounted the coil to the PVC and then secured the trailing end up the coil to a piece of aluminum tubing inserted inside the PVC. The element gets mounted above the coil and I secure the tap at the base of the element.
Once I had everything together, I went outside and mounted the coil section to the top of a tripod, inserted the 8′ aluminum element above the coil, set the tap at the top of the coil, ran a length of wire out as the other half of the dipole, ran some RG-58 out from my Icom 706 and after playing with the tap a bit was able to get out to Texas on 20M.
I have some more work to do:
– better secure the SO-239’s center pin to the bracket and bottom of the coil
– attach a banana plug to the ground side of the SO-239 to allow quick changes for switching bands
– find a way to secure the base of the antenna to a painter’s pole
I know the antenna will work on 20M, now I would just like to get it working on 40M.