Dipole for 40m with loading coils

I started my 20 meters activities with a simple wire dipole antenna. This dipole gives me a SWR of 1:1 and I made contacts all over the world using it.
After obtaining the DXCC for 20m my attention shifted to 40 meters and I wanted to use a similar dipole. Unfortunately my garden didn't allow it. I could only put up about 15 meters of wire.

Therefore I made the 40m dipole out of wire with loading coils. The wire I use is military antenna-wire: a combination of steel and copper-wires with a thin layer of green plastic covering.

I learned that most energy is radiated by the antenna by the high-current parts of the antenna. With a resonant dipole these are the center-parts. So I didn't want to put the coils at the feeding point, but somewhere halfway each of the legs of the dipole.

Also I don't like solder-joints or bolted joints in an antenna if I can avoid them. Joints and years of rainy weather (as we sometimes have here in Holland) always cause trouble and require rigourous measures for making everything weatherproof.

I ended up with a design where I use one continuous wire for the antenna and the loading coils.


For the coils I took a short piece of 32mm PVC tube. I screwed in two parker-screws over which the antennawire is bent and then coiled 17 turns around the PVC-tube. Finally the wire is bent around a second parker-screw and continues as antenna wire. Two tire-wraps are used to fixate the wire on the tube.




















Tuning the dipole required a trial-and-error method using a MFJ 259 antenna-analyser or the like. I ended up with dipole legs of .. meters each, with loading coils of 17 turns at 2 meters from the center. Fine tuning is done by trimming the dipole ends.


The result is presented as the output measured with my mini antenna analyser.


This antenna gave me good contacts both inside and outside Europe, as far as the Galapagos Islands, Antarctica and New Zealand.