In a previous post I wrote that building a half wave antenna for 20m is on my todo list. The reason for this that my groundplane needs counterpoises or radials. For the half wave or end fed this is not needed. That is what people usually say.
A few days ago I started building one. For the radiator I took 10 meter wire, 2.5 mm thick. That was the easiest part
To support the radiator I went searching for a fishing rod on the website of a known sport- and outdoor store. The Geopole series seems to meet my expectations with a length of 9,5 m (about 30 ft). I overlooked one thing in the description : it was made from carbon fiber. But I went to the store, the price was 50 euro. Just minutes before I got to the counter I noticed a small sticker. It was barely visible, but there it was : Carbon.
This goes back into the rack. Now what ?
I started searching again and the best alternative was a 7m pole. This time I looked for all kind of descriptions, texts, stickers, etc. I didn’t found the word Carbon written somewhere. And the price was just 16 euro. For that price they can’t build a carbon fishing rod. It is made of glass fibre.
Back home I started to wind the wire around the pole like a big helical. I used papertape to fix it temporarely. The fishing rod just fitted my garage.
The next step : The matching unit.
The impedance of a half wave is rather high, so you can’t feed it directly with your coax. You can use an LC coupler or an L tuner. I have choosen for the LC method. The radiator has a dc path to ground and is isolated from the coax.
After a while I changed the capacitor by a piece of coax cable and mounted the antenna in a more suitable place.
See my other more recent blog entry here