New antenna: 40 / 80 dipole

I like vertical antennas a lot. They have served me well on the low bands (40-80-160). But sometimes a relatively low dipole is better. EUHFC comes to mind. I started with an 80m dipole years ago. Then I converted it into a 160m dipole, and made me a 80m vertical. Verticals work better for me in DX contests. But they don’t in local contests. So this year I’d like to do EUHFC with low band dipoles.

And so I made a dual band dipole for 40m and 80m, sharing the same feedpoint. The 80m dipole acts as support for the 40m element. Spacing is done with leftovers of electrical conduit I saved from the trashbin.

I’ve made a lot of wire antennas in my 10 years as an amateur radio operator. Nothing easier than calculating and cutting a dipole. The classic dipole formula and math don’t do much here because of the interaction between the wires. But it’s a starting point. I calculated the basic length for 7025 and 3550 kHz. Then I added some extra wire (1.5m on 80m and 0.8m on 40m). From then on it’s pulling the antenna into the air and trim to resonance. When the antenna is up, I find its resonant frequency by looking at the lowest SWR. Then I calculate the theoretical length that corresponds with this dip. I compare this actual length with the initial length for the desired resonance. So I know the length of the excess wire. This is what I cut off, leaving some leeway. I had to repeat this twice to achieve a satisfying resonance.

Here are some images, mostly from the antenna analyzer.

You can always buy these things, but a quick search told me that this antenna would cost about 120 US $ or more. That’s very expensive. I paid 8 Euro for the centerpiece if I remember well. I tried to negociate when ON4BHQ and I would buy a few but the vendor didn’t bite. The wire is leftover from previous antenna projects. And nothing beats making contacts with a homebrew antenna.

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