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I am intending to build a two element fan dipole for 80 and 20m. How should I go about choosing a ferrite toroid and number of windings for the balun, to operate effectively over such a range of frequencies?

I'm planning on constructing a 1:1 Guanella current balun with bifilar windings, and using 12 AWG landscape lighting wire for the arms at no more than 100W.

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I ended up choosing to use two FT240-31 toroids, based on this chart, which suggests that there should be at least good performance on each of the bands of interest, using 9 turns of bifilar wire, like I'm planning. According to the chart, I could get better results by winding RG58 coax on the same core, but I prefer to use the materials I already have as much as possible.

I will report back once the antenna is constructed and tuned.

She may not be an "ugly balun", but she certainly ain't pretty

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  • $\begingroup$ It will perform better at the high end of the frequency range, if you tape the two wires together snugly before winding. If it's a 50 / 50 ohm balun, the reason they say winding coax works better is because you actually want a 50 ohm transmission line. Wires taped together will be ~ 110 ohms, but open like that will be ~200 ohms which is even worse. Best would still be to use some thin coax - you can buy RG316 cables on Amazon etc. $\endgroup$
    – tomnexus
    Apr 19 at 17:01

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