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I want to make myself a antenna for 40m and 20m wavelength band, but i don't have enough space for a full scale dipole, and even for more compact configurations like delta-loop or inverted v, so i want to create a shortened dipole in configuration of a whole-length solenoid with small (compared to wavelength) diameter. It should work the same as a wire in terms of transmitting energy (J. S. Belrose article, QST, Sep 1953) but with increased inductance throughout whole length of it.

And if i recall correctly, that for a shortened dipole it's input impedance starts to have a reactive capacitive component which needs to be compensated with a "lengthening inductance".

So the question is, how much inductance i need to have to appropriately compensate for a shortened regular dipole? And what the active resistance will be so i can match the antenna? I'm having trouble finding the formulas for overall input impedance.

Thanks in advance.

ZecosMAX
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ZecosMAX: The calculation that doesn't really tell you specifically what you need to do for a dual-band antenna can simply be found here: https://www.66pacific.com/calculators/coil-shortened-dipole-antenna-calculator.aspx The issue is using one dipole antenna for two bands, where the input may be a current loop on one band, and a current node on the other, if not designed specifically for what you are trying to do. If you have an antenna tuner, you can make your radio happy, but that may not make for an efficient antenna on one or both bands. Also, keep in mind that inductors narrow bandwidth. Finally, I would make some recommendations if you disclosed your dimensional parameters...but that's your choice.

Louis Seaman
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