There are a bunch of online calculators that will give you the inductance for a given coil, but I need to design a coil for a given inductance. I’m wanting to build an air-core coil antenna for HF reception only, essentially a continuously-loaded electrically short monopole. I’m using length of two feet, diameter of 1 inch, and estimated capacitance of 12 pF to make things easy (I’d have to dig through Evernote to find the site that gives 6pF/ft as a reasonable estimate for reactance of electrically-short monopoles). An online calculator for loaded monopoles gives me an inductance of 424uH for a 2ft monopole at 3.9MHz. I’m not sure if it’s reasonable to assume for the sake of that calculation that a continuously-loaded antenna will behave like an electrically-short monopole of similar height, so I’m not considering the inductance to be a known variable. Is there an online calculator for such a thing, or at least a formula? The variables I have are: - resonant frequency - length of coil - diameter of coil - diameter of wire - spacing/pitch (insulated wire makes this easy ) I don’t think I need super precision—this is going to be a strictly receive-only antenna, and all it has to do is out-perform a 9ft whip!