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There seem to be plenty of construction articles on center-fed wire fan dipoles with pairs of arms of different lengths, each pair dimensioned for a different band (e.g. half-wave 80M+40M+20M).

Would a wire fan dipole work with arms of equal physical lengths, but each pair with a different loading coil configuration (perhaps none, plus other pairs of arms tuned for different bands/frequencies with different inductors)?

If so, is there a rule-of-thumb for how far apart the wire fan elements need to be spaced (say in degrees or radians)?

Or could an (insulated) wire fan element be fed coaxially through the loading coil of another fan element? Or could a single loading coil be shared, with different taps for different top segments?

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    $\begingroup$ I, too, haven't ever seen this described. Seems like a fruitful area for investigation. I would start with a modeling exercise to narrow down the parameters you identified. $\endgroup$
    – Brian K1LI
    Commented Jul 5, 2019 at 18:11
  • $\begingroup$ Why not just build a trap dipole without all those extra antennas? Or are you trying to minimize the number of antennas? $\endgroup$
    – Mike Waters
    Commented Jul 5, 2019 at 19:23
  • $\begingroup$ By loading coils, did that also include traps? HamSE search for trap dipole $\endgroup$
    – Mike Waters
    Commented Jul 5, 2019 at 19:27
  • $\begingroup$ A trap dipole would be the longest for the lowest band. A bunch of possibly inductor loaded dipoles could be of a length appropriate for (one of) the shorter/higher bands. $\endgroup$
    – hotpaw2
    Commented Jul 5, 2019 at 20:19
  • $\begingroup$ The basic idea is not new. One can Google "multiband hamstick dipoles". $\endgroup$
    – Cecil - W5DXP
    Commented Jul 6, 2019 at 15:38

2 Answers 2

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This is already a commercially available antenna. Alpha-Delta makes several variations, with the DX-LB-Plus being the one I'm using. It covers 10,15, 20, 40, 80 and 160, with loading coils for 80 and 160, both shared on the longest legs. Overall length is 100 feet. The antenna works pretty well on 10, 15 and 20 and is excellent on 40! On 80 and 160 it's about what one would expect from a shortened dipole. On 160 on a good night I can get some DX during the winter, but Asia and Middle East won't happen for me!

What you're asking sounds like it would be a very worthwhile project! Probably more so if you drop 160 and 80 from the design. Check out Alpha-Delta for more information, and I'm sure there are designs available under "shortened dipoles".

73 es GL Dave - KB3MOW

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As an extension to the above answer, which mentioned the commercially available option, there is this calculator to make your own. This covers the necessary inductance of the loading coils.

https://marmes100.dreamhosters.com/Ant_Short_Multi_Band_Dipole.html

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  • $\begingroup$ That's an interesting resource, but unfortunately the calculations are only in imperial units: feet, inches, AWG, etc. Hams in countries that use the metric system can get out their calculators, I suppose. $\endgroup$
    – rclocher3
    Commented Aug 11, 2021 at 18:06

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