Fan antenna - attach elements directly to balun?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by M7JDJ, Feb 14, 2020.

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  1. M7JDJ

    M7JDJ Ham Member QRZ Page

    Hi,

    I currently have a 20m dipole in my attic, but I’d like to get on to 40m, so I was wondering if I could just connect elements for 40m draw them up a bit from the balun and then run it parallel above the 20m elements to create a fan dipole?

    Thanks in advance!
     
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    Yup. THat's how to do it.

    Ed
     
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Try to run the second pair of wires so that they form an angle of at least a couple of degrees with respect to the first pair. The angle difference can be either in the vertical (side view) or horizontal (birds eye view) plane...

    The goal is to get the ends of the 20m dipole at least 2ft from the 40m wires...
     
    NH7RO and EA1DDO like this.
  4. EA1DDO

    EA1DDO Ham Member QRZ Page

    Were is that data coming from?
    I meant, Is that a wavelength size?

    I remember to see both models, with wire completely parallel, and with wires with angle.

    [​IMG]

    [​IMG]

    Thanks
    73, Maximo
     
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    Experience! The further the ends of the short(er) dipole are from the longer wires, the less interaction there is when tuning the respective dipoles to resonance.
     
    EA1DDO likes this.
  6. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Well you might not find an exact reference to 2 feet (though I agree with Mike that's a pretty good guideline for a 40m/20m set of wire elements) but this is a good resource that's often quoted (and misquoted) regarding antennas including multiband dipoles fed from a common feed point (aka fan dipoles). https://apps.dtic.mil/dtic/tr/fulltext/u2/684938.pdf

    I've found their recommendation to create feed point spacers that provide at least 14cm of spacing between elements at the feed point really helps in terms of minimizing tuning interaction between the different band elements.
     
    EA1DDO likes this.
  7. EA1DDO

    EA1DDO Ham Member QRZ Page

    KI7HSB likes this.
  8. M7JDJ

    M7JDJ Ham Member QRZ Page

    Thanks for all of the advice. As it is the elements were quite a few degrees out in both vertical and horizontal due to the geometry of the attic, so it didn’t affect the 20m at all.

    I’ve attached the SWR readout from my NanoVNA.
     

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