Help with making 20 Meter 2 or 3 element beam

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI5AAI, May 22, 2020 at 11:05 PM.

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  1. KI5AAI

    KI5AAI XML Subscriber QRZ Page

    I got the plans down on how I want to make my beam. I am still deciding on either two or three-element. My question is: what material should I use?

    I am going to push max power coming out of an Ameritron AL-80B fed by an IC-7300.

    What size aluminum tubing should I use for the beam (square stock I assume) and for the elements? I see lots of folks making them for low powered applications with 22-14 gauge wire on a fishing pole. I want something more solid and one that will handle the power.

    I figure aluminum stock would be best but I am not opposed to fiber glass poles with wire as the elements.

    If I use aluminum stock I will probably use Texas Towers. Prices seem good.

    ETA: I am still not sure if it will be a full size (1/2 wavelength) or a mini. Something similar in size to a Mosely Mini 33 or 32.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd use aluminum tubing just like all the major antenna manufacturers do, although the SteppIRs use fibreglass tubing for the elements because the actual "element" is inside the tubing and not the tubing itself.

    Aluminum is lightweight and when formed into tubing also very strong. I have very large birds landing on my beams quite often and the landing and takeoff stress applied to the elements might be >100 lbs. They actually land more gently than they take off, it seems. When a hawk launches into the sky, an element can look like you just dropped an anvil on it.:p

    But in terms of "power handling," ordinary copper wire, even thin wire like #20AWG, can handle a kilowatt just fine. The elements aren't supposed to "dissipate" power, and unless they have unusually high resistance, they won't.
     
    KI5AAI likes this.
  3. NH7RO

    NH7RO Ham Member QRZ Page


    Just a suggestion since you're considering a 2 el. beam; have you considered a Moxon? Full-size antenna but only 70% of the width of a Yagi or dipole; great F/B and can easily be built with wire or tubing. SAL Electronics sells ready-made Moxons for all bands 70cm to 20m in case you want to look at those for ideas.

    The Moxon Antenna Project is another good source for Moxon info (and it even has a nifty calculator that can tell you dimensions depending on wire or tubing gauge or diameter).

    73,

    Jeff
     
  4. KI5AAI

    KI5AAI XML Subscriber QRZ Page

    I have not ruled out a Moxon. I thought I would try something different and go with a 2-3 element beam. Depending on how things go, I might do both!. 40 Meter Moxon and a 3 element 20 meter beam.
     
    NH7RO likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    A 40m Moxon is pretty big. L-o-n-g spreaders required.
     
  6. KI5AAI

    KI5AAI XML Subscriber QRZ Page

    I know LOL. But it might be worth a challenge. I am actually quite pleased with my homebrew 40 meter dipole I put up a couple of weeks ago. One projects at a time :)

    Back to the current project. I am leaning toward 14 gauge copper TTHN for the conductor draped over fiberglass supports. It will be a mini yagi with loading coils (same wire of course).

    The reason I am going to use 14 gauge THNN is that I already have an entire roll of it.

    Sound like a plan? It will be about the same size as a Mosely Mini-33A.

    I would like to go with aluminum tubing but I want to keep the weight down so I can put it on a telescoping mast.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Loading coils reduce functional bandwidth and of course are failure points both mechanically and electrically, so hopefully find a solid design that's already been proven and be careful.:)
     
    KI5AAI likes this.

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