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UnUn Build Question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KT5WX, Jun 10, 2021.

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  1. KT5WX

    KT5WX Ham Member QRZ Page

    Good morning one and all!

    I haven't thought about building an antenna in some time, but I found something recently that's brought back the interest. In fact, I was out of radio for a couple of years for a variety of reasons. But now I'm getting back into the whole thing again.

    The catch is, I need to create a 49:1 UnUn to make the long wire work. I found some instructions, but they only go up to 50W SSB / 20W CW. So the question is:

    What needs to be done to make this work with 100W for both SSB and CW?

    The instructions include a T140-43 Toroid, 100pF ceramic disc capacitor, and 22 gage wire. They used magnet wire to do the wrappings.

  2. W1VT

    W1VT Ham Member QRZ Page

    A larger core such as a FT 240-43 will allow it to handle more power. For even more power you can buy 4" diameter cores or stack several 2.4 inch diameter cores.

    If you change the core size but keep the number of turns the same, a larger core will require more wire and create more inductance. This will move the frequency range of the UNUN lower.
    The maximum frequency of the UNUN is typically a function of the wire length. Shortening the wire should allow it to work higher in frequency.

    Zak W1VT
    WA9PND likes this.
  3. N3TGY

    N3TGY Ham Member QRZ Page

  4. N3TGY

    N3TGY Ham Member QRZ Page

    I built a dozen or so of these and gave them to new hams and to those who needed them. Plans are here:

    I used T130-2 cores in my builds because I didn't have magnet wire just insulated, and the wire was a bit thick to fit on the 105 cores. They handle 100 watts with the 130-2 Amadon cores. Also I used cheap electrical 'LB' ( pull through boxes) they work really well, great for a jump kit. Very inexpensive 16233602549723239264094988534156.jpg
  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    The EARCHI balun is not a 1:49 transformer! The 1:49 transformer is used with resonant EFHW wire antennas. The EARCHI balun is used with not-resonant random wire antennas. They are not interchangeable!
  6. N3TGY

    N3TGY Ham Member QRZ Page

  7. N3TGY

    N3TGY Ham Member QRZ Page

    I realize that, I thought he wanted an unun that could handle 100 watts. So I figured cheap and easy to give some ideas.
    N5SJS likes this.

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