Doublet - Coax Length

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by G5TM, May 21, 2018.

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  1. AB0CD

    AB0CD Ham Member QRZ Page

    Hmmmm...looks like if you followed all the advice herein one thing would not happen: getting on the air. I've played with the Cebik 44-foot doublet off an on for many years with results. Notice I did not say good or bad results, just results. I operate QRP and propagation is a big factor. My upcoming experiment with it will be a squished version in my townhouse attic with a 300 ohm twinlead feed into a 4:1 balun and from there, coax to the tuner and rig. This is for an upstairs operating position in my bedroom. I also have a basement shack but finding a feed line path from the attic to the basement is a bit of a challenge. I have outside feedlines for several "temporary" antennas. So for the first attic doublet at this QTH I plan to build it with junque boxxe parts, string it amongst the rafters, and see how it works - ASAP. So far, with about a half dozen different configurations of the 44-foot doublet, I have always been able to tune it. As to actual efficiency? That's always another matter. The Reverse Beacon Network is a big help in this regard. You can call CQ 3-5 times (on CW) and then see where your signal is going and what its strength is. Because of its relatively short length and potential for working 10-40 meters with it, it sure is a fun antenna to experiment with. 73
     
  2. WB2JIX

    WB2JIX Ham Member QRZ Page

    I see nothing wrong with your proposal, overall.
    Nobody has asked about the tuner and balun? What are you using?
    I assume you're not running legal limit with the 300 ohm twinlead.
    There are tuners such as the SGC and MFJ versions, that will tune a doublet and you won't require an external balun.
    Use decent coax, such as LMR-400 and you'll be good to go.
    Now, I use and sell the 600ohm open wire line however, I've helped and seen many use this same setup with no issues whatsoever.
    I'm not speculating; I'm relaying real experience.
    I suspect you are correct about the current feed length causing your tuning issues.
    Now, before you go cutting the feedline, simply fold back the ends of the dipole say a foot or so and try again. That alone may solve the tuning issue.
    Best of luck............
    Go for it!
    Brian
    http://www.trueladderline.com
     
  3. 2E0VSS

    2E0VSS Ham Member QRZ Page

    Wives and long 300 ohm feeder runs??
    Wives won’t have what???

    Come on man, stand up and be counted...

    Kiss kiss
    M
     
  4. G5TM

    G5TM Premium Subscriber QRZ Page

    Jolly decent of you all to dig up an old thread sans Burke and Hare but its all sorted now.

    73
     
  5. G0JUR

    G0JUR Ham Member QRZ Page

    o_O :D
     

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