trapped dipole? help, ideas ?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N9OXO, Aug 8, 2009.

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  1. N9OXO

    N9OXO Ham Member QRZ Page

    I have been working on a 80M 40M trapped dipole and not having such good luck with it, anyone out there have any ideas? I have made two traps for 40M and it seems to work but when I tune the 40M section and it looks good then add the ends for 80 its throws it all off! I have seen where coax can be used but don't have a grid dip meter to get it tuned. What I did was put a cap in series with the coil to tune it then put it parallel. It dips on 40M right where I want it. I just cant add the ends! Its driving me nuts! I have a 1:1 balun at the feed point also. If I can get it working I would like to add 20M and 17M and maybe even 10M traps in line too. Thanks in advanced for any help. At least my 6M amp is working good! along with my 3 ele home brew beam. I do have the mfj 239B so that helps! Amie N9OXO The 2 40M traps...
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  2. W9GB

    W9GB Ham Member QRZ Page

    Amie -

    This tutorial by Tom, W8JI - should be helpful in your 40 m trap construction.
    Traps should not be resonant at the actual planned operating frequency.
    Loss is highest when the trap is resonant at the operating frequency!
    http://www.w8ji.com/traps.htm
    What are you using for trap design or DIY build instructions?

    The W5JO design uses 33 feet of wire from the center insulator, then the trap and 16 feet of wire to end insulator.
    His traps are built by winding 9 turns of wire around a 2 inch diameter PVC pipe, in parallel with a 100 pf capacitor
    at a proper voltage rating (Doorknob capacitor at > 3 kV work well).

    MFJ-259B Calibration by W8JI
    http://www.w8ji.com/mfj-259b_calibration.htm

    IF you use coax cable, then Multiband Trap Dipole Antenna by Al Buxton, W8NX
    http://www.oz6frs.dk/2008/TRAPS/improved trap dipole.pdf

    ARRL technical reference for Trapped Dipoles:
    http://www.arrl.org/tis/info/Trapped.html

    w9gb
     
    Last edited: Aug 8, 2009
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