Vertical Dipole, Theory meets practice

Nashua Area Radio Society Topics In All Forums Elmering Forum Vertical Dipole, Theory meets practice

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  • #12760

    Hamilton
    Participant

    My main antenna is a full wave 40m delta loop which also matches well across 20m where EZNEC predicts numerous nodes and nulls and a high take off angle. I’ve been looking for a better 20m DX antenna while I wait to get a beam up.

    At the recent VE session, Fred (AB1OC) once again held up the Radio Wavz 20m dipole as a good performer when mounted as a vertical.  At $39 including a 1:1 choke balun, I decided to try it.

    I shot a rope over a branch at 65′ and hauled the dipole up. The coax comes off at 45*, there is a rope from the balun in the opposite direction to oppose the pull of the coax to keep the antenna wire vertical. A water bottle weighs down the lower wire. Start to finish it took an hour to install.

    The EZNEC plots are included, the poor ground was used. The performance continues to improve as the antenna is raised higher but it is good above 55′.

    All of the following measurements were all on 20m.

    The antenna analyzer showed <1.8:1 match from 13.4 MHz to 14.35 MHz with a 1.2:1 at 13.9 MHz. Antennas are always “long” out of the package. With a little shortening a match <1.5:1 is possible across the full 20m band. ( The VSWR measurement includes 100′ of LMR-400 and the balun isn’t 1:1 as claimed).

    A comparison with the delta loop showed the vertical’s noise floor to be an S unit higher (S3) and the mid day 20m Net with stations from NY, NJ, PA, etc were stronger using the delta loop. So far the vertical was certainly a good antenna and a close second behind the loop.

    EZNEC shows a low 10-45 degree take off angle and no NVIS capability with the top of the vertical dipole at 65′. In theory, it should be better for DX than for local communications.  In practice it is: 20m was fairly dead today with only a few stations on the panadapter. Tuning the band I found Vancouver BC, OR, CA, and Ireland. Only Ireland could be heard with the Loop. I have never heard <u>any</u> 20m stations in the Pacific NW  while using the loop. (The loop is pointed NE but is somewhat omnidirectional). Also, several European reverse beacons detected my signal with the vertical and the loop was not detected.

    In summary when mounted high the vertical dipole retains the low take off angle of a 1/4 wave ground mounted Vertical. It does not need ground radials and ground losses are reduced. It can be placed above obstructions. It only needs one high support and it does not require a tuner.

    It isn’t a hex beam or a yagi, but at $40, no tower required, it is a great antenna. It is very stealthy as well.

     

    Hamilton (K1HMS)
    Amherst, NH

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    #12766
    Fred Kemmerer
    Fred Kemmerer
    Keymaster

    Thanks for the through analysis Hamilton. Good information!

    73,

    - Fred (AB1OC)
    President, Nashua Area Radio Society

    ab1oc@arrl.net
    Visit us on the web at - https://www.n1fd.org

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