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Thread: Trial Run Results for Three Types of Whip Antennas

  1. #11
    Captain abcd567's Avatar
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    Sep 2013
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    @majo:
    In antennas, there is a phenomenon called "end effect". Due to this effect the physical length of antenna is slightly shorter than its electrical length by about 97% to 98%. This is mainly due to radio waves travelling slower in metallic wire than in the air, and also due to capacitance effect at the ends of the antenna.

    Taking an average figure of 97.5%, the physical length of full wave wire is 275x0.975=268mm, and 1/4 wavelength wire is physically 1/4x268=67mm
    Last edited by abcd567; 2016-07-11 at 21:00.

  2. #12
    Flight attendant majo's Avatar
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    Nov 2014
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    @abcd567:
    Thank you for this quick and competent reply!
    Now I`m confident and can start cutting...

  3. #13
    Passenger
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    Aug 2019
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    i have a question on this.

    If 1/2 wavelenght for 1090 MHz is 138 mm and I want my antenna to be 1/4 weavelenght (=69 mm)

    what happen if an antenna is working at 1/2 wavelenght? it will work?

  4. #14
    Captain
    Join Date
    Apr 2018
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    It won't have good performance.

    You can look up antenna impedance but it's a very complicated topic.
    Let's just say, monopole antennas with groundplane are gonna be best at 1/4 wavelength.

    Or you can build a dipole antenna (the half-wave dipole antenna is most common): https://en.wikipedia.org/wiki/Dipole...lf-wave_dipole

    Note that using other than half-wave dipole antennas means you need impedance matching.

  5. #15
    Passenger
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    Aug 2019
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    wow, this is a really interesting topic.

    i will keep working with the cantenna, i had the whiped antenna but is not working as desired, maybe because it doesnt have a filter on that location ( possibly)

    i found a coffee can, but is 6 inches diameter, can work as cantenna? i will install a new raspberry just to test antennas.

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