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Trial Run Results for Three Types of Whip Antennas

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  • AlejandroM
    replied
    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.

    Leave a comment:


  • wiedehopf
    replied
    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.

    Leave a comment:


  • AlejandroM
    replied
    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?

    Leave a comment:


  • majo
    replied
    @abcd567:
    Thank you for this quick and competent reply!
    Now I`m confident and can start cutting...

    Leave a comment:


  • abcd567
    replied
    @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, 21:00.

    Leave a comment:


  • majo
    replied
    Thank you for this great and easy to realize idea!

    But before I cut my antenna allow one question:
    If 1/2 wavelenght for 1090 MHz is 138 mm and I want my antenna to be 1/4 weavelenght (=69 mm) why should I make the cut at 67 mm (15 mm base + 52 mm whip)?

    Leave a comment:


  • CX6BX
    replied
    Great info abcd567, i will try this with my old antenna

    Leave a comment:


  • abcd567
    replied
    @Ben311

    Hello Ben
    There is another step to further improve: Enlarge the tiny ground plane provided by the 1 inch (25mm) dia mag mount base by placing it over a metallic surface like a metallic sheet, plate or a can.

    Please see the following thread which demonstrates the boost when antanna was placed over a metallic surface (a food can), compared to when it was placed over a non metallic surface (inverted glass).

    Trial Run Results for Four Sizes of Ground Planes

    .

    Leave a comment:


  • Ben311
    replied
    Hello all,

    I just registered a new account to let everyone know, that this is a genius idea. As I already ordered a new antenna yesterday, I gave it a try and cut the old indoors-antenna. Now lots and lots of planes show up and my range increased by about 30-40 nm.

    Thanks
    Ben

    Leave a comment:


  • HNJAMeindersma
    replied
    So we may conclude; bigger is not always better. It's how you use your antenna.. :P XD haha

    Leave a comment:


  • abcd567
    replied
    Originally posted by HNJAMeindersma View Post
    Is the stock whip exactly 1/2 wavelength?
    Yes, it is 1/2 wavelength.

    The total length of whip is 115 mm removable part + 15 mm inside the base = 130 mm.
    The 1/2 wavelength at 1090 MHz is 138 mm.
    Therefore for all practical purposes, the stock whip is 1/2 wavelength.

    However the impedance of 1/2 wavelength whip, even with ground-plane enlarged, is several hundred ohms. This gies a poor impedance match with 75 input impedance of the receiver (db-t usb dongle) and SWR is higher than 2.5

    On the other hand, the impedance of 1/4 wavelength whip with ground-plane enlarged is between 50 and 75 ohms, and provides an almost perfect impedance match & SWR is 1.5 or less.

    This is the reason the whip chopped to 1/4 wavelength performs better than full length whip.
    Please note that 52 mm removable part + 15 mm inside base = 67 mm = 1/4 wavelength at 1090 MHz.

    25164814131_839b1981bc_o.png. . . . 24872604509_2bc46a22db_o.png
    Last edited by abcd567; 2016-05-29, 02:05.

    Leave a comment:


  • HNJAMeindersma
    replied
    Is the stock whip exactly 1/2 wavelength?

    Leave a comment:


  • dedicados
    replied
    very interesting, im going to try it

    just to get a more info... why a trimmed antenna works better? did you start cutting little and test?

    i found really interesting your tests and results. thanks for sharing with us!

    If someone need space to upload a .iso .img or any kind of software i can help you, i have spare space in my servers.

    Leave a comment:


  • Oblivian
    replied
    So essentially, if you aren't using it for tv or any other frequency. Chop it!

    Leave a comment:


  • Trial Run Results for Three Types of Whip Antennas

    Please scroll down to see the test result graphs at the bottom.

    (1) The three antennas under test were:
    • (a) Coiled Whip
      (b) Stock Whip
      (c) Optimized Whip


    (2) In order to minimize number of variables, only the removable parts of Whips were interchanged. All other hardware, location, and software/gain settings were identical. Even the same mag mount base & RG174 coax cable was used for all the three whips.

    (3) In order to be sure that results are not influenced due to fluctuation in traffic, test were conducted twice.
    • (a) First test between 2pm & 3 pm
      (b) Repeat test between 4pm & 5pm



    Photo 1 - Three Antennas


    Photo 2 - Test Setup


    Photos 3 & 4 - Results of First Test






    Photos 5 & 6 - Results of Repeat Test


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