Helical --- Flat matching strip vs Triangle matching strip ?!

  • Because I have no hardware to check for the SWR, I tried many different kind of antennas ,looking for the best performance.

    I home-browed many kind of antenna for the uplink, eg, patch antenna a helical antenna with flat matching strip etc. the performance was poor.


    The last one I was built is a helical antenna with a triangle strip. the perform is much better comparing to other antennas .

    My signal report jumps to 58-59 !!.


    I built it around an empty toothpast pump tube :-)

    D=4 cm.

    Space between turns 28 mm.

    Number of turn 3.

    The strip is right angle trangle 71mm*17mm one corner attached to to the SMA pin on flat Alu reflector - dimention 12 cm * 12cm .

    The tube clued by epoxy at the front side ,plus the nozzle of the tube pass throught a hole at the center of the reflector.

    Dish =1 meter.


    Here are the links I was used.


    http://f5ad.free.fr/Liens_coup…A3FYM%20Helice%202300.htm


    https://www.qsl.net/oh4jzj/13cmhelixframe.htm









    73 de Nader / st2nh

  • St2nh Nader, that is a very old publication from me, I think almost 20 years old ; -) It was intended as 'WLAN' antenna.

    In order to illuminate an offset dish properly with a helix, there is a rule of thumb saying: 1 turn for every 0.1 f/D.


    So in order not to over illuminate the dish, make another helilx with 6 turns, as most commercial broadcast dishes have f/D's of around 0.6.

  • Hi,


    the triangular strip is propably fairly repeatable to produce without test gear, which is an obvious bonus.


    Here is an old design I made for our Ilmari balloon project (weight around 40 grams) that uses an oblong shaped matching section (don't seem to have a plot of thre return loss, but it is around 20 dB for the 23cm ATV band):


    https://73.fi/oh2aue/23cm_helix_1.jpg


    Though I still prefer the bother of making the capacitive base wire loading for good broadband matching (the markers are at seemingly weird frequencies as I wanted to get an idea of the attenuation at these) :


    https://73.fi/oh2aue/13cmhlx1.jpg


    https://73.fi/oh2aue/helix.gif


    /michael, oh2aue

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    "If you have data, you have something, if you do not, you have nothing." (Bengt Hultqvist, SK 24.02.2019)