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Thread: best antenna

  1. #2311
    Captain abcd567's Avatar
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    Quote Originally Posted by kucengemok View Post
    which one is stub?
    The U shaped / hairpin shaped part in this one:

    Franklin Spider.PNG
    Last edited by abcd567; 2015-04-12 at 18:09.

  2. #2312
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    Re VNA: I use miniVNA Tiny but the DG8SAQ is supposed to work very well.

    Re antenna:
    before finsishing experiments, I wanted to optimize the design of the thick/thin antenna.
    I used MMANA and get the following results:
    1090v1.png
    If you have a few minutes, could you tell me the what the result is with 4NEC2?

    As you can see on the wire definition, this starts with a ground plane using 4 x 69mm long 2mm diameter wires at an angle of 20 deg below horizon.
    Then a vertical section of 65mm long 8mm diameter
    Then a sequence of 3 times : 138 mm long .2mm diameter followed by 130 mm long 8 mm diameter

  3. #2313
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    Quote Originally Posted by JLD View Post
    ......If you have a few minutes, could you tell me the what the result is with 4NEC2?

    As you can see on the wire definition, this starts with a ground plane using 4 x 69mm long 2mm diameter wires at an angle of 20 deg below horizon.
    Then a vertical section of 65mm long 8mm diameter
    Then a sequence of 3 times : 138 mm long .2mm diameter followed by 130 mm long 8 mm diameter

    The 4NEC2 simulation I posted earlier had dimensions (from top to bottom):
    138mm long/10mm dia + 138mm long/0.1 mm dia + 69mm long/10mm dia + 4 radials 69 mm long/2mm dia/45 degrees from horizontal.

    Your latest dimensions with which you have done MMANA simulation are different from what I have used in 4NEC2 simulation.
    I will have to do a new geometry and simulation in 4NEC2 using your latest dimensions.
    I will do this shortly and post the results.

    The results of previous simulation are again given below, but with addition of wire geometry screenshots.

    Thick Thin Collinear Monopole Short Feed+Groundplane.PNG . JLD Wire definition.PNG . JLD Geometry.PNG
    Last edited by abcd567; 2015-04-18 at 17:15.

  4. #2314
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    @JLD
    I have now done 4NEC2 simulation with your revised configuration (a ground plane using 4 x 69mm long 2mm diameter wires at an angle of 20 deg below horizon. Then a vertical section of 65mm long 8mm diameter. Then a sequence of 3 times : 138 mm long .2mm diameter followed by 130 mm long 8 mm diameter.)

    Seems 4NEC2 goes crazy with thick-thin design.
    MMANA results seem to be closer to your measured results.

    JLD Revised Dimensions Thick Thin Collinear Monopole+Groundplane.PNG . JLD (Revised Dimensions) - Wire definition.PNG . JLD (Revised Dimensions) - Geometry.PNG

  5. #2315
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    Quote Originally Posted by JLD View Post
    Just confirms CoCo is not trivial to tune, at least for UHF and above.
    Small variation on cable VF and construction technique can result in unpredictable results which are imposible to correct without a VNA.

    I am still experimenting with my CoCo to see if I can make it robust to construction variability but this is not easy.

    I am also going to test some variation of collinear which does not require coaxial cable and could be easy to build.

    Attachment 5799

    Need to test. 2 stacked half wave like on the picture should be OK but feed impedance might be very low when stacking more half wave phase/radiating sections above.
    If there are antenna specialists on the forum, would like to hear what they think.
    The top sections could be assembled on a fiber glass rod (8mm rods used for kites) which would allow to make the assembly precise and easy.
    The phasing line is just very small diameter copper wire.

    Will try to get something done for next weekend.
    JL
    i've got the materials and i think ihave worked out a way to keep things apart, but you have a gap between the 1/4 radials and the first 1/4 10mm section how big should that be? and what thickness is the link between those bits?

    edit:

    Well i have made one but i thought i had a connector for the cable but i dont so going to have to order one. Means i cant reliably test it yet.

    Heres some pictures.

    6.jpg
    1.jpg
    4.jpg
    3.jpg
    5.jpg
    Last edited by SpaxmoidJAm; 2015-04-25 at 17:21.
    T-EGLF8

  6. #2316
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    Cant see that design getting anywhere NEAR working... sorry :-(

    There will be phase differences requiring at least one coil between the top sections... and no idea what the short link is all about

  7. #2317
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    @Rooster: You changed your Avatar picture!

  8. #2318
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    EASY SPIDER, MADE OF COAX-ONLY.
    No SO239 or PL259 or N-Connectors required.
    No Soldering Required.



    TRIAL RUN



    IN 5 STEPS

    Step #1


    Step #2


    Step #3


    Step #4


    Step #5
    Last edited by abcd567; 2015-05-02 at 19:26.

  9. #2319
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    Quote Originally Posted by abcd567 View Post
    @Rooster: You changed your Avatar picture!
    Sorry mate...did it throw you ? lol

  10. #2320
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    Quote Originally Posted by Rooster View Post
    Sorry mate...did it throw you ? lol
    I was so much used to your old Avatar picture that for a moment I thought you are some new member

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