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Thread: best antenna

  1. #1791
    Captain abcd567's Avatar
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    An analogy to what we are trying to do with taming of CoCo:

    A virus infected patient receives following simple instructions from a doctor:

    Antibiotic "xyz" 500mg capsules every 8 hours, for 5 days.

    The patient follows these simple instruction and gets cured.

    Before the doctor could write the above prescription, a full team of scientists, doctors, biologists, biochemists etc have conducted xfundamental reasearch & experiments on the virus & the antibiotic medicine "xyz" for several years.

    The paitient is never given, nor is interested, in the sceintific details, but wont get this medication if the research was not conducted.

  2. #1792
    Captain abcd567's Avatar
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    Empirical, No-Math, CoCo Experiment

    I am planning to do following experiment (when I find free time):

    Make and try a new 8 and 1/2 element shorted top CoCo with different lengths of top 1/2 element.

    CoCo made of RG6 cable (FPE insulation, 0.83 VF).
    The full elements length = 1/2 x 275 x 0.83 = 114 mm.
    The top half elements length = 1/2 x 114 = 57 mm.

    Since top shorted element modifies the SWR, I will make many pieces of 1/2 element with length varying in steps of 5 mm i.e. 57mm, 52mm, 47mm, and 42mm and try the coco by changing top element, to find out which one gives the best range.

    simulation result

  3. #1793
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    Since top shorted element modifies the SWR, I will make many pieces of 1/2 element with length varying in steps of 5 mm i.e. 57mm, 52mm, 47mm, and 42mm and try the coco by changing top element, to find out which one gives the best range.
    Or, make ONE 57mm - and trim it ! LOL

  4. #1794
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    Quote Originally Posted by Rooster View Post
    Or, make ONE 57mm - and trim it ! LOL
    Yes, an easier option. Thanks.

    After fabrication & trial run of over half a dozen miserably failed CoCos, I really dont feel any appetite to go through this distasteful experience once again.

  5. #1795
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    Yes I was surprised to see so much discussion about the coco especially after the failed attempts in the past. I still reckon my whip design is the easiest to reproduce over and over again, and know its right. All thats needed is to follow the formulas for wavelength, with no alterations for velocity effect. The problem is acquiring the fibreglass blanks
    Mike

    PS abcd did you get to do my extended whip on 4nec2? You were going to show me how to add elements / coils to the YWYY_double_whip
    Last edited by YWYY; 2014-10-25 at 10:45.

  6. #1796
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    Quote Originally Posted by YWYY View Post
    .....PS abcd did you get to do my extended whip on 4nec2? You were going to show me how to add elements / coils to the YWYY_double_whip
    Sorry, I forgot .... will do as soon as I find time

    Yes I was surprised to see so much discussion about the coco especially after the failed attempts in the past. I still reckon my whip design is the easiest to reproduce over and over again, and know its right. All thats needed is to follow the formulas for wavelength, with no alterations for velocity effect. The problem is acquiring the fibreglass blanks
    Mike
    Apparently true, but as deceptive as the CoCo.

    Both theory and simulation show that the antenna's performance (SWR & Gain) are very sensitive to coil diameter (equal to the diameter of the fiberglass whip on which the coil is wound) AND the coil length.

    If a US whip is used, it will be 1/4 inch = 6.4 mm dia. If European (metric) whip is used, it will be 6mm dia. There will be profound change in SWR due to this little change of dia. Similarly if you change the coil length by compressing or expanding the coil a few mm, this will also have profound effect on SWR.

    But your design has advantage over CoCo of possibility of some adjustment by trimming the top element's length.

    Later additon: If heat shrink tube is not applied, the antenna can be tuned (i.e. SWR & Gain can be adjusted) by expanding or compressing the coil.
    Last edited by abcd567; 2014-10-25 at 22:39.

  7. #1797
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    Quote Originally Posted by YWYY View Post
    .....abcd did you get to do my extended whip on 4nec2? You were going to show me how to add elements / coils to the YWYY_double_whip
    Click the links below to download .nec files for 2, 3 & 4 coiled whips.
    There is negligible advantage in having more than 3 coils.

    ywyy whip - 2 coils.zip

    ywyy whip - 3 coils.zip

    ywyy whip - 4 coils.zip

  8. #1798
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    Various methods of reducing SWR of CoCos
    Verified by Simulation.
    Verification by making these CoCos and putting these to trial run is yet to be done.


    4 Element CoCo from RG6, FPE insulation, 0.83 VF
    # Number of Full Elements Impedance Matching Element SWR GAIN dBi
    (in Hoizontal Direction)
    (1) 4 elements 114mm NIL 5.03 6.13
    (2) 4 elements 114mm Above 4th element - 57mm Coax, shorted top (1/4 wavelength) 3.04 4.09
    (3) 4 elements 114mm Above 4th element - trimmed (35mm) Coax, shorted top 2.75 5.18
    (4) 4 elements 114mm Below 1st (bottom) element - 35 mm Coax, shield removed and replaced by single wire new-animated-1.gif
    (see sketch below)
    1.66 5.68


    Twin Wire TL Matching.jpg
    Last edited by abcd567; 2014-10-27 at 04:45.

  9. #1799
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    Thanks mate I appreciate your work
    Mike

  10. #1800
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    I have made a new 4-Element CoCo from RG6 and put to trial run now.

    (1) Under trial run now: 4 elements 114mm, No matching element.

    (2) Next trial run will be: 4 elements 114mm + 57mm, shorted element at top.

    (3) Next trial run will be: 4 elements 114mm + trimmed (35mm), shorted element at top.

    (4) Last trial run will be: 4 elements 114mm + 35mm, shield removed, between lowest element & feed line. (refer to post#1795 item#4)

    DSC03398-R.jpg . DSC03395.jpg
    Last edited by abcd567; 2014-10-27 at 18:15.

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