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“Magic antenna” radiation pattern as MMANA sees it - FYI

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AA7EJ, Oct 23, 2013.

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  1. AA7EJ

    AA7EJ Ham Member QRZ Page

    There was a brief discussion here about something called “Magic (wire) antenna”.
    Not to be confused with “Magic whip”.


    The group came to a conclusion that is is basically a collinear array with questionable – lossy - usage of coaxial cable as phasing lines. ( Not a subject of this post )



    So I model it using MMANA modeling software as a three element collinear array.
    Using ideal, theoretical phasing, no real coax , the radiation pattern came out as a clover leaf inline of the antenna wire, as advertized.


    The biggest surprise – the takeoff angle of the main lobes is whopping 40 degrees when the antenna is modeled at half wavelength height.
    And gets progresivelly higher with more height.



    73 Vaclav
     
  2. W6OGC

    W6OGC Ham Member QRZ Page

    It may be stretching it to dignify the thread as coming to any conclusion.

    Something is anomalous, in that there is a vast difference between expectations based on analytical efforts, and reports of effectiveness by users. Either the reports are, like reports of Mark Twain's death, greatly exaggerated, or the analytics so far have overlooked something.
     
  3. K4SAV

    K4SAV Ham Member QRZ Page

    What is a magic antenna?
     
  4. AA7EJ

    AA7EJ Ham Member QRZ Page

    Did more thinking, which in my case is always dangerous , and now I like to present this to the radio amateurs who are more familiar with software modeling than I am.


    I wanted to make a comparison between G5RV and “Magic antenna”.


    Assuming that basic antenna is a ½ wavelengths dipole I was looking at both of these antennas as three ½ wavelengths dipoles “in line”.


    From this assumption their theoretical radiation pattern MUST be same under same theoretical assumptions.



    Since G5RV has all of these dipoles connected end to end – serial, the feed point impedance of the center dipole reflects that, and is around 150 Ohms. IMHO that clearly explains the need for matching section of the G5RV feed line when used as intended as a single band antenna.



    The “Magic antenna” dipoles are phased, each one being 180 degrees from the center dipole and the center dipole maintains its feed point impedance of around 50 Ohms.
    .
    Here is my “conclusion” from this theoretical analysis.


    Using MMANA, it shows than the feed point impedance is the only real difference between both antennas.


    I would like to make it clear that I do not question anybodys practical experience with these antennas. Your mileage will vary.



    Any commentaries and opposing opinions / views are welcome.


    73 Vaclav
     
  5. AA7EJ

    AA7EJ Ham Member QRZ Page

    Unfortunate naming choice for 3/2 wavelength long collinear phased array with improperly designed phasing "stubs" from coax. The inherited high take - off angle of main radiation lobes does not help much.
    Your mileage will vary.
    73 Vaclav
     
  6. AA7EJ

    AA7EJ Ham Member QRZ Page

    Correction - used wrong name.

    I had a senior moment, again, and mislabeled the antenna.
    So I am not going to reveal the real name, just to be fair.
    It is still a phased collinear 3 element in-line wire array.

    I am not sure if MMANA can model real phasing line, but I'll give it a try.

    73 Vaclav
     
  7. W1FBV

    W1FBV Ham Member QRZ Page

    Are you talking about the so-called mystery antenna?

    Jim, W1FBV
     
  8. K8JD

    K8JD Ham Member QRZ Page

    Phasing stubs

    I would try to find and buy as much 300 ohm TV twinlead as you can before it finally vanishes from the market and use it to make phasing lines for your co-linear arrays. It sure works better than coax for the prupose.


    OTE=AA7EJ;2985363]I
    It is still a phased collinear 3 element in-line wire array.

    I am not sure if MMANA can model real phasing line, but I'll give it a try.

    73 Vaclav[/QUOTE]
     
  9. G3TXQ

    G3TXQ Ham Member QRZ Page

    If you are referring to the W5GI "Mystery Antenna", it is not a collinear!

    Steve G3TXQ
     
  10. K4SAV

    K4SAV Ham Member QRZ Page

    I knew the magic antenna was a mystery antenna because there is no magic antenna. I just didn't know which mystery antenna it was.

    If you want to see an analysis of the mystery antenna by someone that knows what he is doing, here it is:
    http://vk1od.net/antenna/W5GI/
     
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