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insulated split driven element

Discussion in 'CB Antennas' started by GunSlinger338, May 17, 2010.

  1. GunSlinger338

    GunSlinger338 Active Member

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    i thought i would share my new project with the antenna gurus hear
    this is my insulated split driven element for my M107
    all the hardware and tubing comes from DX engineering , i got the 1/2" Teflon from ebay , and the tubing ends came from Charger.
    I plan on direct feeding this element , but have the materials to do a hairpin and balun match if needed



    thanks for looking


    [​IMG]
    [​IMG]
    [​IMG]
     

  2. RickC.

    RickC. Hopeless antenna junkie

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    Nice looking stuff!

    You may be able to get an acceptable match with direct feed (Cebik lists a 7 element yagi with a 1.043 wavelength boom at 46 ohms +8X), but I'd still use a balun.

    Palomar Engineers sells a choke balun kit (ferrite beads and heat shrink) to fit RG8/213/LMR400 for 17 bucks plus shipping. I just ordered one last week. Not bulky, fairly light.

    Just curious-- I'm assuming M107 has a gamma match from the factory (since most commercially made yagis do). Why the change to the insulated DE and direct feed? Were you having bandwith or mechnical problems with the gamma, or just decided to try something different (nothing wrong with that, by the way).

    Nice tile floor, too.

    Rick
     
  3. GunSlinger338

    GunSlinger338 Active Member

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    i wanted something different and like playing around with stuff
    The M107 is very narrow banded . when tuned per the instructions you don't have to get very far from center frequency to see an unacceptable match.
    I am hoping the change with the larger diameter element will broaden the bandwidth some
     
  4. RickC.

    RickC. Hopeless antenna junkie

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    Fair enough, sounds like a good project. Post pics when you have it working, and if you can get charts here of the bandwidth with the direct feed and larger dia element vs. the original setup that would be interesting to see.

    Good luck!

    Rick
     
  5. that looks very clean 338 :) . if you try both the hairpin and direct feed can you also let us know if either has any peformance effect over the other as far as tx and rx ? im sure you already know the larger diameter elements can affect the tuning length of the driven element , which affects its directors and reflector lengths also .
     
  6. GunSlinger338

    GunSlinger338 Active Member

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    in computer modeling the director lengths worked out well
    the driven and reflector elements will have to be adjusted

    spacing was also adjusted some .. Boom length is factory for the M107

    if it works as good as the factory M107 with a little better band W , i'll be happy
     
  7. straight razor

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    insulate the driven elements

    hey gunslinger dxengeerning has better insulation parts for seperateing the
    driven elements and they are cheap



    straight razor
     
  8. straight razor

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    hey gunslinger something is really bothering me how come you bought the elements
    from dxengeerning and you didnt see the 2 inch boom to element saddle mounts

    [​IMG]
     
  9. straight razor

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  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur
    Staff Member

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    Gunslinger, what type of feed are you going to use? Direct feed or use a hairpin (Beta) match? Direct feed results in an unbalanced feed while the hair pin match preserves the balance but you have to feed it with a balanced feedline or use coax and a balun. I built a six element yagi for 6m and used a balanced feedpoint and made a 4:1 halfwave coaxial balun to feed it because the feedpoint impedance was so low. I used a piece of fiberglass rod as the centre insulator and mounted it with a saddle bracket just like all the other elements but with the U-bolt through the fiberglass rod instead of the aluminum tubing. It works like a charm.


    4:1 coax balun design.
     
  11. MrSuburban

    MrSuburban Guest

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    Those clamps dont allow the driven element to be split like he wanted to do. Nothing wrong with the one he made it maybe a little heavy but shouldnt be a problem seeing that this thread is over a year old and he has been running it for a while.
     
  12. C2

    C2 Sr. Member

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    I'm not following you, CK.

    Are these DC Yagi's unbalanced?

    Beam Lengths


    http://www.qsl.net/w4sat/tiny2.htm
     
  13. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Yes they are unbalanced. Anytime you feed any type of balanced antenna directly with coax cable it results in an unbalanced condition at the feedpoint. Coax cable is an unbalanced feedline with one side grounded (the shield) and connecting it directly to a balanced antenna results in one side of that antenna being grounded and the other side not and thus unbalanced. You can make a 1/2 wave coaxial balun as shown in my link above which preserves the balance as well as performs a 4:1 impedance ratio for use where the feedpoint impedance is low, as in my 6m yagi. Using the hairpin (Beta) match allows the driver element to be grounded but since both sides are grounded equally thru the hairpin it remains balanced.
     

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