HomeBrew 20m Mini Yagi - Reflector?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W2SHT, Aug 11, 2009.

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  1. W2SHT

    W2SHT Ham Member QRZ Page

    Hey fellow hams,

    Running my Icom-703 into a random long wire outside my house in Queens, NY has been an absolute pleasure, with signal reports from places like Morocco, Kuwait, Russia and Brazil in the 58s and 9s on only 10W. But I would like to build my own 2 element beam for 20m and these plans seem very doable.

    http://uts.cc.utexas.edu/~hansongr/Miniyagi.htm

    I do have some questions though, before I go out to purchase parts from Home Depot today. Am I reading correctly that the reflector wire never has an electrical connection to my coax? Is it supposed to be just a piece of wire some distance back that is at the right length with no electrical connection?

    Also, is that line that is labeled as RG58U considered the feed line? Is that what has to be cut to a half wavelength? On the driven element, there will be a PL259 connected to both sides of wire. (Where does the ground of the connector connect to? to the reflector?) I think what it means is I have to attach my coax to that connector, run it horizontally across the boom then turn at a right angle and continue running it down the mast to my radio. Is that all one run of wire? and should the wire length starting from the 90 degree turn at the mast be half a wavelength, or the entire length starting from the driven element?

    Also, does the length of my coax really matter?

    Thank you!

    KC2UOK - Stephan
     
  2. W2SHT

    W2SHT Ham Member QRZ Page

    A response would be appreciated! also how critical is the distance between the reflector and driven elements as there is conflicting information on this website.

    Thx in advance
    KC2UOK - Stephan
     
  3. W0EA

    W0EA Ham Member QRZ Page

    Correct Stephan, the reflector/director is not electrically connected to the driven element on yagis (IIRC).

    The line labeled RG58U is a gamma match. It is usually a fraction of wavelength, certainly not a half or even a quarter. Someone with more experience with Yagis should fill in here.

    The driven element is simply a dipole with some matching element (the RG58 in this case).

    You will need to have some sort of 1:1 balun or current choke at the feed point and that will keep the RF off the shield and thus you will be able to use any length of coax for the run back to the shack.

    Lets hope some more people chime in, as I don't have all the knowledge in this area.

    Good luck, 73!
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes. I suggest you pick up an ARRL Antenna Manual and read it...

     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    No it's not. A gamma match is something entirely different, and there isn't one included in this design at all. It's just the feedline.


    WB2WIK/6
     
  6. KC2TAU

    KC2TAU Ham Member QRZ Page

    I think he was just curious why the feed line was being taped to the boom and if this was critical to the design.
     
  7. W0EA

    W0EA Ham Member QRZ Page

    eeek! My bad... thanks for the correction Steve. I always get matching stuff confused anyway. Should have left that comment out.
     
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