Phased dipole model

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K7URX, May 17, 2019.

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  1. K7URX

    K7URX Ham Member QRZ Page

    Hello,

    Can anyone help me with a model for phased 20 meter dipoles implementing the christman feed method? I will be building it this weekend. I can model the dipoles but dont know how to properly add the phasing scheme to the model in MMANA. Any help greatly appreciated!
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I use EZNEC not MMANA, but typically phasing of networks is modeled in one of two ways:

    - Add an independent source to each driven element (each dipole) and adjust the phase of one source relative to the other in the same way your phasing network would.

    - Actually model transmission lines feeding the driven elements from a single source and adjust the line lengths, impedances, velocity factors, etc. as you would with actual coax.
     
  3. W5DXP

    W5DXP Ham Member QRZ Page

  4. K7URX

    K7URX Ham Member QRZ Page

    Thanks guys for getting me on the right track.
     
  5. UA3TW

    UA3TW Ham Member QRZ Page

    It is possible to build a simmetrical antenna. One can switch it back and forth with two relays in the center. The relays send the phasing capacitors forth or back. Here is MMANA model attached for the wire version.
     

    Attached Files:

  6. W1VT

    W1VT Ham Member QRZ Page

    Roy W7EL not only sells EZNEC, but he wrote the array phasing material in the ARRL Antenna Book.

    I worked him on 40M from Hawaii when he was trying out his new 40M phased array!
     
  7. K7URX

    K7URX Ham Member QRZ Page

    Nick, Thanks for sharing your model. I need to spend some time to learn more about antenna modeling beyond the basics.
     
  8. K7URX

    K7URX Ham Member QRZ Page

    Something I hadn't considered is how to implement a common mode choke for this antenna. One at each feed point? If so, would winding coax on a core mess anything up?
     
  9. KL7AJ

    KL7AJ Ham Member QRZ Page

    Here's a VERY IMPORTANT note...regardless of the actual NEC implementation. Be sure you use CURRENT sources, not voltage sources!
     
    K7TRF likes this.
  10. KL7AJ

    KL7AJ Ham Member QRZ Page

    Here's a handly lil spreadsheet for Christman feeds, by the way
     

    Attached Files:

    K0UO likes this.

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