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Choke location

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W5EDF, Jun 13, 2019.

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  1. W5EDF

    W5EDF Ham Member QRZ Page

    Before I go drop my off center fed dipole to do this, where would the best location for a choke be? Antenna feedpoint or outside shack entry? Both locations?

    I have 6 mix 31 snap on beads that will fit my coax. Dio I beed more? I would use the nice round donut ones, but I can't solder worth anything, so that is out of the question. I know I could get a inline one, but I am trying to limit the number of connecters in the path.

    Thanks
     
  2. K2CQW

    K2CQW Ham Member QRZ Page

    Antenna feedpoint. Beads in the shack just to keep rf out of yer computer.
     
    K0UO likes this.
  3. W5EDF

    W5EDF Ham Member QRZ Page

    Will do. I assume using my 6 sbao on beads would be like wrapping coax though a donut style one 6 times?
     
  4. KU3X

    KU3X Ham Member QRZ Page

    Put the choke /balun at the feed point of the antenna. Next put a choke at the point of entry for the house.
    61 material? What frequency range are you working on? Usually numerous turns around a ferrite core offer more choking reactance then a few clip on beads.
    Search K9YC and read his material on chokes.

    Barry
     
    EA1DDO likes this.
  5. W9IQ

    W9IQ Ham Member QRZ Page

    Not really. When winding a toroid, the ideal impedance goes up by the number of turns squared.
    So if everything else were equal, 6 turns through a toroid would be equivalent to 36 of your snap on cores.

    But it isn't nearly that simple in reality. Chances are your snap on beads have a longer magnetic path length than a typical toroid so they may present a higher impedance per turn. Winding capacitance plays a significant role in the broadband effectiveness of a balun as well.

    To give you a relative perspective, each of your snap-ons will give you less than 300 ohms of choking impedance. A well engineered balun will present greater than 5,000 ohms of choking resistance and an even greater impedance.

    - Glenn W9IQ
     
    Last edited: Jun 13, 2019
    NH7RO likes this.
  6. W5EDF

    W5EDF Ham Member QRZ Page

  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    The advice you have gotten in this thread is wrong!

    Most commercial off-center-fed dipoles will not tolerate a Common-Mode-Choke near the feed-point; putting one there will make the antenna useless. These things are poorly designed to include radiation off the coax feedline as part of achieving a match. Even routing the coax down the leg of metal tower will screw them up.

    I learned all of the this the hard way, as covered in these previous forum threads.
     
    NH7RO likes this.
  8. W5EDF

    W5EDF Ham Member QRZ Page

    I do have plans to replace the OCF with a fan dipole. But I wanted to relocate the OCF to the backyard as a inveted V due to space restrictions (I still want to have something up that is more multi band than the fan dipole I will have). I guess I could do a dublet for the backard,
     
  9. KP4SX

    KP4SX XML Subscriber QRZ Page

    With an antenna such as the Butternut HF6V that has a matching section of 75-ohm in series where would you place a choke? At the antenna feedpoint or at the junction of the matching section>feedline?
     
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    For that vertical antenna, I would ask what you are doing for radials before answering the question?
     

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