Common Mode Choke Question-Inverted L

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N1LOU, Dec 12, 2019.

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  1. EA1DDO

    EA1DDO Ham Member QRZ Page

    Install two chokes.
    One at the remote tuner´s coax output, and a second choke at entry of the shack.
    For choke selection, use famous K9YC´s Choke Cookbook:

    73, Maximo
  2. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    The choke at the tuner should be at the input to the tuner, in other words on the radio side of the tuner.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Last edited: Dec 12, 2019
  4. N1LOU

    N1LOU Ham Member QRZ Page

    I bought two it will be a bit of trial and error. Also because of the frozen ground here, I don't have a ground rod installed where the cable enters the house. I will fix that as well. And I will be sure to bond it to the electric service ground rod. I'll just have to hire a guy with a backhoe. The ground rod will have to go in horizontally. I tried to sink one vertically and at 3-4 ft of depth I hit bedrock (what we in New England affectionately call "ledge"). The only way to sink an 8 foot ground rod on this side of the house would be to drill into the bedrock. Probably easier to put it in horizontally.
  5. WB5YUZ

    WB5YUZ Ham Member QRZ Page


    The conventional way to operate an inverted "L" (or other Marconi antenna) with a remote tuner is to choose a non-resonant length of wire, to avoid very high impedances on harmonic bands.

    If this is the case, I'm not sure changing the length of the "L" would fix the RF, but it will definitely lower stress on the tuner components during harmonic operation, and quite possibly lead to more efficient matching. Because of the "one variable at a time" law of troubleshooting, I would fix that first, then proceed with other measures if necessary, as per Mike's advice above.

    That's probably a pretty good radial field, BTW.
  6. N1LOU

    N1LOU Ham Member QRZ Page

    Last edited: Dec 12, 2019
  7. KK5JY

    KK5JY Ham Member QRZ Page

    It's your house and antenna. :)

    None of that stuff changes an RF-on-the-coax issue. It may mask it if the impedances work out so that the ground rod can shunt a big chunk of it to ground, but that isn't guaranteed just because you drive rods, and it just hides the problem, rather than fixing it. The fix is to choke the cable shield. Start out at the antenna end of the coax (where I believe you said you had a remote tuner -- so between the coax and the remote tuner close to the tuner). If that doesn't fix it, then put the second one at the building entrance. Some people choke the cable inside the shack, but that's not optimal, since it allows you to have "RF hot" cable close to your gear.

    Good luck.
    K0UO likes this.
  8. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Because in this case
    a) A remote tuner is used at the base of the L, so it’s likely that the wire output is being used, not the coaxial.
    b) The output impedance is high on the antenna side on the troublesome bands so choking will likely be less effective than on the relatively low impedance input side.

    Do you see it differently?
    K0UO likes this.
  9. N1LOU

    N1LOU Ham Member QRZ Page

    this is correct
  10. EA1DDO

    EA1DDO Ham Member QRZ Page

    Yes, in the radio side, to "protect" the coax towards the radio shack.

    73, Maximo
    N0TZU likes this.

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