Is a Choke Balun Needed Under an AH-4 Antenna Tuner for Inverted "L" Antenna?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA3MOJ, Oct 12, 2018.

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  1. WB4SPT

    WB4SPT Ham Member QRZ Page

    I'd be curious to know what effect placing the balun on a piece of sheet metal has on R and Xl. There MIGHT be some capacitive shorting effect causing a loss of CM performance. Of course, DM would not be affected.
    K7TRF likes this.
  2. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    So for common mode, I've decided to do 12 turns of RG58 on a FT240-31 core and place it inside a 4" x 4" junction box with a cover and place (2) S0-239 connectors on each end. Just like the commercial ones.

    My question is:
    Can I also use the same FT240-31 core to wind the 4-conductor control cable from the AH-4 tuner and place it into the "same" junction box?
    Would there be any interaction between the two cores with coax and control cable in the same box?

    Last edited: Oct 16, 2018
  3. AA7QQ

    AA7QQ Ham Member QRZ Page

    I would just wrap the coax around the torroid & plug it into the tuner. Same with the control cable. A cover might be nice if you are ice prone.
    Saves a bunch of work & parts.

  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I'd use separate cores so you don't flux couple RF and or control signals onto each other. As Ed posted above, a box isn't really necessary but there's no real harm in using one if you're so inclined. If you do go with the box, both cores can reside in the same box but separate them a bit or even mount them at right angles to one another if possible. The control cable choke can be wound on a much smaller core as there's very little common mode power to dissipate on the control lines and any signals on those lines have very low duty cycles and are inactive most of the time.
  5. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    I've decided to go with a single core for the CM: one for the coax and one for the control cable, 12 winds each. The cores will not be placed inside the AH-4 housing as is shown in one of the photo's. There was a post here that offered good advice regarding that and I think there would be some interaction between the two.
    However, I do plan to install the AH-4 tuner and both cores into a weather resistant enclosure of some sort that will be mounted outdoors. This is in a business location and the enclosure will help to keep the installation from drawing attention to itself.

    A sketch of the installation plan is attached. I will post progress photos as I go along.

    Attached Files:

  6. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    So the AH-4 tuner project has begun.

    I was able to find an outdoor enclosure that was an "exact" fit for the AH-4 antenna tuner.
    This housing couldn't have worked out any better! It's a First Alert locking security box.
    Not exactly weather tight, but I have an idea for that I'll disclose later.

    The coax and control cables were wired into the AH-4 tuner. The cover of the tuner screwed and secured.
    Holes were drilled in the bottom of the outdoor enclosure for the coax and control cable to pass thru. And
    additional holes drilled in the bottom to secure the aluminum angle grounding bus and grounding wire.
    One hole drilled into the top of the enclosure for the antenna wire to pass thru.
    Two torroids were wound, one for the coax for common mode and the other for the control cable.

    Now I need to solder a PL-259 on the coax and attach a female molex connector on the control cable.
    Maybe tomorrow night.

    Attached Files:

  7. AA7QQ

    AA7QQ Ham Member QRZ Page

    To secure the chokes, use stubs of PVC pipe, wrap with tape for snug fit if needed.

  8. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    Rubber grommets were placed into the drilled holes in the bottom of the enclosure for the coax and control cable,
    and into the top of the enclosure for the antenna wire pass-thru. Then the grommets were sealed in place.

    Also, photo of the chokes and unterminated cables. I've decided against soldering a male PL-259 on to the coax and
    instead opted to attach a Female UHF connector on the coax end. Since I don't have one, I ordered a female connector
    and will have to wait for that to arrive.

    Attached Files:

    KD6RF likes this.
  9. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    For those that are interested, a photo is attached of the project box that I used and that fits the AH-4 antenna tuner perfectly.
    Antenna wire is measured, cut and terminations installed.

    Attached Files:

    VK2DMH likes this.
  10. EA1DDO

    EA1DDO Ham Member QRZ Page

    Hi George,
    An RF choke is always a very good idea, or even a necessary device.
    Narrowband chokes are easier to build, but wideband are not that easy, mostly because you need a VNA "to see" how much impedance you are getting, and where (frequency) is that impedance located.
    "Ugly balun" style choke are low performance designs.
    I like the high performance well know designs from Jim K9YC or Steve G3TXQ;

    73, Maximo - EA1DDO

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