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. KD9WTF

    KD9WTF Ham Member QRZ Page

    George -

    I bought this 1:1 balun for my AH-4 after talking with the owner. In my case I wanted to use my AH-4 with a ladderline fed dipole but honestly below could work for any AH-4 setup. I have my balun placed between my AH-4 and the antenna wire and ground. As in:

    Coax & control lines from shack > AH-4 > AH-4 positive to balun positive, ah-4 ground to balun ground > balun positive to wire antenna / balun negative to ground radials/counterpoise if using vertical, or to second half of dipole.

    Model 1171 - 1:1 ATU Current Balun, 1 - 54 MHz, 5kW
    Model 1171ts - Studs Input & Output

    "Actually the best choice would be the model 1171 installed between the ladder line and your tuner. This will transform the feedline to unbalanced for the tuner and keep common mode out which creates a false match. You can use the 1171tx which has studs for the input and output."
  2. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    I came across several RF choking projects on the internet designed for the Icom AH-4 Antenna Tuner.
    These are methods used by others. I attached a photo for one of them.

    The attached photo shows the coax wound on a ferrite torroid and the control cable wound on a
    second torroid. The sheathing from the control cable was stripped, seemingly to allow more turns
    around the torroid.
    It appears that these torroids will remain inside the AH-4 when the cover is closed, making for a tidy
    weather-tite design.

    Again, the reasons are to eliminate and/or minimize common mode traveling along the coax and
    control cable from the AH-4 tuner back into the shack.

    Thoughts on this design?

    Attached Files:

  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Clever, but somewhat unnecessary to put the chokes inside the housing. Neither the cables nor the cores need weather protection but it does make for a clean looking package. I don't know what core material they used but with 16 or 17 turns that looks to be optimized for 160m/80m use at the expense of common mode choking on higher frequency bands. Check out the chart on Steve's page to get an idea of how many turns you'd want on different core materials to get high choking impedance across your primary bands of interest but generally speaking more turns helps with low frequency choking but the extra distributed capacitance hurts high frequency choking so finding a balance is a good idea:
    VK2DMH likes this.
  4. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    Not sure I'm understanding this chart very well.
    I could go either way with the method of choking. . .

    With either:
    a) The Air-Cored on a 4.25" form, or
    b) A single or a 2-stacked FT240-31 torroid.

    What would be my best scenario as to number of turns to optimize 3.5 MHz to 14 MHz ?
  5. AA7QQ

    AA7QQ Ham Member QRZ Page

    The key part of the chart is the black lines. In those ranges, it is resistive, what you want.
    Looks like 12 turns of RG58 on an FT240-31 core should do just what you want.

  6. WA3MOJ

    WA3MOJ Premium Subscriber QRZ Page

    Ed, thank for the clarification.
    Would that be a single core, or would a double core be more beneficial?
    Just for comparison, how many turns (or feet) for the air cored?

    Also, would more turns increase or decrease the operating frequency?

    Last edited: Oct 14, 2018
  7. AA7QQ

    AA7QQ Ham Member QRZ Page

    The chart is for 1 core, so far as I know. I would think a recalculation for 2 cores would be needed.
    Unless you are running limit, I would think 1 core should work, in this situation.
    More cores are to handle higher amounts of CM. You are coming out of the output of the tuner & should be alright with 1.

  8. WR2E

    WR2E Ham Member QRZ Page

    I didn't see where any of the 'grounding gurus' have chimed in with the question, but maybe I missed it?

    Nothing to do with the choke question, but only FYI.

    The ground rods at the tuner should be bonded to the homes electric service ground rod.
  9. WA7F

    WA7F Premium Subscriber QRZ Page

    The CMC-154-3K common mode chokes have worked well for me. I’ve used them in a few applications including AH-4 tuned Inv-L .
  10. WR2E

    WR2E Ham Member QRZ Page

    What happens when one puts different chokes in series?

    For example, 17T of RG58 on FT240-43 in series with 11T RG58 on 2X FT240-52.

    Would this create a super broad choking impedance? or would they somehow interact with each other and bollix up the whole game?

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