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7$ 1:1 Balun Common mode choke

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by S21RC, Jun 10, 2021.

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  1. S21RC

    S21RC Ham Member QRZ Page

    Hello all,
    I have bought two unit 1:1 Balun from aliexpress, and seems the design is faulty. The core is a 1" OD core (I haven't measured the inductance yet to find what kind of core it is - similar other item says NX-100).

    It has 4 turn of trifiller winding with thin magnet wire as like the picture- I am skeptical if it will work in this configuration. I might user the enclosure to make a new common mode choke for vertical GP and simple dipole antennas.

    My questions are:

    1. Does the winding (as in drawing) is wrong?
    2. Can I use a Yellow T80-6 core (which I have) and do 10 turns bifiller winding using #20 magnet wire for 100W SSB?
    3. Instead of magnet wire, does twin clear speaker cable will be better?

    Thanks in advance, 73, S21RC cmc1.jpg cmc.jpg
  2. KU3X

    KU3X Ham Member QRZ Page

    Look like a very poorly designed balun. I would not even qualify it as a balun.
    Your T80-6 is a powered iron core, not usable as a current balun.
    Want to make a small balun? Use an FT 140-43 core.
    With that I would use some RG 316 coax.
    What I just suggested is a starting point.
    A really good 1 to 1 current balun uses an FT 240-31 or 43 core. Next wrap 12 to 14 turns of RG 400, RG 142 or RG 303 coax around the core. This is a very good balun to cover the HF bands.
    AK5B, S21RC, K0UO and 1 other person like this.
  3. K1SZO

    K1SZO XML Subscriber QRZ Page

    Looks like a hackjob to me.

    EDIT: Here is a detailed link explaining how I made mine from a previous QRZ post. Though mine is capable of high power as I built it with that in mind.

    They are pretty simple to make if you're up for it. Otherwise, I would buy from a reputable seller rather than Aliexpress.

    Good luck,
    Dave ~ K1SZO
    Last edited: Jun 10, 2021
    KN4ULD, AK5B, S21RC and 5 others like this.
  4. VA3RR

    VA3RR Ham Member QRZ Page

    That ferrite core looks very much like two I obtained from Aliexpress. The vendor advertised them as being the same size as the Jaycar LO1238, which is popular in VK. So I ordered them on a whim...

    When the cores arrived in the post, they were 31mm in diameter, so Aliexpress refunded my money, and I got to keep the ferrite cores!

    Incidentally, the LO1238 cores are somewhere between #43 and #31, so good for HF common mode chokes.
    S21RC and K1SZO like this.
  5. S21RC

    S21RC Ham Member QRZ Page

    Thanks Barry. I used 6" PVC wrapped ugly balun for some time years (2010) ago with my beam (I miss my antenna - new place do not allow such monster)
    ugly balun.JPG

    Now building an STL and for that I have already got the nice choke. Waiting for the vacuum variable which is shipped some weeks ago.

    ** The cheap balun from aliexpress is just to see if it can be used for something, guess only the connectors are salvageable :(

    Thanks, 73' S21RC
    US7IGN likes this.
  6. WA9PND

    WA9PND XML Subscriber QRZ Page


    That's not even 1:1, that's 9:1.

    For 80-10m, 12-15T RG316 on FT140-31 core should make a nice Guanella (current) choke for you.

    Below is a composite balun (1:1 Guanella followed by a 4:1 Ruthroff) for an 40/20/15/10/6m OCFD. 1:1 Guanella (lower) is 15T RG316 on an FT140-43 core, and the 4:1 Ruthroff (upper) is 12T bifilar on a ft14-61 core.
    SM0GLD, S21RC and WA7ARK like this.
  7. VK4FUQ

    VK4FUQ Ham Member QRZ Page

    G'day all, which balun connects to the feedline, the 1:1 choke balun or the 4:1 voltage balun? Regards, Felix vk4fuq.
  8. WA9PND

    WA9PND XML Subscriber QRZ Page

    On my picture, the transmitter is coming in from the bottom to the 1:1 Guanella, and the OCFD antenna is connected on top to the secondary of the Ruthroff. Screenshot 2021-06-11 155424.jpg
    Extra Guanella choke at the entry to the house to kill any remaining common mode current.
  9. VK4FUQ

    VK4FUQ Ham Member QRZ Page

    G'day mate, that is interesting as opinions vary on this withe some preferring the opposite configuration. In my versions the 1:1 choke balun feeds the antenna feedline. Regards, Felix vk4fuq.
  10. WA9PND

    WA9PND XML Subscriber QRZ Page

    I understand it works the same either way. I just find it easier to build a choke at 50 ohms than at 200 ohms.
    S21RC likes this.

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