Ferrite for baluns

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC0LWN, Feb 8, 2015.

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  1. G3TXQ

    G3TXQ Ham Member QRZ Page

    Don't be misled by that comment; many baluns - including some 4:1 current baluns - are formed from interconnected common-mode chokes.

    I've been working on a paper that illustrates exactly that point - it analyses balun operation by treating them as combinations of ideal common-mode chokes. It's still very much an early draft, but I've just uploaded it here if anyone is interested:
    http://www.karinya.net/g3txq/baluns/baluns.pdf

    Section D describes the 4:1 Guanella current balun, Section E demonstrates why it can't be wound on a single core, and Section F describes a 4:1 hybrid balun attributable to ZS1AN that is preferable to the 4:1 Guanella where the load is asymmetrical - for example an OCFD.

    Section G shows a 4:1 current balun wound on a single core; it's a conventional transformer rather than a transmission line balun and therefore has more limited bandwidth, but it has some attractive features.

    The paper needs a bit more work; then I'll make it directly available on my web site.

    Steve G3TXQ
     
  2. N0FN

    N0FN Ham Member QRZ Page

    This is the best explanation of how and why these baluns actually work that I have ever seen. Lots of sources say "just do the analysis" but your use of the three simple properties is what makes the analysis doable! Section E where you destroy the myth of the single-core 4:1 current balun will hopefully put that design to rest once and for all.

    I would like to see more discussion of where departures from ideality create advantages and disadvantages for the different designs. Like where you discuss phase differences between the two windings: "The phase
    difference increases with frequency and limits the SWR bandwidth of this type of choke". It seems like the analysis in terms of ideal chokes and the various currents and voltages could serve as a useful base case for departures from ideality. Thanks for this great resource!

    -Neil N0FN
     
  3. G3TXQ

    G3TXQ Ham Member QRZ Page

    I'm not holding my breath - but thanks for the kind comments! Thanks too for the suggestions for further material.

    Steve G3TXQ
     
  4. KC0LWN

    KC0LWN Ham Member QRZ Page


    Thank you so kindly. I will make a hybrid design from 31 material. I will be using a windom antenna so it is perfect or my needs. This discussion has been a real eye opener for me an an education.
    Most of all I think I sked an intelligent question that got some responces. (joke)
     
  5. KC0LWN

    KC0LWN Ham Member QRZ Page

    UPDATE

    I did some research on ferrite. 77, 73, and 31 mix are not for transmitting because of their high resistive nature and low curie values. The alloy is manganese zinc. They make good receiving only baluns. Also fantastic for choe use.

    43, 61, 67, K and 52 mixes have high curie values and are low resistance and are nickel zinc alloyed.
     
  6. G3TXQ

    G3TXQ Ham Member QRZ Page

    The "resistive nature" as you call it is one of the attractive attributes we look for in material for a transmitting balun; that's why Type 31 is a popular choice for the low HF bands. The balun's high resistance ensures that we always have high Zcm whatever the impedance of the other CM path components. More details here:
    http://www.karinya.net/g3txq/chokes/#inductive_chokes

    The design challenge is to ensure that we have sufficient balun CM impedance that the residual CM current flowing through it is small enough not cause excessive heating.

    Steve G3TXQ
     
  7. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    Steve,
    I think the low resistance is in reference to the volume resistivity where the material can conduct significant DC current. I had an issue when a recipe went wrong. Luckily we were able to sort the good from the bad with and ohmmeter:). Otherwise they looked the same usual dull gray. Along with the lower volume resistivity the eddy current losses became very high causing the cores to dramatically heat up. Another physical thing about ferrite is how they absorb ink from a marking pen. While sorting samples I tried to mark them and the ink soaked right in. I now use a paint based marking pen and have to let the first application dry sometimes to get a good permanent mark. I guess the organic binder that burns out during the sintering and leaves the material porous and also causes them to shrink by 10 or 15%.
    73
    Pete
    WB2UAQ
     
  8. N8CBX

    N8CBX Ham Member QRZ Page

  9. W5DXP

    W5DXP Ham Member QRZ Page

    FT-240-K is an excellent mixture and two of them stacked would be about as good as it gets for HF.
     
  10. W0BTU

    W0BTU Ham Member QRZ Page

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