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

    If we feed a 50 Ohm, perfectly balanced, antenna with 1500W we have the possibility of 19W dissipated in a 1000 Ohm resistive choke - that's above the Fair-Rite recommended limit for a single core. If the SWR is worse than 1:1, and/or the load is reactive, that dissipation rapidly escalates.

    That's why Jim Brown and I both recommend shooting for the highest Zcm (and particularly Rcm) you can achieve if you are running QRO. The challenge is not necessarily trying to achieve balance - it's choke dissipation that becomes the limiting factor.

    I'll take the 10,000 Ohms Zcm using two cores (or three), versus 1000 Ohms and one core, any day.

    Steve G3TXQ
    Last edited: Feb 8, 2015
  2. W5DXP

    W5DXP Ham Member QRZ Page

    A quick web search indicates that type K ferrite material is still available in the USA from a number of suppliers as is technical information. Years ago, it was promoted as the be-all/end-all material for HF baluns. Since type 52 material is less expensive, I only mentioned it because the poster said he already had the K material core. A $33 type K balun kit is still available from Amidon.

  3. G3TXQ

    G3TXQ Ham Member QRZ Page


    Have you ever found complex permeability data for the K mix? It would be interesting to compare with the 52 mix.

    Steve G3TXQ
  4. W5DXP

    W5DXP Ham Member QRZ Page

  5. G3TXQ

    G3TXQ Ham Member QRZ Page


    Thanks very much - also for the data sent via PM. Some of that material lists the initial permeability as 1500, so I think it's something quite different.

    If you ever get the time to do an AIM run with one turn or two turns - to avoid the SRF - I could extract u' and u'' directly.

    Steve G3TXQ
  6. W5DXP

    W5DXP Ham Member QRZ Page

    It appears that there exist two different kinds of ferrite materials with the designation 'K' so caution is advised.
  7. W5DXP

    W5DXP Ham Member QRZ Page

    Using my AIM4170D, I just ran some common mode impedance tests with 12 turns of #20 wire on an FT240-K and an FT240-52 and the K material looks good. The K material had an impedance of 2340 ohms on 80m, 4110 ohms on 17m, and 4290 ohms on 10m. The 52 material had an impedance of 1630 ohms on 80m, 3270 ohms on 17m, and 3200 ohms on 10m. Two stacked FT240-K cores with 12 turns of RG-400 coax should make a dandy HF balun slightly superior to the two FT240-52 cores. Of course, the K cores are more expensive than the 52 cores.
  8. G3TXQ

    G3TXQ Ham Member QRZ Page

    With thanks to Cecil for the data, here's a comparison of Rs and Xs for two turns on the respective cores. Using 2 turns allows us to see the underlying material properties without inter-winding capacitance materially affecting things:


    Steve G3TXQ
  9. KC0LWN

    KC0LWN Ham Member QRZ Page

    Thank you for your replies. Techinal support at FairRite wrote me 31 is only used for common mode chokes.
    Yes I am interested in a 4:1 balun and would be interested inother designs.
  10. WA7DU

    WA7DU Ham Member QRZ Page

    I forgot to say thank you. No one deserves it more for your continual participation in these forms. There are a couple of you--you guys are a select and valuable resource.
    K3XQ likes this.
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