New tool - toroidal ferrite core inductor calculator

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by SP3L, Jun 14, 2021.

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  1. SP3L

    SP3L Ham Member QRZ Page

    After writing an article for the QEX Magazine: “Designing Antenna Systems for Low Common Mode Current in Coaxial Feed Lines” (this article should be published in the July-August issue if not postponed again), I realized that there was a need for a calculator that could enable you to calculate the common-mode impedance of an RF choke (a.k.a. 1:1 balun or “line isolator”).

    Thanks to the effort of a few fellow hams, we have got some web resources showing the measurement results of such chokes. I used in the article the measurement results published by K9YC ( and GM3SEK ( Especially the publication of K9YC contains a lot of information. But the number of possible chokes designs is large and K9YC could not build and measure all of them. And I wanted to be able to find impedances of the chokes wound on various core types and having various turn numbers. That’s the origin of the calculator.

    From the very beginning, I realized that I could do myself only a very basic calculator based on the MS Excel spreadsheet. Something of very limited possibilities and not very easy to use. Fortunately, I know Dan, AC6LA, who is an indisputable Guru of Excel and Visual Basic. Who does not know the AutoEZ, Zplots, TLDetails or Moxon Rectangle Generator to name but a few of his software tools? When I asked him, Dan immediately agreed to team up with me and, after a few of weeks, we managed to create the calculator.

    The calculator enables you to plot |Z| vs. frequency and R vs. frequency for up to three different choke designs on the same chart.



    You can also find the choke common-mode impedance for any single frequency of interest.


    But that’s not all. The calculator enables you to find an equivalent circuit of the choke in the form of either one parallel RLC circuit or two parallel RLC circuits connected in series. Such equivalent circuit differs slightly from the calculated impedance but is very convenient to use when you want to model the choke in the antenna simulation programs like AutoEZ+EZNEC, 4nec2 or MMANA. Such model is valid for a very wide frequency band.



    You can find more info about modeling common-mode chokes in my article.

    On top of that, the calculator enables you to find an equivalent circuit of the real choke if you enter its measurement results in the workbook or paste the picture showing its |Z| vs frequency plot.

    I cannot present all the calculator details here (its help file is 13 pages long). Just follow this link

    and download your copy of the calculator and its help file.

    WA7ARK, N3RYB, KM1NDY and 5 others like this.
  2. W9IQ

    W9IQ Ham Member QRZ Page

    It sounds very interesting but unfortunately, your download link seems to not be working. It reports 'file is in owner's trash'.

    - Glenn W9IQ
    K0UO likes this.
  3. NK7Z

    NK7Z Ham Member QRZ Page

    Same here...
    K0UO likes this.
  4. SP3L

    SP3L Ham Member QRZ Page

    I am sorry. The file syncing was off. Try it now, please.
  5. W9IQ

    W9IQ Ham Member QRZ Page

    Thank you - it works now.

    - Glenn W9IQ
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    Will not work with Excel2003, which is what I use with AutoEz. Can .XLSM be converted to .XLS?
  7. SP3L

    SP3L Ham Member QRZ Page

    Well, I saved the calculator in the XLS format but most likely some of its functions will not work in Excel 2003. Before Dan explains what and why can not work, you may try it yourself.

    [attachment has errors - removed by moderator]
    Last edited by a moderator: Jun 17, 2021
  8. AC6LA

    AC6LA Ham Member QRZ Page


    The color backgrounds and some of the chart formatting will be incorrect with Excel 2003 and earlier. Also, clicking on many of the buttons and check boxes will cause a run-time error 438. It might be possible to come up with workarounds for some of those problems; I'll look into it.

    In the meantime, you should be able to use the *.xls file that Jacek posted above (after doing "enable content" and "enable macros"), but if you get any kind of error just click "End" and continue.

    Dan, AC6LA
    Last edited: Jun 14, 2021
  9. W4KJG

    W4KJG Subscriber QRZ Page

    Jacek -- Dziękuję.
    Dan -- a big thank you too.

    As soon as I read this post I downloaded the file from

    I've only played with it for a few minutes. But just the comparison table between Fair-Rite, Amidon and Feroxcube is invaluable.

    It seems to work with the spreadsheet programs in Open Office 4.1.7 and Libre Office Version: (x64). I haven't yet tried it with Google Sheets.

    I've been doing much of what is in your spread sheet by trial and error, Google searches, old book referencing, and using G3TXQ's (SK) old website. I've mostly been doing it with pencil paper in my Antenna-Related notebook.

    For the last couple of months, when the weather has been agreeable, I've been doing QRP-to-100 watt core testing for 9:1 and 49:1 ununs for a variety of end fed multi-band wire and vertical pole antennas. Your calculator should be very helpful.

    Ken Gry(z)mala
    (My family is from near Bialystok on the opposite side of Poland )
  10. SV1IYF

    SV1IYF Ham Member QRZ Page

    Thanks to both of you for a very useful piece of software!
    The popular wisdom has it that better is the enemy of good. Where does this fit in here?
    All the baluns I have constructed lately are implemented on two stacked torroids of different materials, like 43 and 61.
    Is there a possibility that you include such a combo in the relevant selection?

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