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Discussion in 'Home Brew' started by unit_399, Feb 1, 2012.

  1. unit_399

    unit_399 EL CAPO

    Jun 17, 2008
    Likes Received:
    How can you determine the permeability of a ferrite toroid core? I want to construct a 2:1 current balun. I have a box full of toroids, but have no idea of their permeability. They are various colors, mostly red, yellow, or blue.
    Anyway, is the core material that important in a balun, or will any core that will handle the wire size and # of turns I need suffice? There is a lot of info online about baluns, but none I've found talks about how permeability affects balun performance. I want to use this on my 2 element quad to replace the RG11 stub match I'm using now. I never exceed 300w pep on my rig, and will be using #12 enameled magnet wire for the windings.
    Any help and suggestions will be greatly appreciated. 73s

    - 399


  2. RatsoW8

    RatsoW8 Supporting Member, W9WDX ARC Member - WD8T

    Nov 3, 2009
    Likes Received:
    I'm pretty sure this is determined by manufacturer specs based on the core materials used. If you know the manufacturer and part/model number of the cores you may be able to find the data sheets on the cores.

    Otherwise you need a piece of equipment most of us don't have on the bench. If I were you I'd just start building and see how they work.
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
    Staff Member

    Apr 6, 2005
    Likes Received:
    The colour determines the mix and the mix determines the useful frequency range. Click on the link and scroll to the bottom for info regarding color and frequency range of the various mixes.

    Micrometals, Inc. - Power Cores
  4. KC9Q

    KC9Q Supporting Member

    Jan 14, 2012
    Likes Received:
    The cores you are describing are Iron Powder cores, which will work fine for your low power application. Higher power devices would work better with ferrite cores, which are all dark gray in color. It would be best to know the permeability from the manufacturer. Here is a hint to determine a cores permeability: Equation for Permeability of an electromagnetic core.

    Here is the Palomar Engineering and the Amidon pages to help you determine the values of the Iron cores you have.

    Amidon: https://www.amidoncorp.com/pages/specifications
    Palomar: Iron Powder

    I hope this helps.

    1 person likes this.
  5. rodham

    rodham Member

    Feb 6, 2012
    Likes Received:

    The way I determine permeability (mu) is to kinda back into it. I take the unknown core and wind 10 turns of wire onto it and measure its inductance with a LCR meter. Then I determine its value A (uH per 100 turns) from the formula: A = L x 10000/N(squared), where L = measured inductance for N turns.

    Example: for a given FT-50 toroid with 10 turns, I measure 5.9uH. A = 59000/100 = 590. Looking up specs for FT-50 ferrites, I find that FT-50-43 has a nominal A = 520 with mu = 850. This apparently is a FT-50-43.

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