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  • Bruce Sparrow
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    July 3, 2018 at 5:10 pm
    Post count: 24
    #25782

    I received a letter asking me how someone can select a device without buying several and trying them. An open-ended question, for sure. Here is my response:

    Fair-Rite sells all types of EMI suppression devices for all kinds of applications. Your question is opened ended so I do not know exactly where to go with it. Ham Radio can be from 7MHz up – I’ll assume you are talking 10 Meter.
    1.) Knowing the frequency of interest is the start. You select a material based on that. For 10M our 31 material is great.
    2.) What do you want to do? Are you trying to suppress radiated noise or noise that is picked up on near by devices? This will tell you where you need to put a suppression device.
    3.) What level of attenuation is required? This one is hard because you need lots of numbers to crunch the math that are just difficult to get. Input impedance, output impedance, starting amplitude, ending amplitude.
    4.) What type of device is appropriate? Beads on wire? Clam Shell (Snap Its), solid core, SMD component?
    5.) Find a device that is suitable knowing that you may need more than 1 or multiple turns through a core to get suitable results.
    This can be distilled to 2 major issues: What material to use and what level of attenuation is needed. The first one is to use our 31 material. The second question is something that drives us to experiment. Can’t afford to fail? Get the part with the highest impedance and a big cable opening so you can wrap the wire through it a few times.
    Greatly simplified… yes. But its realistic.

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