EMI Filter

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  • 12-15-2003, 10:33 PM
    iceblue8
    EMI Filter
    Hello,

    I have a question regarding EMI filters. You know, one of those plastic clamps that you put on your cables. Do they really work? If so, how does clamping a piece of plastic helps remove electromagnetic noise (if that's what EMI stands for)? Sorry if this sounds silly to some of you. But I'm trying to justify the costs of paying lots for those plastic clamps on those Transparent or MIT interconnects. I have just been wondering what those things are for. Any input would be appreciated. Thanks.
  • 12-16-2003, 07:23 AM
    FLZapped
    Quote:

    Originally Posted by iceblue8
    Hello,

    I have a question regarding EMI filters. You know, one of those plastic clamps that you put on your cables. Do they really work? If so, how does clamping a piece of plastic helps remove electromagnetic noise (if that's what EMI stands for)? Sorry if this sounds silly to some of you. But I'm trying to justify the costs of paying lots for those plastic clamps on those Transparent or MIT interconnects. I have just been wondering what those things are for. Any input would be appreciated. Thanks.

    EMI=Electromagnetic Interference.

    Those clamp on devices shouldn't be all plastic, they should have a ferrite material in them. Yes, they do work, if the frequencies you want to supress are high enough. They also have to be placed as close to the source, or load - depending on whether you're trying to stop something from getting out, or in, respectively. They should also fit the wire snugly.

    Now, are you saying you have an interference problem that you've actually identified?

    -Bruce
  • 12-27-2003, 04:43 PM
    robinc
    emi interference ?
    I was wondering about these , since I moved all my equipmentaorund I am getting more video interference on low end channels through the cable box and in fact even channel2-7 is a bit messy- our family room is very close to the kitchen - would this constitute emi interference- would these little clamps work on the cable and or s video or audio cables?
    or is this a whole different thing?- are there real examples somewhere of what emi interference might look or sound like?
    thanks in advance
    RobinC
  • 12-27-2003, 06:32 PM
    E-Stat
    Quote:

    Originally Posted by robinc
    I would this constitute emi interference- would these little clamps work on the cable and or s video or audio cables?
    or is this a whole different thing?- are there real examples somewhere of what emi interference might look or sound like?

    That does sound like EMI / RFI interference. I would begin by ensuring that power and signal cables do not come in close contact. While I've seen many a cable that contains a ferrite trap (like my Digital camera USB cable), I am not aware of clamps that you can attach to existing cables. For my main HT system, I use a Monster conditioner for both signal and power that cleans up both the audio and video a bit. Sonically, quieter. Visually, darker.

    Sonically, EMI interference tends to be more subtle. It creates a fog that obscures musical detail. Consequently, the very best cables I've heard at first tend to sound dark. Not because of capacitive frequency rolloff found in some designs, but for a lack of high frequency grunge. More real high frequency content comes through.

    rw
  • 12-28-2003, 08:32 AM
    skeptic
    EMI (rf) interference is very hard to pin down. Without suitable test equipment, it's hard to know the source and if it is intermittent, it's hard to know whether you have really gotten rid of it or if it wouldn't have been present at the time you no longer notice it anyway. It is also very unpredictable.

    I had an interesting situation once where a contractor had installed some new smoke detector heads in a laboratory building by extending existing runs down corridors and the smoke alarm panels were experiencing nuissance alarms but not strong alarms, intermittant flashing of their indicator lamps and momentary periodic alarm relay closures. Upon investigation, I found out that the contractor had wirenutted solid wire from his new runs to stranded wire from the existing runs. I guessed that the unshielded wire was acting as an antenna for lots of RF noise in that building and that the junction between the new and old wires were acting as detector diodes. Adding small capacitors, probably about 0.5 mf (I can't remember, it's been about 12 years since) cured the problem by shunting out the input on the alarm panel.

    Don't try to cure RF problems if you don't have any. (Don't fix it if it ain't broke.) Try moving your wires around or re-routing them. Sometimes direct coupling of rf between wires or a wire an electronic box is cured by moving wires around by a few feet or even inches. Try covering wires you suspect of being affected with aluminimum foil and run a thin bare copper wire under or around it which you ground to the amplifier or preamplifier chasis. (I do this with all of my phono coax.) You can try a small value capacitor across a high level input but don't put it across your speakers. You could damage your amplifier. It is not necessary to buy expensive ferrite rings, cheap ones work just as well. Never put ferrite rings on a power cord, especially the ground. If you suspect an rf problem coming through the power line, use a UL listed filter designed specifically for this purpose, DIY projects for this problem are sometimes very dangerous. Replacement power cords are probably less satisfactory and much more expensive.