Using Ferrite to eliminate Interferences & Noises

Discussion in 'Wireless & RF Design' started by NiCeBoY, Mar 23, 2012.

  1. NiCeBoY

    Thread Starter Active Member

    Aug 20, 2008
    I want to apply a ferrite to the bundle + and – line.
    Maximum load current is about 3Amps at 24V DC.

    I can use both tubular or clamp-on but would like to use the best one. Which one will you recommend? The diameter of the cable is 5.7mm.

    We want to add ferrite on Ethernet, serial and usb cable as well. What will you recommend. All the cable sizes are 5.7mm in diameter. Only the Ethernet cable is 7.6mm in diameter.

    For the frequencies, Please read below :

    We have performed a radiated emissions test requipment. Significant high radiated disturbances have been measured that exceed the Class A limit. Highest measured disturbances were (in vertical polarisation):
    166.5MHz 13.6dB above Class A limit
    99.6MHz 8.5dB above
    40.9MHz 4.1dB above (broadband)
    232.3MHz 3.6dB above
    199.2MHz 2.1dB above (broadband)
    53.0MHz 2.0dB above (broadband)
    117.8MHz 1.3dB above (broadband)
    33.3MHz 1.0dB above
    107.0MHz 0.8dB above (broadband)
    Broadband disturbances would be attributed to switching circuits (eg power supplies), narrowband with clock frequencies. Measurements were made with the AdaptMAC powered from a 24V linear power supply and with the MOXA box switched off.
    Emissions do reduce when cables are disconnected from the equipment. However, with all cables removed except power. disturbances were still seen above the Class A limit, especially 166MHz. A ferrite with 2 turns on the power cable dropped this emission further but 232MHz was still just on the limit.

    Can anyone recommend me anything from the website?

  2. K7GUH


    Jan 28, 2011
    I don't think ferrites will eliminate all the noise and fluctuations in any environment, but they will reduce the garbage to a tolerable level for most applications. Personally, I like the clamp on ferrites -- they are easy to apply and not prohibitively expensive. And they come in almost any size for common cables. If one ferrite doesn't reduce the garbage level enough, try two, then three, and so on until you reach the point of diminishing returns.