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I need to place some filtering on the IO lines of a DC powered device. The RF noise is induced or conducted into the chassis of the equipment and also into the interconnecting cables. The frequencies can be anywhere from 10Hz to 8 GHz. (basically DO-160G standard)

The question for me is, how should I connect a filtering capacitor to the I/O line. Should it be connected to the chassis of the device or to the power input return?

The power return can be connected to shield somewhere along the cable, but also may not.

enter image description here

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  • \$\begingroup\$ The shield is shown around all connections. I don't see a problem here. Is the shield poorly bonded to Device? \$\endgroup\$
    – Tim Williams
    Sep 14, 2022 at 16:46
  • \$\begingroup\$ In DO-160 there are tests where 30 mA interference current in wires must be achieved no mater what. But There is no previous experience with those tests, its kinda hard to predict what will happen, so I want to implement some countermeasures to be sure. \$\endgroup\$
    – tarmogr
    Sep 14, 2022 at 18:05
  • \$\begingroup\$ Cables yes, individual wires no \$\endgroup\$
    – Tim Williams
    Sep 14, 2022 at 18:50
  • \$\begingroup\$ Im still interested in answer, which way would be the correct way and why. \$\endgroup\$
    – tarmogr
    Sep 15, 2022 at 5:01
  • \$\begingroup\$ You haven't given motivation for why this filter component should be connected in the first place, let alone how it's connected, what value, or any other details. Remember that EMC is a very holistic subject: reductive questions lead to irrelevant or wrong answers, and general questions lead to elaborate (literally book-sized) answers. You may find it is easier to get answers for a particular, highly detailed situation. In short, please provide more detail surrounding your system arrangement, types of signals, which test and at what level, etc. \$\endgroup\$
    – Tim Williams
    Sep 15, 2022 at 5:51

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