Tech Notes

EMI Filter Selection Guide

  1. Determine whether system 1, looking into the filter is of high or low impedance at the frequency of interest. Choose the filter with the opposite (inverse) impedance: i.e., if the system is high impedance, the filter should be low impedance; if the system is low impedance, the filter should be high impedance.
  2. Do the same for the opposite side of the filter (System 2).

See The Chart Below

  • Power lines should be considered low impedance.
  • When performing EMC Testing such as in MIL-STD-461, a 10µƒ capacitor is specified in the line. (a low impedance) Therefore, a filter of high impedance should be used, such as in 'L' (with the inductor toward the 10µƒ capacitor), or at 'T'.

Insertion loss data is normally provided in a 50 OHM System. TSE has the computer capability to design your real impedances and convert to a 50 OHM System for your QA Testing.

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