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Ten Most-Important EMC Problems/Issues and How to Correct Them:
1. Ground Impedance, Open Slots, and Poor Shielding



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Ground Impedance

The primary cause of most high-frequency (EMC, EMI, RF) issues, whether related to emissions, immunity or self-compatibility are due to high ground return impedance.

  • Wires and traces innately have high impedance. Hence: ground return plane should be used at high frequencies
  • High-frequency effects begin to be noticed around 1 MHz
  • Wire inductance in free space = ~ 20 nH/in.
  • A 1" wire (or trace) has an impedance of 2 * Π * f * l = 12 ohm at 100 MHz

EMI/RF-penetrating “slot” found in a design review (this is the long “channel” under handle)

Shield integrity: An example of poor design


Above: Copper-plated module halves: An attempt to shield this module did not connect halves!

       

This guide was adapted from Agilent by Kenneth Wyatt, DVD, Colorado Springs

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Updated: Sunday, 2008-08-17 14:14 PST