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

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