Ten Most-Important EMC Problems/Issues and How to Correct Them:
5. Stray Internal Coupling Paths and Data lines running under crystal oscillator

Stray Internal Coupling Paths

Above: Stray capacitances between clip and connector can bypass on-board filters.

Solutions:

• Adding external ferrite choke on I/O cable works well
• Use a Faraday shield to disrupt coupling path

Data lines running under a crystal oscillator

Above: Data lines couple 100 MHz (and its harmonics) going through I/O connector to second PCB (printed circuit board) – which, in that area, is referenced to the power plane (with gaps).