Reducing high frequency conducted noise

This paper investigates the effectiveness of commercial AC power electromagnetic interference (EMI) filters, RF bulkheads, toroids, and ferrite beads in reducing common mode conducted noise. At frequencies below 30 MHz, commercial and military specifications only provide for conducted noise limits, which indirectly causes an increase in environment noise when the noise is radiated by long power or data lines. The author concentrated on investigating techniques for reducing conducted noise so that noise from industrial or "Class A" devices can be reduced to meet the more benign, residential or "Class B" limits. Techniques include what is known as "barrier-filter-ground" or BFG technique, and loop impedance modification technique. Results indicate that the BFG technique is effective at HF when AC power filters and cable shields are used in conjunction with Faraday shields. For the impedance modification technique, toroids are more effective than ferrite beads below 30 MHz.