Common-Mode to Differential-Mode Conver- sion in Shielded Twisted-Pair Cables (Shield-Current-Induced Noise)

Neil Muncy [1] has shown that audio frequency current flowing on the shield of twisted-pair audio wiring will be converted to differential mode voltage by any imbalance in the transfer impedance of the cable. He hypothesized that the effect is magnified by the presence of a drain wire and increases linearly with frequency. Whitlock [2] and others have shown that conversion also occurs with capacitive imbalance. This paper confirms Muncy's hypotheses and shows that shield-current-induced noise is significant well into the MHz range.