Importance About Noise (Signal Interference)

Written by Julianus Yu

Controlling noise is of major importance to cable and connector designers because uncontrolled noise will overwhelm the data signal and bring a network to its knees. Twisted-pair cables utilize balanced signal transmission. The signal traveling on one conductor of a pair should have essentially the same path as the signal traveling the opposite direction on the other conductor.

Resistance unbalance occurs when the dimensions of the two conductors of the pair are not identical. Mismatched conductors, poorly manufactured conductors, or one conductor that got stretched during installation will result in resistance unbalance. Capacitance unbalance is also related to dimensions, but to the insulation surrounding the conductor. If the insulation is thicker on one conductor than on the other, then capacitance unbalance occurs.

You’ve likely experienced crosstalk on a telephone. When you hear another’s conversation through the telephone, that is crosstalk. Crosstalk occurs when some of the signal being transmitted on one pair leaks over to another pair. The more the conductors are parallel, the worse this phenomena is, and the higher the frequency, the more likely crosstalk will happen. In general, the shorter the twist intervals, the better the cancellation and the less crosstalk. That’s why Category 5 and higher cables are characterized by their very short twist intervals.