Balanced Line

In telecommunications and professional audio, a balanced line or balanced signal pair is a transmission line consisting of two conductors of the same type, each of which have equal impedances along their lengths and equal impedances to ground and to other circuits. The chief advantage of the balanced line format is good rejection of external noise. Common forms of balanced line are twin-lead, used for radio frequency signals and twisted pair, used for lower frequencies. They are to be contrasted to unbalanced lines, such as coaxial cable, which is designed to have its return conductor connected to ground, or circuits whose return conductor actually is ground. Balanced and unbalanced circuits can be interconnected using a transformer called a balun.

Circuits driving balanced lines must themselves be balanced to maintain the benefits of balance. This may be achieved by differential signaling, transformer coupling or by merely balancing the impedance in each conductor.

Lines carrying symmetrical signals (those with equal but opposite voltages to ground on each leg) are often referred to as balanced, but this is an entirely different meaning. The two conditions are not related.