A signal that may assume either of two polarities, neither of which is zero. Note 1: A bipolar signal may have a two-state non-return-to-zero (NRZ) or a three-state return-to-zero (RZ) binary coding scheme. Note 2: A bipolar signal is usually symmetrical with respect to zero amplitude, i.e., the absolute values of the positive and negative signal states are nominally equal. 2. A pseudoternary signal, conveying binary digits, in which successive "ones" (marks, pulses) are of alternating, positive (+) and negative (-) polarity, equal in amplitude, and in which a "zero" (space, no pulse) is of zero amplitude. Synonym alternate mark inversion signal.