Bipolar Telegraphy

a method of direct-current telegraphy in which current sent along the communication line in one direction or polarity (for example, plus) is followed by current sent in the opposite direction (minus).

In bipolar telegraphy polarized relays are used as high-sensitivity receivers. In comparison with unipolar telegraphy, the bipolar method has the advantages of higher speed of transmission for steel conductors, less distortion of signals in telegrams (since the bipolar method is less subject to electrical interference from nearby conductors), and diminished influence of current leakage in inclement weather (from the conductor through insulators and telegraph poles to the ground) on the stability of communication.