Polarential telegraph system

A polarential telegraph system is a direct-current telegraph system employing polar transmission in one direction and a form of differential duplex transmission in the other. [cite book|title=IEEE Standard Dictionary of Electrical and Electronics Terms|author=Frank Jay|year=1977|pages=501|quote=A direct-current telegraph system employing polar transmission in one direction and a form of differential duplex...|url=http://books.google.com/books?id=U-tSAAAAMAAJ]

Two types of polarential systems, known as types A and B, are in use. In half-duplex operation of a type A polarential system, the direct-current balance is independent of line resistance. In half-duplex operation of a type B polarential system, the direct current is substantially independent of the line leakage. Type A is better for cable loops where leakage is negligible but resistance varies with temperature. Type B is considered better for open wire where variable line leakage is frequent.

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