Quadruplex telegraph
From Wikipedia, the free encyclopedia
The Quadruplex telegraph is a type of electrical telegraph which allows a total of four separate signals to be transmitted and received on a single wire at the same time (two signals in each direction.) Quadruplex telegraphy thus implements a form of multiplexing.
The technology was invented by American inventor Thomas Edison, who sold the rights to Western Union in 1874 for the sum of $10,000.
The problem of sending two signals simultaneously in opposite directions on the same wire had been solved previously by Julius Wilhelm Gintl and improved to commercial viability by J. B. Stearns.
To send two signals in a single direction at the same time, the quadruplex telegraph used one signal to control the polarity of the line, i. e., the direction of current flow imposed upon the wire. The other signal was used to vary the absolute strength or voltage of the signal.[1]
