Edison patentIn 1876, Thomas A. Edison was issued three patents for "Duplex Telegraphs" (U.S. No. 178,221; -3). These were for "an Improvement in Duplex Telegraphs" which enable a transmitted signal be sent on the same wire that could be receiving a signal. In patent 178,222, Edison describes "A balanced battery is used for transmitting when the balance is disturbed. An electromagnet is used, through which both the received and transmitted pulsations pass, and the connections are made so that the action of the current sent is balanced, while that coming from the distant station is operative, to work a balanced relay and local circuit or sounder." |
