multiplexer(redirected from Demultiplexor)
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in telegraphy, a switching device that is used to reduce the number of telegraph transmitters in a telegraph office as compared with the number of incoming communication lines. A distinction is made between manual and automatic multiplexers. They are used on lightly loaded lines, where the daily traffic does not exceed 30-80 telegrams.
The main element of a multiplexer is a switch, whose handle may be set in three positions: the horizontal (off) position; the upper position, which connects one telegraph transmitter to a communications line; and the lower position, which connects the other telegraph transmitter. The number of switches in a multiplexer is equal to the number of communications lines. Each switch is connected to its own communications lines, and all switches are connected to two telegraph transmitter stations for receiving and transmitting telegrams through the lines.
Upon receiving a call signal from the city communications office, the telegraph operator moves the handle of the switch located under the lighted signal to, for example, the upper position (thus connecting the first of two telegraph transmitter stations). If a call is received from another city communications office while the first transmitter station is still in operation, the telegraph operator moves the handle of the appropriate switch to lower position, thus connecting the second station. After completion of transmission or reception of a telegram the switches of the multiplexer are moved to the horizontal position.
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