The Varioplex System

With a multiplex system, four two-way telegraph channels are made available over one telegraph circuit which may be a single grounded wire of an open-wire line. The transmission is not simultaneous; in fact, use of the wire is shared on an equal time basis by the four two-way channels. If one channel becomes idle for any reason, the time assigned to it is lost, and hence the transmission circuit, or other facility, is not worked to maximum efficiency.

With the varioplex arrangement a number of subchannels are connected through the varioplex equipment to a multiplex system (or to a carrier telegraph system). Each subchannel terminates in printing telegraph equipment. As many as 36 subchannels have been connected through varioplex equipment to one four-channel multiplex system that operates over one grounded transmission line wire.

An operator of a subchannel sends at will. The incoming message signals operate a tape reperforator in the varioplex equipment and temporarily store the message. The varioplex apparatus connects the various subchannels in sequence to the multiplex system, giving each subchannel an opportunity to send a character. However, a "sensing circuit" causes the transmitting sequence equipment to "skip" any subchannel that at the instant has nothing to send, and to transmit immediately from a channel that does have a character to send. In this way, the transmitting speed is increased or decreased to accommodate the number of subchannels that are in operation, and the transmission circuits are loaded to maximum capacity a large percentage of the time.

Varioplex has found wide application in providing printing telemetered telegraph service to customers who have considerable traffic to send, but who could not use a circuit continuously. The subchannel provided to such customers is available to them instantaneously and at all times, and they pay on the basis of the words sent as measured by a telegraph character counter.