High-speed voice-frequency carrier telegraph system

Abstract

NARROW-BAND voice-frequency carrier telegraph systems for the operation of a single teleprinter over each carrier channel have been developed to a high degree of perfection both in this country and abroad. These have been admirably described in technical literature. The theory and basic principles of carrier systems have also been well covered. This paper therefore will confine itself to a working description of a wide-band system developed to meet the requirements of a telegraph plant in which all trunk traffic between large centers is handled by the multiplex telegraph method of operation in which three or four automatic printers are operated over each carrier channel. For those not familiar with telegraph terminology and practices a brief exposition of the differences between single-printer operation and multiplex operation is perhaps in order. The single-printer method of operation secures synchronism between transmitting and receiving machines by means of what is known as the start-stop principle. A start pulse is transmitted by the sending machine preceding each group of five letters-code pulses and a rest pulse follows each group of code pulses. For 65 words per minute maximum printing speed the single-printer method results in a line frequency of 22.75 cycles per second. In the multiplex method of operation synchronism between transmitter and receiver is maintained without recourse to start and rest pulses, resulting in a more favorable ratio between printer words per minute and line signaling frequency. At a printer speed of 66 words per minute, the line frequency by the multiplex method is 16 1/2 cycles per second for each printer or 66 cycles per second on the four-printer circuit commonly used.