A Carrier Telegraph System for 

 Short-Haul Applications 



By J. L. HYSKO, W. T. REA and L. C. ROBERTS 



(Manuscript received May 14, 1952) 



A compact frequency-shift carrier telegraph system is described which pro- 

 vides channels in the voice range and above the voice. The channel ter- 

 minal unit incorporates arrangements for handling TWX supervisory sig- 

 nals and employs no electro-magnetic relays. 



INTRODUCTION 



Most short Bel] System telegraph circuits, particularly those in the 

 less-densely populated areas of the country, have customarily been 

 operated over direct-current facilities obtained by compositing or sim- 

 plexing physical telephone circuits. Many of these extend from a tele- 

 graph repeater in a central office to another arranged as a subscriber set 

 and mounted in the knee-well of the customer's teletypewriter table. 

 Thus, for example, circuits are extended to Teletypewriter Exchange 

 Service (TWX) subscribers located far from the switchboard. The TWX 

 facilities are arranged to handle supervision as well as transmission. 

 The form of supervision is identical to that obtained when local facihties 

 are employed and hence uniform operating procedures are obtained at 

 TWX switchboards for all subscriber stations without regard to their 

 geographical location. 



During and immediately following World War II, the growth of the 

 Bell System's telegraph business resulted in some shortage of dc 

 facilities. It was foreseen that this shortage would be rapidly intensi- 

 fied by the use of new short-haul carrier telephone systems, such as 

 type Nl,^ in providing telephone circuits without adding physical con- 

 ductors. Moreover, many of the existing direct-current facilities would 

 be absorbed to meet signaling needs for the rapid expansion of tele- 

 phone toll dialing. It therefore became evident that carrier telegraph 

 methods must be adopted for relatively shoi't hauls in fringe areas. 



The existing 40C1 voice-frequency carrier telegraph system ' was 



