246 BELL SYSTEM TECHNICAL JOURNAL 



There are two principal ways in which two-way working may be 

 secured: messages may be sent simultaneously in the two directions 

 or the cable may be used alternately in either direction. The first 

 method is commonly called duplex and the second, simplex. Although, 

 as was pointed out earlier in this discussion, the loaded cables which 

 have been laid were designed primarily for simplex operation, it 

 would be entirely possible to operate them duplex; but to do so 

 would require the employment of an artificial line having nearly the 

 same impedance as the cable over the range of frequencies involved 

 in the signals. The speed of duplex operation would, of course, 

 depend on the accuracy with which the artificial line could be made 

 to balance the cable and this would be largely a matter of cost. 

 Simplex operation, if the reversal of direction is made automatic, 

 has much to recommend it over duplex. It does not require an 

 expensive and complicated artificial line which would need frequent 

 readjustment and it permits using the full speed of the cable to the 

 best advantage to accommodate traffic. Means for reversing the 

 direction may readily be associated with means for automatic printing 

 operation and many of the objections to simplex working which are 

 commonly thought of by the cable engineer do not apply when the 

 reversal is thus made automatic. 



Apparatus for the high-speed automatic operation of loaded cables 

 has been described in recent papers by A. M. Curtis and A. A. Clokey. 

 The Curtis paper '^ deals principally with the apparatus for signal 

 shaping and amplification, while the Clokey paper ^ describes the 

 special methods and apparatus for automatic printing telegraph 

 operation. Some of the outstanding features of both classes of 

 apparatus will be discussed in the following sections of the present 

 paper. 



Apparatus for Restoration of Signals 



A typical circuit diagram of a loaded cable with its terminal net- 

 works for signal shaping and amplification is shown in Fig. 5. For 

 the sake of simplicity the circuit details required for two-way operation 

 have been omitted. Such a circuit arrangement applied to a trans- 

 oceanic permalloy-loaded cable serves to connect a telegraph trans- 

 mitting instrument with a receiving or recording instrument for one- 

 way operation nearly as effectively as they could be connected by an 

 overland telegraph line. 



^ "The Application of Vacuum Tube Amplifiers to Submarine Telegraph Cables," 

 B. S. T. J., July 1927. 



" "Automatic Printing Equipment for Long Loaded Submarine Telegraph Cables," 

 B. S. T. J., July 1927. 



