HIGH-SPEED OCEAN CABLE TELEGRAPHY 245 



use a condenser in series with the cable at the sending end and to 

 provide further means for signal shaping at the receiving end. The 

 use of partial sending-end shaping has also been found desirable for 

 the loaded cable though a modified circuit arrangement has been 

 found more effective than the simple sending condenser. 



Within recent years it has become common practice in the operation 

 of cables to employ means for amplifying the received signals prior 

 to relaying or recording them. This has been necessitated by the 

 limited sensitivity of relays and recording instruments. Most of the 

 amplifiers which have proved successful have been instruments of the 

 moving-coil type in which a slight motion of the coil of a D' Arson val 

 galvanometer is caused to control a much larger source of power than 

 that which is required to move the coil. Instruments of this type 

 possess an advantage in that their mechanical inertia and stiffness 

 may be used to assist in the processes of signal shaping and inter- 

 ference elimination. On account of mechanical limitations they are 

 not, however, well adapted to operate at the high speed of the loaded 

 cable. 



Vacuum-tube amplifiers have been used to a limited extent on non- 

 loaded cables and have many advantages over the moving-coil instru- 

 ments, notably in their mechanical ruggedness and in the large amount 

 of amplification which can readily be obtained with them. For use on 

 loaded cables they have a further great advantage in that they have 

 no frequency limitations within the range employed on cables and 

 serve as well for high-speed cables as for low. By the use of suitable 

 electrical networks in connection with the vacuum tubes the signals 

 may be restored in shape, and interfering disturbances outside of the 

 signal range of frequencies may be eliminated. A vacuum-tube 

 amplifier which combines means for amplification, correction of 

 distortion, and elimination of interference has been called a "signal- 

 shaping amplifier." 



With the combination of sending-end shaping network, loaded 

 cable and signal-shaping amplifier, means are provided for conveying 

 signals in the form of combinations of electrical impulses from one 

 terminal to the other. Any type of telegraphic apparatus for con- 

 verting messages into signals and reconverting signals into messages 

 may be applied to complete the steps involved in one-way operation. 

 None of the standard types of cable or land-line apparatus, however, 

 are well adapted to meet the needs of commercial operation at the 

 speed of the fastest loaded cables ; to gain the full advantage permitted 

 by the cable requires apparatus of special design. Special provision 

 is also required to permit two-way operation. 



