HIGH-SPEED OCEAN CABLE TELEGRAPHY 



247 



At the sending end in place of the usual sending condenser there is 

 employed the network Ni shown in the figure. The condenser C« 

 may have a capacity of from 30 to 80 microfarads. It is shunted by 

 a resistance Ri of several thousand ohms. The resistance R^ con- 

 necting the sending end of the cable to earth may be of the order of 

 100 ohms, and serves approximately to equalize the input impedance 

 of the system over the important range of frequencies. The desira- 

 bility of the resistance i?2 is peculiar to the loaded cable and is occa- 

 sioned by the manner in which its characteristic impedance varies 

 with frequency. 



N, 



TO BATTERY 



TRANS 



MITTER 



CABLE 

 CORE 



/BALANCING 

 RESISTANCE 



Fig. 5 — Terminal networks for signal shaping and amplification 



Other sending-end circuit arrangements can, of course, be used and 

 networks combining inductances with capacities and resistances have 

 been effectively employed. The sending-end shaping network may 

 even be dispensed with entirely and all of the shaping done at the 

 receiving end. There are, however, certain conditions under which 

 this leads to the production of distortion due to hysteresis in the 

 magnetic material of the cable and in general it is preferable to reduce 

 the current flowing into the cable by employing sending-end shaping 

 networks which reduce the amplitude of the low-frequency components 

 of the signal. 



The circuits employed at the receiving end for completing the 

 process of signal shaping and for amplifying the signals may con- 

 veniently be considered in three parts, the receiving shaping network 

 Ni, the shielded transformer T, and the amplifier which includes the 

 interstage shaping networks A^3, ^^4 and N^. 



The receiving network N2 provides means for correction of a con- 

 siderable part of the distortion introduced by the cable and in so 



