416 BELL SYSTEM TECHNICAL JOURNAL 



range of frequencies which extends considerably below the signal fre- 

 quency, so that the resultant interference due to employing a resistance 

 termination for the sea earth conductor will be attenuated to such a 

 degree by the signal correction networks that it will in general have a 

 negligible effect upon the receiving instrument. Moreover, it is prob- 

 able that a considerable amount of low frequency disturbance is picked 

 up beyond the sea earth and the gain obtained by improving the 

 balance for these frequencies would not be very great. 



A practical design for the terminating resistance consists of a length 

 of several hundred feet of stranded wire, approximately 0.05 inch in 

 diameter, of high resistivity material, insulated with gutta percha. 

 After being joined at one end to the sea end of the sea earth core, the 

 insulated conductor is served with jute and laid up with the main core 

 for armoring exactly in the same manner as any other portion of the 

 sea earth core. The free end of the conductor is grounded by connect- 

 ing to the armor wires in the usual manner. A structure of this sort 

 satisfies very completely the requirement of simplicity and lightness, 

 and is as easily maintained as a length of ordinary cable similarly 

 located. 



There is a second characteristic of the loaded type of cable that 

 tends to simplify the problem of the design of a balanced type of sea 

 earth. It has been shown that the portion of the extraneous interfer- 

 ence that it is most desirable to eliminate consists of the components of 



2 M/LL/VOLTS 



O. f SfCO/v^ 



frequencies in the neighborhood of the signal frequency. Since the 

 operating speed of a loaded caljle is five to ten times that of the cor- 

 responding non-loaded cable, it is evident from the preceding discussion 

 that in order to effect a given reduction of interference in any particular 

 locality, the sea earth of the loaded cable can be located closer to shore 

 and in sliallower water than in the case of the non-loaded cable. 



In the case of the New Vork-Azores cal)le the balanced type of sea 

 earth has been very effective in reducing extraneous interference. 

 Fig. 7 is an oscillographic record of tiie terminal interference between 



