CABLE DESIGN AND MANUFACTURE 



215 



20 



40 60 80 100 120 140 



FREQUENCY IN KILOCYCLES PER SECOND 



160 



180 



Fig. 14 — ■ Laying effect or deviation of measured attenuation from predicted 

 attenuation as a function of frequency, as observed in Gibraltar trials. 



between measured values of attenuation at the ocean bottom and values 

 predicted from factory measurements. It was further established that 

 the difference in 2,300 fathoms was about twice that in 300 fathoms. 

 The measured differences are shown in Fig. 14. 



It was established during these trials that the difference increased 

 slightly with time. Measurements made on the cable in 300 fathoms 

 immediately, 18 hours, 48 hours, and 86 hours after laying indicated 

 that measurable changes in attenuation were taking place. However, 

 the change between 48 and 86 hours was so small that it was concluded 

 only very small changes would occur in a moderate interval of time. 

 The tests also indicated that the attenuation of the two lengths of cable 

 decreased somewhat during loading of the cable ship. 



The total difference between the attenuation at the ocean bottom and 

 the values predicted from factory measurements, taking the temperature 

 and pressure coefficients into account, was designated "laying effect". 

 Various theories, such as the consolidation of the central conductor, 

 consolidation of retvu'n structure, and changes in the dielectric material 

 have been advanced to explain these differences. Each of these has been 

 under study, but at the time of writing this paper, no conclusive ex- 

 planation has been established. 



The shape of the "laying effect" versus frequency characteristic was 

 such that the adjustment of repeater section lengths in conjunction with 

 several fixed equalizers, which had approximately 4 db loss at 160 kc and 

 0.6 db loss at 100 kc, would provide a good system characteristic. The 

 matter of equalization is covered in greater detail in the article^ on the 

 overall system. The magnitude of the laying effect observed during the 

 laying of the two transatlantic cables substantiated the trial results. 



