46 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



type, each block junction was located at approximately mid-repeater 

 section to minimize the effects of reflections between equalizer and cable 

 impedances. 



The actual adjustments at block junctions were determined by a series 

 of transmission measurements during laj'ing, as described in the com- 

 panion paper on cable laying.^ Six equalizers were used at block junctions 

 in the 1955 (No. 1) cable, and eight in the 1956 (No. 2) cable. 



The result of all the precautions taken to control initial misalignment 

 was, in the 1955 cable, to hold the initial level difference between highest 

 and lowest-level repeaters to about 6 db near the top frequency and to 

 values between 4 and 9 db at lower frequencies, the 9 db value occurring 

 in the range 50 to 70 kc where there is noise margin. In the 1956 cable, 

 the level difference was about 4 db at the top freciuency, and from 2 to 

 7 db elsewhere in the band. 



Shore Equalization 



The equalization to be provided at the transmitting and receiving ends 

 of the North Atlantic link had these primary functions: 



1. For signal to noise reasons, to provide a signal level approximately 

 flat with frequency on the grid of the third tube of the undersea repeaters. 



2. To equalize the system so that the received signal level is approxi- 

 mately constant over the transmitted band. 



3. To keep the system net loss flat, regardless of temperature varia- 

 tions in the ocean. (A change of 1° F in sea-bottom temperature would 

 cause the cable loss to change by 2.8 db at 160 kc and less than this at 

 lower frequencies. The amplifiers are relatively unaffected by small 

 temperature changes.) 



4. To provide overload protection for the highest level repeater. 



5. To incorporate some adjustment against possible cable aging. 



20 



40 60 80 100 120 140 



FREQUENCY IN KILOCYCLES PER SECOND 



160 



180 



Fig. 3 • — Undersea equalizer — loss-frequency characteristic. 



