SYSTEM DESIGN ^ NEWFOUNDLAND-XOVA SCOTIA LINK 235 



to indicate the attenuation of the transmission path; these pilots are 

 normally located just outside the main transmission bands in each 

 direction. In the Clarenville-Sydney Mines system the frequency bands 

 just outside the main transmission bands are occupied by telephone 

 speaker and teleprinter circuits and by monitoring frequencies associated 

 with the repeaters (see Fig. 5) ; this prevents the use of out-of-band pilots. 



Fortunately, the standard Bell System group equipment is designed 

 to apply 92-kc pilots to each group and to measure the corresponding 

 received level. Although these are essentially group pilots, being applied 

 and measured at points in the 60-108-kc band, it was decided that 

 they could reasonably replace the out-of-band pilots. These pilots are 

 blocked at each end of the system and therefore function as section pilots 

 only. 



Normal Post Office practice, both on land and submarine systems, is to 

 use recording level meters to provide a continuous and permanent record 

 of the pilot levels. In the present system such recording meters are used 

 on the 92-kc pilots of two groups in each direction of transmission. 



In addition to the section pilots the system carries the 84.080-kc 

 end-to-end pilots in each of the three transatlantic groups. 



MAINTENANCE FACILITIES 



Speaker and Printer Circuits 



It was part of the planning of the transatlantic system that two low- 

 grade telephone (speaker) and two telegraph (printer) circuits should 

 be provided over the submarine cables, outside the main transmission 

 bands, and that the speaker circuits in particular should be reasonably 

 independent of the main terminal equipment. One speaker circuit is re- 

 quired for local communication between the terminals of each section, 

 the other to form part of an omnibus circuit connecting the principal 

 stations on the route including Montreal. The arrangement for tele- 

 printer communication was that one channel should be an overall 

 all-station omnibus printer, the other being a direct London-New York 

 printer. 



Independent frequency-translating equipment is provided to connect 

 the speaker and printer bands (each 4 kc) to the line. The carrier fre- 

 quencies required for the speaker are provided by independent oven- 

 controlled crystal oscillators, but for the printer the independent genera- 

 tion of high-stability 572-kc carriers was not considered to be justified 

 and the main station supplies are used. 



Two half -bandwidth telephone circuits are provided in the 4 kc speaker 



