SYSTEM DESIGN — NEWFOUNDLAND -NOVA SCOTIA LINK 229 



(ii) Basic power plant and the carrier supplies for supergroup and 

 group translation were provided by the A.T. and T. Co. for both ter- 

 minal equipments at Clarenville. 



(iii) Terminal equipment special to the Clarenville-Sydney Mines 

 link was provided by the Post Office. 



In view of the importance of the link, the power-feeding and trans- 

 mission equipment are completely duplicated. 



The submarine-cable terminal equipment is arranged to transmit 

 the basic supergroup, directly over the cable in the east-to-west direc- 

 tion. In the west-to-east direction the supergroup is translated to the 

 range 20-260 kc, using a 572 kc carrier. 



DESIGN OF TRANSMISSION SYSTEM 



Performance Requirements 



The agreed transmission objects for the Clarenville-Sydney Mines 

 link were as follows : 



Variation of Transmission Loss. 



The variation in the transmission loss of each group should have a 

 standard deviation not greater than 0.5 db; this implies that the varia- 

 tion from nominal should not exceed 1.3 db for more than 1 per cent 

 of the time. 



A ttenuation/ Frequency Characteristics. 



Only the overall characteristics of the individual circuits were pre- 

 cisely specified, the limits being the C.C.I.F. limits for a 2,500-km cir- 

 cuit and the target one-half of this. With this objective in view, the group 

 characteristics in each link must clearl}^ be as uniform as is practicable. 



Circuit Noise. 



The total noise contributed by the link to each channel in the busy 

 hour (i.e., including intermodulation noise) should have an r.m.s. value 

 not exceeding -(-28 dba* (corresponding to —56 dbm) at a point of zero 

 relative level. 



* This refers to the reading on a Bell System 2B noise meter (FIA weighting 

 network); the noise level (dba) is relative to a 1 kc tone at —85 dbm. In Europe, 

 noise is measured on a C.C.I.F. Psophometer (1951 weighting network), which is 

 calibrated in millivolts across 60(? ohms; this is commonly converted to picowatts 

 (pw). The white noise equivaleTir<^ of the two instruments is given bj' dba = 10 

 logio pw — 6 = dbm -f- 84; the agreed limit of -{-28 dl)a is therefore equivalent 

 to 2513 pw (1.2.3 mv or —56 dbm). The corresponding C.C.I.F. requirement at 

 4.0 pw/km would be 2,400 pw, this vidue not to be exceeded for more than 1 per 

 cent of the time. 



