442 BELL SYSTEM TECHNICAL JOURNAL 



balancing networks designed for each toll circuit. By this means 

 intermediate gains of from 4 to 10 db were inserted at the switching 

 points when connection was made between two toll circuits. 



The use of cord circuit repeaters has been an outstanding element 

 in the provision of improved transmission on switched connections. 

 It has, however, some disadvantages which have increased in impor- 

 tance with the increase in transmission efficiency of circuits and with 

 the rapid development of toll business. The routine for inserting the 

 cord circuit repeaters when needed is necessarily somewhat cumber- 

 some, involving considerable expense for operators' labor and for 

 increased use of the toll circuits by operators. Furthermore, under 

 practical conditions it was found to be not possible to insure that the 

 cord circuit repeaters would always be used when required by the 

 routing instructions. 



Recent developments in the types of toll circuit have greatly 

 increased the numbers of toll circuits provided with repeaters at their 

 terminals as a part of the most economical design of a circuit. When 

 such repeaters are available, the desired switching gain can be obtained 

 by making use of the gain available in these repeaters. The great 

 increase in the number of terminal repeaters required for other reasons, 

 important reductions in the cost of repeaters and the savings of 

 operators' labor and circuit time have made it practicable to adopt a 

 plan of providing, at certain points, terminal repeaters for every 

 circuit, thus doing away entirely with cord circuit repeaters at these 

 points. With the terminal repeater arrangement, the insertion of 

 transmission gain on switched connections is done automatically by 

 taking out of each circuit on such connections a section of artificial 

 line. This is, of course, the equivalent of increasing the gain of the 

 terminal repeater. 



Satisfactory transmission results for all connections under the 

 general toll switching plan involve the insertion of repeater gain on 

 all connections switched at important switching points. This will be 

 carried out by the terminal repeater plan just described. The artificial 

 lines or pads which are cut out of the circuit on switched connections 

 have losses of from 1 to 4 db, depending upon the circumstances of 

 each case. This means that when two toll circuits are switched 

 together, from 2 to 8 db is automatically subtracted from the con- 

 nection at each switching point. The arrangement is indicated 

 schematically in Fig. 10. The design of each circuit must, of course, 

 be such that when either end of the circuit is connected to a subscribers' 

 station, the repeater gain at that end will not be greater than that 

 permissible under the terminating condition, but that when two or 



