142 BELL SYSTEM TECHNICAL JOURNAL 



changed about 0.1 db. If now the pilot current level is within 0.5 db 

 of normal the operation is complete. If not, it is repeated and the 

 device keeps periodically testing the circuit so long as it is away from 

 satisfactory compensation. There are also alarm circuits for attracting 

 attention in cases of wide variations in equivalent. In severe ice 

 conditions where a single regulating repeater has not sufficient gain 

 to make up for the great loss in the line, the next succeeding repeater 

 will do its utmost to make up the deficiency. 



Conclusion 



In what has preceded, developments have been described which 

 are making it possible to provide a very substantial increase in circuits 

 on open-wire pole lines without additional wire stringing. Photo- 

 graphs showing typical office installations of type J carrier equipment, 

 unattended repeater stations, and filter huts are shown in Fig. 10. 



Three stages in the development of the open-wire line over the past 

 twenty years, giving successive increases in circuit capacity, are shown 

 in Fig. 11. Prior to the application of carrier systems, a four-crossarm 

 pole line would yield thirty voice circuits. Now, on a new line 256 

 circuits are potentially obtainable. Thus it is probable that the open- 

 wire line will continue as an important factor in furnishing facilities 

 in moderate numbers, particularly in the less densely populated sec- 

 tions of the country and where climatic conditions are not unfavorable. 

 Installations of type J systems have already been made in various 

 parts of the country. 



