PRACTICAL APPLICATION OF CARRIER SYSTEMS 



however, and this may prove out the further addition of carrier. 

 Even if it appears economical to install additional carrier systems, a 

 point will soon be reached where the cumulative annual charges of 

 the carrier systems will exceed that ot the cable. The first few sys- 

 tems prove in over the (-able because the carrier provides only for the 

 immediate circuit requirements while the cable must take care of 

 growth and therefore includes many idle facilities when first in- 

 stalled. Where carrier is used to provide facilities in place of a toll 

 cable it should always be considered an intermediate and temporary 

 step between open wire and cable plant. 



The use of carrier as outlined above may effect further economies 

 after the apparatus has been removed as the equipment may be 

 reused at some other point to advantage. A typical example of the 

 use of carrier apparatus to defer a cable is the Boston-Bangor carrier 

 system which was put in to defer the installation of the first section of 

 the Boston-Portland cable. The layout of this system is given in 

 Fig. 7. It will be seen that this system is fairly short but the first 



I Cable 

 i Circuits 



4" 



ZSO Miles 



To 

 Rockland 



"~! 



- IJ4MI. 



=s nl 1 -Wm ^l a^t=f-irTO 



To 

 I Bangor"— 1 



J^ka ^m=>c=mLi »?. ays 



PORTLAND 



BOSTON 



WAKEFIELD 



BANGOR 



CONVENTIONS 



M Carrier Repeater 

 X Voice Repeater 

 CD Low Pass Line Filter 

 QD High Pass Line Filter 

 [Q Phantom Coil 



=S Circuit Terminated 

 — RegularCircuit 

 —Z Circuit Used in Emergency 

 ra Cable Loaded for Carrier 

 Li Non Loaded Cable 



Fig. 7 — Boston-Bangor Carrier Telephone System 



vear's annual charge on the first 50 miles of the Boston-Portland 

 cable would have been sufficient to pay the entire first cost of this 

 carrier project. It is possible that further carrier may be installed 

 on this route before the cable is finally installed. The present system 



