TYPE-O CARHIKH SYSTKM ()93 



aboYG exi.stiiig carrier systems, such as (■, wliich has a top frcfiuency of 

 30 kc. With the aid of the compandor, it is possible to apply the OB 

 system to practically an.y open-wire pair transposed for C carrier opera- 

 tion, thus nearly doubling the number of circuits without additional line 

 rearrangements. Transposition arrangements which are expected to be 

 less expensive to apply are being made available where the higher- 

 frequency type-0 groups are invohed. Line losses of the order of 35 to 

 40 db can be spanned under normal wet weather conditions, and 50 db 

 loss under sleet conditions with some transmission impairment, since 

 sleet is relative^ infrequent in occurrence. This will result in repeater 

 spacings of the order of 50 miles in sleet areas for the OB group, and 100 

 miles in other areas. For the higher frequency groups (OC and OD) those 

 spacings will be approximately halved. 



CHOICE OF DEVELOPMENT APPROACH 



The type-0 carrier system followed the type-N system closely in 

 time, and, in effect, covers the same range of circuit lengths for open 

 wire lines that N provides for cables. It was both natural and expedient 

 that many of the N features were carried over directly into the O design. 

 It was necessar}^, however, to make important distinctions as well. These 

 similarities and differences will be discussed m some detail. 



The transmitting and receiving voice frequency subassemblies are 

 reused with substantially no modification. This provides the O system 

 with the same compandor and the same 3700 cycle signaling system as 

 used in X. 



An important difference between the two systems is concerned with 

 the use of single sideband in the rather than double sideband as in 

 the N. This choice is an economic one. The double sideband system is 

 relatively easier to design and less expensive than the single sideband 

 arrangement. The use of double sideband in cables is practicable in 

 many cables because of the relative abundance of conductors as com- 

 pared with open wire pairs. In some cases the use of single sideband in 

 cables may be attractive as compared with the cost of new outside plant 

 for certain length ranges. 



Another distinction between the two systems is the provision of cir- 

 cuits in smaller groups in 0. In N the basic group is 12, although systems 

 may in some instances be partiallj^ equipped. In O, the desire to furnish 

 smaller circuits groups resulted in the choice of a basic four-channel 

 group. The full complement per pair for O, including a channel replacing 

 the voice circuit, is sixteen channels. 



The regulation problem is more severe in the O design. It is necessary 



