NEW SINGLE CHANNEL CARRIER TELEPHONE SYSTEM 173 



only a few single-channel systems are involved, it is sometimes possible, 

 by separating the systems widely on the pole line, to operate with only 

 the regular voice-frequency transpositions, but, in general, additional 

 transpositions are required. A comparatively inexpensive trans- 

 position system for this purpose was designed at the time the Type D 

 system was developed. It permits operation of Type H systems on all 

 pairs of a four-crossarm line with the exception of the pole pairs, and 

 Type C three-channel systems on the top crossarm. In addition to 

 transposing it is important that reflections at junctions between open 

 wire and cable be reduced as described above, in order that near-end 

 crosstalk will not through reflection appear as crosstalk at the distant 

 terminal of the system. 



Range of Operation 



The terminals and repeaters have sufficient load carrying capacity 

 so that they may be operated at an output level 16 db above that at 

 the transmitting toll switchboard. About 19 db transmitting gain and 

 14 db receiving gain are available at each terminal, of which a total of 

 20 db may be used at the east terminal and 22 db at the west terminal. 

 The lower permissible loop gain (sum of transmitting and receiving 

 gains) at the east terminal is not controlling, since the line loss is 

 greater for the frequencies used in the east to west direction than for 

 those used in the west to east direction. Thus, the terminals are 

 capable of providing a 9 db circuit over a line the attenuation of which 

 does not exceed 31 db at 8150 cycles and 29 db at 6150 cycles. These 

 figures correspond roughly to the wet weather attenuation of about 280 

 miles of 104-mil open wire where no intermediate cable or equipment 

 is involved. The presence of even a small amount of cable will con- 

 siderably increase the attenuation so that in most cases the distance 

 which can be spanned is not greater than 150 to 200 miles, and may be 

 even less. 



Where greater distances are to be covered, an intermediate repeater 

 may be added. The repeater has a useful gain of about 23 db in each 

 direction, with some flexibility as to allocation of gains between the 

 two directions of transmission. More than one intermediate repeater 

 can, of course, be employed, although as the system is lengthened 

 maintenance effort will be increased, as more frequent adjustments of 

 the overall net loss will be required to compensate for the variations 

 in line attenuation with weather. No provision is made for a pilot 

 channel such as is generally provided on the long multi-channel 

 systems, and adjustments of overall net loss must be made manually. 

 Also, no provision has been made for equalizing the variation in line 



