96 



BELL SYSTEM TECHNICAL JOURNAL 



As was mentioned earlier, an additional correction for the residual 

 effect or "twist" is required about every six repeaters to supplement 

 the flat gain adjustment. This distortion is a function of frequency 

 and has been found to vary from cable to cable. A network the 

 characteristics of which are shown in Fig. 14 has been developed to 

 meet this condition. Certain fixed resistances in the network are 

 selected to correspond to the length and twist characteristic of the 

 cable section considered. A variable resistance in the network is 

 adjusted automatically using a control similar to the flat gain regu- 

 lator. Figure 15 gives the transmission characteristics of a 150-mile 

 regulator-controlled circuit under two temperature conditions. 



-2 



15 20 25 30 35 40 45 50 

 FREQUENCY IN KILOCYCLES PER SECOND 



55 



60 65 



Fig. 15 — Overall transmission-frequency characteristic of 150-mile line. 



Auxiliary Repeater Stations 



Cable carrier systems are expected to be used largely on existing 

 toll cable routes which now carry voice-frequency circuits. The aver- 

 age spacing of the stations housing the voice-frequency repeaters on 

 these routes is about 50 miles. The same buildings with their power 

 plants will also care for the cable carrier repeaters. Since the maxi- 

 mum spacing for the carrier repeaters is about 19 miles, additional 

 carrier repeaters must be provided at intermediate stations (two is the 

 usual number). The various design features of the equipment to be 

 located in these stations have been made the subject of extensive 

 development work and field tests. These stations are designed to 

 function with a minimum of attention and are visited at intervals for 

 routine testing work or as required by some emergency, but resident 

 maintenance forces are not planned for them. The present equipment 

 is expected to be suitable not only for auxiliary stations on existing 

 cable routes but also for cases where a greater spacing than 50 miles 

 between the attended stations may be desired on new routes. 



A voice-frequency repeater station for a single cable and a cable 

 carrier auxiliary station are shown to approximately the same scale 



