A MILLION-CYCLE TELEPHONE SYSTEM 



The central conductor of the coaxial units is a 13-gauge copper wire 

 insulated with hard rubber discs at intervals of 3/4 inch. The outer 

 conductor is made up of nine overlapping copper tapes which form a 

 tube 0.02-inch thick; this is held together with a double wrapping of 

 iron tape. 



The transmission losses of this coaxial conductor at various fre- 

 quencies are shown in Fig. 3. This attenuation is about 4 per cent 

 higher than is calculated for a solid tube of the same dimensions and 

 material. Another matter of importance is the shielding obtained 

 from one conductor to the other or to outside interference. Inasmuch 

 as the most severe requirement is that of crosstalk from one coaxial 

 unit to another, this has been usad as a criterion of design. Figure 4 



30 50 100 200 500 1000 2000 5000 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 3 — Attenuation of the coaxial conductor. 



shows the average measured high-frequency crosstalk in this particular 

 cable on a 10-mile length without repeaters, both near-end and far-end. 



Repeaters 



The amplifiers used in this system were designed for a 10.5-mile 

 spacing and a frequency range of 60 to 1024 kc. A total of 10 complete 

 two-way repeaters has been provided including those at the terminals. 

 Two of the intermediate repeaters are at existing repeater stations 

 along the route, the other six being at unattended locations along the 

 line. Four of these are in existing manholes, while the other two are 

 placed above ground for a test of such operation. Figure 5 shows a 

 manhole repeater with the cover removed for routine replacement of 

 vacuum tubes. Figure 6 shows one of the installations above ground. 



The measured gain of a typical repeater is shown by the points on 

 the curve of Fig. 7. The curve itself is the line loss that the repeater 



