OPEN-WIRE TELEPHONE LINES 



731 



There will be studied in this paper those inherent characteristics of 

 open-wire lines which are used most frequently in telephone transmis- 

 sion work. These characteristics are: first, the attenuation, second, 

 the impedance, and third, the phase characteristic, with which must be 

 coupled its near relative, the velocity of propagation. The range of 

 frequencies to be covered is fixed on the one hand by the d.-c. telegraph 

 systems, as well as by the program transmission circuits, whose lower 

 frequencies extend to 100 cycles or less, and on the other hand by the 

 carrier telephone and telegraph systems, which make the range up to 

 about 50,000 cycles of interest. 



Line Construction Arrangements 



In order to study the characteristics of open-wire lines it is necessary 

 to know something of the constructional arrangements which are em- 

 ployed. The conductors most commonly used for the open-wire tele- 



•10-0 



12 — ---12 — 5-5- 



^, ^2 ^3 ^^ ^^( ^ ^6 -r^ B^ .^ ,0^ 



Fig. 1 — Configuration of an open-wire line with 12-in. non-pole pairs. 



phone lines of the Bell System are of 165-mil (No. 8 B. W. G.), 128-mil 

 (No. 10 N. B. S. G.), and 104-mil (No. 12 N. B. S. G.) hard-drawn cop- 

 per. These are the conductors usually employed for carrier systems. 

 Other gages of copper, as well as a small amount of iron or steel wire, 

 are used to some extent for voice-frequency and d.-c. telegraph trans- 

 mission only. 



The wires of the lead (as an open-wire line is frequently designated in 

 telephone parlance) are strung on poles, the normal spacing and num- 

 bering of wires being generally as shown in Fig. 1. Starting at the left 

 end of the crossarm, the adjacent horizontal wires are grouped in pairs, 



