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BELL SYSTEM TECHNICAL JOURNAL 



a satisfactory length within which Hne variations are corrected. The 

 lock joint proper, Fig. 19, comprises an insulator of the same design 

 as the intermediate insulators but made with an outer diameter equal 

 to that of the outer sheath. It is held in place by a sleeve sweated 

 to the sheath, the sleeve continuing the electric circuit. The insulator 

 is also fixed to the inner conductor^by means of rings. Since the lock 

 joint is in a position symmetrical with respect to the two expansion 



Fig. 20 — An experimental selector switch for connecting several antenna lines to 

 one transmitter line. The small coil antiresonates the capacity of the switch for the 

 operating frequency associated with the particular contact to which it is connected. 



joints it is required to withstand a shearing load brought about only 

 by inequalities in the expansion of the conductors. In order to dis- 

 tribute the line expansion uniformly among the expansion joints it is 

 necessary to clamp the outer sheath of the lock joint to a substantially 

 braced support. 



The joints described above are required to accommodate a total 

 annual variation of 0.5 inches. After one year's period of experimental 

 operation the few faults found in a line containing these joints were 



