LOADING rOR TELEPHONE CIRCUITS 



227 



Fig. 3 illustrates the dependency of the characteristic impedance 

 of a coil loaded line upon the terminal condition. The most frequently 

 used loading terminations are "mid-section" and "mid-coil." In the 

 mid-section termination, the first loading coil is located at a dis- 



4000 



3500 



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2500 



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1500 



1000 



1000 



13000 



1000 1500 2000 



FREQUENCY CYCLES 



0.18 0.36 0.53 0.71 0.89 l!0 



RATIO OF FREQUENCY TO CUT-OFF FREQUENCY 



Fig. 3 — Impedance-frequency characteristics of loaded and non-loaded No. 19 A. \v. 



cables of Fig. 1 



tance equivalent to one-half of a regular loading section from the 

 beginning of the line. Mid-coil termination is obtained by installing 

 at the beginning of the line, a coil having one half of the inductance 

 of the regular coils, the first full coil being installed at the end of the 

 first complete loading section. For mid-coil and mid-section termina- 

 tions, the characteristic impedance is approximately a pure resistance, 



