LOADING FOR TELEPHONE CIRCUITS 



225 



[If the loaded line has distrihutcd inductance, a correction is re- 

 quired in equation (4).] 



The dififerences between the characteristics of a coil loaded line and 

 its corresponding smooth line are sometimes designated "hnnpiness" 

 effects. They are due to repeated internal reflections at the points 

 of electrical discontinuity in the line caused by the insertion of the 

 loading coils. The lumpiness effects are usually small for the fre- 

 quencies below approximately 75 per cent, of the cut-off frequency. 

 As the frequency exceeds this value, however, the lumpiness efi^ects 

 increase at an accelerated rate. 



Figs. 1, 2 and 3 illustrate the differences in the attenuation, velocity, 

 and impedance characteristics of a typical telephone cable, with and 

 without loading. The characteristics of the corresponding smooth 

 loaded line are also given to illustrate the theoretical differences 

 between uniform loading and coil loading. Fig. 1 includes curves 



1000 1500 2000 

 FREQUENCY-CYCLES ' 



0.18 0.36 0.53 0.71 0.89 1.0 

 RATIO OF FREQUENCY TO CUT-OFF FREQUENCY 



Fig. 1 — Attenuation-frequency characteristics of loaded and non-loaded No. 1^ 



A. w. g. cable 



