1232 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 



ence between the times it takes the signal mode and the unused mode 

 to travel a distance in which there is a large difference between the ohmic 

 losses in the unused-mode and signal mode. This concept may be ex- 

 panded as follows: Energy is transferred at an imperfection located at 

 coordinate Zi on the axis of propagation, producing an amplitude in 

 unused mode x. At Zo on the axis of propagation the amplitude in mode 

 X will be attenuated relative to the signal-mode amplitude at the same 

 point by the factor 



— (aj;— ai)(02— zi) 



where a^ and on are the normal heat loss coefficients in mode x and the 

 signal mode respectively. When the exponential factor is small enough 

 (i.e., 02 large enough), reconversion will no longer be important com- 

 pared to reconversion near Zi . For order of magnitude we might assume 

 that 10 db more attenuation for the re -mode amplitude than for the sig- 

 nal-mode amplitude would render further reconversion unimportant. 





Fig. 18 — Schematic of signal distortion due to conversion and reconversion 

 effects in a line with randomly placed conversion points. 



