. Le journal technique de Bell System . 232 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBRE 1954 entre les temps qu'il prend le mode signal et le modeto inutilisé Voyage une distance dans laquelle il y a une grande différence entre les ohmiclovers dans le mode inutilisé et le mode signal. Ce concept peut être ex-pandé comme suit: L'énergie est transférée à une imperfection situé atcoordonnée ZI sur l'axe de propagation, produisant une amplitude inunused mode x. A Zo sur l'axe de propagation, l'amplitude dans Modex sera atténuée par rapport à l'amplitude en mode signal au point de passage par le facteur —(aj;
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. The Bell System technical journal . 232 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 ence between the times it takes the signal mode and the unused modeto travel a distance in which there is a large difference between the ohmiclosses in the unused-mode and signal mode. This concept may be ex-panded as follows: Energy is transferred at an imperfection located atcoordinate Zi on the axis of propagation, producing an amplitude inunused mode x. At Zo on the axis of propagation the amplitude in modeX will be attenuated relative to the signal-mode amplitude at the samepoint by the factor —(aj;—ai)(02—zi) where a^ and on are the normal heat loss coefficients in mode x and thesignal 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 assumethat 10 db more attenuation for the re-mode amplitude than for the sig-nal-mode amplitude would render further reconversion unimportant. i^. Fig. 18 — Schematic of signal distortion due to conversion and reconversioneffects in a line with randomly placed conversion points. WAVEGUIDE AS A COMMUNICATION MEDIUM 1233 TluMi we know the distaiico (s.j — ^i) from 1.15 (--.. - zi) = The correspoiuling upper limil on lime dohiy hclwccn tlic signal andtlie reconverted energy in the fsignal mode i.s t= fe-^x)(---) (1) where Vx and Vs are the groiij) velocities in the mode x and tlie signalmode. It is well known that the unused modes of a circular electric waveguidehave attenuation coefficients which are appreciably larger than attenua-tion coefficients for the circular electric wave itself. In the light of thisattenuation to the unused modes plus the fact that the reconvertedenergy has undergone two mode conversion losses before it reaches thesignal mode again, one might wonder whether the mode conversion-reconversion phenomenon wn)uld really be an important effect. The firstindication that t
