. The Bell System technical journal . rsion pulse appears at a time which is the sum of the time takenor the TEoi to go down to the filter and the TE02 to go from the filteruo the piston and back to the receiver. Because of the slower velocitybf the TE02, this appears at the time shown, since it was in the TE02node for a longer time than it was in the TEoi mode. The second con-[/ersion, which happened when TEoi came back to the mode filter, comesjiarlier in time than the first conversion, since the path for this signalivas in the TEoi mode longer than it was in the TE02 mode. This arrange-,nen
. The Bell System technical journal . rsion pulse appears at a time which is the sum of the time takenor the TEoi to go down to the filter and the TE02 to go from the filteruo the piston and back to the receiver. Because of the slower velocitybf the TE02, this appears at the time shown, since it was in the TE02node for a longer time than it was in the TEoi mode. The second con-[/ersion, which happened when TEoi came back to the mode filter, comesjiarlier in time than the first conversion, since the path for this signalivas in the TEoi mode longer than it was in the TE02 mode. This arrange-,nent gives very good time separation, and makes possible a measure-Inent of the amount of mode conversion taking place in the mode filters,viode conversion from TEoi to TE02 as low as 50 to 55 db down, can beneasured with this equipment. Randomly spaced single discontinuities in long waveguides can beocated by this technique if they are separated far enough to give in-lividually resolved short pulses in the converted mode. Fig. 17 shows. CONVERSION FIRST CONVERSION AT FAR END SECOND CONVERSION AT NEAR END SQUEEZED AT NEAR END SQUEEZED SECTION SECTION SQUEEZED SECTION TO RECEIVER TEJo —*- TEq, TE2, -• »- TE,o NEAR END 250 FT OF FAR END TRANSDUCER COUPLED LINE SQUEEZED 3DIAM ROUND SQUEEZED TRANSDUCER SECTION GUIDE SECTION Fig. 17 — Arrangement used to explain the measurement and location of modeonversion from isolated sources. A deliberately squeezed section was placedt each end of the long waveguide, producing the pulses shown in the trace photo. 60 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1956 an arrangement having oval sections deliberately placed in the wave-guide in order to explain the method. Pure TEoi excitation is vised, andthe converted TE21 mode observed with a coupled line transducer giv-;ing an output for that mode alone. ; Let us consider first what would happen with the far-end squeezed;section alone, omitting the near-end squeezed section from considera- •
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
