. The Bell System technical journal . e maximum possible,but not necessary, pulse length is equal to the difference in time re-quired for the TEoi mode and the converted mode to travel the totalwaveguide length being observed. The phasing effects within the broad-ened pulse change its height and shape as a function of frequency andline length. Measurements of mode conversion from TEoi to TE31 in these wave-guides illustrate distributed sources and piston phasing effects. TheTE3, mode has a group velocity per cent slower than the TEoi a full round trip in the 500-foot lines, assumi
. The Bell System technical journal . e maximum possible,but not necessary, pulse length is equal to the difference in time re-quired for the TEoi mode and the converted mode to travel the totalwaveguide length being observed. The phasing effects within the broad-ened pulse change its height and shape as a function of frequency andline length. Measurements of mode conversion from TEoi to TE31 in these wave-guides illustrate distributed sources and piston phasing effects. TheTE3, mode has a group velocity per cent slower than the TEoi a full round trip in the 500-foot lines, assuming conversion at theimput end, this causes a time separation of about two and one halfpulse widths between these two modes. The received pulse is about twoand a half times as long as the injected pulse, indicating rather closelyspaced sources over the whole line length. For one far-end piston posi-tion, the received pattern is shown as the upper trace in Fig. 19. Asthe piston is moved, the center depressed part of the trace gradually. ImK. 10 — Hocoivcd pulsr patterns willi llic .irraiijicnuMit of Fig. IS used forstudying conversion to tlie Tlvn mode. WAVEGUIDE TESTING WITH MILLIMICROSECOND PULSES 63 rises until the pattern shown in the lower trace is seen. As the pistonis moved farther in the same direction the trace gradually changes tohave the appearance of the upper photo again. Moving the far-endpiston changes the phase of energy on the return trip, and thus it canbe made to add to, or nearly cancel out, conversion components thatoriginated ahead of the piston. When the time separation becomesgreat enough to prevent overlapping in the pulse ^^^dth, phasing effectscannot take place, therefore, the beginning and end of the spread-outreceived pulse are not affected by moving the piston. Energy convertedat the sending end of the guide travels the full round trip to the pistonand back in the slower TE31 mode, and thus appears at the latest time,which is at the right-hand end
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
