. The Bell System technical journal . ower pulse coming at a time corre-sponding to the center of the broadened pulse at the top. Further fre-quency change in the same direction returns the shape to that of thetop traces. At the frequency giving the received pulse shown on thenext-to-the-bottom trace, moving the far-end piston causes a gradualchange to the shape shown on the lowest trace. This makes it appearas if the mode conversion were coming almost entirely from the part ofthe guide near the piston end at this frequency. The upper traces appearto show that more energy is converted at the t
. The Bell System technical journal . ower pulse coming at a time corre-sponding to the center of the broadened pulse at the top. Further fre-quency change in the same direction returns the shape to that of thetop traces. At the frequency giving the received pulse shown on thenext-to-the-bottom trace, moving the far-end piston causes a gradualchange to the shape shown on the lowest trace. This makes it appearas if the mode conversion were coming almost entirely from the part ofthe guide near the piston end at this frequency. The upper traces appearto show that more energy is converted at the transducer end of thewaveguide at that frequency. It would seem that at certain frequenciessome phase cancellation is taking place between conversion pointsspaced closely enough to overlap within the pulse width. At frequenciesbetween the ones giving traces like this, the appearance is more likethat shown for the TE31 mode on Fig. 19 except for the slope across thetop of the pulse being reversed. The highest part of this TEoi pulse is. Fiff. 20 — Received pulse patterns witli the urrangemeiit of Fig. 18 used forstudying conversion to the TE21 mode. WAVEGUIDE TESTING WITH MILLIMICKOSECOND PULSES 65 24 to 27 db below the injected TEoi pulse level for the 5 diameterHolmdel waveguides. 12. CONCLUDING REMARKS The high resolution obtainable with this millimicrosecond pulseequipment provides information difficult to obtain by any other examples of its use in waveguide investigations indicate thepossibilities of the method in research, design and testing is being used for many other similar purposes in addition to the illus-tratio)is given here, and no doubt many more uses will be found forsuch short pulses in the future. REFERENCES 1. S. E. Miller and A. C. Beck, Low-loss Waveguide Transmission, Proc. , 41, pp. 348-358, March, 1953. 2. S. E. Miller, Waveguide As a Communication Medium, B. S. T. J., 33, pp. 1209- 1265, Nov., 1954. 3. C. C. Cutler, The R
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