. Das Bell System technische Journal . Mengen vonVerzögerung und Dämpfung. Die ersten drei Bilder von Abb. 10 wurden mit der Bahnlänge genau gleich genommen. Als die Amplituden ebenfalls gleich waren, gab es eine vollständige Anmuung. Da das Signal in einem Ast abgeschwächt wurde, stieg die Amplitude des resultierenden Impulses an, bis es dem des ursprünglichen Impulses, wie im dritten Bild gezeigt, gleichkam. Eine Erhöhung um eine halbe Wellenlänge brachte die Signale von den beiden Zweigen in die Phase und addierte sich zu doppelter Amplitude, wie im vierten Bild zu sehen. Es sollte darauf hingewiesen werden, dass obwohl in ou
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. The Bell System technical journal . amounts ofdelay and attenuation. The first three pictures of Fig. 10 were taken with the path lengthsexactly equal. When the amplitudes were also equal there was completecancellation. As the signal in one branch was attenuated the amplitudeof the resultant pulse increased until it became equal to that of theoriginal pulse as shown in the third pictiue. Increasing one path by one-half wavelength brought the signals from the two branches into phaseand they added up to double amplitude as seen in the fourth picture. Itshould be pointed out that although in our experiment we changed delayby 0.36 millimicroseconds in going from the fiist minimum to the firstmaximimi, in free space a change of delay of only 0.125 millimicroseconds SIDE ARM A--> /W^ ATT E N U ATORE PLANE ARM J Nk. H PLANE ARM PLUNGER A PULSE INPUT OUTPUTTO DETECTOR -//V/AT T E N U ATO R SIDE ARM B--> PLUNGER B Fig. 9—Apparatus to simulate two-path transmission. PROPAGATION STUDIES AT MKUOW AVI-; FUlXjlTKNCIKS 101. Fig. 10—Simulated two-path transmission. would be rec[iiired. The discrepancy lies in the large ratio between thephase elocity and group velocity in the wave guide used whereas infree space this ratio is, of course, ec^ual to unity. In free space the amountof delay rec^uired to go from a maximum to a minimum signal correspondsto a change of path difference of only about one and one-half inches.With only this slight shift rec^uired to change conditions from those shownIn the first picture of Fig. 10 to those shown by the last, it is not at allsiuprising that the received signal is very unstable during time of multi-path transmission. Fig. 11 shows the effect of changing relative phases in 90° steps whilekeeping the amplitudes equal to each other. It is seen that even with thecarriers in direct opposition cancellation is far from complete due to the •^ ^NwijiiW