. Le journal technique de Bell System . 1.12 0.92 8 10 12 14 16 18 20 22FREQUENCY EN MÉGACYCLES 24 26 28 30 FIG. 6—abaissement. Caractéristiques expérimentales d'impédance d'entrée de 300 ohms en ligne avec terminaisons illustrées sur la Fig. 5. Supérieur. Caractéristiques d'impédance d'entrée du50mètre 600 : ligne de 300 ohms de conducteurs n° 6. Des pouces ont été insérés, ce qui a donné une courbe expérimentale 3. Ici themaxima et minima sont déplacés, ce qui indique que l'effet de la capacité parasite a été réduit au même ordre de grandeur que celui dû à la déviation de la résistance par rapport à la valeur désirée. Ce TRANSMISSIO EXPONENTIEL
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. The Bell System technical journal . 1.12 0.92 8 10 12 14 16 18 20 22FREQUENCY IN MEGACYCLES 24 26 28 30 Fig. 6—Lower. Experimental input impedance characteristics of 300 ohm linewith terminations shown in Fig. 5. Upper. Input impedance characteristics of50-meter 600 : 300 ohm line of No. 6 conductors. inches were inserted, resulting in Experimental Curve 3. Here themaxima and minima are displaced, indicating that the effect of thestray capacitance has been reduced to the same order of magnitude asthat due to the deviation of the resistance from the desired value. This EXPONENTIAL TRANSMISSION LINE 569 termination was accordingly removed to the exponential line, resultingin the Experimental Curve at the top of Fig. 6. It agrees withinexperimental error with the Theoretical Curve. The slight verticaldisplacement of the experimental curve at the higher frequencies isattributed to deviations in the impedance of the pencil lead, which was. Fig. 7—Photograph of one of the changes In conductor size. used as a resistance standard, from a pure resistance equal to its directcurrent value. To increase the power carrying capacity of the exponential line, onewas built with larger wire size at the lower impedance end. Thisincreased the breakdown voltage by increasing the spacing and con-ductor diameter and at the same time increased the current carryingcapacity by decreasing the resistance and increasing the heat dissipat- 570 BELL SYSTEM TECHNICAL JOURNAL ing capacity of the conductors. This was a 600 : 300 ohm Hne con-structed of 20 meters No. 6 wire, 10 meters 1/4 tubing and 20 meters3/8 tubing. Here again the correct termination was determined bymeasurements on a 300 ohm uniform Hne of 3/8 tubing. The totallength of terminating loop that gave the best termination was 63/^in this case compared with 103/^ for the 300 ohm line of No. 6 wire.Since no attempt was made to reduce the variations in input impedanceto less than ± 1
