. The Bell System technical journal . eliminary tests on a full size model of exponential line impedancetransformer showed deviations from the theoretical that might be at-tributed to improper termination, irregularities along the line, irregu-larities introduced at the change in conductor size or capacitance of thespacing insulators. Since it was impossible to determine which ofthese was the predominant cause of the deviations from the ideal, it EXPONENTIAL TRANSMISSION LINE 567 was decided to introduce each of these factors one at a time. This testwas made on a 600 : 300 ohm Hne constructed
. The Bell System technical journal . eliminary tests on a full size model of exponential line impedancetransformer showed deviations from the theoretical that might be at-tributed to improper termination, irregularities along the line, irregu-larities introduced at the change in conductor size or capacitance of thespacing insulators. Since it was impossible to determine which ofthese was the predominant cause of the deviations from the ideal, it EXPONENTIAL TRANSMISSION LINE 567 was decided to introduce each of these factors one at a time. This testwas made on a 600 : 300 ohm Hne constructed of No. 6 copper wire withlockstitch insulators except at the terminals. The correct terminationwas obtained by tests on a uniform 300 ohm line with the same physicalstructure at the termination. Of necessity the tying of the wire to thestrain insulators at the end introduced a shunt capacitance whichaugmented the inherent additional capacitance due the end additional capacitance is equal to that of a short length of Fig. 5—Photographs of terminations of 300 ohm right for curve 1 1lower for curve 2 ^ of Fig. 6. upper left for curve 3 J If the correct amount of inductance is inserted in series with theresistance load the combined effect of the additional capacitance andinductance becomes the same as the addition of a small length of linefor all frequencies up to those for which this length of line is an appre-ciable fraction of a wave-length. Accordingly a small amount of induc-tance was inserted in series with the resistance as shown in the rightpicture of Fig. 5. The input impedance of the uniform line with thistermination is given by Experimental Curve 1 at the bottom of Fig. 6. 568 BELL SYSTEM TECHNICAL JOURNAL A three-inch length of No. 18 wire was inserted as shown in the lowerpicture of Fig. 5 and Experimental Curve 2 resulted. This reducedthe irregularities in the input impedance to about half, so another three 648 624 576 522 336 ,EXPERIME
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
