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BELL SYSTEM TECHNICAL JOURNAL 



constructed of No. 12 tinned copper. At the low impedance end the 

 strain was taken by a victron insulator which also served as a line 

 spreader and terminal mounting. At the high impedance end the 

 strain was taken by 1/4" manila rope without other insulation. The 

 line spacing was adjusted by "lock stitch" tension insulators spaced 

 1 meter and 1/2 meter apart on the low and high impedance end re- 

 spectively of the 9-meter line. The 3-meter line was supported at the 

 1/4, 1/2, 2/3, 3/4 and 7/8th points. 



The impedance was measured by the substitution method. To 

 facilitate the substitution of the reactive component of the line it was 

 bridged by an antiresonant circuit. Pencil leads calibrated on direct 

 current were used as the resistance standards. Type BW IRC 1/2 



0.3 



0.4 



f/fo 



0.7 



0.8 



Fig. 4 — Input impedance characteristic. Comparison of theoretical curve with 

 experimental points for 600 : 300 ohm lines. 



Solid circles — 9-meter line. 

 Open circles — 3 -meter line. 



watt resistances were used for terminations. The solid circles of Fig. 4 

 represent measurements on the 9-meter line. The agreement with 

 theory is as good as is usually found for actual "uniform lines." In 

 order to check the theory further toward the lower frequency end — 

 beyond the range of the measuring equipment — ^measurements were 

 made on a 3-meter line. These measurements are shown by the open 

 circles. The agreement with theory is not so good, but here the lengths 

 of the connecting leads are an appreciable fraction of the length of 

 the line. 



Preliminary tests on a full size model of exponential line impedance 

 transformer 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 the 

 spacing insulators. Since it was impossible to determine which of 

 these was the predominant cause of the deviations from the ideal, it 



