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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 meters 

 3/8" tubing. Here again the correct termination was determined by 

 measurements on a 300 ohm uniform line of 3/8" tubing. The total 

 length of terminating loop that gave the best termination was 6)^" 

 in this case compared with lOj^" for the 300 ohm line of No. 6 wire. 

 Since no attempt was made to reduce the variations in input impedance 

 to less than ± 1 per cent these lengths may be as much as an inch off. 

 These measurements indicated that the exponential line would per- 

 form satisfactorily as an impedance transformer if it could be con- 

 structed to have the desired mechanical features without impairing its 

 electrical properties. The greatest difficulty appeared to reside in the 



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FREQUENCY IN MEGACYCLES 



P'ig. 8 — Input impedance characteristics of 50-meter 600 : 300 ohm 

 line of 3/8", 1/4" and No. 6 conductors. 



insulators. Special isolantite insulators were designed that would be 

 satisfactory commercially and still keep the additional capacity to a 

 reasonable value. Figure 7 shows the construction of the line at the 

 supporting poles where the conductor size changes. 



The results of measurements on this line are shown in Fig. 8. The 

 solid curve was calculated from the equations developed earlier. The 

 two broken curves are the results of measurements on the line, one 

 without insulators and one with insulators. While the insulators affect 

 the line somewhat they do not increase the deviation from the ideal 

 appreciably. [The improvement in the agreement between experiment 

 and theory in this set of curves over that in Fig. 4 is presumably due 

 to the fact that the comparison resistance for Fig. 8 consisted of 3-IRC 



