530 



BELL SYSTEM TECHNICAL JOURNAL 



When the characteristic impedance of the system under consideration 

 is not the same for both directions, the delay obtained in this way is 

 one half that of two such systems connected in tandem "back to back." 

 Furthermore, when the impedance bridged across the measuring trunk 



3.0 



2.5 



10 2.0 



o 



z 



o 



o 



i^ 1.5 

 10 



1.0 



0.5 



10 



2 



o 



600| 



400 



200 



+ 400 



+ 200 



CO 



I 

 O 



-200 



-400 



1200 

 FREQUENCY 



2000 



Fig. 3 — Computed curves illustrating method of Fig. 2. 



is not the characteristic impedance of the system being measured, then 

 the delay measured is the insertion delay between two such impedances 

 as the bridging impedance. Fundamentally, it is the periodicity of 

 the difference of the impedance curves for open and short termina- 

 tions which determines the insertion delay, and it follows that the 

 periodicity obtained from the intersections of these curves gives the 

 same delay. 



