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BELL SYSTEM TECHNICAL JOURNAL 



erence branch. The balancing line shown in the reference branch of Fig. 

 5 can be adjusted in length so that it balances out the average delay in the 

 measuring branch. The measured remainder will then be the distortion 

 in the measuring branch, since a good transmission line does not have 

 phase or delay distortion. The use of a balancing line in the reference 

 branch simplifies measurements by reducing the range of movement of the 

 slider, and it greatly decreases the errors in the calculation of the delay 

 distortion due to inaccuracies in the measuring interval A/. 



The simphfied diagram of Fig. 7 will be used to show how the delay of 

 the unknown network can be calculated. With the signal oscillator set at 

 frequency /i the slider is adjusted until the signals at C and E are in phase 



DELAY BALANCING LINE 

 (VELOCITY = V) 



Fig. 7 — Simplified circuit electrically equivalent to the circuit of Fig. 5. 



as indicated by a straight line on the oscilloscope, and the corresponding 

 distance Xi is measured. The relationships between the phases of the 

 signals at the various points in the circuit are: 



<t>C — <f>A ~ <f>AB — <f>BC 



(4) 



ms 



<t>B — <f>A — <f>AD 



(5) 



0c = 



where ^ is the phase shift in the unknown network at frequency /i. Solving 

 for /3, 



, = M'[^+2..-.] 



(6) 



