248 



BELL SYSTEM TECHNICAL JOURNAL 



the reference point for phase. Departure of /3 from the linear relationship 

 given by (1) is the phase distortion in the circuit. 



5.5 



5.0 



^ 4.0 



< 



O 



a 3.5 



z 



<:::^3.0 



(/I 



< 2.0 



Q. 



0.5 



0.4 0.5 0.6 0.7 



0.9 



1.0 1. 



1.2 



1.5 



1.6 



Fig. 1 — Typical phase shift curves for various types of circuits 



a. A Transmission line terminated in its characteristic impedance. 



b. A single tuned circuit. 



c. Two tuned circuits with approximately critical coupling. 



The time of transmission^ or the delay in passing through the circuit is 

 obtained by differentiating (1): 



Delay = f 



To seconds 



(2) 



Variation in To with frequency is the delay distortion in the circuit. 



Figure 1 shows some typical phase curves, and Fig. 2 shows the corre- 

 sponding delay curves. In each figure curve (a) represents an ideal dis- 

 tortionless circuit with linear phase and constant delay such as a simple 

 transmission line. Curves (b) are obtained for single resonant circuits, 



• To has also been called the group delay and the envelope delay. 



I 



