G52 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



-4 



-6 



_i 



LU 



U 



LU -16 



Q 



Q -20 



-24 



-28 



-32 



-20 



20 40 60 60 100 120 140 



ECHO PHASE, pT, IN DEGREES 



160 



180 



200 



Fig. 2 — Plot of D2 as a function of echo phase when f = fb 



The term A depends only on the rms deviation a, the round-trip 

 echo delay T of the hne, the ratio a = f/fb , and the echo phase pT. The 

 term D2 is plotted in Fig. 1 as a function of aT for two channels, one at 

 the top and the other at the bottom of the signal band. Since the carrier 

 frequency may be expected to be very high, the carrier phase 2pT will 

 be a very large number of radians even with ver}^ short wave guide runs. 

 Hence the curves on Fig. 1 are plotted for the average value of cos 2pT 

 which is zero. 



The curves on Fig. 2 show how D2 depends on pT and the parameter 

 (tT. In this case the channel is taken at the top of the signal band. When 

 pT is an odd multiple of 90 degrees, it turns out that we have even order 

 modulation products onlj'-; and when pT is a multiple of 180 degrees, 

 odd order products only. The curves show that the distortion becomes 

 less dependent on the echo phase as the quantity aT increases. 



REFERENCE 



1. W. R. Bennett, H. E. Curtis and S. O. Rice, Interchannel Interference in FM 

 and PM Systems, B.S.T.J., 34, pp. 601-636, May, 1955. 



