PHASE DISTORTION IN TELEPHONE APPARATUS 



497 



lineJ These curves as well as those in the following three figures are 

 for non-dissipative networks terminated in their image impedances. 

 However, the insertion phase characteristic with dissipation and the 

 usual terminations, i.e. a resistance of fixed value, would not noticeably 



180 



160 



140 



120 



100 



80 



60 



40 



20 







20 



40 



-60 



-80 



-lOO 



-120 



-140 



-160 



-160 



7 



0.6 



0.9 



1.0 



1.2 



1.3 



FREQUENCY f^^ 



Fig. 4 — Image transfer phase characteristics of typical band-pass filter sections 



be different in most of the transmitting range. For filters in the latter 



case in the neighborhood of jc the slope would be modified so as to 



remain finite. This will be discussed further in the next section. 



The curves of Figs. 4 and 5 show respectively the image transfer 



' It will be noted that the second derivative of these low pass filter phase curves 

 are positive at all frequencies. However, special sections exist for which this is not 

 true and such sections are occasionally used as discussed later where it is desirable to 

 keep the characteristic as a whole nearly straight over a wider frequency range but 

 low pass filters when considered as a whole generally have phase characteristics of the 

 type shown. 



