PHASE DISTORTION IN TELEPHONE APPARATUS 



501 



Fig. 7 is the insertion phase and delay characteristic of a 600 mile 

 length of medium heavy loaded cable including repeaters. This cable 

 has a theoretical cut-off of about 2500 cycles. Fig. 8 shows the dis- 

 tortion for two simple waves ^^ of the above type, for one /o = 1000 

 cycles and for the other /o = 1500 cycles. The oscillographs show as, 

 predicted, that practically nothing in either case is received until 

 after the time given by the minimum value of dBjdo}, i.e. .0654 seconds. 

 After this time a distorted form of the sent wave occurs. Since for 

 /o = 1000 most of the energy of the wave as analyzed by the Fourier 

 Integral method of analysis falls in the neighborhood of 1000 cycles 



SENT 



1000 CYCLES 



Fig. 8 — Distortion resulting from 600 mile length of cable of Fig. 7 for signals of the 

 form y sin uut + 6 between t = and t = T and zero for all other time. 



where the delay characteristic is reasonably constant this wave is not 

 distorted much. In the case for/o = 1500 cycles a larger portion of the 

 energy falls in the neighborhood of 1500 cycles where the delay char- 

 acteristic is changing more rapidly and it is therefore distorted more. 

 {dBjdio)/^ — {dBldw)m\n. may be taken as a fair measure of the dis- 

 tortion of such simple waves although higher derivatives are also 

 involved. 



Fig. 9 shows the insertion delay characteristic for a system consisting 

 of four band filters in tandem. The attenuation characteristic is also 



" Reproduced from the paper by Sallie P. Mead, loc. cit. 



