FILTERS FOR CARRIER SYSTEMS 



IV) 



incomplete in the frequency ranges occupied by channels 5 and 9 due to 

 the steep phase shift slope of the band elimination fdter near its cut-off 

 points, no telegraph channel are assigned to these channels of tyi)e "A'" 

 carrier circuits equipped with branching points. 



The phase shift of the band elimination filter is discontinuous between 

 its cut-off frequencies and has a positive slope with frequency in its pass 

 bands. As the phase shift of a delay section increases continuously with 

 frequency, it is impossible to provide the exact counterpart of the filter in 

 a delay network. However, the addition of any multiple of 211 radians 

 does not change the transmission characteristic. Hence 611 radians (3 



CD 90 



O 32 33 34 35 36 37 38 39 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 17 — Delay of the phase simulating network at program^frequencies. 



24 28 32 36 40 44 48 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 18 — Insertion loss-frequency characteristic of the phase simulating network. 



revolutions) are added to the phase shift of the elimination filter above the 

 upper cut-off to simulate its phase characteristic in the 10 to 12 message 

 channel range, as well as to provide an almost linear phase slope in the 32 

 to 40 kc program channel range resulting in minimum delay distortion. 



The delay distortion of the network over the program channel is approxi- 

 mately 16 microseconds as shown in Fig. 17. The loss distortion over the 

 program channel is approximately 0.05 db and over any one message channel 

 it is less than 0.05 db as shown in Fig. 18. 



The self loss equalizing feature of a delay section is evaluated at zero 

 frequency in the form of a resistance pad by making the pad loss approxi- 

 mate the insertion loss at the critical frequency of the delay section. The 



