t 



I 



CABLE^CARRIER TELEPHONE TERMINALS 



117 



The channel frequency characteristic which has been attained in the 

 terminals is shown in Fig. 6. The solid curve below shows the fre- 

 quency characteristic of a representative channel, while the dotted 

 curves near it show the limits within which the characteristics of all 

 single channels, so far measured, would fall. Above in the figure is 

 shown the characteristic of five representative channels in tandem, each 

 channel having its two voice terminating circuits included. 



The delay distortion and time of transmission, contributed by all 

 terminal apparatus at both ends of a system except voice terminating 

 sets, are shown in Fig. 7 for a single channel. 



I 



V) 6 

 Q 



z 



O 5 

 O ^ 

 LU 



(rt 

 _J 

 S 3 



z 



a. 2 



5 

 ^- I 



0.2 0.4 0.6 0.8 1.0 1-2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 

 FREQUENCY IN KILOCYCLES PER SECOND 



3.2 3.4 3.6 



Fig. 7 — Delay characteristic. 



The channel modulators have been adjusted so that they will cut off 

 the peaks of excessively loud talk to prevent overloading the carrier 

 repeaters or other parts of the circuit, but this cutting is not enough to 

 degrade the quality of speech. The single-frequency load curve of 

 one complete channel is plotted in two ways in Fig. 8. 



The frequency stability of the oscillating tuning forks is expected to 

 be within ± 1 X lO"*^ parts per degree Fahrenheit on all systems, with 

 negligible variations due to other causes. The amplitude stability of 

 each frequency at its distributing bus is expected to be within ± 1/4 db 

 over a period of months. The impedances of the bus-bars are suffi- 

 ciently low so that crosstalk from one system into another through this 

 path is unimportant. The effectiveness of the protective resistances 

 at the carrier supply bus-bars is such that a short circuit on one modu- 

 lator or demodulator will increase the loss in the remaining modulators 

 and demodulators less than 1/2 db. The speed of switchover to emer- 

 gency carrier supply is such that the disturbance to transmission will 

 be less than 10 milliseconds. The effect on speech is not detectable. 



