THE TIME FACTOR IN TELEPHONE TRANSMISSION 59 



frequencies, they will evidently add up to give the same over-all wave 

 shape at the receiving end of the line as at the sending end. 



If, on the other hand, the velocity is not the same for all frequencies, 

 there will be more or less distortion and transients in establishing the 

 wave, though ultimately the pure wave of frequency F will be estab- 

 lished. Several oscillograms \\'\\\ be shown to indicate transient effects 

 which are experienced under various conditions. 



Fig. 3 is an oscillogram showing a spurt of 1,600-cycle current as 

 applied to and received from a loaded circuit having fairly large delays 

 in the upper part of the transmitted range compared to the delay at 



Fig. 3 — -Transients in 522 miles of medium heavy loaded repeatered circuit. Upper 

 trace — transmitted 1600-cycle wave. Lower trace — received wave. 



lower frequencies. Remembering the nature of the oscillations at the 

 beginning and end of the applied spurt, it will be observed that the cur- 

 rent at the receiving end consists at first of a fairly low frequency which 

 builds up in frequency and magnitude to the steady-state value. At 

 the end of the spurt the same transient is experienced, but in this case 

 the higher frequency currents which have been delayed in the line are 

 at the tail end of the train. 



Fig. 4 shows a 200-cycle current with many harmonics of higher de- 

 gree transmitted over a circuit having large delay at low frequencies. 

 It will be noted that these high or harmonic frequencies are received 

 in advance of the 200-cycle w^ave. This is because the 200-cycIe wave 

 is subject to appreciable delay while the higher frequencies are not. 

 This circuit, while actually made up of artificial networks, had char- 

 acteristics similar to certain types of long cable circuits for the lower 

 part of the telephone frequency range. 



