START-STOP RECEIVERS 



209 



Hence, the signals are received as sent. When biased reversals are trans- 

 mitted, the longer pulses are further lengthened and the shorter pulses are 

 further shortened, causing the bias of the received signals to be of greater 

 magnitude than that of the transmitted signals. 



Fig. 1 (E) shows a wave in which the current overswings the steady-state 

 value, and fails to complete the return to steady state within the duration 

 of the shortest pulse. It will be seen that the operation of a relay will be 



(A) 



' (C) 



A 





Fig. 1 — Signal diagrams illustrating causes of distortion. 



delayed more after a short pulse than after a long one, and that this is true 

 whether the pulse in question be marking or spacing. This effect is known 

 as positive characteristic distortion, and it tends to shorten long pulses and 

 lengthen short ones. When unbiased reversals are transmitted, a steady- 

 state condition is reached, in which the delays become equal on all transi- 

 tions. Hence, the signals are received as sent. When biased reversals are 

 transmitted, the shortening of the long pulses and lengthening of the short 

 pulses causes the bias of the received signals to be less than that of the trans- 

 mitted signals. 



