5 TA RT-STOP RECEI VERS 2 1 3 



Maximum Displacements Caused by Characteristic Distortion 



The maximum MB displacement will occur when the start transition is 

 delayed as much as possible and some space-to-mark selective transition is 

 delayed as little as possible. This will take place, in the case of negative 

 characteristic distortion, when as long a marking signal as is possible precedes 

 the start transition and a combination of pulses as predominantly marking 

 as possible precedes the space-to-mark transition in question. A marking 

 signal sufficiently long to permit a steady state to be attained, followed by 

 any signal train having the first selective pulse marking satisfies this condi- 

 tion, as shown at "X" in Fig. 4(B), but it will be noted that the MB dis- 

 placement extends into the start pulse, where, in the case of a start-stop 

 receiver, no selection is made. Hence it will not affect the margin of 

 operation of the receiver, provided it is not so large as to prevent the receiver 

 from starting. This particular distortion will, however, affect a start-stop 

 distortion measuring set^ or regenerative repeater which is so designed that 

 measurements or selections are made during both the selective pulses and 

 the start pulse. As far as a start-stop teletypewriter, in which no selection 

 occurs during the start pulse, is concerned, the maximum MB displacement 

 occurs on the fourth transition of the letter K following as long a marking sig- 

 nal as possible, as shown at "F" in Fig. 4(B). This space-to-mark transition, 

 being preceded by a spacing pulse of unit length which, in turn, was preceded 

 by signals which are predominantly marking, is delayed for a short time, 

 whereas the mark-to-space start transition, which was preceded by a long 

 marking signal, is delayed for a longer time. Except in the case of unusual 

 wave forms, there will be very little difference between the magnitudes of 

 the displacements shown at "X" and "F" unless they are both very large, 

 since the wave will usually attain steady state during the steady marking 

 interval constituted by the first, second, third and fourth selective signal 

 intervals. 



In the usual case of positive characteristic distortion, the maximum MB 

 displacement will occur when the start transition is preceded by a combina- 

 tion of pulses as predominantly spacing as possible, and some space-to-mark 

 transition is preceded by the longest spacing signal possible in the start-stop 

 code. These conditions are met by repeated, "BLANK" signal trains, 

 shown in Fig. 4(E). 



The maximum SB displacement will occur when the start transition is 

 delayed as little as possible, and some space-to-mark selective transition is 

 delayed as long as possible. This takes place, in the case of negative char- 

 acteristic distortion, when a combination of pulses as predominantly spacing 

 as possible precedes the start transition and the longest possible spacing 

 signal precedes the space-to-mark transition in question. As noted in the 



