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BELL SYSTEM TECHNICAL JOURNAL 



checking the characteristic distortion. The possible use and mean- 

 ing of such measurements are discussed in the following : 



Bias In-Bias Out 

 For the purpose of discussion consider the particular code indicated 

 by Fig. 26. 



+ E 



-E 



Fig. 26 — Special telegraph signal. Each character consists of ten time units. 

 Each time unit is one-fiftieth second and ma>' be -\-E or —E depending on the 

 character transmitted. 



Each character to be transmitted is composed of ten time units, 

 each unit being 1/50 second, so that it takes 1/5 second to transmit any 

 of the 1024 possible characters. Although the nominal speed of signal- 

 ing is 25 dots per second, the fundamental frequency of any character 

 sent repeatedly is 5 cycles per second considered in the Fourier sense. 

 Among the many possible signal combinations are the following 

 which are equivalent to 5-cycle reversals with the amounts of bias 

 indicated below. 



Time Units Time Bias 



A, u c = 100^^, 



Marie Space M +6 



10 -f-100% 



9 1 +80% 



8 2 +60% 



7 3 +40% 



6 4 +20% 



5 5 0% 



4 6 -20% 



3 7 -40% 



2 8 -60% 



1 9 -80% 



10 -100% 



It is obvious for a symmetrical circuit that if signals with any amount 

 of positive bias are transmitted accurately signals with the corre- 

 sponding amount of negative bias will be transmitted since this corre- 

 sponds to a reversal of the sending polarities. 



The transfer admittance for distortionless transmission of these 

 signals will now be derived for the case in which the band width is a 

 minimum. It has been shown in a previous paper ^ that the minimum 

 band width required is equal numerically to the speed of signaling. 



