START-STOP RECEIVERS 



225 



observing both ends of the orientation range with positive and negative bias 

 rather than observing the upper end with positive bias and the lower end with 

 negative bias. This type of measurement is merely equivalent to using a 

 fairly large percentage of bias and zero per cent of end distortion. The dis- 

 advantage of this measurement is that no account is taken of the curvature 



(A) 



Cb= center of bias = 26 



Tr= TOLERANCE TO BIAS =34 



BIAS PARALLELOGRAM 



"END DISTORTION" 



PARALLELOGRAM 



DISTORTION TOLERANCE 



t 16 "To SKEW 



Cs= CENTER OF SWITCHED BIAS= 30 

 Ts= TOLERANCE TO SWITCHED BIAS = 30 

 Cc,-Cb= + 4 

 Ts-Tb=- 4 



(B) 



Cb= CENTER OF BIAS = 4b 

 Tb= TOLERANCE TO BIAS = 



+50 



DISTORTION TOLERANCE 

 + 4°7„ BIAS -4% SKEW 



Cs= CENTER OF SWITCHED BIAS = 50 

 Ts= TOLERANCE TO SWITCHED BIAS = 46 

 Cs- Cb = +4 

 Tc- Tn = -4 



Fig. 8 — Switched bias measurements 



of the end displacement parallelogram, and hence the indicated values of 

 tolerance may not be an accurate measure of the receiver's ability to receive 

 distorted signals. 



Internal Fortuitous Distortion 



It is usually considered, in measurements of miscellaneous signals, that the 

 difference between the maximum distortion tolerance and 50 per cent (the 



