TRANSISTOR BINARY PULSE REGENERATOR 1069 



may change the phase of indi^•idllal pulses. The change of amplitude of 

 the sinusoidal timing wave in one pulse period will be 



AAr = Ar[l - e-''"^""] (11) 



w here Q = wL/R and tm is the timing interval. In a similar manner the 

 \ariation of the amplitude of the voltage across Ci will be 



AAc = AcW - e-'-'/^i^^] (12) 



If now 7?i and Ci are adjusted until 



TV 1 



Q RiC, 



(13) 



and Ro varied initil the amplitude Ac is eriual to the a^•erage value of 

 At , the charge on the interstage coupling condenser should be effectively 

 neutralized at all times. Since both loops are made up of passive elements 

 with common inputs and outputs a single adjustment should suffice 

 even though the pulse amplitude, width, or signal pulse density may vary. 

 In the repeater circuit shown on Fig. 3 this neutralizing principle is 

 used but is more difficult to see. When a pulse is regenerated, a large 

 emitter current flows in Di , which produces a sharp negative voltage 

 spike. This voltage adds a charge to C2 which tends to neutralize the one 

 the timing wave adds to it. The time constant of C2 and its associated 

 circuit may be made to equal the decrement of the tank circuit and the 

 two amplitudes made equal by adjusting the level of the timing wave. 

 By this means effective dc transmission of the timing wave is achieved 

 through capacity coupling. 



2.5 Line Equalization 



The line equalizer is not essentially a part of the repeater itself. It is 

 however so intimately connected with the repeater it is logical that they 

 be considered together. One of the important ecjualizer requirements is 

 simplicity, another, that the impedance seen from the repeater input 

 shall be substantially constant over a relatively large frequency range. 

 This latter requirement comes from the need of transmitting the feed- 

 back pulse around the feedback loop to the emitter of the first transistor 

 without too much distortion. The equalizer is not used to equalize the 

 low frecjuency losses of transformers but only the frequency characteris- 

 tic of the line. The eciualization must be such that the individual pulses 

 are allowed to widen but not enough to cause inter-symbol interference. 



