SELF-TIMING REGENERATIVE REPEATERS 927 



train the resonant circuit will not be excited by every pulse, unless the 

 shape of the received pulses is such that there are virtually no overlaps 

 between pulses so that the triggering level will be penetrated by each 

 pulse. 



With a pulse shape as assumed in the previous analysis, the amplitude 

 of a pulse train midway between pulses is half the peak amplitude of the 

 pulses, as indicated in Fig. 9. In the presence of noise, triggering will in 

 this case occur on the average for every second pulse, as indicated in the 

 above figure. If it is assumed that the resonant circuit has the maximum 

 permissible phase shift of about 20° allowed with timing from the output, 

 the amplitude of the timing wave with excitation from e\'ery pulse will 

 be -^-irtually equal to the peak pulse amplitude. With excitation from 

 half the pulses, the amplitude of the timing wave ^vill rapidly reach half 

 the peak amplitude of the pulses. When this initial timing wave is com- 

 bined with the pulse train, triggering will occur for virtually all pulses, 

 as indicated in Fig. 9. It will thus reach its normal value. If the phase 

 shift is greater than 20° as assumed above, say 60°, the initial amplitude 

 of the timing wave will be | the peak pulse amplitude. Combination of 

 this initial timing wave with the pulse train will increase the number of 

 pulses exciting the resonant circuit, which in turn increases the amplitude 

 of the timing waves, etc. 



Self-starting with a pulse shape as assumed in this analysis is thus 

 insured. 



VII SUMMARY 



In self-timing regenerative repeaters as considered here, a timing 

 wave is derived from either the received or regenerated pulse train with 

 the aid of a simple resonant circuit tuned to the pulse repetition fre- 

 quency. This timing wave is combined linearly with received pulse trains 

 as indicated in Fig. 1, and pulses are regenerated when the combined 

 wave penetrates a certain triggering level. 



It is concluded that if these timing principles are implemented bj^ 

 appropriate repeater instrumentation, a performance can be realized 

 that approaches that of ideal regenerative repeaters. To this end it is 

 necessary to meet certain requirements with regard to the loss constant 

 Q of the resonant circuit, its frequency precision, the shape of received 

 pulses and the amplitude of the timing wave in relation to that of re- 

 ceived pulses. 



Equalization of each repeater section should preferably be such that 

 the received pulses have a shape and duration in relation to the pulse 



