892 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1957 



method, attenuation increases nearly in proportion to the square root of 

 the channel bandwidth. For this reason, rather short repeater spacings 

 may be required for binary pulse S3^stems, so that for economical appli- 

 cations to wire circuits it is imperative to have reliable regenerative 

 repeaters of simple design. 



In their principle of operation regenerative repeaters are by nature 

 more complicated than ordinary repeaters. In addition to providing gain 

 to off-set attenuation in the transmission medium, as in ordinary re- 

 peaters, they must also perform gating operations for sampling and 

 regenerating the received pulse train. This, however, does not pre- 

 clude the possibility that these operational principles can be implemented 

 in repeater design by instrumentation that is simpler than required foi' 

 ordinary repeaters. 



The possibility of simple instrumentation resides partly in the cir- 

 cumstance that equalization circuitry for regenerative repeaters can be 

 substantially simpler than for ordinary repeaters, owing to less exacting 

 requirements on equalization. Furthermore, satisfactor}' performance 

 in pulse regeneration can be achieved without very precise timing in 

 sampling and regeneration of pulse trains. It is thus possible to secure 

 nearly the same performance as for ideal regenerative repeaters bj' par- 

 tial rather than complete exact retiming of pulse trains at each repeater. 

 This facilitates simple gating arrangements for regeneration of pulses. 

 Moreover, it permits a timing wave for control of gating operations to 

 be derived from either the received or regenerating pulse trains with the 

 aid of a simple resonant of circuit. 



The simplicity of instrumentation permitted by these considerations 

 is exemplified in a self-timed regenerative repeater for baseband pulse;? 

 invented by L. R. Wrathall of Bell Telephone Laboratories. The cir- 

 cuitry of the repeater together with the results of tests on laboratory 

 models are dealt with elsewhere^ and not considered here. The purpose 

 of this paper is an analysis of the timing principles underlying this typo 

 of repeater together with its regeneration characteristics as deter- 

 mined by various basic design parameters, on the assumption of ideal 

 implementation of the timing principles by appropriate instrumentation. 

 In the Wrathall repeater "ciuantized feed-back" is employed as a mean;- 

 of reducing the effect of low-frequency cut-off in transformers. Since thit< 

 is not an essential feature of self-timing repeaters and has no direct 

 bearing on the timing principles, it is disregarded herein. 



1 L. R. Wrathall, Transistorized Binarj' Pulse Regenerator, B.S.T.J., 35, pp. 

 1059-1084, Sept., 1956. 



