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BELL SYSTEM TECHNICAL JOURNAL 



pulses pass through both sections of the circuit; hence by proper choice of 

 Ci and C2 the amphtudes of the damped sine wave and the exponential may 

 be proportioned so that the rate of change of their combined potential 

 becomes zero at successive points one pulse period apart. In fact it has been 

 found possible to make both the first and the second time derivatives of 

 potential equal to zero simultaneously at such points. 



1 2 3 4 5 6 7 



C2^ R2> l; 



TIME 



TO GATE 



TO CATHODE 

 FOLLOWER 



Fig. 22. Shannon-Rack decoder. 



Fig. 23. Output of Shannon-Rack decoder for a signal giving 100% modulation. 



By this modification, not only the times of application of the charges but 

 the time of sampling is made much less critical. Of course this presumes 

 that the sampling circuit is designed to complete its operation near the center 

 of a level region. In Fig. 22, the voltage transient due to a typical pair of 

 pulses is sketched, and Fig. 23 shows an oscilloscope screen, on which the 

 waveforms delivered by the cathode follower of one of the Shannon-Rack 

 decoders of the system are superimposed for a full set of 128 possible code 

 combinations in sequence. 



