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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



were designed by N. D. Newby and the authors of this paper. The sig- 

 nals after passing through a bandpass filter are amplified to a standard 

 level by a circuit incoporating backward acting automatic volume con- 

 trol. The arrival of each signal pulse is detected by a threshold device. 

 Since the minimum time interval between the generation of a pulse 

 and the next succeeding pulse is 3.2 milliseconds, the threshold device 

 is arranged to disable itself upon the detection of a pulse for about 3 

 milliseconds. This prevents false operations of the detector either by 

 tail transients resulting from distortion of a pulse in the transmission 

 medium or by noise occuring in this interval. 



When the silent or blank interval which exists between the complete 

 transmission of a number and its next repetition is recognized by the 



Fig. 8 — Pulse-position-dialing receiver. 



start circuit attached to the detector, the time-decoder circuit is en- 

 abled as well as the steering and digit absorbing circuit. The time de- 

 coder subsequently measures the length of time between each detected 

 start pulse and the following detected stop pulse, and energizes the 

 corresponding digit value leads into the registers. The steering circuit 

 enables a separate set of register elements for the storage of each decoded 

 digit which is to be used by its associated circuits and withholds such 

 enablement through its digit absorbing features for digits wliich are 

 not of immediate intei-est. The steering circuit also enables a check 

 circuit associated with the registers. 



Several features of the signaling code permit a check to be made 

 that the received signals are in accordance mth the code. The number 

 transmission cycle has been already described but a brief restatement is 

 made here to emphasize the checkable features : The first pulse following 



