TUBE FOR PULSE CODE MODULATION 



45 



input voltage on the Y deflection plates is held constant, causes the electron 

 beam to sweep across the aperture plate along the dashed line a-b. A time 

 sequence of output pulses is produced at the output plate when the beam 

 passes through the apertures of the code p'ate along the path a-b. 



A series of output pulses or a ''pulse group" is characterized by the pres- 

 ence of pulses at time positions corresponding to the several vertical columns 

 of apertures. The code plate shown in Fig. 1 is laid out in accordance with 



OUTPUT 

 PLATE 



B^fj' 



(b) 



Fig. 1 — Electron beam deflection tube for coding. 



the binary number system pattern^ which was chosen for the present pulse 

 code work because of the simplicity of decoding. The four-digit code plate 

 shown in the tube of Fig. 1 provides for coding only 16 amplitude values 

 and was used to facilitate the illustration. The tube developed for the ex- 



^ The four vertical columns of the four-digit code plate in Fig. lb provide four positions 

 in time for output pulses. Vertical columns marked 1, 2, 3 and 4 correspond to the first, 

 second, third and fourth digits, respectively, of the pulse code transmitted. Pulses lo- 

 cated in time in accordance with this notation are given "weights" of 1, 2, 4 and 8, respec- 

 tively. Sixteen pulse group combinations are indicated by the 16 dashed horizontal 

 lines in Fig. lb. The pulse group defined by beam sweep a corresponds to a total "weight" 

 of 15; beam positions ^ and 7 correspond to total "weights" of 14 and 13, respectively, 

 and so on, with the bottom horizontal dashed line in the figure corresponding to zero. 



