MULTICHANNEL MODULATION SYSTEM 



19 



By a process to be considered later, each coder produces a 7-digit PCM 

 code representation of its set of samples. The two coders deliver their code 

 groups alternately on a common output lead during the final 10 ^^ micro- 

 seconds of each 16-microsecond holding interval mentioned above. In- 

 dividual pulses last about 1.5 microsecond, although as delivered from the 

 coders they are somewhat irregular in timing and waveform. It will be 

 noted that the interval allotted to the code group from each channel is just 



FRAMING CONTROL 

 PULSE (+) 



CHANNEL 12 / CHANNEL 1 



(CODER 2) / (CODER 1) 



CHANNEL 2 

 (CODER 2) 



CHArJNEL 3 

 (CODER 1) 



>N_/v\_A^_/\/vv\l 



C - 



D 



(-) 



OUTPUT OF CODERS 

 0.4|JS-H h- * 10 5/12 |JS- 



^^^i^^^U 



672 KC TIMING PULSES 



^^ 



LJ^ 



SLICED AND GATED PCM PULSES 

 1.5|JS(APPROX.) 



OUTPUT OF PULSE REGENERATOR 



I'- • 



H 



MODULATED I.R OR MICROWAVE SIGNAL 



Fig. 8. Waveforms of the pulse regenerator. 



YT^ of the 125-microsecond frame period and that a continuous train of 

 code groups is thereby produced. 



The common output circuit of the coders goes to a pulse regenerator which 

 standardizes the pulses in height by slicing, and in time by gating, as illus- 

 trated in Fig. 8. The peaks of the coder output pulses (line A) are lined up 

 in time with the gate control pulses (line B) supplied from the timing gear. 

 The latter have a constant repetition frequency of 672 kilocycles and a 

 uniform pulse length of 0.4 microsecond. Accordingly, the sliced and gated 

 PCM pulses (line C) are also 0.4 microsecond long, and require lengthening 

 to fill their allotted 1.5-microsecond intervals. This is accomplished by a 



