TELEVISION BY PULSE CODE MODULATION 



43 



bination with the expansion of the kinescope, results in an overall linear 

 system. This method of operation, as is well known, results in a wide range 

 of tone values between black and white. The PCM system used, employed 

 steps of equal size; in other words, within the limits of the quantum steps 

 it is a linear system. The combination of the signal from the film scanner, 

 including the rooter, and the linear PCM system, followed by an expanding 

 viewing tube, results in an overall system which employes the limited num- 

 ber of steps in the PCM system to essentially optimum advantage. 



Fig. 7 — Test signal, RMx\ test chart: five-digit transmission. 



While in practice, synchronization would probably be derived from the 

 code pulses, for the purposes of this experiment it was not necessary to trans- 

 mit the synchronizing pulse through the PCM system. Synchronization of 

 the monitor was obtained by a separate path. This was done, since in an 

 operating system it would not be necessary to use more than one or two 

 levels to send the synchronizing pulse as compared with 25% or more of 

 the levels that would be necessary in an unmodified standard television 

 wave-form. 



The pictures shown on the figures were taken with a one-second exposure. 

 It will be realized that in a photographic still picture obtained in this manner 

 the exact effect in the viewing tube cannot be conveyed because it is not 

 possible to see motion due to noise. 



