TELEVISION BY PULSE CODE MODULATION 



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Description of Experiments 



The experiments to be described were confined to tests with a transmitting 

 terminal connected to the receiving terminal by short coaxial transmission 

 lines. The transmitting terminal performed the functions of sampling, quan- 

 tizing and coding, while the receiving terminal decoded the PCM signal. 

 No regenerative repeaters were included since they are not necessary in 

 tests designed to evaluate the fundamental limitations of sampling and 

 quantizing of a television signal. 



Figure 3 gives a block diagram of the system used in these experiments. 

 The input filter band limits the signal so that the highest frequency is less 

 than one-half of the 10-megacycle sampling rate. The input sampler sam- 

 ples the wave and holds the amplitude value obtained until the next sam- 

 pling interval. It uses the same type of circuit as that described in the paper 

 by Meacham and Peterson in The Bell System Technical Journal for January 



Fig. 3 — Block schematic of PCM system. 



1948. In general, much of the circuitry described by them has been used in 

 this equipment, but the units of course function at greatly increased speeds. 



The coder and quantizer use a coding tube which produces the code simul- 

 taneously in five-digit output circuits. Quantization is accomplished by using 

 a special code, together with suitable slicing units in the output of the digit 

 amplifiers. Further discussion of the coder and quantizer will be given in 

 connection with Fig. 4. 



In these experiments the transmission medium consisted of an appropriate 

 number of wire circuits, no regenerative repeaters being used. At the receiver, 

 a decoder regenerates the pulses and adds the weighted digits to obtain the 

 quantized PAM signal, as already shown in Figs. 1 and 2. The output 

 sampler is similar to the one used at the input. It will be recalled that step 

 samples are produced, i.e., the signal is sampled at the beginning of each 

 interval and this value is held until the next sampling time. The output 

 filter band limits the signal and removes extraneous components above 5 

 mc, particularly the 10 mc sampling frequency. As is well known, these 



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