Television by Pulse Code Modulation

HE papers that have so far appeared on pulse code modulation have dealt primarily with the transmission of speech. The present work deals specifically with the problems involved in the transmission of television, but in its general aspects it is pertinent to the transmission of any broadband signal by PCM. The chief difference between a system for telephony and one for television resides in the required speeds of operation. The use of the wide band required for this system would be justified by the well known advantages of a pulse-code system which have been pointed out by Oliver, Pierce and Shannon1. Regenerative repetition of the on and off binary pulses at repeater points permits the relaying of the signal to great distances without introducing any significant degradations due to noise or distortion arising in the medium. In addition, the coding process permits the trading of bandwidth for noise advantage on a very favorable basis. GENERAL CONSIDERATIONS As is well known, PCM is a form of time-division modulation. The information to be transmitted is sampled at regular intervals. This process results in a definite and limited number of amplitudes per unit of time which replace the original wave in subsequent operations. When the sampling frequency is at least twice the highest frequency present in the original wave, the resulting distortion falls outside the desired band and can be removed by a low-pass filter in the output of the system. For a system of fixed * Presented orallv before the I .