Picture transmission using time modulation

The transmission of still pictures by the method of time modulation is investigated and found to be not only entirely practicable but also to provide pictures over line and by short-wave transmission in which the interference due to fading is much less than is the case with the usual amplitude modulation method. Time modulation consists in translating picture tone values into corresponding times of interruption of a constant frequency carrier. Two means of time modulation are devised and tested; one using a gasfilled discharge tube and the other a mechanical vibrator with a photoelectric cell. The latter arrangement is found to be steadier than the former, it has been employed sucessfully on various occasions since 1935 for long-distance experimental transmissions, e.g., Tokyo to Berlin, London and San Francisco.