Abstract :
Proposals are made for Television and Broadcasting Transmission Systems. These proposals visualise television standards and Transmission methods different from those previously used. It is proposed that:? (a) Two polarisations be used for television transmission, vision signals using vertical and sound signals horizontal polarisation, both transmissions sharing a common frequency spectrum. (b) Interference between the vision and sound transmissions be combated by the introduction of an antiphase sound signal into the vision signal, and by the use of a time modulated pulse transmission for sound. A method of combatting interference between sound and synchronising by having some synchronising between the different pulse trains used for sound transmission and synchronising is suggested. (c) Each transmitted picture has 640 lines due to a three-way interlacing, and that provision be made in the transmission for increasing the line structure up to 1,280 lines per picture. (d) Two methods of frame synchronising be available, one due to a difference in duration between line and frame synchronising pulses, and the other due to the changing of the basic carrier frequency during the frame synchronising period. It is further proposed that frame synchronising makes provision for automatic colour phasing in an experimental colour transmission system. (e) The time modulated pulses used for sound transmission have a repetition frequency of 32 kc/s, and that these pulses retain up to the ninth harmonic of the pulse repetition frequency. The signal to noise improvement as compared to amplitude modulation is discussed ; an improvement, as compared to amplitude modulation of 29 2 db. in the case of random noise, and 34 db. in the case of car ignition noise is claimed. By the adoption of three ranges of service area for different services, two polarisations, and a time modulated pulse. system with a repetition frequency, of 20 kc/s for local sound services, it is shown that one televis- ion transmission with stereophonic sound, and 21 broadcast sound transmissions can be provided in any one location. It is shown that the number of frequency channels or spectra required to give adequate television programme coverage to a large area of country can be decreased by increasing the frequency ; this decrease being due to the greater attenuation beyond the horizon for higher frequencies. In order to avoid interference between transmissions in different areas served by a common television programme, it is suggested that if frequencies in the neighbourhood of 42 Mc/s were used, seven channels would be required, as against five channels when using frequencies in the neighbourhood of 250 Mc/s. It is pointed out that there may be advantages for local sound services in covering an area by the use of a large number of low power transmitters, rather than by a smaller number of higher powered transmitters. The author suggests that the existing air raid syren poles and power supplies could form the basis of such a low power transmission system.
