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11/17/36
"Everyone is saying that television is in its infancy, and, although, the results are far better tha.n most people expect, this statement is essentially true, and true to the extent that it is difficult for anyone at the moment to say what is the right number of lines and pictures to use and the best method of synchronization. This was one of the difficulties which faced the original Television Committee under Lord Selsdon, appointed by the Postmaster-General in May, 1934. Eventually, it was recommended that a television station should be set up in London to establish a service, but at the same time try out what they considered to be the two best systems available. These two systems use different transmitting conditions, and, although ultimately there must be standardization, this obviously should not be attempted until sufficient knowledge has been obtained to permit of a decision being reasonably permanent.
"Thus it came about that the two systems installed at the Alexandra Palace that is, those develooed by Messrs. Baird Television, Limited, and Messrs. Marconi-E. m". I . Television Co , Ltd. , respectively are to be used during alternate weeks. As already mentioned, the number of lines, the number of pictures, and the synchronizing pulses are not the same in each case. Receivers, therefore, must provide for this, ana a switch will be found, usually marked either with the two systems by name or with the number of lines used in each case, which is 240, 25 pictures per second, for the Baird system, and 405, 25 pictures per second interlaced (50 frames Der second), for the MarconiE.M.I. system.
"So much for the question of system, number of lines, and. pictures, etc. , but there are other important differences • which make. the performance of the new station less easy to pre¬ dict than in the case of an ordinary broadcasting station. The great width of the side-bands , or modulation frequencies which -lS essential for high-definition television, makes it impossible ^0 use ordinary broadcasting wavelengths, and we are forced aown to what are called the ultra-short wavelengths. In this case the wavelength used for vision is 45 megacycles per second
metres) and for sound 41.5 megacycles per second (7 24 metres).
_ "Most readers of this paper will know that, while great
stnaes have been maae in the technique of transmission on these ery short wavelengths during the past year or two, there is always some doubt as to the range to be expected. This is not because no measurements have been taken, but rather because reception depends very much on local conditions. We know already ^ at m some directions strength of reception does not die away reguiariy as the distance is increased. In fact, some places on ground will have a stronger signal than others which are i.. / nearer the station but on lower ground. Screening from
amgs containing a lot of metal is probable, while in all ases much better reception will be obtained from an aerial ected on a roof as compared with one erected nearer to the
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