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1950 LARGE-SCREEN TV PROJECTION 511
preselected introductory material can be transmitted before an eagerly expected event the nature of which does not allow of accurate timing. Thereby one of the criticisms of instantaneous projection in comparison with the intermediate film method of large screen television is removed.
The relay station chosen for the first experiments stands on the highest ground in the South of London, and our aerials are located on the top of a water tower in the grounds of the Crystal Palace, giving an undisturbed coverage of the London basin containing most of the suburbs, and particularly the West End area.
I would like to remark that it is a peculiarity of English television that, while being so eminently modern, it seems to be located in nineteenth-century palaces, the Alexandra Palace and the Crystal Palace, neither of which is in fact a palace and one of which does not now exist.
Construction of Equipment
The circuit of the receiver and the video chain of the projector are similar to those being described by Mr. J. E. B. Jacob in a separate paper to this convention.3
Figure 1 is a block diagram of the projector which shows considerable simplification over that shown last year.
To meet installation requirements the equipment is divided into four groups of units :
1. The units contained in the projector itself, which is located in the auditorium and should for this reason contain as little equipment as possible;
2. The units contained on the racks in the television operating room, which can be remote up to 100 ft from the projector, and by virtue of the separate picture monitor and indicating instruments need not be in a place where the large screen can be seen by the operator;
3. The high-tension unit which can be located anywhere within the cinema building; and
4. A small control unit which can be installed in the auditorium or the projection box at which small adjustments can be made to the picture quality, brightness, electrical focus and sound volume.
Video Chain
The function of the main units in the video chain is self-explanatory from an examination of the diagram. It will be noted that a gamma corrector is included. This is only at present an approximate correc