A variable-definition camera channel for the appraisal of television standards

The paper describes an apparatus constructed for the study of various alternative standards of definition in television systems. The problem of appraising and comparing pictures produced by such television systems is discussed, and a consideration of the instrumental weaknesses in any method which involves two separate channels presenting the alternatives side by side, leads to the conclusion that the use of a single flexible channel may be a more desirable approach. A single equipment is described which is capable of being switched rapidly between any of six preselected scanning standards covering the range of line frequency from 10 to 32 kc/s, the frame frequency being, in all cases, that of the main supply. The apparatus also permits the effects of bandwidth restriction, phase distortion and aperture loss to be studied. Each of the more interesting units is described in some detail, and the results of some of the investigations which have been carried out with the aid of the apparatus are discussed.