The design of dual-standard television receivers for the French and C.C.I.R. television systems

Abstract

There are several regions near the borders of France with Germany, Switzerland and Italy where a demand exists for a television receiver capable of functioning on either the French or C.C.I.R. systems. An inspection of typical television receivers for each of the two systems shows that there are essential differences in all parts of the circuit except the power supply, frame time-base and audio frequency sections. Consequently direct switching from one system to the other could involve a very large number of switching operations, including many in critical circuits where switching may introduce difficulties. It is therefore necessary to see whether, by a suitable compromise, it is possible to use the same circuits for both systems with little or no degradation of performance. Where an acceptable compromise cannot be found the problem may be simplified by duplicating circuits and simply switching the h.t. supply. The extra cost of material in this case must be balanced against the extra complication of switching in critical circuits, taking account of the limited demand for dual-standard receivers which restricts the amount of effort which can reasonably be spent on development. The design of a complete dual-standard receiver is treated section by section, alternative methods of switching are examined against the background of current practice and a preferred solution is outlined where possible or the lines along which such a solution may be sought are indicated.