| 摘要 |
1,177,571. Colour television. GENERAL ELECTRIC CO. 10 Jan., 1967 [18 Feb., 1906]. No. 1233/67. Heading H4F. A N.T.S.C. (or similar) type of colour subcarrier wave is synchronously detected at three phase angles by an arrangement as shown in Fig. 2 (which is specifically directed to the N.T.S.C. system) where the reference carrier at 270 degrees from source 2 is applied via a first transformer 12 to produce outputs at 90 degrees and 270 degrees to operate the R-Y detector 26 and is also applied via a 90 degree phase shift circuit 28, 30 to produce from a second transformer 34 outputs at 0 degrees and 180 degrees to operate the B-Y detector 40, the transformers each having further secondary windings 44, 46 and 48, 49 which are interconnected to combine the quadrature phase signals in such manner as to produce outputs at 57 degrees and 237 degrees to operate the G-Y detector 42. Production of the desired phases of 57 degrees and 237 degrees is effected by appropriate selection of the coupling and/or turn ratio of the further secondary windings. The arrangement may be set up so as to produce phases other than those indicated, reference being made to the use of a phase shift in source 2, other than a 90 degrees phase shift for network 28, 30 and the use of auxiliary phase shifters and attenuators. Modified arrangements are described with reference to Figs. 3 and 4 (not shown) which produce carrier signals at 0 degrees, 90 degrees and 237 degrees only and are intended for use where the synchronous detector each require only a single phase for their operation. A detailed construction of transformers 12 and 34 is described with reference to Figs. 5-7 (not shown). |
