| 摘要 |
<p>1,175,427. Delay equalizers. COMPAGNIE FRANCAISE THOMSON HOUSTONHOTCHKISS BRANDT. 29 March, 1967 [29 March, 1966], No. 14397/67. Heading H1W. Group delay distortion in a V.H.F. or U.H.F. signal, e.g. a television signal, is corrected by means of a hybrid network having a pair of conjugate ports terminated by equal or opposite reactances in the form of overcoupled resonant cavities. In the example shown, a ring hybrid AH has two conjugate ports 2, 4 connected by lines el, e2 of equal length respectively to identical overcoupled, concentric-line, resonant cavities R1, R2, the coupling to R1 being inductive and that to R2 being capacitative. Such a circuit behaves in the same manner as an all-pass lattice network, an input applied at port 1 being transmitted to port 2 without reflection or attenuation but with a phase shift which varies from 0 to - 360 degrees as the frequency varies around the resonant frequency of the cavities. The rate of variation is determined by the degree of coupling of the cavities. In order to obtain a required delay v. frequency characteristic, a number of such circuits are connected in tandem and the characteristic of each is adjusted separately. The couplings to the cavities R1, R2 may be of the same type, i.e. both capacitative or both inductive, if the distances el, e2 are made to differ by one quarter-wavelength. The arm 3-4 of the ring may either incorporate an inversion I producing a 180 degrees phase-shift or may be one halfwavelength longer than the other three arms. The ring hybrid may be replaced by a directional coupler or by a magic-T.</p> |
