GB1055443A - Improved wired broadcasting systems and apparatus therefor - Google Patents

Abstract

1,055,443. Distributing music etc.; colour television. COMMUNICATIONS PATENTS Ltd. Aug. 16, 1963, No. 32408/63. Headings H4F and H4R. In a wired broadcasting system pertaining to colour television, there is applied to a conductive network a modulated carrier wave brightness information component and a modulated carrier wave colour information component, the frequencies of the carrier waves differing from each other by a multiple of the line scanning frequency and one carrier wave being phasereversed with respect to the other at the field scanning rate. Also the frequency of the carrier wave of the brightness information component corresponds to an odd multiple of half the line scanning frequency. Beats which arise due to second order distortions take the form of a relatively unobtrusive dot pattern. The system is suitable for use with 625-line S.E.C.A.M. transmissions. The transmission equipment comprises two similar transmitters 7, 8 (Fig. 1) energizing signal paths 1, 2 adapted to feed subscribers' receivers 3, 4. Transmitter 7 includes a radio wave receiver 9 adapted to receive, from an aerial 10, colour television signals. Receiver 9 extracts brightness information signals which include colour bursts and synchronizing signals, and modulated carrier wave colour information signals. These signals are applied to a balanced modulator 12 having as an input an electric wave from an oscillator 13 comprising an ovencontrolled crystal drive. The output from modulator 12 comprises an amplitude modulated carrier wave brightness component having a carrier wave 15 (Fig. 2, not shown) of frequency f 1 which corresponds to an odd multiple of half the line scanning frequency (e.g. 693 P/ 2 = approx. 5À4 Mc/s.), the modulation thereof by the brightness information signals occupying the band 16. The output also comprises a complex frequency and amplitude modulated carrier colour information component occupying band 17. The frequency f 2 of the colour carrier (approx. 9À83 Mc/s.) is such that f 2 -f 1 is the same as that adopted for the television line standard concerned (approx. 4À43 Mc/s.). The difference f 2 - f 1 may be such that band 17 lies outside, or partially within, band 16. Transmitter 8 is similar. Receiver.-An amplifier (Fig. 3, not shown) is connected by a switch 29 (5 or 6 of Fig. 1) to the signal path 1 or 2. A detector provides an output comprising brightness and colour information signals. This output is applied to a matrix 32 and to a band pass filter 33, the latter passing only the colour information signals. These are fed to switches 34, 35 and to a delay device 36 from which delayed colour information signals are fed to switches 37, 38. Output signals from switches 34, 37 are combined and fed to a demodulator 39 whilst output signals from switches 35, 38 are combined and fed to a demodulator 40. A colour burst separator 41 separates synchronizing signals by which the frequency and phase of a switching signal, produced by a switching signal generator 42, are controlled. The switching signal effects switching of the delayed and non-delayed colour information signals to demodulators 39, 40. Matrix 32 produces signals appropriate for controlling colour tube 43. A monochrome receiver may be connected to the system. Sound is transmitted at audio frequency.