GB1056078A - Improved wired broadcasting systems and apparatus therefor - Google Patents

Abstract

1,056,078. Distributing music etc.; colour television. COMMUNICATIONS PATENTS Ltd. Aug. 16, 1963, No. 32409/63. Headings H4F and H4R. In a wired broadcasting system pertaining to two colour television transmissions, there is applied to a conductive network, in respect of each transmission, a modulated carrier wave brightness information component and a modulated carrier wave colour information component. The frequencies of the carrier waves in respect of each transmission differ from each other by a multiple of the line scanning frequency and one carrier wave is phase-reversed with respect to the other at the field scanning rate. Also the frequency of the carrier wave of the brightness information component which pertains to one transmission corresponds to an even multiple of sixths of the line scanning frequency, which multiple is indivisible by six to produce a quotient which is an integer. The frequency of the carrier wave of the brightness information component which pertains to the other transmission corresponds to a different even multiple of sixths of the line scanning frequency which multiple is indivisible by six to produce a quotient which is an integer. Beats which arise due to second order distortions take the form of a relatively unobtrusive dot pattern. Preferably the two brightness information carrier wave frequencies differ by a frequency which corresponds to an even multiple of sixths of the line scanning frequency, which multiple is indivisible by six. The system is suitable for use with 625-line S.E.C.A.M. transmissions. The transmission equipment is generally similar to that described in Specification 1,055,443 but the output of the modulator 12 comprises an amplitude modulated carrier wave 15 (Fig. 2, not shown) which corresponds to an even multiple of sixths of the line scanning frequency P which multiple is indivisible by six (e.g. 2080 P/6 = approx. 5À4 Mc/s.). The frequency f 2 of the carrier wave of the colour information component (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 output of the modulator 20 has a carrier frequency f 3 (e.g. 2084 P/6 = approx. 5À4 Mc/s.) in respect of the amplitude modulated carrier brightness information component and a carrier frequency f 4 in respect of the complex frequency and amplitude modulated carrier colour information component. The difference f 4 -f 3 is again the same as that adopted for the television line standard concerned. Receiver.-The description of the receiver is identical with that of Specification 1,055,443.