| 摘要 |
<p>1,160,862. Colour television; wired broadcasting. COMMUNICATIONS PATENTS Ltd. 19 May, 1967 [27 May, 1966], No. 23879/66. Headings H4F and H4R. A wired broadcasting system comprises a transmitting apparatus 1 which receives PAL type colour television signals radiated from a broadcasting transmitter and modifies them for transmission on conductive network 2, 3 to receivers 6 and 7. In the transmitter 1 the received signals are fed to device 16 which provides on line 17 brightness information and suppressed carrier wave colour carrier information in respect of first and second colour carrier information signals, the phase of the second colour carrier information signal being periodically reversed, on line 18 line scanning pulses, and on line 19 colour bursts. The bursts are fed to a comparator 20 and frequency control arrangement 24 to synchronize an oscillator 21 which generates a pilot carrier wave at the burst frequency. The frequency of the pilot carrier wave is doubled, 26, and phase inverted, 30, every line and the resulting oscillations are modulated, 32, by the brightness and colour carrier information on line 17. After passing through a vestigial sideband filter 34<SP>1</SP> and being added, 25, to the pilot carrier wave, the signal transmitted over conductors 2, 3 comprises a brightness information carrier component having a carrier wave 8, a suppressed carrier wave colour sub-carrier information component in respect of the first and second colour carrier information signals, having a suppressed sub-carrier wave 10, and a pilot carrier wave 12, the phase of the brightness and first colour information components being reversed at line frequency. The frequencies of the pilot carrier wave 12, the carrier wave 8 and the suppressed sub-carrier wave 10 are related in the ratio 1:2:3. In the receiver 6 the signals from conductors 2, 3 are fed to a bandpass filter 37 which selects the brightness and colour information components. These signals are amplified, 38, and demodulated by an envlope detector 39 to produce on line 40 a brightness information signal of video frequency. The suppressed carrier wave colour sub-carrier information signals are derived from the output of detector 39 by means of a band pass filter 41 and two synchronous detectors 42 and 43. The second colour information signal is obtained from detector 42 by means of a re-insertion carrier wave of constant phase derived from the pilot carrier wave by means of a narrow band pass filter 44 and amplifier 45. The first colour information signal is obtained from detector 43 by means of a reinsertion carrier wave the phase of which is reversed at line frequency derived from a balanced mixer 48 fed with the amplified pilot carrier wave and the brightness carrier wave, the phase of which is reversed at line frequency. The brightness carrier wave is derived from the output of amplifier 38 through a narrow band pass filter 49.</p> |
