GB596011A - Television system - Google Patents

Abstract

596,011. Multiplex pulse signalling. STANDARD TELEPHONES & CABLES, Ltd. July 13, 1945, No. 17955. Convention date, July 17, 1944. [Class 40 (v)] Television signals include a pair of pulses superimposed on the picture blanking signal one being a synchronizing pulse and the other a time-modulated pulse carrying a sound channel. In one embodiment, Fig. 1, a base wave oscillator 1 of twice the horizontal synchronizing frequency feeds a cusper time modulator 13 through a phase shifter 12. The source 14 of audio signals also feeds the modulator. 13 whose output pulses are shaped in amplifier 28 and one in four of which are selected by the gated amplifier 41 and fed to mixer 44. The conventional vertical synchronizing pulse producer 3 is controlled by oscillator 1, and feeds frame retrace blanking pulses over lead 3b to mixer 44, and synchronizing pulses over lead 3a to mixer 44 and to the picture signal source 43, whose output is fed to the mixer 44. A multivibrator frequency divider 4 fed from oscillator 1 supplies horizontal synchronizing pulses over lead 8a to the picture signal source 43 and mixer 44 after shaping in circuit 8 while horizontal blanking pulses from shaper 10 are fed to the mixer 44 and as gating pulses to amplifier 41. The output from mixer 44 modulates the radio transmitter 45. The wave forms at various points of the system, Fig. 2, are the base wave a from source 1, the output b of multivibrator 4, the horizontal synchronizing pulses c from shaper 8, the horizontal blanking pulses d from shaper 10, the output audio pulses g from the cusper modulator 13, and the same h after gating in amplifier 41. The composite signal output from mixer 44, curve i, shows the fixed horizontal synchronizing pulses 9 and blanking pulses 11, the time modulated audio pulses 32 and the lines of picture signals 47. In a modification, Fig. 5 (not shown), the time modulator for the audio pulses is operated from the horizontal synchronizing pulses. In a further embodiment, Fig. 6, the base wave from oscillator 1 is shifted in phase in circuit 51 and feeds the horizontal blanking pulse producer 52 which comprises a multivibrator 53 and clipper 54. A second multivibrator 56 synchronized by oscillator 1 and controlled by audio source 14 produces pulses 57, Fig. 7o, the leading edge of which is fixed and the trailing edge, 58, of which is modulated in time by the audio signal. Differentiation of these pulses in circuit 59 produces the synchronizing pulses 60 and audio pulses 61, Fig. 7p, which are clipped at levels 62, 64 respectively by shaper circuits 63, 65 respectively and fed to mixer 44. The horizontal synchronizing pulses, equalizer pulses and vertical synchronizing pulses are of different duration so that they can be separated by width discriminator circuits.