GB871238A - Television apparatus - Google Patents

Abstract

871,238. Television. ASSOCIATED TELEVISION Ltd. April 11, 1958 [April 11, 1957], No. 11957/57. Class 40(3) A television system includes means for producing a "cue" signal and for inserting it in a television signal waveforms so that it may be reproduced as a visible indication on a picture tube to which the waveform is supplied. The "cue" signal is derived from a train of pulses produced by a multivibrator 5 under the control of each pulse of a train of twelve pulses produced during each vertical scan by a gate 4 to which line and frame frequency pulses of variable width derived from the line and frame synchronizing pulses of the system via multi-vibrators 2, 3 and 9, 10 respectively are supplied. The output of multivibrator 5 is then modulated in a circuit 6 by a 0À5 Mc/s. signal to produce the "cue" signal which is supplied via an amplifier 13, rendered operative or inoperative at will by means of a switch 17, to a mixer circuit in which it is combined with the composite television signal. The "cue" signal is also combined with the composite synchronizing and blanking signals of the system in a mixer 15 and supplied to picture monitor tubes. The output of multivibrator 5 is also supplied via an isolating stage 12 and phase reversal stage 11 (the operation of both of which is controlled by the switch 17) as a blanking signal to the camera control circuits so that when it is desired to insert the "cue" signal in the composite signal (by operation of switch 17) the latter is blanked out in the position in which the "cue" signal appears. The "cue" signal, which is arranged to occur in the top right-hand corner of the picture, is primarily intended to be displayed on a monitor tube at one or more transmitting stations receiving a programme from a central studio to convey a warning that a break in the programme is about to occur so that each of them may prepare to transmit other individual programme material (e.g. advertisements). Alternatively, the presence of the "cue" signal may be arranged to effect automatic control of the new programme material e.g. by bringing into operation a telecine machine. Since the "cue" signal occurs at the top of the reproduced picture it is effectively concealed from ordinary viewers by the normal tube mark provided on overscanned domestic receivers. Reference has been directed by the Comptroller to Specification 633,424.