Patent GB-586034-A (GB)
Title: Intelligence transmission system using modulated pulses
IPC: H04N7/084
Filed: 1944-05-30
Abstract: 586,034. Pulse modulation ; television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 30, 1944, No. 10413. Convention date, May 29, 1943. [Classes 40 (iii) and 40 (v)] The invention relates to a television system of the kind in which the accompanying sound is transmitted in the form of modulated pulses. Fig. 1 shows the general arrangement at the transmitter. The video signal from a television scanner 10, after amplification at 16, 17, 18 is fed to a valve 25, the output from which is combined with the output from a sound signal amplifier 26. The combined vision and and sound signal, after amplification at 113, is fed to a modulator 23, where it is modulated on to a carrier wave from oscillator 31 for radiation from an antenna 33. A master pulse generator 14 controls the operation of sawtooth generators 11, 12 which produce the horizontal and vertical synchronising pulses, respectively. These pulses control the scanner 10 and are also fed to amplifier 17 for blanking during retrace periods. The combined outputs from 11 and 12 are also fed from combining amplifier 21 to modulator 23 for radiation on the carrier wave. The sound channel comprises a multivibrator 72, controlled by the horizontal (line) sychronising pulses from 11, which produces pulses which after shaping are modulated in amplitude in modulator 37, in accordance with the output from sound channel 34, 35, 36, and then passed through wave shaper 39 to produce width-modulated pulses occurring during the retrace periods. The vertical (frame) blanking interval is notched by a special generator 69 to provide an interval for the sound pulses during the frame retrace period. The modulated sound pulses pass through valve 26 for combination with the video signal from valve 25 and thence to the carrier modulator 23. The combined wave form for modulation on the carrier wave at 23 is shown in Fig. 14, in which 114 are the horizontal or line synchronising pulses, and 115 are the width modulated sound pulses. The .vertical or frame synchronising pulse 119 is shown notched by the special generator 69 to provide a space for the sound pulse 115. Fig. 2 shows a receiver of the superheterodyne type, in which the output from detector 47 includes the sound and vision signals, together with the synchronising pulses which after separation at 48, control vertical and horizontal deflection generators 53, 52 to control the scanning of the image reproducing device 56, to which is fed the output from a picture amplifier 57. The composite output from 57 is also fed to a selector 60 which is rendered conductive only during the sound pulse periods by means of pulse from a generator 64, controlled by the horizontal defection generator 52. The selected pulses are demodulated in a low-pass filter 63 and the signal modulation is reproduced at 68. The generator 64 also supplies by lead 155 pulses for blanking the image reproducing device during the sound pulses. The usual blanking connections are also employed. The audio amplifier is biassed off except when the receiver is in synchronism with the incoming signal (Fig. 15, not shown). Figs. 3 and 4 show a circuit for producing the modulated sound pulses in units 34 ... 39 and 72, Fig. 1. A multivibrator 72, Fig. 3, produces pulses Fig. 7, which are differentiated at 76, 77, 78 and inverted at 85 to give the wave form of Fig. 8. This is combined at the anode of 81 with the original pulse fed over line 80 to give a current wave, Fig. 9, which provides across condenser 89, a voltage wave, Fig. 10. This wave, taken from the anode of 88 is combined at the anode of 96, Fig. 4, with the output of low-pass filter 36 (Figs. 1 and 4) fed with the audio signal. This produces in lead 97, Fig. 4 a wave as in Fig. 11 which, after passing the dipper stages 102-104, produces width modulated pulses as in Fig. 13, ready for combination with the video sighal.