GB592741A - Combined television and sound receiver system - Google Patents

Abstract

592,741. Television receivers; pulse multiplex signalling. STANDARD TELEPHONES & CABLES, Ltd. June 1, 1945, No. 13816. Convention date, June 12, 1944. [Classes 40 (iii) and 40 (v)] A receiver for' combined television and sound signals in which the sound signals comprise time modulated pulses occurring during the horizontal blanking intervals employs the sawtooth voltage source of the image reproducer for the demodulating wave of the sound channel pulse demodulator. The combined signals are amplified and detected in channel 6, Fig. 2, which may include a R.F. amplifier, a mixer, I.F. amplifier and seconddetector. The output of this channel curve a, Fig. 1, comprising vision signals 2, blanking signals 3, synchronising pulses 4 and sound pulses 5 is passed through a threshold clipper 7, Fig. 2, which produces the signal b, Fig. 2. This signal which is fed to a saw-tooth generator 9, adapted to be triggered by the synchronizing pulses 4 but which is not affected by'the sound pulses 5, is also fed to the first grid of valve 12 via the condenser 13 which has a capacity such that when a first pulse reaches the grid, grid current flows and 13 is charged thereby applying a negative potential to the grid which is sufficiently high so that 12 accepts only the tips of the pulses. The amplitude of these pulses should be at least large enough to drive the valve to plate current cut-off. The output of generator 9, curve c, Fig. 1, which provides scanning signals for the image reproducer 11, Fig. 2, is fed to the second grid of valve 12 so that when each of the pulses 4 appears on the first grid the potential of wave 10 is at its lowest point 15. At a time between points 15 and 16, determined by the time modulation of the individual pulses, one of the pulses 5 appears and the resultant output of the valve 12, curve d, Fig. 1, in which the amplitude of the sound pulses 5 defining the sound signal envelope 18 is proportional to the time interval between pulses 4 and 5, is fed via a low pass filter 17, Fig. 2, to the audio reproducer 19.