GB612533A - Multiplex signalling systems - Google Patents

Abstract

612,533. Multiplex radio signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 18, 1946, No. 12095. Convention date, April 20, 1945. [Class 40 (v)] In a television transmitter a low-frequency signal, e.g. sound, is transmitted as a frequency modulation of a sub-carrier generated only during line fly-back periods of the vision signal. The invention is stated to be applicable to other communication systems in which intelligence signal modulations of one character are transmitted with an interspersed series of control pulses which repeat at a uniform rate at a predetermined signal amplitude. Transmitter.-As described, video signals from an image pick-up unit 11, Fig. 1, are applied through amplifier 13 to a mixer 15 feeding the transmission channel 79. The synchronizing signal generator 17 feeds line and frame synchronizing pulses and horizontal and vertical blanking pulses to the mixer 15 from terminals SH, SV and BH-V respectively. Sound signals from the microphone 19 and amplifier 21 are passed through the low-pass filter 23, having a cut-off frequency of substantially half the line-scanning frequency, to control a thermionic reactance tube 27. Keying pulses at line frequency are taken from terminal 29 of generator 17 and lead slightly with respect to the horizontal synchronizing pulses at terminal SH. The horizontal blanking pulses are suitable for this purpose and they are shaped in unit 31, which emphasises the highfrequency components and suppresses the lower frequency components, and then fed through a peak power amplifier 43 to'the anode of a sub-carrier oscillator tube 45. This tube is thus arranged to generate oscillations until cut off just prior to the termination of the line synchronizing pulses and their frequency is modulated by the reactance tube 27 under the control of the sound signals. The resulting pulses of frequency modulated sub-carrier are fed to a frequency tripler 71, the output from which is passed to the mixer 15 through an amplifier 75. Receiver.-The signal receiver 85, Fig. 2, passes the video signals to the grid 97 of the image-producing tube 100 over conductors 95, 96 and to the filter 107 over conductor 89. This filter removes the sound sub-carrier from the synchronizing pulses which are then derived from the synchronizing separator 109 and fed to the deflection control circuits 112, 113 associated with the deflecting coils 102 ... 105 of the tube 100. The sound channel comprises a gate amplifier 121 following an inverter stage 117 and feeding the selected frequency modulated pulses to a discriminator 129 amplifier 131 and reproducer 120. The gating control pulses are derived from a generator 125 synchronized by circuit 123 controlled by the output from amplifier 121. Detailed circuit arrangements are described in the Specification, Figs. 3, 4 and 6 (not shown). Specification 595,730 is referred to.