GB1204190A - Multiplex communication system - Google Patents

Abstract

1,204,190. Multiplex pulse signalling. MAINICHI BROADCASTING SYSTEM and NIPPON ELECTRIC CO. Ltd. 22 Dec., 1967 [26 Dec., 1966], No. 58533/67. Heading H4L. Means are provided for transmitting a signal A, e.g. a facsimile signal, in repetitive gaps in a signal B, e.g. a television signal. As described, a facsimile signal in the form of a binary pulse train is transmitted during the vertical blanking intervals of a television signal, the pulses being positioned so that they avoid the blacker than black level and being such that they do not exceed the peak white level. The pulses of signal B are written into a store by a continuous pulse train and read out at a higher speed by pulse groups during the vertical blanking period, the converse occurring at the receiver. At the television transmitter the output of a facsimile transmitter 1 is detected at 2 and supplied to a twenty bit shift register 6 under the control of pulses from 7. The television signal is supplied via terminal 13 to a mixer 11, the vertical and horizontal sync. signals being selected at 12 and supplied to control the oscillator and frequency multipliers 3 and 5 respectively. Oscillator 3 produces an output frequency of 1200 c/s. in response to the input of 60 c/s. and oscillator 5 produces an output of 63 kc/s. with an input of 15À75 kc/s. The output of oscillator 5 is gated at 8, to produce a group of twenty pulses at an appropriate time within each vertical blanking interval, by a pulse from generator 4 controlled by the vertical sync. signal. These pulse groups together with the 1200 c/s. pulse train are supplied via the mixer 7 to the shift register 6, the facsimile signal being written in by the 1200 c/s. pulse train and read out by the pulse groups. The output of the register is supplied via a pulse shaper 10 controlled by the pulses from gate 8, to a mixer 11 where it is combined with the television signal. Similar equipment is provided at the receiver for extracting the facsimile signal. In a modification, instead of the presence or absence of pulses representing the facsimile signal, two different pulse durations are used so that the timing information for the pulse groups is contained in the groups, thus enabling the pulse generator 4, oscillator 5 and gate 8 to be dispensed with at the receiver. In a further arrangement a group of reference pulses may precede or follow the group of pulses carrying the facsimile signal.