GB1307653A - Television systems - Google Patents

Abstract

1307653 Multiplex radio signalling INTERNATIONAL STANDARD ELECTRIC CORP 19 April 1971 [25 March 1970] 24508/71 Addition to 1306467Heading H4L In a television transmission system of the type disclosed in the parent Specification, the transmitter includes a storage device to store during n frame periods where n is greater than 1, a plurality of audio signals occurring during those periods and is arranged to transmit the stored signals during normally unused line sweeps between the end of said n frame periods and the start of the next frame, a line identification signal being derived from the transmitted signal at the receiver to select a desired one of the audio signals. As described, Fig. 1 (not shown), two different signals are transmitted, each signal being stored in separate stores over two frame periods, (n= 2) so that the two signals are interlaced frame-by-frame, but more than two frame periods may be used. When storage extends over two frame periods in systems employing line interlacing the phase relationship between the line sync. pulses and the frame sync. pulse may be used to provide an identification signal of half the frame frequency, Fig. 2 (not shown). When the storage of a signal extends over more than two frames special line identification signals must be transmitted. As described, where the storage extends over n frames, a high frequency sinusoidal identification signal is transmitted between two of the equalizing pulses of the frame sync. signal. At the receiver, Fig. 3 (not shown), a tuned circuit responsive to the identification signal is gated by the frame sync. signal and the output rectified to produce a D.C. identification signal. Fig. 4 shows a transmitter circuit where n=2. With switches 37, 38, 41, 42 as shown audio signals on lines 32, 33 are supplied to stores 35, 36 respectively, at a low rate f T supplied via terminal 39. During this period the video signals from line 34 are supplied to the output 43. A counter 44 counts line sync. pulses applied at 48 and is reset by frame sync. pulses applied at 47. Oppositely polarized identification signals are supplied via terminals 49, 50 to AND gates 45, 46 respectively. Gate 45 transmits a control signal to change over the switches 37, 42 during line one of the "first" frame blanking interval and the samples stored at 35 are read out in timecompressed form at a high frequency F T applied to terminal 40 after which switches 37, 42 return to their original position. During line two of the second frame blanking interval, gate 46 transmits a signal to change over the switches 38, 41 so that store 36 is read out at high frequency F T . Other sound channels may be transmitted by using further AND gates and outputs of the counter. A similar arrangement is used at the receiver, Fig. 5 (not shown), for two audio channels and, Fig. 6 (not shown), for more than two audio channels. These circuits are controlled by the above mentioned identification circuits, Fig. 2 or 3 (not shown). The storage devices may be of the type disclosed in Specification 1,307,652.