Patent GB-1132303-A (GB)
Title: Television message system
IPC: H04N7/035
Filed: 1966-05-24
Abstract: 1,132,303. Multiplex radio signalling; television. RADIO CORPORATION OF AMERICA. 24 May, 1966 [28 May, 1965], No. 23239/66. Headings H4F and H4L. In a television system for transmitting and receiving message images in addition to television images, line scan signals representative of the message images are sequentially multiplexed with the synchronizing signals of the television images at the rate of one line scan signal per message per field time interval of the television images. Although a number of messages may be transmitted simultaneously, a television field interval is required for each message line scan. The message video information is preferably inserted into the interval between successive horizontal synchronizing pulses during the vertical blanking interval although for educational purposes it may be inserted during the picture interval of the television signal i.e. in an active line of the field interval. Message code signals e.g. different frequency bursts or digital code pulses, may be transmitted in addition to the message information, the receiving units being conditioned to respond to only particular code signals which tag the required messages. The receiving units sequentially store the individual message lines from the transmitted composite signal and after a complete frame is stored the message is viewed as a transient display on a television receiver screen or on a separate storage CRT, or a photographic print is made. A transmitting unit, Fig. 2, comprises a synchronizing signal generator 10 for a conventional television studio equipment 14, the programme signal from which is combined in adder 18 with the single line video message signal. The horizontal synchronizing pulses are coupled directly to a message pick-up deflection circuit unit 22 and the vertical synchronizing pulses are coupled via vertical synchronizing pulse phase shifter 28 to unit 22. A message pick-up unit 34 which may include a vidicon camera or a slide scanner is controlled by the deflection signals and is focused on to a message 36, which is driven in front of the pick-up unit. The video message signals so developed are coupled to a message line selector 40 which is a gated unit which sequentially selects a predetermined line of the video message signal for coupling to adder 18. The gating of selector unit 40 is controlled by an internally generated enabling pulse which bears a predetermined time position relative to the vertical pulse developed at output terminal 26 of generator 10 and coupled to unit 40 along with the horizontal pulse developed at terminal 24. This enabling pulse is timed to coincide with that space or interval between successive horizontal synchronizing pulses. during the vertical blanking interval into which the video message signal is to be inserted. Phase shifter 28 includes a pulse delay network selected to provide a constant phase shift to the vertical synchronizing pulses such that the single line video message signal occurs during its field interval at a point where introduced focus problems are minor e.g. near the middle of the field interval. This phase shift together with the movement of message 36 is such that different and relatively distortion-free lines of message signal information are inserted into that horizontal space of each vertical blanking interval coinciding with the predetermined position of the enabling pulse generated within selector unit 40. The speed of movement of message 36 determines the vertical resolution of the message system. Different horizontal intervals may be used for different types of message information but when there are more types of messages to be transmitted than there are spaces available more than one type of message information may be transmitted in a given horizontal period of the vertical blanking interval by means of a coding arrangement including a message code generator 42 and a second message line selector unit 44. Generator 42 assigns a different message code e.g. a burst of energy of different frequency or a series of pulses of different position, for each type of message while the message line selector 44 is a gated unit arranged to select the horizontal interval into which the identifying code is to be inserted i.e. transmission of code signals frequencies f 1 , f 2  . . . in horizontal interval S 1  may indicate transmission of different types of message information in the succeeding horizontal interval S 2 . The message code generated and the horizontal space into which the message line is inserted may be controlled by a message category detector 46 comprising an array of photo-detector devices and matrix switching arrangements aligned to scan coded segments of the moving message 36 e.g. light reflecting strips B and C (line A represents the line of the message scanned). In a second embodiment of a transmitting unit, Fig. 3 (not shown), in which the message (36) is stationary rather than moving, the single line video message signals are injected into predetermined horizontal spaces of the vertical blanking intervals through the action of a vertical synchronizing frequency slipper (48) which provides a slip of exactly one horizontal line per interlaced television field (or for greater resolution per television frame) between the vertical deflection for the studio equipment unit (14) and the vertical deflection for the message pick-up unit (34). A message signal may be inserted into a conventional television signal, or a message signal may be removed and replaced by a new message signal at a point remote from the television studio, Figs. 4 and 5, not shown. A transmitting unit in which the message signal lines are transmitted during the picture interval of the television signal is described with reference to Fig. 10, not shown. A receiving unit may comprise a rotating magnetic drum recorder which stores the individual message lines and then displays the entire message on a television receiver screen, Fig. 6, not shown. A " Polaroid " (Registered Trade Mark) camera may be used to obtain a print of the stationary message by exposing the film to successive message lines formed on a display cathode-ray tube, the camera shutter being opened at the start of message transmission and left open until the entire message is received, Fig. 7, not shown, and for a moving message, Fig. 8, not shown. A moving message having any number of lines may be recorded by using a thin window tube which displays only one line at a time and focusing the successive lines on to a moving film so that each message line is written below the previous line, Fig. 9, not shown.