Patent GB-712985-A (GB)
Title: Improvements relating to the display of information in code
Inventor: THOMAS DAVID CALDWELL
IPC: G09G1/22
Filed: 1951-02-20
Abstract: 712,985. Television. BRITISH THOMSONHOUSTON CO., Ltd. Jan. 23, 1952 [Feb. 20, 1951], No. 4114/51. Class 40 (3). [Also in Group XL(c)] In television apparatus for the display of coded image information in which the in formation is derived by means of a signal-generating system, e.g. a monoscope or flying-spot scanner, the signal obtained from the system is mixed with a further signal from a second signal-generating system and the combined signal passed through an amplifying channel possessing a characteristic such as to invert the sense of the signal voltage from the first signal-generating system when a signal voltage of a predetermined value is obtained from the second signal-generating system whereby the information conveyed by a particular image may be increased. As shown in Fig. 1 image information derived from the signal plate 12 of a monoscope 10 is reproduced on a cathode-ray tube 11. The two tubes are scanned in a common raster in synchronism by means of unit 14 applying signals through amplifiers 15 and 16, and the signals from plate 12 are applied to the modulating grid 18 of the cathode-ray tube through amplifier 17. The signal plate may contain a large number of symbols, such as that shown at 26 in Fig. 3, arranged in rows and columns, the required symbol being selected by displacing the origin of the raster in the monoscope so that the raster covers the symbol. The symbol may be displayed in a corresponding position on the screen of the cathode-ray tube, a common shift circuit 19, 20 being employed to effect this, or, alternatively, the raster of the cathode-ray tube may be adjusted independently of that of the monoscope in order that the position of the selected symbol may convey information, e.g. the plan position of a radar echo. In accordance with the invention the signal derived from the plate 22 of a second monoscope 21 is combined with that derived from monoscope 10. The second monoscope is scanned in synchronism with the monoscope 10 by unit 23 synchronized over connection 24 and has an independent shift circuit 24', 25. The signal plate is provided with a number of rectangles of different sizes in white on a black background located at different parts of the plate. Amplifier 17 (see Group XL(c)) has an input/output characteristic as shown by curve (f) in Fig. 2 whereby an input signal (h) representing, say, white on black, produces a corresponding output signal (i) but an input signal (k), derived by the addition of a signal (j) to signal (h), produces a reversed signal (l) corresponding to black on white. Signals such as (j) are added to the normal signal by monoscope 21, the signals being arranged to correspond to selected parts of the symbol by suitably positioning the raster on a rectangle in the monoscope. By the addition of such signals variations in the reproduced image as illustrated at (a) to (f) in Fig. 3 may be produced, thus permitting one symbol to convey more information. If more information than can be accommodated on the signal plate of monoscope 10 is desired, two or more monoscopes may be operated in parallel. It is stated that further information may be conveyed by increasing the size of the displayed raster for the duration of a selected raster. A circuit for this purpose is described, Fig. 6 (not shown). Reference is made to the use of a radio link for the transmission between the monoscopes and cathode-ray tube 11.