Patent GB-1420746-A (GB)
Title: Visual display apparatus
IPC: G01S7/26
Filed: 1972-01-19
Abstract: 1420746 Pulse radar EMI Ltd 8 Jan 1973 [19 Jan 1972 24 June 1972] 2471/72 and 29702/72 Heading H4D Apparatus for providing a visual P.P.I. display of echoes in an azimuth-scanning pulseecho, e.g. radar, system comprises a rotatable member, e.g. a turntable 1, separately energizable light sources on said member, a digital store on said member having a storage location corresponding to each source and timing means for controlling the digital store, the store controlling the energization of the source and the store and timing means causing energized ones of said sources to remain energized for a major part of the inter pulse period of the energy pulses causing the echoes. Echo signals are passed via slip ring 4 (or an inductive or capacitive coupling) and a binary-quantizing threshold circuit (not shown) to gate 6, enabled by clock pulses from circuit 7. The signals are passed into shift register 3, a counting circuit 8 determining when the register is full. When register 3 is full, circuit 8 produces a signal on line 9 which inhibits circuit 7 via NOR gate 7<SP>1</SP> and which simultaneously enables gates G1 to GN to transfer the stored data to light sources, in this case gallium phosphide diodes, D1to DN. The diodes remain energized or de-energized, according to the data, for a period corresponding to the inter-pulse period of the radar. The brightness of a display element may be made proportional to the amplitude of the corresponding echo signal by cyclically varying the threshold of the quantizing device at a rate less than the display rotation rate or by using a number of shift registers with their outputs in parallel but their inputs fed via separate threshold circuits. In the embodiment of Fig. 2 (not shown) the analogue nature of the echoes is preserved by feeding the diodes in parallel with the analogue echo signal and enabling each diode sequentially by a shift register. The light source array may be composed of a number of sub arrays (25) to (28) (Fig. 5, not shown) placed end to end. In this case, certain of the diodes (29) to (32) are removed from the main array and placed along a radial offset from the radial of the main array, to enable the sub arrays to be sufficiently sealed together. The display may be arranged to give different maximum ranges in different sectors of the display and to give a non-linear range display along a particular radial by carrying the clock pulse frequency. The turntable 1 may be translucent or transparent to enable other information, presented behind the apparatus, to be viewed. Luminous range rings may be provided and the persistence of the display may be increased by (I) placing a luminescent screen in front of the light sources or (II) recording the echo signals by a storage tube or magnetic tape or wire recorder having a high speed playback. The radial brightness variation due to the different circumferential speeds of the light sources may be compensated by suitably (I) controlling the amplification of the signals applied thereto in Fig. 1, or (II) biasing the light sources in Fig. 2. Reference has been directed by the Comptroller to Specification 1,241,369.