Patent GB-1487221-A (GB)
Title: Methods of displaying radar video signals
IPC: G01S7/06
Filed: 1974-07-04
Abstract: 1487221 Pulse radar MARCONI CO Ltd 15 Oct 1974 [4 July 1974] 29620/74 Heading H4D Radar video signals have their instantaneous amplitudes sampled and measured at a first predetermined rate, their measured instantaneous magnitudes are stored, and are read out at a second predetermined rate, which is greater than the first predetermined rate. A retimed video signal is thereby obtained, which is used in a display unit. As described, a computer system 10, Fig. 1, comprises an arithmetic and logic processor 12, a display processor and buffer 14, a store 16, and a radar service module 18 connected to a common highway 20. The system 10 receives azimuth and sync information and provides, by way of an X-Y integrator and deflection generator unit 22, one output which controls the scanning of a display unit 26, and another output which controls the retiming of the incoming video signal in a unit 24. The computer system is programmed according to the off-centre and expansion conditions required in the display. The module 18 utilizes azimuth and sync information derived from the radar head to update information held in the store 16, from the contents of which the display processor and buffer 14 produces digital signals representative of the starting position of the scanning spot on the display unit 26 and of the X and Y scanning speeds. The unit 22 produces corresponding scanning circuit voltages from said digital signals. In the video retimer 24 an analogue/digital converter 30, Fig. 2, samples the incoming video signal each time it receives a command signal from an encode rate and control circuit 32, and produces a digital output which is fed into one or other of two shift registers 34, 36 via a changeover switch 38. Whilst a video signal is being written into one shift register the immediately previous video signal, recorded in the other shift register, is being read out at a different rate by a digital/analogue converter 39 responsive to a decode rate and control circult 40. The retimed video output appears on an output terminal 42. The encode rate and control circuit 32 is connected to the computer 10, to a sync terminal 48, and to a start range circuit 46, which is also connected to the computer, and which has stored in it a number indicative of the range from which display is to commence. Upon receiving a sync pulse, the circuit 32 sets a counter 44, which then counts pulses fed to it from a clock 50. When the stored number value is reached, the circuit acts on the converter 30 to commence sampling. The decode rate and control circuit 40 is enabled by the aforesaid output from the unit 22 to read the information in the other shift register at the rate determined by the computer to match the read out rate to the speed of movement on the scanning spot. As with the encode rate and control circuit 32, the decode rate and control circuit 40 is connected to a counter 52, which counts the pulses from the clock 50. Changeover of the switches 38, and consequently of the functions of the shift registers 34, 36, is effected by the sync pulses. By making the read out rate greater than the write in rate, a dead time is created, which may be utilized for inserting additional information in the display.