Patent GB-972776-A (GB)
Title: Improvements in or relating to radar display apparatus
Inventor: AYLETT DOUGLAS ARTHUR
IPC: G01S7/24
Filed: 1962-04-02
Abstract: 972,776. True motion radar displays. DECCA Ltd. March 20, 1963 [April 2, 1962]. No. 12560/62. Heading H4D.  Radar true motion display apparatus for a mobile craft comprises a sine-cosine digitizer set in accordance with the direction of movement of the craft, means for applying input signals to the digitizer at time intervals corresponding to units of distance travelled by the craft, the digitizer providing, on receipt of an input signal, outputs in digital form representative of the sine and cosine of the digitizer setting, separate adding means for summing respectively the sine and cosine outputs from the digitizer and digital to analogue conversion means for converting the two summed components into analogue signals representative of the required displacements of the display. In the embodiment shown, which is for use on a ship, a log 16 feeds pulses to a sine-cosine digitizer 19, via switch 17 and pulse shaper 18, every time the ship travels 30 feet through the water. The digitizer 19 is set by a compass 15 via a repeater motor 21 and gears 22, such that every time a pulse is received from the log the digitizer produces signals proportional to the sine and cosine of the ship's compass heading, multiplied by the unit distance, 30 feet. These signals are produced in an eight-bit binary coded form with the eighth on highest code position representing 15 feet. The sine component signal is fed to a bi-directional counter 23 comprising eight bi-stable flip-flops, the coded bits being added to or subtracted from the respective flip-flop in accordance with signals fed to the counter on lines 24 and 25. The output of the last flip-flop unit 23 is coupled via switch 27 to a digital to analogue conversion unit 29, comprising a register 30 having nine bi-stable flip-flops 31. A pulse is thus fed to the register every time the sine component of the ship's movement increases by 30 feet, and is added to or subtracted from the total in the register, depending on the signals on lines 24 and 25, via switches 54. The register thus stores the total component distance gone by the ship, in a digital form, which is then converted to an analogue form by feeding the outputs of the nine flip-flops to a feedback amplifier 32, via suitably dimensioned attenuators 34. The output of the amplifier 32 is fed to a current amplifier 35 which feeds a signal to a coil 12, forming one of a pair of orthogonal true motion deflection coils 12 and 13. The cosine component output of the digitizer is similarly treated to produce a deflection current for coil 13. If smaller range scales are to be used, going down in divisions of two, the range changing switches may be ganged with switches 27 and 42, such that in the half range position, dividers 60 only pass every other pulse, and so on. If, due to fast current &c., the log 16 reads incorrectly, a manually operable pulse generator 65 can be switched into the circuit to give the estimated movement of the ship over the ground. The position of the ship's own image on the display tube 11 can be reset by connecting to the registers a pulse generator 50 manually controlled as described in Specification 915,194. The compass 15 may be manually adjustable. Reference has been directed by the Comptroller to Specification 919,239.