Patent GB-877159-A (GB)
Title: Improvements relating to radar display systems
Inventor: THOMAS DAVID CALDWELL
IPC: G01S7/24
Filed: 1958-10-15
Abstract: 877,159. Radar. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Dec. 1, 1959 [Oct. 15, 1958], No. 32935/58. Class 40(7) In a ship-borne radar with a true motion PP and CRT display, when the spot representing the position of the ship crosses a selectable one of four imaginary threshold lines AB, CD, EF and GH, Fig. 1, defining a square symmetrical with respect to the screen, the spot is automatically reset to a diametrically opposite position, outside the square, the selected threshold line being selected automatically and continuously in accordance with the instantaneous heading # of the ship. As described the north threshold line AB is selected if the ship's heading is within the sector bounded by the directions NW and NE and the other threshold lines are selected in a corresponding manner. As shown in Fig. 2 the ship spot is displaced in accordance with the movement of the ship by applying shift voltages V N  and V E  to orthogonal shift coils 6 and 7. A sine-cosine potentiometer 1 set in accordance with the heading # produces output voltages. V cos. # and V sin. 0 where V is a constant and the voltage V cos. # is applied to an RC network 4 which includes a switch 8 operated by the ship's log at a rate proportional to the ship's speed to. give a pulse train which is integrated in a Miller integrator 5, Fig. 3, to give the shift voltage V N ; the voltage V E  is derived from the voltage V sin 0 in a corresponding manner by a separate pulse network and integrator. The scale of the shift voltage may be adjusted by varying the resistance R1 in the integrator or by providing an input potentiometer to R1. When the amplitude of the shift voltage V N  or V E  exceeds a threshold voltage corresponding to the selected threshold line a reset relay is actuated to close the switch S in the corresponding integrator to reset the integrator to a voltage level determined by a resetting voltage applied to the terminal X. The resetting voltages V 2 , V 3  for the N-S and E-W integrators are V 2 =V R  cos. (180+#) and V 3 =V R  sin. (180+#) where V R  is the voltage required to produce a radial deflection to the edge of the screen. The voltages V2 and V3 are derived from a further sine-cosine potentiometer coupled to the potentiometer 1 but having voltages of opposite polarity applied to it. In one embodiment, Figs. 4 and 5, the N-S and E-W threshold voltages V13 and V14 are obtained by limiting the amplitudes of the voltages V cos. # and V sin. # to about half their peak values, Fig. 4 (not shown). The resultant voltages V13 and V14 are applied to terminals 21 and 22 respectively, Fig. 5, and the voltages V cos. #, V sin. #, are applied to a voltage comparator V4 such that if V cos. # is greater than V sin. # a relay 24 operates to apply the N-S threshold and shift voltages V13 and V N  to another comparator V5 such that the reset relay 26 operates when V N  exceeds V13; similarly when V sin. # is greater than V cos. # the relay 24 operates to apply the E-W threshold and shift voltages V14, V E  to the comparator V5. In another embodiment, Fig. 6, the positive and negative values of both the N-S and E-W threshold voltages are determined by the settings of potentiometers P1 and P2 and the voltages +V1 and - V1 at the junctions of resistors R10, R1 1 and R12, R13 connected in parallel with the potentiometers P1 and P2 are arranged to be substantially equal to these values, the scale factors being such that /V1/ is less than /V cos. 45 %. The N-S or E-W shift voltage V N  or V E  is selected by the contact L2 of a relay L/2 in an amplitude comparator V1 similar to V4 in Fig. 5 but in this case the voltages applied to the comparator are /V cos. #/ and /V sin. #/ which are derived from a sine-cosine potentiometer coupled to the potentiometer 1, Fig. 2, but having opposite diagonal points connected to voltages of the same polarity and the intervening diagonal points earthed so that the output voltages will be of the same magnitude as the outputs from the potentiometer 1 but they will always be of the same sign. The relay L/2 is thus energized or de-energized according to which of the two voltages is of greater magnitude. Another contact Ll of the relay L/2 selects the voltage V cos. # or V sin. # from the potentiometer 1 and applies it through oppositely connected diodes Dl and D2 to the junctions of resistors R10, Rll and R12, R13 respectively. Contacts L1 and L2 are connected to the outer ends of two equal resistors R14, R15 whose junction is connected to the right-hand grids of the double triodes V7 and V8, the left-hand grids being connected respectively to the sliders of the potentiometers P1 and P2 and the reset relay 27 being so connected that it operates either when the right-hand side of V7 is more positive than the left-hand side or when the right-hand side of V8 is more negative than the left-hand side. When the ship's course is in a N-S or S-N direction the contact L1 applies the voltage V cos. # to the diodes Dl and D2 and in either case /V cos. #/ is greater than /V1/. Accordingly if the ship's course is northward the diode D1 will be conductive and the diode D2 will be cut-off so that the voltage +V1 is applied to the resistor R14, conversely when the ship's course is southward the voltage - V1 is applied to the resistor 14. Similarly the voltage applied to R14 will be positive for an eastward course and negative for a westward course. When the spot reaches the threshold lines AB or GH the voltage V N  or V E  will be +V1 and accordingly the voltage at the junction of R14 and R15 will also be +V1. Thus when the spot crosses the line AB or GH the voltage at the junction of R14 and R15 goes more positive than +V1 and the right-hand side of V7 will conduct to actuate the reset relay 27. Similarly when the spot crosses the line CD or EF the voltage at the junction of R14 and R15 goes more negative than - V1 and the left-hand side of V8 will conduct and operate the reset relay 27. In a modification (not shown) the portion of the circuit of Fig. 6 comprising the valves V7, V8 relay 27 and potentiometer R14, R15 is duplicated, the relay contact L2 is omitted and the shift voltages V N  and V E  are connected to their respective potentiometers R14, R15.